The best time-saving measure a gardener can take is applying mulch. This goes for everywhere from vegetable gardens to flower beds. Mulched gardens grow healthier, have fewer weeds, and resist drought than unmulched ones. Done properly, it’ll allow you to spend less time watering, weeding, and fighting pest problems.
- How to Mulch
- Picking Mulch for Your Garden
- Grass clippings
- Straw or hay
- Plastic mulch
- Controlling weeds in flowerbeds
- 5 Weed Killers that Won’t Harm Plants
- Mulch Weed Control – Tips On Getting Rid Of Weed Growth In Mulch
- Getting Rid of Weed Growth in Mulch
How to Mulch
There are two cardinal rules for using mulch to combat weeds. First, lay the mulch down on soil that is already weeded, and second, lay down a thick-enough layer to discourage new weeds from coming up through it.
It can take a 4- to 6-inch layer of mulch to completely discourage weeds, although a 2- to 3-inch layer is usually enough in shady spots. If you know that a garden bed is filled with weed seeds or perennial roots, you can use a double-mulching technique to prevent a weed explosion. Set plants in place, water them well, then spread newspaper and top it with mulch.
Mulches that also retains moisture (like wood chips) can slow soil warming. In spring, pull mulch away from perennials and bulbs for faster growth. A wet mulch piled against the stems of flowers and vegetables can cause them to rot; keep mulch about 1 inch away from crowns and stems.
Mulch piled up against woody stems of shrubs and trees can also cause rot and encourages rodents (such as voles and mice) to nest there. Keep deep mulch pulled back about 6 to 12 inches from trunks.
Picking Mulch for Your Garden
There are two basic kinds of mulch: organic and inorganic. Organic mulches include formerly living material such as chopped leaves, straw, grass clippings, compost, wood chips, shredded bark, sawdust, pine needles, and even paper. Inorganic mulches include black plastic and geotextiles (landscape fabrics).
Both types discourage weeds, but organic mulches also improve the soil as they decompose. Inorganic mulches don’t break down and enrich the soil, but under certain circumstances they’re the mulch of choice. For example, black plastic warms the soil and radiates heat during the night, keeping heat-loving vegetables such as eggplant and cherry tomatoes cozy and vigorous.
Learn more about using different types of mulch below:
Wood chips or shredded leaves
You can purchase bags of decorative wood chips or shredded bark from a local garden center to mulch your flower garden and shrub borders. A more inexpensive source of wood chips might be your tree-care company or the utility company. Many community yard waste collection sites offer chipped yard debris or composted grass clippings and fall leaves to residents for free (or for a small fee). Also, consider chipping your Christmas tree instead of tossing it to the curb.
If you have trees on your property, shredding the fallen leaves creates a nutrient-rich mulch for free. You don’t need a special machine either; a lawn mower with a bagger will collect leaves and cut them into the perfect size for mulching.
Spread a wood chip or shredded leaf mulch anywhere on your property, but it looks especially attractive in flower beds, shrub borders, and garden pathways. Of course, it’s right at home in a woodland or shade garden. Wood chips aren’t a great idea for vegetable and annual flower beds, though, since you’ll be digging these beds every year and the chips will get in the way.
Grass clippings are another readily available mulch, although it’s a good idea to return at least some of your grass clippings directly to the lawn as a natural fertilizer. It’s fine to collect grass clippings occasionally to use as mulch, and the nitrogen-rich clippings are an especially good choice for mulching vegetable gardens.
If you have enough compost, it’s fine to use it as a mulch. It will definitely enrich your soil and make your plants happy, but keep in mind that when any kind of mulch is dry, it’s not a hospitable place for plant roots. So you may want to reserve your compost to spread as a thin layer around plants and top it with another mulch, such as chopped leaves. That way the compost will stay moist and biologically active, which will provide maximum benefit for your plants.
Straw or hay
Another great mulch for the vegetable garden is straw, salt hay, or weed-free hay. It looks good and has most of the benefits of the other mulches: retaining soil moisture, keeping down weeds, and adding organic matter to the soil when it breaks down. Ensure the hay you use is weed and seed free, or you’ll just be making trouble for your garden. And don’t pile hay or straw up to the stems of vegetables or the trunks of fruit trees or you’ll be inviting slug and rodent damage.
Mulching a vegetable garden with sheets of black plastic film can do wonders. When it’s spread tightly over a smooth soil surface, black plastic will transmit the sun’s heat to the soil beneath, effectively creating a microclimate about three degrees warmer than an unmulched garden. Because the plastic film remains warm and dry, it protects the fruits of vining crops such as strawberries, melons, and cucumbers from rotting and keeps them clean. And of course, the mulch prevents weed growth and retains soil moisture.
Infrared transmitting (IRT) plastics cost more than standard black plastic, but they can result in even higher yields. These plastics warm the soil as well as clear plastic does, but also control weeds as well as black plastic does. In raised bed gardens, lay down a sheet of plastic over the entire bed. Bury it at the edges or weigh the plastic down with rocks. Then punch holes in it for the plants. A bulb planter makes quick work of hole cutting.
