Soil solarization black plastic

Contents

How to Manage Pests

Pests in Gardens and Landscapes

Soil Solarization for Gardens & Landscapes

Published 5/19

In this Guideline:

  • Impacts
  • Method
  • Solarizing soil in containers
  • About Pest Notes
  • Publication
  • Glossary

Solarizing planting beds in a garden.

Steps for solarizing soil.

Solarizing soil in containers.

Nursery planting media under double-layer plastic for solarization.

Soil solarization is a nonchemical method for controlling soilborne pests using high temperatures produced by capturing radiant energy from the sun.

The method involves heating the soil by covering it with clear plastic for four to six weeks during a hot period of the year and when the soil will receive the most direct sunlight. Plastic tarps allow the sun’s radiant energy to be trapped in soil, heating the top 12 to 18 inches to temperatures lethal to a wide range of soilborne pests; including weeds, plant pathogens, nematodes, and insects. When properly done, the top layers of soil will heat up to as high as 140°F, depending on the geographic location. Soil moisture is important in this process, as wet soil conducts heat better than dry soil. Moisture also makes soil pests, weakened by the heat, more vulnerable to attack by beneficial soil microorganisms during and after treatment.

Solarization leaves no chemical residues and is a simple method appropriate for the home gardener and small- or large-scale farmers. Solarization is primarily used as a broad-spectrum pest control technique, but it may also improve soil health by increasing the availability of nitrogen and other nutrients to growing plants and by beneficially altering the soil microbiome.

The effect of solarization is greatest at the surface of the soil and decreases at deeper soil depths. The maximum temperature of soil solarized in the field is usually from 108° to 140°F at a depth of 2 inches and from 90° to 99°F at 18 inches. Control of soil pests is usually best for organisms found in the upper 6 inches of earth.

IMPACTS

Solarization during the hot summer months can increase soil temperature to levels that kill many disease-causing organisms (pathogens), nematodes, and weed seeds and seedlings.

Soil solarization also speeds up the breakdown of organic material in the soil, often resulting in the added benefit of releasing soluble nutrients such as nitrogen (from nitrate and ammonium), calcium, magnesium, potassium, and fulvic acid, making them more available to plants.

Plants often grow faster, with higher and better-quality yields, when grown following soil solarization. This may be attributed to improved disease and weed control, increased availability of nutrients, and greater proportions of beneficial microorganisms.

Effectiveness on Various Pests

The degree to which various pests can be controlled is related to the intensity, depth, and duration of the elevated soil temperatures, as well as to the sensitivity to treatment of each pest species. Although some pests may be killed within a few days, 4 to 6 weeks of exposure to full sun during the summer is required to ensure control of many others.

Fungi and Bacteria

Solarization controls many important soilborne fungal and bacterial plant pathogens, including those that cause Verticillium wilt, Fusarium wilt, Phytophthora root rot, Southern blight, damping-off, crown gall disease, tomato canker, potato scab, and many others. A few heat-tolerant fungi and bacteria, such as those causing melon decline and charcoal rot of many crops, are more difficult to control with solarization.

Nematodes

Soil solarization can be used to reduce soil populations of many species of nematodes. This is particularly useful for organic and home gardeners. However, soil solarization is not always as effective against nematodes as it is against fungal disease and weeds. This is because nematodes are relatively mobile and can move deeper in the soil profile to escape the heat, rapidly returning to recolonize soil and plant roots following solarization treatment. Furthermore, control of nematodes by solarization will be greatest in the upper 12 inches of the soil. Nematodes living deeper in the soil may survive solarization, later causing damage in plants with deep root systems.

Weeds

Soil solarization controls many of the annual and perennial weeds present in California. While some weed species seeds or plant parts are very sensitive to solarization, others are moderately resistant and require optimum conditions for control; that is, good soil moisture, tight-fitting plastic tarps, and high solar radiation.

Solarization generally does not control perennial weeds as well as annual weeds because perennials often have deeply buried underground vegetative structures such as roots, corms, tubers, and rhizomes that may resprout. Rhizomes of bermudagrass and johnsongrass may be controlled by solarization if they are close to the soil surface.

Control of purple and yellow nutsedge, as well as field bindweed arising from rhizomes and some clovers, can be inconsistent, even under favorable conditions. For more information about common weeds and their management, see the Pest Notes: Weed Management in Landscapes.

Beneficial Soil Organisms

Although many soil pests are killed by solarization, many beneficial soil organisms are able to either survive solarization or recolonize the soil very quickly afterwards.

Important among these beneficials are mycorrhizal fungi, and fungi and bacteria that parasitize plant pathogens and aid plant growth. The increased populations of these beneficials can make solarized soils more resistant to pathogens than nonsolarized soil.

Although detailed information is lacking, earthworms are generally thought to burrow deeper into soil to escape the heat.

See Soil Solarization: A Nonpesticidal Method for Controlling, Diseases, Nematodes, and Weeds (PDF) in References for more information about solarization and the specific pests controlled.

Biosolarization

For more experienced solarization practitioners, research and field practice has shown that it may be possible to increase the pesticidal effects of solarization treatments by incorporating organic materials, such as crop residues and composts, into the soil prior to solarization. This experimental treatment is often termed “biosolarization.”

During the decomposition of organic materials, chemical changes occur, releasing certain natural products, such as organic acids, that are toxic to organisms residing in the soil. However, caution should be exercised to not incorporate excessive amounts of organic materials during biosolarization, as treated soil may be temporarily “soured” for an extended period of time by these natural toxins. In such cases, planting must be delayed until soil conditions are suitable. Alternately, treated soil may be detoxified via irrigation, leaching organic acids and other toxins below the root zone. Research to determine effective materials and protocols for biosolarization is ongoing.

METHOD

WHERE

Soil solarization is most effective in warm, sunny locations such as the Central Valley, desert valleys, and other inland areas of California. It has also been used successfully in the cooler coastal areas of California during periods of high temperature and no fog. Soil treatment by anaerobic soil disinfestation (ASD) may be done where soil heating is insufficient for solarization.

WHEN

Highest soil temperatures occur when days are long, air temperatures are high, skies are clear, and wind is minimal. The soil heating effect is not as great on cloudy days. Wind will disperse the trapped heat and may loosen or damage the plastic sheets. Shady areas may not be effectively treated by solarization.

