Growing herbs in greenhouses

Herb Growing In Greenhouses: How To Grow Greenhouse Herbs

If your environment includes months of frozen cold or equal amounts of time in scorching heat, you may think you’ll never be able to grow a successful herb garden. The answer to your problem is a greenhouse. Greenhouses provide an artificial environment that’s perfect for growing tender plants, and using a greenhouse for growing herbs can extend your season and increase the variety of plants you grow. Learn how to grow greenhouse herbs and some of the best varieties that thrive in a greenhouse environment.

Using a Greenhouse for Growing Herbs

Using a greenhouse allows you to control the heat, moisture, and shade for your plants, giving them the most perfect environment in which to grow. Greenhouse herb gardening can protect tender annuals from extreme summer heat, while extending the season and allowing your plants to grow earlier and later in the season. The key to getting the most out of your greenhouse is in setting it up before you add a single plant.

Install a misting system and automatic drip hoses in order to ensure a steady supply of moisture to your plants. Herbs fail for many reasons, but lack of adequate moisture is among the most common. With an automatic system that gives a regular, smaller supply of water each day, you’ll be assured of steady herb growth.

Another key item for herb growing in greenhouses is a system of shading the plants. If you are building a new greenhouse, don’t create a roof made entirely of glass or plexiglass. Some skylights or sunroof-type installations are great for air circulation, but more herbs need shading from the most brilliant of the afternoon sunshine. If your greenhouse is already built, create a shade system with rip-stop nylon and hooks or Velcro to attach it to the roof. This system will be easy to attach and remove, depending on the needs of your plants.

Types of Herbs for Greenhouses

The best herbs for greenhouse growth are those tender annuals that are too sensitive for the average garden or any herb you wish to grow stronger and in a longer season than normal. Some of the more common herbs grown in a greenhouse include:

  • Basil
  • Chives
  • Cilantro
  • Dill
  • Parsley
  • Chamomile

Mints are also ideal for greenhouse growing, and because mint is such an invasive plant, it should almost always be planted in a container. Growing your mint in a greenhouse will allow you to experiment with the hundreds of different mint varieties available to the home grower.

There are few things as delightful as a fragrant bouquet of fresh herbs.

Whether collecting a combination from the garden for a culinary treat, or strolling through a glasshouse brimming with the essence of seasonings, herbs are quite simply heavenly.

It‘s no wonder they‘ve played a prominent role in many cultures throughout the world, and in medical, cosmetic and culinary practices throughout history.

Although commonly planted outdoors-in containers, as companions to vegetables, or comingled in mixed borders-many herbs are easy to grow as glasshouse or greenhouse plants.

Not only do they (and we) benefit from a longer growing season in a glasshouse or greenhouse, many herbs properly cultivated in spring, or stored over winter in a protected environment, are healthier and more robust than their outdoor counterparts.

Begin in the Spring

Propagating herbs in a greenhouse or glasshouse jump-starts the garden season for the winter-weary, and is less costly than purchasing full-grown garden plants.

Generally speaking, annual and biennial herbs can be started in the greenhouse or glasshouse with seeds; perennial herbs with plant cuttings or plugs.

According to Katherine L. Adam, writing for the National Sustainable Agricultural Information Service:

“Greenhouse production methods for herbs are similar to those for greenhouse-grown vegetables. There are some practices, however, that are specific to herb production.”

And not all herbs have the same growing requirements. Mint (Mentha), for example, is best grown in a controlled, raised greenhouse bed, while rosemary (Rosmarinus) is best cultivated in single pots in poor to moderately fertile soil.

The Essence of Herbs in Winter

A number of herbs, including chervil (Anthriscus cerefolium) and coriander (Coriandrum sativum) like to be sown in autumn, and will grow well during winter in a frost-free glass or greenhouse.

Chervil, for example, grows well in a glasshouse or greenhouse in winter in well-drained soil in sun or partial shade.

In addition to sowing seeds in autumn, root cuttings from chervil may be planted in mid-winter for continuous culinary use.

Coriander can also be cultivated for seeds or leaves throughout the year if grown in light, fertile and well-drained soil in full sun for seed production, and partial shade for leaf growth.

Herbaceous perennial herbs such as chives (Allium schoenoprasum), tarragon (Artemesia dracunnculus), thyme (Thymus) and dill (Anethum) grown outdoors in mild weather can be forced in a glasshouse or greenhouse during winter.

Simply lift the plants from the ground before frost, and replant them in a humus-rich potting mix.