Sow seeds or plant transplants in the holes. Because water can’t permeate plastic, rainwater won’t soaking the planting bed. Thus, the ideal watering system for a plastic-covered bed is soaker hoses or drip hoses laid on the soil surface before you put down the plastic.
Don’t use plastic as a mulch under shrubs. Although it keeps out weeds and can be camouflaged with decorative mulch, black plastic destroys the shrubs’ long-term health. Because water and air cannot penetrate the plastic, roots grow very close to the soil surface — sometimes right beneath the plastic — seeking moisture and oxygen. The shallow roots suffer from lack of oxygen and moisture and from extremes of heat and cold. Eventually the plants decline and die. Stick to organic mulches such as shredded leaves, bark, wood chips, or compost under your trees and shrubs.
Geotextiles, also called landscape fabrics, let air and water through to the soil beneath while keeping weeds from coming up. But geotexiles have some of the same drawbacks as black plastic. When exposed to light, they degrade over time, so to make them last longer, you have to cover them with a second mulch (they’re ugly, so you’d want to, anyway).
Many gardeners have discovered that shrub roots grow up into the landscape fabric, creating real problems when you eventually want to remove it. Weeds that germinate in the surface mulch send roots down into the fabric, too, tearing it when you pull them out.
With luck, your garden is growing some lovely goodies right about now, whether you’ve planted for looks or for food. You may also be growing a few unwelcome weeds here and there as well. Sure, you can pull them up, but they always seem to come back, right? That’s because their seeds are below the surface and they grow quickly. The solution? A simple piece of cardboard from an ordinary cardboard box.
As you can see from this video from the folks at Apartment Therapy, all you need is a piece of carboard—a side of a box will do, as long as it doesn’t have ink on it or isn’t coated in wax. Just put the cardboard down over the spots of your garden where the weeds are known to live, cover it over with a thick layer of mulch, and leave it alone. The cardboard will keep the weeds from growing up through the dirt and insulate the ground to a temperature that kills the weed seeds. Plus, the cardboard is biodegradable and should break down over the next year under the mulch.
Granted, this means that you now have a spot in your garden where you probably shouldn’t plant anything new right now, so don’t go laying down cardboard everywhere and try to grow something in the mulch on top right away. Try this in areas that you’ve cleared already, and leave the cardboard alone for a while. Apartment Therapy doesn’t mention it specifically, but I’ve also heard newspaper works well for this purpose. Looking for some more weed-removal tips? We’ve got you covered. If you have any other garden-friendly weed-killing suggestions, make sure to let us know.
One Minute Tip: How to Kill Your Weed Seeds | Apartment Therapy
Controlling weeds in flowerbeds
Louisianians take pride in the appearance of their landscapes, and weeds detract from this beauty. Along with being aesthetically displeasing, weeds in flower beds compete with desirable plants for water, nutrients and light and soon can get out of control.
Most people rely on back-breaking hand removal to remove weed problems. Hand pulling may be successful for a few weeds, but for most it is only partially effective. Weeds have defense mechanisms that reduce the effectiveness of hand pulling. Annual weeds often break at the stem when pulled, leaving the root or single stem available for potential reestablishment. However, for perennial weeds like purple nutsedge and bermudagrass hand removal is nearly impossible. Perennial weeds have underground structures that are left in the soil after hand removal.
In reality, hand pulling weeds is one of several practices that should be used together for optimum weed control in flowerbeds. These additional practices include the use of mulch, preemergence herbicides and, to a limited extent, postemergence herbicides.
Mulch is an extremely important tool for weed management in landscape beds. Mulch acts as a physical barrier to the emerging seedling, and it prevents sunlight from reaching the soil surface. Blocking sunlight is important because some weed seeds such as crabgrass will not germinate without stimulation from sunlight. Also, sunlight is critical for the new weed seedling to begin photosynthesis for growth and development.
Several materials are suitable for mulch including, compost, leaf litter, pine bark, pine mulch and pine straw. Even newspapers can be used as a barrier to weed emergence. Mulches must be thick enough to block light to be effective. As a rule, mulch trees to a depth of 3-4 inches and shrubs to a depth of 2-3 inches. Though mulch is beneficial, it will not hold back most weed infestations. It is important to use mulch in conjunction with preemergence herbicides.
Using herbicides for flowerbed weed control can be difficult because of the wide array of high-value ornamental plants grown and their varying tolerances to herbicides. When it comes to herbicide use in flowerbeds, ornamentals are most tolerant of preemergence herbicides.
Preemergence herbicides are weed preventers that are used in most every row crop to supplement a bevy of postemergence herbicide choices. However, these types of herbicides are almost exclusively relied upon for flowerbed weed management and are the backbone of chemical weed control in landscape beds. Preemergence herbicides work by forming a barrier in the upper ½ to 1 inch of the mulch or soil where most seeds germinate and kill weeds as they attempt to emerge.