Solarization is most effective when done during the hottest weeks of the year. The best time for solarization of soil in inland California is from June to August, although good results may be obtained starting as early as late May or as late as early September in the southern California desert regions. July is the most reliable time to solarize, except for coastal areas, where persistent, warm, fog-free periods may not occur until August or September. Soil within most regions of California, except high elevation areas and some coastal valleys, can be reliably solarized if treatment is instituted during the period of late June through August.

HOW

1. Soil Preparation

A very smooth bed, with few clods and surface litter, will allow the plastic to lie snugly against the soil, producing fewer air pockets. Air pockets between the plastic and the soil can greatly reduce soil heating and promote “sailing” of the plastic in the wind.

Solarization can be done on flat areas or raised beds. Flat areas are easiest to solarize (prior to lawn reseeding, for example) and ensure more uniform solarization of the entire area. Raised beds are best formed prior to solarization so that tarps can be placed over preformed beds. This practice also minimizes disturbance of the soil after solarization, which may bring up viable weed seeds from deeper in the soil profile.

If possible, lay raised beds out going north to south rather than from east to west to improve the uniformity of heating.

The best solarization will occur on areas where there is little or no slope or where the slope has a south or southwest exposure. Solarizing areas on north-facing slopes is not as effective and may result in reduced pest control.

2. Irrigate the Soil

For best results, wet the soil to at least 12 inches deep. In larger areas, it is easiest to do this prior to laying the plastic, but in smaller areas it can be done after the plastic is applied using a garden or soaker hose or by laying drip tape under the tarp.

If wetting soil beforehand, place plastic covers over the site as soon as possible after the water has been applied to reduce evaporation. Unless the soil gets dry during the course of soil solarization, or you are aiming to do an ASD treatment, do not irrigate again, as this will lower the soil temperature and lengthen the time required for successful solarization.

3. Plastic Tarp Choice

Plastic material. In general, transparent or clear plastic is most effective for solarization, as the heating rays from the sun will pass through the sheet and be trapped to heat the soil below.

Usually black plastic is less effective because it absorbs and deflects part of the heat, rather than trapping as clear plastic does. However, in cooler or coastal areas, black plastic is sometimes better than clear, because weeds won’t grow beneath it, as they will under clear plastic when the air temperatures are too low to kill them. In this case, the black plastic should be left in place for several weeks during the hottest part of the year.

Several thicknesses of plastic tarp are available. (Note: 1 mil = 0.001 inch or 0.025 mm)

  • Thin plastic provides greater heating, but is also more susceptible to tearing from wind or animals walking on it (1 mil).
  • Slightly thicker plastic is better in windy areas (1.5 to 2 mils).
  • Thicker plastic can be used if the treated area is small (4 mil or more).

Plastics designed for large-scale solarization are usually treated with an ultraviolet (UV) inhibitor so they will not break down as quickly in sunlight. For use in gardens, the rolls of 1 to 4 mil “painter’s” plastic are available at larger hardware stores and are easier to obtain. These should last for the 4 to 6 week solarization period without beginning to break down. When available, select clear, transparent film, rather than cloudy, milky, or translucent materials which will reduce solar energy transmission.

Plastic sheets without UV protection should be watched closely, so they can be removed before deteriorating to the point where removal and disposal are difficult. If a longer solarization period is desired, small areas can be covered again with fresh plastic. Any holes or tears should be patched with durable patching tape.

For treating small areas in a garden, or on a lawn in cooler climates, it may be helpful to use a double layer of plastic with air space created by objects such as plastic bottles or PVC pipe between the layers. This has been shown to raise soil temperatures an additional 2° to 10°F over temperatures obtained with a single layer of clear plastic.

4. Plastic Tarp Placement

Flat beds. The plastic must be held as tightly as possible against the soil. One way to hold it down is to dig a trench 4 to 6 inches deep around the area that is going to be solarized. Lay the plastic out over the area with one edge in the trench. Cover that edge with soil to hold it down. Pull the plastic tight from the other side and bury that edge in the corresponding trench. Do the same with the other sides and then walk around the perimeter of the trenched area to pack the soil down around the edges of the plastic. The closer to the soil surface the plastic is, the better the heating.

Raised (formed) beds. As with flat beds, the plastic must be held close to the soil. Multiple beds can be covered by a single sheet of plastic, but heating may be reduced and the plastic may “sail” when it is windy. If only single beds are covered, the furrows between the beds are left uncovered and are not solarized. Each bed is covered with a strip of plastic tarp that is wide enough to cover the entire bed width and have enough tarp left over to bury the edges to hold it down. Avoid moving soil from the untreated furrows to the beds because this may re-infest the treated beds with pests.

5. Solarizing Period

Solarization is both time- and temperature-dependent. The cooler the soil temperatures, the longer the plastic needs to remain in place to raise the temperature to desired levels. The goal is to maintain daily maximum temperatures in the top 6 inches of soil at or above 110º to 125°F. Use of a soil thermometer or temperature probe can verify achievement of these temperatures.

Four to six weeks of soil heating during the warmest time of the year is usually sufficient to control most soil pests. In cool, windy, or cloudy locations, or if there are pests present that are difficult to control, it may be necessary to leave plastic in place up to 8 weeks. Conversely, during very hot weather, pests may be controlled with a shorter period of solarization. For instance, most soilborne pests will be controlled after only 4 weeks of solarization during June through September in California’s Central Valley and desert regions.

6. Post-solarization

Removal of Plastic. After solarization, the plastic may be removed, taking care not to disturb the underlying soil to avoid bringing up viable weed seeds from untreated edges and furrows or from deep layers that did not reach lethal temperatures. The area can be planted immediatly with seeds or transplants for a fall or winter crop or a lawn.

Alternatively, the plastic may be left on the soil as a mulch by cutting holes and transplanting plants through the plastic.

Clear plastic may be painted white or silver to cool the soil and repel insect pests. However, the plastic tarp may degrade and fall apart during the growing season.

If the soil will be cultivated prior to planting, the cultivation should be shallow (less than 2 inches deep) to avoid bringing viable weed seeds and pathogens to the surface.