With a little bit of attention, they will continue to supply fresh culinary fare throughout the stale months of winter.

Overwintering to Protect Herbs

Many herbs benefit simply from the protection of a greenhouse or glasshouse, even if you don‘t plan to harvest them in winter.

Anise (Pimpinella anisum), cumin (Cuminum cyminum), Lemon verbena (Aloysia triphyllia) and parsley (Petroselinum crispum), for example, can be brought into the glasshouse or greenhouse when the weather turns cool, and have their roots and shoots wrapped in plastic, or the plants covered with a cloche.

Gardeners who grow herbs in containers outdoors may also bring the containers inside a heated greenhouse or glasshouse to store them for the winter.

Whether your intent is to harvest herbs year-round, or to simply afford your plants the best protection, glasshouses and greenhouses are the perfect way for herb-lovers to spice up the gardening season in any climate.

Sources:

For details about the production, harvest and care of specific herbs, see Growing and Selling Fresh-Cut Herbs, by Sandie Shores, 2nd edition, Ball Publishing, Batavia, IL.

For a discussion of herb propagation methods, including growing organic herbs and pest management methods, .

Fig. 1. Hydroponic herbs are an excellent crop that are well-suited to production systems similar to those used for other leafy greens. Here, basil and other herbs are grown alongside other greens including spinach and Swiss chard; note the basil being grown in a deep-flow technique system placed underneath a nutrient-film technique system.

Genetics: When considering what to grow, the number of herbaceous culinary herbs can be staggering. However, there are certain herbaceous herbs which are either widely or more commonly grown. The most popular culinary herb is basil, and, more specifically, sweet basil (Ocimum basilicum). There are other basils that are popular, such as citrus, cinnamon and Thai basils, but these are purchased in a much smaller volume than sweet basil. Culinary herb producers can’t grow only basil — a complete palate of herbs must be grown. Some of the other relatively more popular herbs include mint (Menth sp.), flat-leaf parsley (Petroselinum crispum), cilantro (Coriandrum sativum), rosemary (Rosmarinus officinalis), oregano (Origanum sp.), and thyme (Thymus vulgaris), and other seasonal offerings such as sage (Salvia officinalis). There are many other herbs that can be grown, and you can tailor your product mix to suit the market(s) you serve. Regardless of which culinary herbs you select to grow, nearly all herb cultivars were developed for field production and you will want to trial cultivars to see which perform best in your production system and environment. Selecting high-yielding cultivars with good greenhouse performance can be one of the most impactful decisions you’ll make.

Production systems: Culinary herbs are produced in the same systems that are used for other leafy crops, such as nutrient-film technique (NFT) and deep-flow technique (DFT) or raft systems (Fig. 1). Less-traditional production systems such as beds or containers filled with soilless growing substrate may also be used for herb plantings.

Propagation and young plant production: For NFT and DFT systems, phenolic foam and stone wool are the most commonly used substrates regardless of how herbs are propagated. The majority of culinary herbs are propagated by seed. Seed can be sown either individually or in multiples. While covering can benefit the germination of some species, it is generally not required. High humidity and moderately warm temperatures from 73 to 78° F can promote radicle emergence; lower temperature and increase light as cotyledons develop. Fertilize seedlings from the start of propagation with a diluted fertilizer solution of 100 to 150 ppm N. Some herbs may be propagated from cuttings, such as some cultivars of rosemary or specialty sage cultivars (Fig. 2). Culture is comparable to seedling: start off with higher humidity, warmer temperatures and lower light, then as cuttings root and develop, lower the humidity and temperature and increase light. Be sure to check if the varieties you want to propagate by cuttings are protected varieties or not.

Nutrient solution: For culinary herbs grown in water-culture systems like NFT and DFT, the pH and electrical conductivity (EC) of the nutrient solution need to be managed throughout production. Herbs can be grown well across a range of nutrient solution ECs. The EC, if maintained, has little effect on yield, in that increasing EC does not necessarily increase yields. If the EC is consistently maintained at or above 0.5 m and does not fluctuate greatly, the range of ECs suitable for herb production can be relatively wide (0.5 to 4.0 mS/cm). By maintaining an EC of 1.0 to 2.0 mS/cm, you can grow healthy looking herbs with adequate tissue nutrient concentrations. Some herbs have a greater requirement for specific nutrients. Sweet basil is a good example; it requires higher concentrations of magnesium compared to other species, and is also prone to display iron deficiency if inadequate iron is provided or solution pH gets too high.