Because these herbicides have no effect on existing weeds, timing the preemergence herbicide application properly is critical for success. Because they work prior to weed emergence, applications must occur before weed germination. Any existing weeds should be hand removed or carefully spot-treated with a nonselective herbicide prior to treatment. Add water after applying the herbicide. In most cases preemergence herbicides should be applied every 2½ to 3 months. Consult product labels concerning tolerances by desirable plants.
Preemergence herbicides can be effective on several annual weeds including crabgrass, goosegrass, spurges, common purslane and mulberry weed. Most perennial weeds such as purple nutsedge and Florida betony are not controlled with preemergence herbicides.
It is important to control weeds with mulch and preemergence herbicides because once they have emerged your options become more limited. Few selective postemergence herbicides are available, especially for broadleaf weeds. There is good news when it comes to selectively controlling most summer grasses like crabgrass and bermudagrass and sedges like purple and yellow nutsedge. Most summer grasses are controlled with herbicides containing the active ingredients fluazifop or sethoxydim. Sedges can be controlled by directed sprays of halosulfuron (Sedgehammer) or sulfosulfuron (Certainty). Additionally, glyphosate can be carefully spot-treated or applied as a wipe for hard-to-control weeds.
Common weeds infesting flowerbeds
Spurge – Several types of spurges are common in landscape beds. Members of the Euphorbaceae (poinsettia) family, spurges are prolific seed-producing annuals that thrive in hot weather. Under optimum growing conditions, plants can go from seed to flower in only three weeks. Some spurges have a more prostrate growth habit that can form dense mats, whereas many spurge species grow more upright. Spurges emit milky latex from broken stems that can be helpful in distinguishing this plant from other species. The plants are difficult to manage in flowerbeds due to heavy seed production and the inability to be successfully removed by hand. Plants often break at the stem during this process, leaving the root and several buds or a single stem available for potential reestablishment.
Control: Most preemergence herbicides work well on spurge. However, the problem usually is in the frequency of the application because spurge control starts failing four to six weeks after application. Professional herbicides that work well include Free Hand (dimethenamid + pendimethalin), Pendulum/PreM and other trade names (pendimethalin), Barricade and Regalkade (prodiamine), Surflan (oryzalin) and Snapshot (isoxaben + trifluralin). Consumer herbicide options include Preen (dithiopyr or trifluralin) and Amaze (benefin + oryzalin).
Chamberbitter (Phyllanthus urinaria) – A member of the Euphorbiaceae family, chamberbitter is an extremely invasive summer annual. Chamberbitter resembles hemp sesbania or mimosa seedlings. However, the most distinguishing characteristic is the round seed capsules located on the underside of slender branches. Chamberbitter needs temperatures consistently above 75 degrees; therefore, these plants tend to germinate a little later in the spring than many other flowerbed weeds. Populations of chamberbitter have increased significantly since their introduction from Asia because of their prolific seed production and tolerance of most preemergence herbicides labeled for use in ornamental nurseries.
Control: Light may be necessary to stimulate chamberbitter germination, so thick mulch is helpful in reducing plant populations. Chamberbitter hand pulls very easily, but frequent germination and high populations make hand removal only partially effective. Preemergence herbicides have performed erratically, so using hand removal and mulch in conjunction with herbicides are important to optimize chamberbitter control. Professional herbicides that have activity on chamberbitter include Rout (oxyfluorfen + oryzalin), OH2 (oxyfluorfen + pendimethalin), and other oxyfluorfen containing herbicides. Sureguard and Broadstar (flumioxazin) are effective herbicides as well. Most consumer herbicides are weak on chamberbitter. However, Amaze (benefin+ oryzalin) provides partial control.
Common bermudagrass – Common bermudagrass is the most widespread grass problem infesting flowerbeds. It is a perennial, warm-season grass originating in Africa that grows well in our Louisiana climate. The grass is widely used for lawns, athletic fields and golf courses, but it is invasive in flowerbeds. Common bermudagrass is characterized by its dark green color, fine texture and the production of rhizomes (below-ground stems) and stolons (above-ground stems) that allow the plant to establish quickly in the landscape.
Control: Because of its complex stolon and rhizome system, hand removal is not effective for controlling common bermudagrass infestations in landscape beds. Because the weed mainly reproduces vegetatively and creeps into flowerbeds, preemergence herbicides have no effect on the weed either. Frequent applications of grass-killing herbicides like Fusilade and Segment can be effective in managing bermudagrass in landscape beds. These types of herbicides only work on grasses and are usually safe over the top of most nongrass landscape plants such as bedding plants, perennial ground covers and shrubs. Consumer versions of these herbicides include Ortho GrassBGon (fluazifop) and Fertilome Over the Top II (sethoxydim).
Nutsedges – Purple nutsedge ranks as the No. 1 weed problem in the world and is the most common weed infesting residential and commercial landscape plantings. Yellow nutsedge prefers moist environments and is more common in irrigated beds or during wet growing seasons. Both are grass-like plants with an extensive system of tubers that allow the plants to reproduce rapidly in landscape beds.