SOLARIZING SOIL IN CONTAINERS

Soil solarization has been shown to be effective for disinfesting small amounts of moist, containerized soil and soil in cold frames. Soil can be solarized either in bags, pots, plastic buckets, or flats. These containers are placed on an elevated surface such as wooden pallets and covered with a double tent of transparent plastic.

Soil temperatures should be monitored closely in this planting medium to assure that temperatures are high enough to control pests. As an example, in warmer areas of California, soil inside black plastic bags can reach more than 160°F during solarization. This is equal to target temperatures suggested for commercial soil disinfestation using aerated steam. At these temperatures, all soil pests can be killed within 1 hour.

The double layer of plastic can increase soil temperatures by up to 50°F, and placing containers on pallets allows for heating from all sides of the soil mass.

Alternatively, moist soil in pots, or as a mass, may be placed in closed black trash bags and placed on pallets. Soil temperatures can be monitored using simple soil thermometers inserted into the center of the soil mass, or by using thermocouples and a digital reading logger.

Temperatures can be monitored at multiple locations, but the duration should be lengthened to raise the temperature at the coolest location to the desired level. As a guideline, to completely eliminate pests, maintain 158°F or higher for 30 minutes, or 140°F or higher

WARNING ON THE USE OF PESTICIDES

Stapleton JJ, Dahlquist-Willard RM, Achmon Y, Marshall MN, VanderGheynst JS, Simmons CW. 2016. Advances in biosolarization technology to improve soil health and organic control of soilborne pests. (PDF) In: 2016 Organic Agriculture Research Symposium Proceedings.

Stapleton JJ. 2018. UC Statewide IPM Program, Kearney Agricultural Center, Parlier, CA. Soil Solarization Informational Website.

Wilen CA. 2018. Pest Notes: Weed Management in Landscapes. UC ANR Pub 7441, Oakland, CA.

PUBLICATION INFORMATION

Pest Notes: Soil Solarization for Gardens & Landscapes Management
UC ANR Publication 74145

AUTHORS: James J. Stapleton, UC Statewide IPM Program, Kearney Agricultural Center, Parlier, Cheryl A. Wilen, UC Statewide IPM Program/ UC Cooperative Extension, San Diego County, Richard H. Molinar, UC Cooperative Extension, Fresno County.
TECHNICAL EDITOR: K Windbiel-Rojas
ANR ASSOCIATE EDITOR: AM Sutherland
EDITOR: B Messenger-Sikes

PDF: To display a PDF document, you may need to use a PDF reader.

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Soil solarization

Managing weeds

Soil solarization takes advantage of the sun’s heat, trapped under clear plastic sheeting, to control many kinds of weed seeds as well as harmful fungi, bacteria, and some nematodes. The process is carried out in summer and works best in regions that have hot, sunny weather for 4 to 8 weeks straight; daytime temperatures above 80 degrees F/27 degrees C are ideal. Solarization isn’t very effective in coastal climates with summer fog, nor does it work well in very windy areas.

Plan to solarize areas you intend to use for fall vegetables, ornamental beds, or lawn. Follow these steps:

1. Cultivate soil, clearing it of weeds, debris, and large clods of earth. It is important to get rid of growing weeds, because clear plastic ― unlike black plastic ― doesn’t halt growth of plants in the soil beneath it.

2. Make a bed at least 2 1/2 feet wide (narrower beds make it difficult to build up enough heat to have much effect). Carve a small ditch around perimeter and rake to level surface.

Soak soil to a depth of 1 foot: moist soil conducts heat better than dry soil and initiates germination of weed seeds, which will then be killed by heat.

3. Cover soil with 1- to 4-mil clear plastic; use UV-resistant plastic if it’s available, since it won’t break down during solarization. Stretch plastic tightly so that it is in contact with the soil. Bury the edges in the perimeter ditch. An optional second layer of plastic increases heat and makes solarization more effective; use soda cans as spacers between the two sheets.

Leave plastic in place for 4 to 6 weeks (8 weeks for really persistent weeds); then remove it. (Don’t leave it down longer than 8 weeks, or soil structure may suffer.) You can now plant. After planting, avoid cultivating more than the upper 2 inches of soil, since weed seeds at deeper levels may still be viable.

Can You Solarize Garden Woes Away?

Q: Mike: Late blight is our chief tomato headache. (Our tomato leaves and fruits develop little grey-brown patches that spread, especially in damp weather.) I saved two old double-pane glass sliding doors with the intention of making them into some sort of greenhouse contraption, but could I instead lay them on last summer’s tomato plot for a few months to solarize the soil and kill any blight spores there? You don’t have to use plastic, do you? And does solarization work only in the summer? Or could heating the soil from March thru May or June do the job?

    —Kate, near Boone, NC

Mike: My cucumbers have had severe wilt problems for the past four years. The plants die off before they can produce more than one or two cukes; sometimes before they can produce any. I solarize the soil every year in late spring to try and kill off whatever disease may be in the dirt, but it keeps coming back. This year I thought for sure the soil was sufficiently heated due to a few hot days. Thanks for any help.

    —Lorraine in Torrance, CA

A. Soil solarization is probably the best way to get rid of otherwise insurmountable problems, like persistent weeds, soil-borne disease and even destructive root-knot nematodes. (Not to be confused with the beneficial nematodes we’re always recommending, ‘bad’ nematodes are pretty much only a problem in the South; which is good, because solarization is really only practical in very warm climates.)

Here’s the basics of soil solarization: You take the plot of land you wish to purge, till it all up, remove any rocks or clumps of plant material, carefully level it out, soak it until the soil is saturated at least 70% two feet down, then stretch clear plastic tightly overtop, making sure the sides are well anchored. Several sources suggest burying the sides of the plastic in trenches dug next to the plot to insure a tight fit for the length of the project.

And sorry folks, but the length of time necessary for this project to succeed is an absolute drop-dead minimum of six to eight weeks in the hottest, deep-South areas of the country during the hottest months of the year, in a year with lots of sunny days. In the mid to upper South, we’re talking all of June, July and August (and pray for sun). In more Northern parts of the country, its only going to work if you leave the plastic on ALL season in a full-sun site during a hot and sunny summer. And you should use two sheets of plastic, which heats the soil more by trapping warm air between the layers.