Temperature: Herbs vary in their response to air temperature, with respect to growth and development, and can be classified as cool, moderate or warm-growing species. The majority of herbs, including favorites like dill, parsley and cilantro, grow well at moderate greenhouse temperatures with average days up to 72 to 75° F. While these species also tolerate cool temperatures, production time will be increased the cooler they are grown. Alternatively, basil species grow fine at standard temperatures but grow best at warm temperatures into the upper 80s° F. When trying to determine which air temperature(s) to use in your facility, consider the requirements of the different species that you are growing, as well as the area each species occupies in your production area; this is one of the challenges of growing a variety of species in a common environment.

Light: Most culinary herbs grow best with moderate to high daily light integrals (DLI) of 12 to 15 mol·m–2·d–1 or greater. Depending on where you are located, supplemental light is beneficial for increasing DLI during those times of year that are light-limiting, from late fall, through winter, to early spring in many parts of the country. While some herbs have a photoperiodic flowering response, photoperiod is usually not managed for flowering as herbs can be harvested prior to flowering.

CO2: Like other crops, supplemental carbon dioxide (CO2) can increase basil productivity and this is especially true when CO2 can be limiting in the greenhouse (i.e. late fall, winter, and early spring). Maintain CO2 concentrations at up to 1,000 to 1,500 ppm to enhance growth rates. Only add CO2 when vents are closed so additions aren’t lost to the atmosphere

Fig. 2. These rosemary cuttings were direct-stuck into perlite beds after being harvested and dipping the basal end in rooting hormone.

Pollination: Since culinary herbs are produced for foliage, not fruit, no flower pollination is required. Some herbs are produced for their seed. But those herbs are produced in the field, not in controlled environments.

Pruning and training: Culinary herbs do not require pruning or training during production.

Pests: Aphids, greenhouse whitefly and spider mites are some of the more common pest problems of greenhouse herbs. Aphid infestations can explode if not caught early and spot-treated. Biological control using beneficial insects is certainly one option for control but, unlike fruiting vine crops, beneficial insects may still be on foliage at the time of harvest.

Diseases: Like any crop grown in NFT and DFT systems, Pythium in nutrient solutions can be problematic if it gets established. Fusarium can also be problematic. Botrytis can be problematic if herb canopies are dense and/or the greenhouse is too humid; for plants that are harvested multiple times, the wound from cutting can be an entry point for the disease. Downy mildew has also been increasingly challenging for basil growers to control if established. Preventing diseases is key, as there are few chemistries which are registered for controlling diseases of greenhouse herbs.

Physiological disorders: There are few physiological disorders associated with culinary herbs. The most common is bolting, or premature flowering. For some species such as cilantro and dill, this can occur if plants are grown with excessively warm temperatures like those seen during summer greenhouse production.

Harvesting: Since herb shoots are harvested, then aggregated and sold in bunches or clamshells, there are two different options for harvesting plants: a single harvest or multiple, successive harvests. A single harvest can be beneficial for turning crops and replanting with clean material to reduce the chances of pest or disease pressures building up. Multiple harvests result in greater cumulative yield per plant, but the crop time is longer and successive harvests may not be as good as the initial harvest. When making multiple harvests off the same plant, be sure to leave enough leaves to support shoot regrowth.

Postharvest care: Like other crops, herbs should be cooled down after they are harvested and packed. While species vary in their requirements for storage temperatures, most importantly basil should not be stored below 50° F to avoid chilling injury; most other herbs can be stored at cooler temperatures (32 to 35° F) to maintain quality.

Christopher ([email protected]) is an assistant professor of horticulture in the Department of Horticulture at Iowa State University.

Have you ever wanted to set up an herb garden greenhouse in your own backyard?

Growing herbs in a mini greenhouse has many benefits

It may sound like an extravagant proposal. After all, can you really afford a greenhouse? Do you have the space? But year-round gardening may just be more accessible and affordable than you realize.

The benefits of greenhouse growing are numerous:

• You can extend the growing season, planting earlier in the year. A greenhouse protects plants from major temperature swings, retaining heat and moisture. This not only allows you to garden in the winter but to enjoy and sell out-of-season produce. Whether you are gardening to put food on your own table, or you are doing it to make some extra income, that is a great boon.

• Protect your plants from pests such as caterpillars, snails, rodents, and larger animals that may be interested in eating your produce. Your plants should also stay safe from blight, so you don’t need to worry about the disease affecting the neighbor’s plants from infecting yours.