Control: Nutsedges are difficult to manage consistently in landscape beds. Neither purple nor yellow nutsedge can be controlled by hand removal, and mulches are only slightly effective. Yellow nutsedge can be partially managed with preemergence herbicides with the active ingredients metolachlor (Pennant Magnum) or dimethenamid (Tower and Free Hand). Unfortunately, there are no good preemergence options for purple nutsedge.
Postemergence herbicides Sedgehammer (halosulfuron) and Certainty (sulfosulfuron) are two effective herbicides registered for the selective removal of sedges in landscape beds. In most situations, these herbicides should be applied as directed sprays. Consult product labels for lists of tolerant plants and application techniques. For most situations, the best defense against weed infestations in the flowerbed is reliance on mulch, periodic hand pulling and an aggressive preemergence herbicide program.
Certain weeds prevalent in Louisiana landscapes are almost uncontrollable.These include torpedograss, bushkiller vine and cogongrass.
Torpedograss – Torpedograss is a perennial, rhizomatous grass that is considered one of the most invasive grasses in the world. Although the plant does produce seed, the seeds are not viable. The weedy grass solely reproduces vegetatively by robust rhizomes. The spread of torpedograss in Louisiana is mainly attributed to the movement of soils infested with torpedograss from the Bonnet Carré Spillway. The spillway is just west of New Orleans and is the main source of torpedograss for southeast Louisiana, especially within the New Orleans metro area. For years, there were no reports of infestations in north Louisiana; however, torpedograss infestations have been confirmed at several locations in northern areas of the state.
Control: Complete control of torpedograss may not be possible. Grass-killing herbicides normally prescribed for flowerbeds like sethoxydim and fluazifop are just not very effective on torpedograss, although fluazifop is a little better than sethoxydim. Glyphosate is the best herbicide on the weed, but high rates are necessary for control. Directed sprays of glyphosate are not always safe in landscape plantings due to the potential for drift. It may be safer to wipe the weed with a glyphosate/water solution that is at least 10 percent glyphosate when it is in a landscape bed. Using a chemical-resistant glove inside a cotton glove to wipe the solution on the torpedograss foliage is an effective method of application. Repeated applications are always necessary for torpedograss.
Bushkiller vine – This perennial herbaceous vine has compound leaves containing five leaflets. It produces salmon colored flowers eventually producing fruit with two to four seeds. Thankfully, the seed are not thought to be viable. The plant solely reproduces vegetatively. Native to Asia, bushkiller gets its name because the vine climbs over desirable plants and kills other plants by blocking out sunlight. Few weeds take over areas as fast as bushkiller vine, and it rapidly overtakes landscape shrubs and groundcovers.
Control: Bushkiller vine can be suppressed with repeated applications of two herbicides, glyphosate and triclopyr, applied as directed sprays. Unfortunately, the vine intertwines in the landscape, making herbicide applications very difficult. Often it is necessary to treat fresh-cut plants or wipe the weed directly when spraying is too risky in the landscape. Don’t expect to get rid of it with one application. Be sure to treat properties nearby because the weed will rapidly re-infest treated areas.
Cogongrass – Cogongrass has been causing problems in the southeastern areas of the United States for several years. Thousands of acres are covered with the perennial grass, and millions of dollars have been spent to control this invasive weed. In Louisiana, St. Tammany Parish has the highest population of cogongrass, another 10 parishes may have some degree of infestation. Cogongrass is native to Southeast Asia and spreads by both wind-blown seeds and underground, creeping rhizomes. The plant produces fluffy, white, plume-like seed heads in early spring. Cogongrass makes about 3,000 seeds per plant, but the seeds need to land on bare soil to get the weed established. The main way the plant gets established is by rhizomes either transported on tillage equipment, through contaminated soil or by creeping into new areas. Rhizomes may make up 80 percent of the plant mass, which allows the plant to recover from most mowing and herbicide applications. Once the cogongrass is established, the area becomes a monoculture of cogongrass with nothing else able to grow.
Control: Cogongrass control is a long-term endeavor that requires the repeated use of glyphosate and imazapyr (Arsenal). Areas treated must be taken out of use potentially for years. This weed problem requires landscapers no option but to declare an all-out war to reclaim the land.
Ron Strahan, Associate Professor, School of Plant, Environmental & Soil Sciences, LSU AgCenter, Baton Rouge, La.
(This article was published in the winter 2012 issue of Louisiana Agriculture magazine.)
5 Weed Killers that Won’t Harm Plants
Weeds are also called “invasive plants” because they invade your garden and spread. If left unchecked, a weed infestation can take over an entire yard and turn it into an eyesore.
Many people have trouble dealing with aggressive weeds because the poisons and weed killers that work on the weeds also harm your regular garden plants.
The following are all options you can exercise that will target weeds specifically and leave your other plants safe and sound.
This method is useful if your yard or garden is new and not already established.
Wait for your plants and seeds to start growing, and then treat your lawn to prevent weeds from appearing. Using your hands, broadcast a thin layer of cornmeal over garden and landscaping areas. The cornmeal prevents seed growth, in this case you’re aiming to stop weeds from seeding, so this is why you want to wait before spreading it on the ground. Doing it sooner will stunt the good seeds for your plants. Cornmeal will also attract worms that naturally churn and enrich the soil, so cornmeal is a good idea even if you don’t have a big weed problem.