Sorry, but it really does take that long and require that much heat. That’s why this is such an extreme procedure—you’re agreeing up front that you won’t have use of those plots that summer.

Studies show that the thinnest plastic (a mere one-mil thick) heats the soil best. But thin plastic also rips easily, and so a common recommendation is to meet somewhere in the middle of heat and strength with a two-mil sheet.

Kate in North Carolina MIGHT be able to use her old door panels to cook the bad news out of two small plots, but I’d worry about getting a tight enough fit, and about the glass breaking, laying flush to the ground all season like that. I would instead cobble those doors into super-groovy cold frame lids, which could extend her salad growing options to virtually twelve months of the year, and rely on plastic to cook her dastardly dirt.

Her disease is a tough one. Many gardeners misuse the word ‘blight’ as a synonym for other, less fatal, diseases; but (unfortunately) her description sounds like the same notorious organism that starved millions of my Irish ancestors when it leveled potato crops during the Great Famine. It is unusual for this bad actor to appear repeatedly in a home vegetable garden, and my first suggestion would be to do everything to try and avoid it up front. Here’s my short list:

  1. Make sure that ALL of last years’ plant debris is removed from the area;
  2. Don’t grow anypotatoes in your garden for awhile;
  3. Cover the soil completely with high-quality compost;
  4. Space the plants twice as far apart as last season;
  5. And do everything you can to keep the leaves of your plants dry, with the exception of a weekly morning spray of compost tea.

And yes, maybe cook up a plot for use the season after that if all those tactics still fall short. Late blight is not among the diseases that solarization has been proven to defeat in scientific studies, but it can’t hurt. And the heating process increases the numbers of many beneficial soil organisms that will help combat all kinds of disease in subsequent seasons. AND it makes several important nutrients (including Nitrogen, Calcium and Potassium) more available to plants. That all adds up to more vigorous, naturally resistant plants if dread diseases do return to play.

Solarization is a sure cure for the most common tomato disease problem, the nasty soil-borne wilts known as verticillium and fusarium. Tuskegee University researcher Dr Clauzell Stevens explained that it can make those bad boys (and Southern blight) go bye-bye for a full three seasons in a little piece he did for ORGANIC GARDENING magazine back in 1991. He also said it should banish bad nematodes for at least two years, and that the buried seeds of crabgrass, purslane, barnyard grass and pig weed should be reliably fried. In a hot enough summer, even the notorious yellow nut sedge may go down!

Lorraine in California seems to be ‘solarizing’ her soil at the wrong time of year and probably for MUCH too short a period of time. And I would not give up a bed for an entire season on a guess that something lurking deep in the soil was to blame for those cucumber woes. The vast majority of cuke diseases are spread by cucumber beetles while they feed, so I suggest she first try using row covers to keep those pests off the plants early in the season, and then have a variety of organic controls (soap sprays; oil sprays; spinosads…) on hand for when the covers have to come off. See this recent Question of the Week for more tips on controlling cuke beetles and the diseases they spread.

But if you got the room, the time, the heat, the patience, the inclination (and of course, the troubles) go ahead and try and a little solar assistance!

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The use of plastic sheeting or mulch in the garden proves to be a useful tool for some garden crops.

Many crops do well with the support of plastic sheeting and plastic mulch. These innovative products have many uses in the garden.

In the article we will explore:

  • The advantages and disadvantages plastic mulch sheeting provide
  • The many different types of polyethylene sheeting used
  • How do you use the mulch in the garden
  • The Pros and the Cons plastic sheeting offers

Let’s get started!

General Advantages of Plastic Sheeting Or Plastic Mulch

There’s a lot to like about using a polyethylene film in the garden. The USDA has even termed the practice as – plasticulture.

For one, plastic sheeting can move your planting date at an earlier, more convenient period. The soil moisture stay more stable effectively minimizing root damage and soil compaction.

It acts as a great insulator keeping the soil warm during the day and staves off the cold during nights.

Laying plastic can mean the big difference in producing sickly green or ripe, red tomatoes, moldy or luscious strawberries, or in a good harvest of melons or none at all.

Clear Vinyl Sheets

The immediate advantage of using clear polythene sheeting is its ability to eliminate seriously annoying weeds such as onion weed, ivy, dock, rhizome grasses and other tough ones which prevent plant growth.

Clear plastic lets the sunlight pass through for optimal soil absorption. It warms up the soil for maximum mulching potential.

The plastic film along with the focused rays of the sun heats the soil temperature underneath a coating of plastic.

This helps rid the soil of organisms, unwelcome pathogens, insects, and disease in an all-natural, non-chemical, organic, affordable option known as soil solarization.

For more read our article – Soil Solarization: How To Kill Soil Pests and Diseases

Black Plastic Sheeting Or Mulch

Black plastic mulch sheeting has been in use since the 1950s. It is the most popular and least expensive of the many-colored mulches available.

This mulch has carbon added to “create” the black color. The dark or black color makes it very good to prevent weeds and allows little or no light to pass.

It also warms the soil very well throughout the growing season in the vegetable garden. This is especially true if a great deal of the plastic is in direct contact with the soil.

Pros Of Using Black Plastic Mulch Sheeting

Black Plastic Warms The Soil

Black polyethylene sheeting is very good for warming up the soil for vegetable crops (tomatoes, strawberries, pumpkins and melons) that love the heat.

How much can the soil temperature increase?

According to the North Carolina State Extension under black mulch a 4 to 5°F increase measured at a depth of 2-inches. At the same depth infrared transmitting (IRT) mulch showed and increase of 5 to 8°F and clear mulch an increase of 8 to 10°F.

Accelerate Plant Growth

The gas carbon dioxide (CO2), is important in the process of photosynthesis. The black sheeting greatly reduces the ability for CO2 to pass through the plastic.

This creates higher levels of CO2 to build up under the sheeting. The CO2 escapes through the holes in the plastic mulch with a “chimney effect” creating increased local concentrations of CO2 around actively growing leaves.

Crop times from planting to harvest are typically 2 to 21 days earlier for crops grown “under mulch.” This extends the growing season allowing you to “get a jump” on the season by planting earlier and growing crops longer into the season.