• Keep your plants safe from inclement weather such as blizzards, hail, high winds, and dust storms. A greenhouse makes it much easier to grow in unpredictable climates (the Midwest for example—which has excellent growing conditions overall, but all it takes is a single severe storm to wipe out an entire crop and force you to start all over).

• Prevent soil erosion resulting from flash floods or ongoing torrential rainstorms. You no longer have to worry about losing all your crops because of a sudden change in the weather, nor do you have to rush out to your garden at the drop of a hat to try and prevent damage from occurring. Your plants will be protected in the safety of the enclosure.

• Take pleasure in the joys of gardening year-round, no matter what the weather is outside. For many people, gardening is a relaxing, centering activity. Being able to do it throughout the year provides a sense of tranquility and well-being. This is a payoff which goes far beyond the culinary yields of your produce.

Basil is a favorite to start early in the greenhouse.

Growing Tips for Greenhouse Herbs

Herbs can grow anywhere: Inside or outside your house. However, almost nothing grows in freezing temperatures. This is why using a sheltered area can help keep the extreme temperatures under control and extend your growing season to include the early spring and late fall.

Here are a few easy tips for healthy year-round growth.

  1. Water occasionally. Water until the soil is moist, but let the herbs dry out slightly in between waterings. This helps to develop a good root system as the roots reach down to the bottom of your pots to get every last drop of moisture.
  2. Let them go dormant. Your herbs may go dormant during the coldest weather. So, don’t worry if the perennial varieties like rosemary or thyme turn brown on top during these months. Let them rest for a while and trim back the brown parts. They should grow back fine in the spring.
  3. Fresh Air is Important. Keep the air circulation going. Stale air can lead to fungus or pest problems, especially in a slightly moist and warm environment. Open the doors (or unzip the tent) every so often and let the air circulate around your plants.
  4. Pinch Your Herbs. To extend the growing season of your herbs, be sure to pinch back any flowering stems. This will keep them nice and bushy and will prevent your plants from going to seed. Once the herb flowers and sets seeds, mother nature will slow the plant’s growth and you won’t see many new leaves.

When your herbs start to flower, the harvest season is just about over.

Which Herbs Grow Best in a Green House?

You can start almost any herbs early in the season, including annuals such as basil and dill by using a greenhouse. The following herbs will also grow really well into the fall in the greenhouse environment.

  • Oregano
  • Thyme
  • Lavender
  • Rosemary
  • Parsley
  • Mint
  • Chives
  • Sage

Affordable Greenhouse Options

A greenhouse doesn’t have to be a significant structure like you would find at a commercial or botanical garden. It can be small enough to fit in a backyard with limited space.

It doesn’t even have to be a walk-in model. You can easily purchase greenhouse kits which are designed to accommodate a small herb garden on a deck. Here are two cheap ways to get your herbs started before the growing season.

  1. Gardman R687 4-Tier Mini Greenhouse

The Gardman R687 4-Tier Mini Greenhouse

I love this style since it is light-weight and fits easily on most decks. I have used it for many seasons to get my indoor grown herb seedlings for the garden. The whole system can be set up in under an hour, even if you are slow to put things together!

Another great feature is that it stores away nicely once summer is in full swing. However, I found myself keeping it up. I used it throughout the growing season to store extra plants, grow seedlings outdoors and for storage. It looks really pretty especially with a few flowering pots set on top.

2. Deluxe Green House

A slightly bigger but still affordable option is the Deluxe Walk-in Greenhouse by GoSunny.

The Deluxe Green House by GoSunny

There are 6 shelves on each side of the walk-in. The frame is made from steel and held in place by 4 stakes. This greenhouse is larger at 56 ” square (length & height) but can be assembled by the average homeowner with no tools required. There is even a window on each side for cross ventilation.

Video: How To Build A DIY Mini Greenhouse For Under $50

Do you actually need to go shopping for greenhouse frame kits, or can you build a small herb greenhouse on your own from scratch? You certainly can do it, and you can do it at a very cheap cost too (some people have erected greenhouses for $50 or less). See the following example from the DIY Experts at Hip Chicks.

We love this example due to the nice portable size which would be perfect for an herb garden.

More Small Green House Kits

If you aren’t keen on this type of DIY projects, a greenhouse kit is another option for you. A kit can make it easy for anyone to build an inexpensive greenhouse in their backyard regardless of their building skills.

The kit provides you with all the materials you need. The parts are already ready; they just need to be assembled. The detailed instructions will walk you through each step.