You probably have a weed killer in your home right this very minute. If not, you can buy one at any grocery store: vinegar.
Get undiluted white vinegar and pour it into a spray bottle. Spray the vinegar directly on the weeds you wish to eliminate, and you’ll notice results within hours. Unlike many chemically-created weed killing agents, vinegar is a natural and perfectly safe substance for you, your children, and your pets. Vinegar can be safely ingested (though the taste is rather unpleasant), and it can be touched with bare skin. Vinegar is also affordable when compared with formulated chemical killers.
For best results, spray vinegar during a sunny day with minimal wind. The wind can carry vinegar away from weeds, and that’s not what you want. Vinegar can have adverse effects on other plants, but if you spray weeds directly it will not harm your other greenery or the soil itself.
- Vinegar is also an effective way to control garden bugs and pests. Spray it in areas where you’ve seen ants, slugs, or stray cats. The smell will keep them away.
3. Baking Soda
You don’t have vinegar on hand? What about baking soda? This is another safe product that can be used for weed control. Spread baking soda directly on weed-ridden areas to make the soil less hospitable to weeds. Baking soda can easily be sprinkled into cracks and crevices where weeds appear, such as sidewalks and driveways.
4. Salt Water
You can also boil two cups of water on the stove and add one cup of salt. Be sure to handle the boiling water carefully as you pour it directly onto weeds.
Plain salt can also be used without the water, but you want to exercise caution with this. “Salting the fields” is known for making the soil inhospitable to plant life of all kinds, so you want to be judicious.
Spread mulch in garden and landscaped areas to smother weed growth. If you notice weeds appearing in these areas anyway, cover the area with newspaper. The newspaper will prevent light and air from getting to the soil, and that will kill weeds.
Don’t cover the plants you want to save.
The best natural way to prevent weeds is to maintain a healthy lawn. Thick, lush grass offers little bare soil that weeds can latch onto. Keep your lawn looking good, and you’ll see a lot fewer weeds.
Eliminate weeds safely by treating them directly and keeping your soil healthy. If you treat the weeds directly, you can get rid of the ones you don’t want and save all the others.
While it’s tempting to call any unwanted plant a “weed,” there are really only a select few weeds that become invasive and problematic. And while some folks turn to dangerous chemicals, many weeds are actually resistant to herbicides and respond better to different methods of control. With these weed control techniques in your gardening arsenal, weeds won’t stand a chance!
Mulch Over Them
Mulch is a covering that blocks weed seeds from sunlight so they don’t germinate, inhibits growth underneath itself, and retains moisture. Also, mulch provides needed nutrients as it decomposes over time, and moderates soil temperatures.
- Cover the soil between your plants and along rows with mulch to prevent weeds from growing.
- Keep the mulch a few inches from the base of your plants to discourage insect invasions and prevent rot, too.
- Common organic mulches include wheat straw, shredded leaves, and wood chips; inorganic mulches include black plastic and landscaping fabric.Layer organic mulches on the ground about 2 inches thick.
If you use leaf blowers, many come with shredders that turn yard debris into garden mulch fast to save you the costs of making or buying your own (like this shredder from Echo).
For persistent or numerous weeds, try covering the area with dampened newspaper (black ink only) and then cover with 2 inches of mulch. Around the bases of trees and shrubs, consider covering the ground with landscape fabric and then an organic mulch. See our mulching guide.
Plant Cover Crops
Cover crops, like wheat, clover, and barley, are generally beneficial plants and are capable of spreading rather easily. In some situations, you can use a cover crop to block weeds. See our list of cover crops.
Pull Them Out
For better or worse, you’ll need to manually pull out most weeds. Wear waterproof gloves and consider a comfortable sitting pad for extensive weeding. The trick to pulling weeds is to get the root out as well, since many common weeds—like dandelions—will regrow from any roots left in the ground. Weeds will slide out of the soil easier when the soil is wet and the weeds are young. Pull the weed from its base (close to the soil line); if you miss the root, try using a fork to gently pry the plant out of the ground, roots and all.
Dig Them Up
If your weeds regrow, then you have a persistent root that you need to dig out. Use a spade or digging fork to dig up persistent weeds by the roots. Remove as many root pieces as you can.
While weeding, hold the trowel vertically (like a child holding a crayon) to eliminate strain on your wrist.
Chop Them Down
If digging out weeds is too much of a hassle, at least resolve to keep them from setting seed. Chop off their heads once a week!
Minimize Soil Disruption
Gardeners used to advocate cultivation—stirring the top one or two inches of soil to damage weeds’ roots and tops, causing them to die. However, unless you are able to fully remove the roots from the soil, cultivation seems to simply expose dormant weed seeds to light and air, awakening them. Instead, it may be best to preserve the natural soil layers.