Reduced Evaporation and Control Soil Moisture

The moisture that would normally evaporate from the soil is held in by the sheeting. The reduced evaporation does not mean less irrigation will be required for optimal plant growth.

Why? Plants grown with mulch often grow twice the size of crops grown on bare soil. Larger plants need more irrigation.

You’ll have better control of soil moisture as excess water runs off the sheets into the rows. This reduces excess water stress and keeps plants from drowning.

Reduce Spread of Diseases

The reduced contact of leaves with the soil and puddles produces a cleaner, healthier crop making plants less likely to diseases spread by splashing water and root rots.

Black Plastic Reduces Problems From Weeds

Black sheeting or mulch does a great job of blocking weed growth and thwarts reproduction of many pathogens and pests.

Clear plastic allows light to pass through. To control weeds with clear plastic may require the application of an herbicide.

Better Crop Yields

Crops can better utilize fertilizer applications, since the “food” is not being leached away of competing with other plants.pplied gets

The combination of warm soil, better soil moisture control, reducing crops battling with weeds for moisture and fertilizer, better use of water and fertilizer not being leached all leads to better crop yeilds.

Reduces Soil Erosion

Covering the soil reduces erosion problems. It also reduces the soil from becoming compacted. This allows roots to enjoy improved oxygen exchange and excellent microbial activity.

The soil under the mulch remains loose and well-aerated.

Clean Looking

Overall using plastic sheeting in the garden produces a clean look, which is always nice in the garden.

Cons Of Using Black Plastic Sheeting For Gardens

Using black plastic for gardens is not all “perfect”, there are some cons!

Some Crops Do NOT Grow Well Under Sheeting

It stands to reason that cold crops (e.g. lettuce, spinach, peas and root veggies) would not do as well growing under plastic ground cover.

Black plastic mulch could potentially overwork and trap in the heat, scorching plants.

Crops that grow in the cool seasons such as root vegetables, peas, spinach and lettuce does much better without the use of plastic sheet cover.

The Effectiveness Goes Down In Cooler Locations

The effectiveness of garden plastic sheets or a black garden tarp goes down when used in the cooler, coastal regions. The warmth wouldn’t be enough to get rid of the weeds.

In very cold areas black garden plastic rolls might not keep the soil hot enough to kill off weeds and pathogens.

Long Rooted Plants Cannot Get Enough Water

Plants with long roots won’t be able to draw as much water as they need with plastic sheets on top. Overhead sprinklers and natural water from rain won’t effectively reach the plants bed.

The contained water could also work to your disadvantage, as it will not evaporate as quickly in the open air and could make the soil soggy and create potential disease issues such as fungal growth.

Increased Costs And Maintenance

  • The additional cost of landscaping plastic sheeting and drip irrigation does add more expense before starting the task of planting.
  • The irrigation will need closer dialy monitoring
  • Since plastic does not break down, plastic mulch and drip tube irrigation should be removed after each season and not ever ‘tilled” into the soil.

More Time Planting

When planting crops the time involved will take longer as each individual plant needs to be planted into it’s own hole.

It’s Hot To Work On And Slippery

As mentioned above plastic sheeting will hold heat making working on the sheeting hot.

Reflected heat can also make it uncomfortable to work on and around. Consider performing any work early in the morning or late in the day.

NOTE: Years ago in the nursery, when laying down black plastic sheeting in the afternoon become too hot to touch! Laying the sheeting early in the days was not an option!

Once water gets on plastic sheeting it can get slippery making it diffuclt to work on. Watch your step!

Before The Plants Are Established, It’s A Bit Of Work To Keep The Plastic Down.

When laying sheeting and waiting for plants to become established make sure the plastic stays securely in place.

Place bricks, large rocks or concrete blocks on the edge to keep the wind from getting under the plastic.

NOTE: Don’t try to “install” plastic sheeting on a windy day!

What Type or Kind Of Black Plastic Mulch Should You Use?

The choice of plastic mulch depends upon both the visual effect you want to create and the type of crop you plan to grow.

There really hasn’t been a lot of research done on the results of using different colors of mulch, so it’s a learn-as-you-go process.

What’s The Best Thickness Of Black Plastic Sheeting For Gardening?

There are several different thicknesses of black poly sheeting available.

The thickness of the plastic garden liner is rated using the term “mil”, which is a measurement equaling 1/1000th of an inch (0.001).

To give you an idea of the size of this measurement, a dime is 53 mils thick. A credit card is 30 mils. A piece of typing paper is 1 mil, but a paper grocery bag may be between 2 and 3 mils thick.

The thickness most commonly used for black plastic sheeting is 6 mil; however, this product is also available in thicknesses ranging from 3 mil to 60 mil.

Naturally, the thicker the plastic for flower beds is the more durable it will be and the longer it will last.

Very thin sheeting must usually be replaced every season. Thicker sheeting may last for several years with good care.

For a very thorough treatment of the qualities of plastic sheeting, visit Global Plastic Sheeting here

Is Landscape Fabric Better Than Plastic Mulch?

Both landscape fabric and plastic mulch can help reduce soil erosion and prevent weeds while keeping the soil in place and keep weeds from sprouting.

I prefer to use the porous landscape fabric in landscape beds and in areas which are longer term and multi-seasonal.

I like to use plastic sheeting in the garden were it is removed after each season.

What Is Embossed Film, Red Plastic, Green Plastic, Biotelo or Sheeting?

These days there are many attractive options available in colored plastic mulch.

Clear, white and black plastic mulch has been used in commercial vegetable production for over 50 years.

Today, homeowners can choose from a rainbow of colors to enhance both the production and the curb appeal of their home food production endeavors.

The Colors Of Plastic Mulch Is Best?

You can choose from many different colors, including:

  • Black
  • White
  • Brown
  • Silver
  • Green
  • Blue
  • Red
  • Biotelo

Black Plastic Mulch

In use since the 1950s, this is the most popular of all the mulches available.

Penn State University has conducted research which shows that the soil directly beneath a layer of black plastic mulch may be as much as 5 degrees warmer at a depth of two inches and 3 degrees warmer at a depth of four inches when compared with adjacent unprotected soil.