Notice the ability to raise the greenhouse top and store garden supplies underneath

The kit above to the right is a unique product because it offers an alternative to the traditional walk-in model of greenhouse. The raised gardening bed can be placed literally anywhere—even on a patio or balcony—so it is perfect even if you are living in an urban environment.

You could set this up even on the balcony of a high-rise apartment, so long as the balcony was large enough to accommodate it. All the plants are at just the right height for easy reach, making it an excellent choice for elderly and disabled gardeners.

The panels are made out of polycarbonate and are built to be extra-strong. They can even protect your plants from hail. They lock in heat and moisture, providing a safe, sheltered microclimate which is ideal for growing plants in and out of season.

Summary

So if you have been on the fence about getting into backyard gardening, or you have been looking for a way you can take the gardening you do already to the next level, you really have no more excuses! A backyard or patio greenhouse is something you can afford—and it is something you have space for, even if you do not have a yard at all.

Once you get set up with it, you will find that it can reduce the amount of work you need to do throughout the year. Greenhouses can make gardening easy and fun and is perfect for beginning gardeners and long-time gardeners alike.

Last updated by Virginia Dodd at March 2, 2019.

Walk-In Greenhouse- Indoor Outdoor with 8 Sturdy Shelves-Grow Plants, Seedlings, Herbs, or Flowers by Home-Complete

Protect your plants and enjoy gardening through the winter with this walk-in greenhouse from Home-Complete. This greenhouse’s clear PVC cover shields your plants from pests or frost, and eight shelves provide plenty of space for growing things or storing supplies. Anchors and zip-ties help ensure the stability of this greenhouse.

  • 8 DURABLE SHELVES- The 8 sturdy shelves provide plenty of room for trays, pots, or planters of anything you want to grow. It’s a convenient option for any gardener!
  • INDOOR OUTDOOR- This versatile greenhouse is ideal for both indoor and outdoor use; keep it on your backyard patio, deck, or in the basement or garage! The clear PVC cover helps protect seedlings from frost or pests for an ideal growing environment.
  • EASY ASSEMBLY- With no tools required, the greenhouse is easy to assemble! Simply follow the included instructions and connect the rods. Rope and anchors are included for stability, and each shelf comes with zip ties to ensure they can’t be tipped over.
  • USE IN ALL SEASONS- The walk-in greenhouse is the perfect way to extend your growing season! This home gardening essential is great for plants, seeds, herbs, vegetables, or flowers, and it could also be used to hold supplies.
  • PRODUCT DETAILS- Materials: Steel frame and PVC cover. Dimensions: (L)56.3″x (W)56.3″x (H)76.7″. Color: Green with clear cover. Rope, anchors, and zip ties included.

Tip 8: Planting Guide

Planting Guide – Greenhouse Growing

Some of our customers when starting out can feel a little overwhelmed when it comes to deciding what to grow and how to grow it. So we’ve come up with a guide to the planting requirements of the most popular fruit and vegetables within your greenhouse.

If you’re growing carrots, beets, turnips and other root crops, they thrive well in deep boxes which can be put under benches. Those that require tub-type containers are tomatoes, peas, cucumbers and pole beans, while lettuce or other low leafy vegetables may be planted in the tub with the taller vegetables.

You can plant corn directly on the floor of the greenhouse, in a special bed prepared for it. To save space, you can plant pumpkin between the rows of corn.

Use room temperature water to water your indoor plants. Let tap water stand for a day to get rid of the chlorine substance. This way you avoid your plants getting brown tips.

Distribute crushed egg shells in your garden to stimulate growth. Sprinkling coffee grounds will add acid to the greenhouse ground.

Before bringing vegetables and fruits from the greenhouse to your house, rinse them well outside; this way dirt and bugs stay outside and will not make your kitchen dirty.

To make more room in your greenhouse, use lower benches for starting seeds and transplants; upper benches for growing flowers and specimen plants. Some vegetables, like tomatoes, should be planted in a warm section of the greenhouse.

Regarding planting of seeds be sure to water lightly for the first few times. Over watering may cause the seeds to come to the surface too soon, preventing them from rooting properly.

Preparation and production must be done in separate areas. Don’t do general preparation on the growing floor. This makes for a tidier greenhouse.

Here is a list of the largest vegetables that will need the most spacing in your greenhouse:

Bush type beans: minimum of five feet between rows

Cabbage: a foot between rows

Peppers: about a foot between rows

Cantaloupes: two to three feet between rows

Squash: two to three feet between rows

Tomatoes and Watermelons: minimum of two feet between rows

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