Some folks say it helps to turn your soil at night to control weeds. Research indicates that weeds may be stimulated to grow by a sudden flash of light, which is what you give them when you turn the soil over during the day. A German study concluded that by turning the soil at night, weed germination could be reduced by as much as 78 percent. You can try this method by working under a full Moon, or at dawn or dusk.
Keep Your Garden Edges Trimmed
Ever noticed many weeds collect at the edges of your yard or garden? Keep the edges mowed; this will help prevent a weed invasion.
However, many lawn mowers aren’t able to do a good job of getting to the weeds along the edges of your lawn, around posts and fence lines, and close to planting beds.
To get to those weeds more easily, consider a trimmer (like these trimmers from Echo), especially if you have medium to heavy rugged weeds that have grown in.
Reduce Open Garden Space
If your soil is rich and drains well, plant your plants closer together. This will cut down weed growth.
Start your warm weather plants as soon as you can to keep the soil from being bare for too long. At the end of the season, plant cover crops such as rye grass, winter wheat, or oats to prevent weeds from finding a home in your garden.
Let Them Grow…Temporarily
Encourage weeds to grow before you plant your garden. Lay sheets of clear plastic over your garden in early spring to warm up the soil and encourage weeds to germinate. Once the weeds are several inches above the soil, pull or hoe them out. Then plant your own crops.
Use Drip Irrigation
If you can water only the plants that need it, you may avoid the cultivation of weeds in unplanted areas, paths, and areas where they are not welcome.
Yes, some weeds—lamb’s quarters, amaranth, purslane and others—are edible when young and tender! Learn more about eating your weeds!
Know Your Enemy
Know how to identify your more invasive and destructive weeds. Check out our list of common weeds to help identify what’s growing in your garden and learn how best to get rid of it.
With these weed control techniques in your gardening arsenal, weeds won’t stand a chance!
Mulch Weed Control – Tips On Getting Rid Of Weed Growth In Mulch
Weed control is one of the primary reasons for applying mulch, yet pesky weeds may persist, even through a carefully applied layer of bark chips or pine needles. This happens when weed seeds are buried in the soil or are distributed by birds or wind. What should you do if you’ve got weeds coming up in mulch in spite of your best intentions? Keep reading for a few helpful tips.
Getting Rid of Weed Growth in Mulch
Manual Mulch Weed Control
Mulch acts as physical barrier against weeds, but it must block sunlight in order to be effective. If you notice weeds coming up in mulch, you may need to thicken the layer as blocking light generally requires at least 2 to 3 inches (5-7.6 cm.). Replenish mulch as it decomposes or blows away.
How to Kill Weeds in Mulch with Herbicides
Other than hand-pulling, mulch is probably the single most important means of weed control. However, mulch works best when used as part of a multi-pronged approach along with pre-emergent herbicides.
When used correctly before weeds sprout in early spring, pre-emergent herbicides are one effective way to prevent weeds coming up in mulch. They won’t, however, do anything for weeds that have already sprouted.
To stop weeds in mulch with pre-emergent herbicides, begin by raking mulch off to the side, then hoe or pull any existing weeds. Apply the product, following manufacturer directions to the letter. Pay attention to the label, as some plants don’t tolerate certain types of pre-emergent herbicides.
Replace the mulch carefully, being careful not to disturb the just treated soil. At this point, you can provide extra protection by applying another layer of herbicide over the mulch. A liquid herbicide works best because it adheres to the mulch instead of falling through to the soil.
A Note about Glyphosate: You can use glyphosate to stop weeds in mulch, but this approach requires extreme care because glyphosate, a broad-spectrum herbicide, will kill any broad-leaved plant it touches, including your favorite perennials or shrubs. Apply glyphosate directly to weeds, using a paintbrush. Be extremely careful not to touch nearby plants. You can also protect plants by covering them with a cardboard box while you’re applying the herbicide. Don’t remove the box until the treated weeds have time to dry completely.
Preventing Weeds with Landscape Fabric
If you haven’t applied mulch yet, landscape fabric or weed barrier cloth is a safe way to block weeds while still allowing water to pass through to the soil. Unfortunately, landscape fabric isn’t a perfect solution because some determined weeds will push through the fabric, and those weeds will be extremely difficult to pull.
Sometimes, good old hand-pulling is still the most effective way of getting rid of weed growth in mulch.
Note: Chemical control should only be used as a last resort, as organic approaches are safer and much more environmentally friendly.
Weed management in landscape plantings is a complex task. The diverse nature of the ornamental plant material and weeds present and differences in the size and slope of the beds create quite a challenge. Herbicide options are limited by the mixture of woody and herbaceous ornamentals, as well as health and environmental concerns. Thus, the integration of multiple strategies is necessary to keep weeds from detracting from the beauty and quality of a landscape.
DESIGN FOR CONTROL. The ideal landscape according to a weed scientist might not win any awards for diversity, but grouping similar plant material together allows for more weed control options in the beds. Herbaceous plants, especially annual flowers, are more sensitive to herbicides than ornamental shrubs or trees. In such flower beds, mulching and hand pulling of weeds are often the only weed control options. More herbicides are registered for use around woody ornamentals, which also help shade out weeds that might otherwise germinate.