These few extra degrees of heat allow you to set your plants out considerably earlier, leading to earlier plant maturity and more fruit sooner in the growing season.

Trials conducted by Auburn University in conjunction with the USDA indicate that okra crops grown using black plastic mulch mature much earlier and produce greater yields.

Interestingly, use of plastic mulch in both red and blue produced similar results.

White Plastic Mulch

In cool climates with short growing seasons, white plastic mulch may not be a good idea.

It can definitely help cool the soil in areas of extreme heat, smother weeds, retain soil moisture and cooler soil temperatures.

These effects make it possible to grow cooler weather crops such as cauliflower, cabbage, peas and broccoli in warmer climates.

Trials show that white plastic mulch is more effective than biodegradable options such as straw.

Although it is more costly initially than these options, the fact that it lasts forever makes it a more economical mulch choice.

Brown IRT Mulch

One exciting new innovation in plastic mulch is a Brown Infrared Transmitting (IRT) option.

This plastic mulch is superior to black plastic mulch for warming garden soil early in the season. It heats the soil as well as clear plastic yet controls weeds as well as black plastic.

To get all of the qualities that brown IRT mulch offers, follow the advice of the University of Vermont Extension in their factsheet.

Make sure you look for IRT labeling when purchasing brown plastic mulch. If it is not labeled IRT, it will not provide all these benefits.

Green IRT Mulch

Like brown IRT mulch, green IRT mulch does a great job extending the growing season and helping crops produce earlier and greater yields.

Trials conducted at the University of New Hampshire and Penn State showed that green IRT mulch is especially conducive to bigger, better cantaloupe crops.

Red Plastic Mulch

According to research conducted by Clemson University in conjunction with the USDA, some crops do much better when surrounded by red plastic mulch.

Red Plastic Mulch reduces nematodes on tomato crops – Image: Richard Nowitz/USDA

Tomato plants produce a greater yield, basil produces larger leaves and strawberries grow in greater abundance with fruit that both smells and tastes sweeter.

The USDA shares that “tomato plants grown with red plastic mulch ward off root-munching nematodes better than plants grown on black plastic mulch.”

In general, home gardeners report greater yields and larger fruit size in a wide variety of crops including peppers, eggplant and tomatoes.

Blue Plastic Mulch

Penn State researchers found that blue plastic mulch is very good to use when growing cucumbers, summer squash and cantaloupe.

Reflective Silver Plastic Mulch

If whiteflies and aphids are a problem, this innovative product can be very helpful.

Furthermore, studies conducted at Virginia Tech indicate that the use of silver plastic mulch discourages cucumber beetles on both squash and cucumber plants.

According to studies conducted at Penn State, bell pepper plants produce significantly more fruit when planted using silver plastic mulch than when black plastic is used.

BioTelo Plastic Mulch Completely Biodegradable

Biodegradable plastic mulch (BioTelo) made of corn starch along with other biodegradable substances is currently available in black and clear.

Research conducted by Cornell University indicates that this mulch works just as well as “traditional” plastic products and can simply be left in place to break down and enrich the soil when it begins to wear out.

Biotelo mulch claims:

  • Leaves no residue in the soil, significantly minimizing its environmental impact.
  • Biodegrades completely without polluting the soil or accumulating over time.
  • Has the same strength, elasticity and effectiveness of traditional plastic mulch film.
  • Does not need to be removed from the soil or disposed of at the end of the growing season. Can be laid with conventional mulch laying machines.
  • Can be used for any crop traditionally grown with plastic mulch film.
  • Provides the same effectiveness of weed suppression as plastic mulch film. Testing has shown that the quality and productivity of the crops grown using BioTelo Agri are identical to those grown with plastic mulch film.

NOTE: In 2015 Canada banned biodegradable plastic mulch films for use in “Certified Organic Farms.”

How Do You Water Your Garden If It’s Covered In Black Plastic Mulch?

When growing plants with plastic mulch irrigation needs to be provided. Homeowners can install soaker hoses under the plastic sheeting to provide the additional water right where it is needed.

At the plant roots!

Learn more in our article: Soaker Hoses – What Are They And How To Use Them In The Garden

How To Dispose Of Plastic Sheeting And Plastic Mulch Responsibly?

It may seem that using plastic in the garden is counterproductive when it comes to providing good stewardship for the earth.

When the time comes to dispose of these products, be sure to seek out a recycling program to prevent having them end up languishing in the landfill or endangering wildlife in the ocean.

Naturally, plastic tears and wears out with the passage of time and exposure to the elements.

When you purchase any plastic product, look for recycled plastic or biodegradable plastic.

Summary

Used and disposed of responsibly, plastic sheeting and plastic mulch can be very wise choices for the thrifty, earth-friendly gardener.

These products help you make better use of precious resources, keep pests and pathogens under control. Prevent soil erosion and allow you to enjoy healthier and more abundant crops.

Source: 2 | 3

Growing Tomatoes and Peppers in the Garden using Black Plastic Mulch

  • Tomatoes planted on black plastic mulch with tomatos cages fastend to the earth with wooden stakes.Photo/Illustration: susan belsinger
  • Space the holes to fit the cages (3 feet apart center to center) and place the plants where you want them and then transplant.Photo/Illustration: susan belsinger
  • Plant each tomato and insert the label beside it in the hole. Then place the cage over the transplant.Photo/Illustration: susan belsinger
  • We plant peppers in two rows rather than a single row since they can be closer together than tomatoes.Photo/Illustration: susan belsinger
  • Closeup chile pepper transplant–be sure to water the transplants in after planting.Photo/Illustration: susan belsinger

Oh boy did I open a can of worms when I started to do research on the pros and cons of using black plastic mulch! Yes, it does warm the soil, extend crops growing time, hold moisture in the soil and keep down a plethora of weeds. No, black plastic is not organic. Most black plastic eventually goes into the landfill in a season or two-unless you use one of the newer biodegradable or photo-degradable black plastic mulches. There are many types of plastic mulch as well as garden cloth available nowadays, which come in all different weights-so you need to do your research here.

Frankly in my mind, plastic and biodegradable are oxymorons. I do not want to contribute to putting plastic in the landfills, however I do want to grow the tastiest tomatoes and hottest chile peppers that I can.

I try to garden organically. Our family has been vegetable gardening here in zone 7 Maryland since the early 70s. At that time, we bought a Troy-Bilt rototiller to turn a lawn of established grass into a plantable garden space and subscribed to Rodale’s Organic Gardening Magazine. We don’t use inorganic sprays and pesticides and we use organic matter to build up the soil every year and for fertilization.

Our neighboring farmers who have grown vegetables on a large-scale, commercial basis have grown their plants on black plastic for many years. Early on, I witnessed how they don’t have to weed and how their crops grow faster and bigger than some of ours. Generally, it works best on hot-weather crops like tomatoes, peppers, melons, squash and pumpkins. (Although I have read of folks getting their best broccoli ever on black plastic.)

1. Temperature: The plastic warms the soil by as much as 5 degrees, which means that you can plant crops earlier. Warm-season crops produce higher yields and mature up to three weeks earlier, according to the Colorado State University Extension. Black plastic mulch might get too hot in warm climates, scorching the plants-so gardeners in southern climes keep this in mind.

2. Moisture: Black plastic mulch can reduce soil evaporation by up to 70 percent. Be aware though, that plants placed in plastic mulch don’t get water readily from rainfall or overhead sprinklers so install soaker hoses under the mulch.
3. Weeds: One of the best things about using black plastic mulch is that it cuts weed growth down enormously.

Reduced weed growth means less dependence on herbicides and less time spent weeding, not to mention helping reduce invasive species. It can also mean healthier crops and fewer insect pests that eat weeds or lay their eggs on them.

4. Environmental Issues: Black plastic mulches reduce soil erosion, a positive environmental consideration. One drawback of using plastic mulches is their contribution to landfills. Biodegradable plastic mulches are currently being developed, and they seem to be as effective as regular mulches at weed suppression and moisture conservation.

We tried planting our tomatoes and peppers on black plastic when we first saw them planted next door and they did extremely well. Being novices, we did not put in drip irrigation under the plastic and when the weather was hot and dry, we had to water by hand with a wand at the base of each plant where there was a hole in the plastic, since the plastic is otherwise impermeable. Also, we learned in the first season of use, that the plastic mulch had to be pulled up at the end of the growing season when spent plants are removed and the garden is cleaned up. If not, the plastic can break down in the garden into small pieces which are laborious and difficult to pick up and remove; you don’t want them blowing around the yard.

We have grown peppers and tomatoes on both black plastic and directly in the soil and mulched with straw. One thing that we do know after years of staking, is that tomato cages are well worth the time and energy to use for growing large plants that don’t sprawl all over the ground and are much easier to harvest.

A few years back, we ordered a 0.6 mil Photo-Degradable Embossed Black Plastic Mulch from Garden Solutions; here is the description from their website: “Photo-Degradable mulch is the latest greatest in agricultural plastics. Now not only do you get all the qualities from non-degradable plastics, but also the ease and eco-friendliness of our photo-degradable plastic mulch. It’s simple, lay the mulch, have an outstanding harvest, & let the plastic break down into H20, CO2, & Biomass.” https://www.growerssolution.com/PROD/photo-degradable-embossed-black-plastic-mulch-0-6-mil/ecoblack

We have used the Photo-Degradable mulch for the past few seasons, however I do pull it up at the end of the season and do not leave it in the garden. We just use it for tomatoes and peppers-a row of each. After working amendments and compost or aged manure into the soil, we make a raised bed with two deep V-channels on either side of the row. Then we place a soaker hose down the center of the bed. We then roll out the plastic the length of the row and fill in the Vs with soil to hold the plastic mulch in place. It is best to do this when the earth is moist so that the soil under the plastic is damp and will hold the moisture. We try to get the beds ready a week or two before planting.

When ready to transplant, use a narrow garden hoe or hori hori to make the holes for each plant. Then I place the plants to be transplanted alongside each hole and go down the row and put them in. I usually put the identifying plant marker in each hole along with the plant and record the same in my garden notebook (so I can still identify cultivars when the tags mysteriously disappear).

Next, the tomato cages are placed around each plant and then stakes are driven into the earth alongside each cage and wired together. This secures the large cages to the earth, so when a heavy-laden plant is loaded with fruit, it doesn’t topple or blow over in a summer wind or rain storm. Two rows of peppers are planted per row of black plastic mulch and we found running stakes down the middle allows us to tie the plants up from either side.

Now we are just waiting for the sun to shine and the plants to grow!

Black Plastic Mulch: Weed Free Gardening

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A couple years ago, after a sob session about my very large garden once again being taken over by weeds, a friend shared with me her tactic for keeping a weed free garden for over 20 years: black plastic mulch.

We decided to try it last year. Friends, I don’t think anyone will convince me to go back to gardening without it.

What is black plastic mulch?

Black plastic mulch gardening basically refers to laying a black plastic film over the space you are using as your vegetable garden so the plastic can prevent weeds from growing. We cut small holes or long trenches in the black plastic in order to plant the things we want to grow.

Where do you get black plastic mulch?

You can head to Amazon or agricultural stores and buy plastic made specifically for this purpose. Be sure to pay attention to length, width, and thickness of the plastic. There are biodegradable black plastic mulch options available, but know that these options are usually very thin (.5 to 1 ml thick) and can be more of a challenge to work with than thicker options.

We headed to a nearby hardware store and bought a 20’x 100′ roll of black plastic, similar to this heavy duty plastic sheeting. The plastic we have used has been anywhere from 3 ml to 4.5ml thick. Because I put this over everything (and not just in growing rows or raised gardens) I prefer something thicker that will hold up to me walking on it.

Pros of using black plastic mulch

Spreading a giant sheet of black plastic mulch over your garden space will help warm the soil up. You know what this does? It helps your seeds to sprout faster. I’m in Minnesota and this is a big deal. Any jump we can get on our growing year is an itty-bitty miracle!

The first year we used black plastic mulch, I had cucumber plants popping out of the soil four days after the seeds had been put in the ground.

Like I said, itty-bitty miracle.

There are no weeds.

No weeds, friends. You’re covering and smothering where the weeds would normally be growing. They can’t grow if there is a black plastic sheet over them.