Certainly, a rich variety of plant types and colors in a landscape is desirable and attractive, but designers should at least consider the require-ments for maintaining the landscape over time.
ON THE SITE. Before establishing a planting, evaluate the site for soil type and slope and identify existing weeds so suitable plant material, mulching and herbicide use can be selected. Control existing weeds with a nonselective herbicide before the beds are established.
Avoid introducing weeds or their propagules (seeds, rhizomes) into the landscape, and eliminate weeds that emerge before they begin to form seed. Root balls of field-grown nursery stock may contain tubers or rhizome fragments of perennial weeds, which are then transplanted into the landscape with the shrubs.
COMPARING MULCHES. Mulches can be classified as organic (bark, wood chips, composted leaves, pine needles), inorganic (crushed rock, gravel) or synthetic (black plastic, landscape fabric). Mulches limit light and physically block seedling growth.
Coarse-textured organic mulches can be applied up to 4 inches deep and provide long term weed control. Fine-textured mulches pack more tightly and should be limited to a depth of 2 inches. They degrade more quickly and consequently provide weed suppression for a shorter period of time.
The optimum mulch is relatively coarse-textured with a low water-holding capacity. Because mulches rarely provide complete weed control, preemergence herbicides can be applied to improve the level of control.
Perennial weeds such as bindweed and mugwort often have sufficient root reserves to penetrate even thick mulch layers. Even annual weeds can grow through mulches or germinate on top of a mulch as it decomposes. Weeds with wind-borne seeds such as horseweed, common groundsel and dandelion are most likely to establish in the mulch.
Natural inorganic mulches like gravel or stone are generally more expensive than organic mulches. However, they are stable over time, allow good water drainage and air flow and can make very attractive mulches.
WEED BARRIERS. Black plastic mulch has been used for years and provides excellent control of annual weeds and suppression of perennials. However, nonporous black plastic restricts water penetration and air exchange; thus, it is not recommended for long-term use in landscape plantings.
Porous, black landscape fabrics (geotex-tiles) have been developed to replace black plastic in landscapes. Landscape fabrics form a barrier and block sunlight from reaching weed seeds, but allow water and gas exchange necessary for plant health. Although relatively expensive and labor intensive, landscape fabrics are cost-effective if the planting is to remain in place for several years.
Landscape fabrics are most useful for long-term weed control around trees and shrubs, but not for annual flower beds that are replanted periodically or where a fabric could inhibit rooting and spread of ground covers. Landscape fabrics can eventually be damaged by tree and shrub roots, and pulling up a fabric may be difficult due to root growth within the material.
When installing a fabric, first remove existing weeds and stones. Cut the fabric to fit snugly around tree trunks and shrubs. For unplanted beds, cut an “X” in the fabric for each planting hole. Avoid leaving soil from the planting hole on top of the fabric since this will serve as a source of weed seeds.
After planting, fold the fabric back down to keep the sheet as continuous as possible and secure to the soil with U-shaped pegs. Apply a thin layer of organic or rock mulch on top of the fabric to prevent its photo-degradation. Remove any weeds that grow into or through the fabric when they are small to prevent holes from forming in the fabric.
Alternative Methods for Applying Herbicides
- Landscape fabrics impregnated with trifluralin are now available (i.e. Biobarrier II). Once in place, the fabric should be covered with 1 to 2 inches of organic mulch. This approach integrates the use of nonchemical and chemical weed control methods. In addition, the trifluralin is applied without the need for calibrating, mixing, spraying, or cleaning up.
Customized hand pruners (i.e. KlipKleen) that apply a postemergence herbicide to the stem as it is cut are useful for controlling woody brush and vines such as poison ivy. Herbicides that are effective with these pruners are one-fourth to full strength solutions of glyphosate, 2,4-D, or triclopyr. Even though concentrated herbicide is needed, the overall amount of herbicide used will be reduced and its placement will be more precise because it is applied directly to the cut stem instead of being sprayed over the entire plant.
THE HERBICIDE OPTION. Landscape managers often use herbicides to improve the efficiency of weed control. Some factors to consider before selecting an herbicide are:
- What weeds are present and what weeds are expected to emerge? Choose an herbicide or combination of herbicides that will be effective on these weeds.
- What ornamental species are present in the planting? Be sure the herbicide is registered for use on these species.
- How close are susceptible ornamentals and turf, and what is the risk that they will be injured by the herbicide?
- What is the potential for residual effects of the herbicide on subsequent plantings, especially those containing annual flowers?
- What precautions need to be taken to protect the applicator and property owners?
- What method will be used to apply the herbicide (granular or spray formulation)?
- How much will the treatment cost?
In the Northeast, herbicides are typically applied in the early spring to prevent summer annual weeds, and in the late summer to prevent winter annual weeds.
The dinitroanilines, a group of preemergence herbicides including Treflan™ (trifluralin), Surflan™ (oryzalin), Pendulum™ (pendimethalin) Barricade™ (prodiamine) and Team™ Pro (trifluralin + benefin) inhibit root development in germinating seedlings. They are most active on annual grasses, but also prevent the emergence of some broadleaf weeds. Other preemergence herbicides for landscapes are Devrinol™ (napro-pamide), Pennant™ (metolachlor), Dacthal™ (DCPA), Ronstar™ (oxadiazon), Gallery™ (isoxaben) and Goal™ (oxyfluorfen).
Devrinol, Pennant and Dacthal prevent the emergence of annual grasses and some broadleaf weeds. Pennant, in addition, has preemergence activity on yellow nutsedge.
Gallery controls a wide spectrum of broad-leaf weeds, while Ronstar and Goal have greater preemergence activity on broadleaf weeds than grasses.
Herbicide combinations increase the weed control spectrum. Applicators may mix two of the “grass” and “broadleaf” herbicides listed above or use one of the following granular herbicide combinations: Rout™ (oxyfluorfen + oryzalin), Ornamental Herbicide 2™ (oxyfluorfen + pendimethalin), Snapshot™ TG (isoxaben + trifluralin), Team or XL™ (oryzalin + benefin). Product labels must be checked carefully for lists of registered ornamental species.
MULCH + HERBICIDES. The characteristics of the organic mulch can dramatically affect herbicide performance. A mulch composed primarily of fine particles can absorb herbicides, making the chemical less active, whereas a mulch composed of coarser particles is less likely to affect herbicide efficacy.
The depth of the mulch layer is also a factor. For an herbicide to work when applied on top of the mulch, it has to leach through to the zone in which weed seeds are germinating. Many of the herbicides used in landscapes have low solubility in water. Thus, if the mulch layer is too thick, the herbicide may not move through the mulch.
Most herbicides work best when applied underneath the mulch layer. Such placement is possible only if the herbicide is applied before the mulch is deposited or if additional mulch is spread after herbicide application. Another reason to apply herbicides under mulch is to reduce volatilization losses.
If tough-to-control weeds such as mugwort, thistles or field horsetail are problems in a planting, the granular herbicide Casoron™ (dichlobenil) may be an appropriate choice. Casoron can be used around established woody ornamentals such as yews, arborvitae and juniper, but not around firs, spruces, or hemlocks. Because of its volatility Casoron should be applied during cool weather and either covered with mulch or watered in soon after application. Of the herbicides registered for landscapes, Casoron provides the best preemergence control of biennial and perennial weeds.
POSTEMERGENCE APPLICATIONS. Postemer-gence herbicides generally provide minimal residual weed control — they are either inactivated by binding to soil particles or rapidly degraded by soil microorganisms. Roundup Pro™ (glyphosate), Finale™ (glufosinate), Reward™ (diquat) and Scythe™ (pelargonic acid) are nonselective herbicides which must only be applied as directed or spot treatments in which ornamentals and turf are not contacted. Reward and Scythe rapidly kill vegetation contacted by their spray, but perennial weeds can regrow. Finale is primarily a contact herbicide, but limited translocation occurs in the plant. Roundup Pro, a slower acting herbicide, is readily translocated to roots and growing points of plants, whereby it kills both annual and perennial weeds.
Several postemergence grass herbicides are registered for use in landscapes. These products include Vantage™ (sethoxydim), Fusilade™/Ornamec™ (fluazifop), Envoy™ (clethodim) and Acclaim™ (fenoxaprop). The postemergence grass herbicides can be safely sprayed over the top of most woody and herbaceous plants (except ornamental grasses), but check the label carefully for any precautions about susceptible species.
The author is assistant agricultural scientist at the Connecticut Agricultural Experiment Station, Windsor.
Gallery, Surflan, Treflan, Snapshot, Team and XL are registered trademarks of DowElanco, Indianapolis. Deverinol, Fusilade and Reward are registered trademarks of Zeneca Professional Products, Wilmington, Del. Barricade and Pennant are registered trademarks of Novartis, Greensboro, N.C. Finale and Acclaim are registered trademarks of AgrEvo, Wilmington, Del. Vantage is a registered trademark of BASF, Research Triangle Park, N.C. Envoy is a registered trademark of Valent, Walnut Creek, Calif. Pendulum and Image are registered trademarks of American Cyanamid, Wayne, N.J. Scythe is a registered trademark of Mycogen, San Diego, Calif. Goal is a registered trademark of Rohm & Haas, Philadelphia, Pa. Ronstar is a registered trademark of FMC Corp., Hoopeston, Ill. Roundup Pro is a registered trademark of Monsanto, St. Louis, Mo. Dacthal is a registered trademark of ISK Biosciences, Marietta, Ga. Rout and Ornamental Herbicide 2 are registered trademarks of The Scotts Co., Marysville, Ohio. Casoron is a registered trademark of Uniroyal Chemical, Middlebury, Conn.
EDITOR’S NOTE: Mention or absence of any product is not meant to be an endorsement or criticism. Lawn & Landscape magazine wants to learn of new products as they are available. Please send product announcements to: Lawn & Landscape, 4012 Bridge Avenue, Cleveland, Ohio 44113. Always read and follow the label.