No. Weeds.

Okay, to be perfectly honest, the only place you might have weeds come up would be in the holes you have cut in the plastic to plant your seeds or started plants. The trick is to a) not make those holes or trenches any bigger than they need to be and b) spend a couple minutes poking around every so often to nip off itty-bitty weeds that do start.

But honestly, the weeds have.not.been.a.problem since we’ve started using this method.

Better yields

Your plants won’t be choked out by weeds. You won’t be searching through a forest of overgrown weedy-ness for those plants you thought you planted but can’t seem to find. Your plants will be healthier when they aren’t competing for nutrients with their friendly neighborhood whatever-that-weed-is-called.

(By the way, what are you planting this year? And if you grow it, will your garden actually save you money?)

It’s beautiful.

It’s actually a joy to look out at the garden. It’s not an overwhelming depressing mess. I enjoy gardening again. I mean, look at my garden!

Cons of using black plastic mulch

In full disclosure and honesty, there are a couple things to be aware of if you choose to use black plastic mulch on your garden. (And remember, some of these things are because we choose to lay the black plastic mulch over our entire garden, not just in the growing rows.)

More time planting

Because you have to cut holes or trenches in the plastic in order to plant your seeds or started plants, it does take a bit more time to plant. But it is completely worth it because have I mentioned, no weeds?

It’s hot to work on

Black plastic is hot to stand on. If there is anything you want to do in the garden, it’s best to try and do it when it’s cloudy, in the morning, or later in the evening.

It can be slippery

It’s important to keep in mind that you’re basically putting a giant slip and slide over your garden space. If it gets wet, it will become slippery. Be careful when you’re walking around. Or, you know, wear a swimsuit and make the most of it.

Before the plants are established, it’s a bit of work to keep the plastic down.

This was our biggest surprise the first year. We had bought garden staples and landscaping stakes with our sheets of black plastic assuming that this would be enough to keep the plastic on the ground.

It wasn’t. It might depend on where you live, the lay of your land, the consistency of your soil, and how big your garden is, but with the first windstorm we got, that plastic looked like one of those parachutes we all played with in gym class. The stakes and staples were trying their hardest to stay stuck in the ground, and they were mostly failing. Our black plastic mulch looked like a tent that was about to launch into the atmosphere. We grabbed every brick and concrete block we could find and even cleaned out my rock garden in an attempt to keep that plastic where it was supposed to be.

Once the plants are established (especially if you’re growing viney things!) this isn’t as big of an issue. Before that, it is very helpful to have heavy items on the plastic. Also, anything used in your garden that happens to poke into the plastic (tomato cages, trellises, t-posts for fencing) is an extra bonus!

Pro tip: the less seams, the better. Every seam is a place the black plastic mulch can potentially lift up in the wind. The first year we had a lot of seams. We planned differently for our second year and only had one long seam, right down the middle of the garden.

How to use black plastic mulch

Here is the way that we go about setting up our garden with black plastic mulch.

First prepare your soil. Whatever it is that you do to your soil before you plant, do it now. Once the plastic is on, it’s much harder to make soil amendments.

On a nice calm day (don’t even try to do this if there is a breeze) we spread out our plastic. This year we made our garden slightly smaller in order to only have to buy one giant sheet of plastic that we could cut in half (therefore only having one seam in the entire garden).

If you have a large garden this might require all hands on deck. Some people may have to lay on the plastic (it’s amazing what a little breeze can do) while other people are staking it down.

Me, laying on a sheet of black plastic. Life is tough.

After landscaping stakes and garden staples are used around the perimeter and along the seam, we place large bricks around the perimeter and along the seam for extra wind insurance. We also place more bricks in random spots.

Our garden is fenced every year so that’s what comes next. We slam t-posts into the ground (through the plastic) which also helps to keep the plastic down. We then put our netting up. (If you’re fencing your garden, don’t forget to build a super easy garden gate!)

Then the garden sits for a few days until I’m ready to plant. I like to have that soil nice and toasty.

How exactly do you plant your garden if it’s covered in black plastic mulch?

For something that you’re planting in rows…

Cut a slit in the plastic the length of the row that you want to plant. Then at both ends of the row, make another perpendicular slit so you have a “T”. (Don’t make it a huge perpendicular slit. Remember, the length of the slit will be the width of your row. The wider your row, the more chance you have for weeds to sneak out.)

Fold the edges of the plastic under, opening up the area you’re going to plant in.

Dig in (these Honey Badger Gardening Gloves work great!), loosen the soil, drop your seeds where they need to go, and cover them up again with soil. It’s okay if you get a little crazy and some of the soil spills over on the plastic. It’s just one more thing to keep that plastic where it’s supposed to be.

You can add more bricks/staples/stakes along the spaces you’ve cut if you’d like. Keeping the plastic where it needs to be while those plants are getting started is super important.

For something you’re planting in hills (or a plant that’s already started)…

Cut an “X” in the plastic where you want the hill to be (or the started plant to be placed). Fold the edges of the “X” under so you have an open square.

Dig in, loosen the soil, pull up a mound of dirt to make a hill, and plant your seeds (or dig a hole and stick the started plant there). Again, you can use extra bricks, staples, or stakes around this new hole if you’d like.

And how do you water your garden if it’s covered in black plastic mulch?

A common question I get is how we go about watering the garden if we’re using black plastic mulch. Some people that use this method will employ the use of a soaker hose placed underneath the plastic. However, that requires knowing where you’re planting what before you lay down your plastic and I will fess up to you that I’m just not that organized.

When using black plastic mulch it is completely okay to use a sprinkler to water, although it’s a little overkill because you’re watering a lot of space that isn’t really going to get the water. Having said that, if you’re in for windy weather and worried that your black plastic is going to parachute off into the sky, running a sprinkler and letting the low spots of your plastic fill up a bit with water is an easy way to add weight and help the plastic stay put.

When we water, I just walk around with a hose or watering can and water the holes or trenches. It’s a nice way to spend 10 minutes (when it’s needed) and it gives me a chance to look closer at what’s going on in the garden.

Do you have any questions about black plastic mulch? Do you think it would work for you in your gardening set up? Leave a comment and let me know!

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