Why & What to Grow in a Greenhouse

Why Grow in a Greenhouse?

Once the fall equinox passes, the days get noticeably shorter. By the winter solstice, many areas are too cold and dark for much to grow outside. Greenhouse growers, though, are getting ready to sow tomatoes, lettuce, eggplant, peppers and other carefully picked vegetables, herbs and flowers. Seedlings may be started or planted in heated or unheated greenhouses or hoophouses, with or without grow lights, depending on latitude, crop and many other factors specific to each operation.

If greenhouse work sounds like a cure for the midwinter blues, and a way to earn income all year, read on to see how greenhouse production might fit your business plan.

The Greenhouse Advantage: Extended Season; Higher Quality; Higher Yield

The main reason to grow vegetables, flowers and herbs in a greenhouse is to have crops when they can't be grown outdoors. Off-season tomatoes, cucumbers, peppers, eggplant, lettuce, basil and other vegetables fetch high prices in some markets.

But growing warm-season crops like tomatoes in winter is very expensive, so only jump in once you're sure you have a market and a price that will pay back your investment. Heat will be your largest cost, then labor. If you plan to keep producing through the coldest, darkest months, you may also need grow lights, especially during long cloudy stretches.

If you've never grown greenhouse vegetables in winter, research thoroughly whether it can pay for you, given your climate, structure and expected fuel costs. Plenty of free resources can help you estimate costs and returns. Searching online for greenhouse tomatoes enterprise budget, for instance, turns up a long list of references. Look for ones from universities and Extension services in your region.

The Northeast Organic Farming Association of Vermont (NOFA-VT) has several cost-of-production resources for greenhouse crops on its website, including a metrics summary, crop-by-crop analyses and a workbook. Look for similar resources in your area.

On timing, a general rule for new growers in the northern U.S. or Canada is to wait until about mid-February to plant into the greenhouse, since the low light before then makes the crop riskier. Experienced growers and those farther south can often produce all winter. By mid-February, many crops can be grown with very little heat and still come in a month or more ahead of field crops.

If you have a spring market for vegetables, greenhouse growing can pay, especially alongside early field crops. Field spinach might be ready in April, but that alone won't fill a market table. Add head lettuce from a heated greenhouse plus arugula, radishes and carrots from an unheated hoophouse, and you have a strong display. Or think about Mother's Day: greenhouse tomatoes, cucumbers, cut flowers, flower baskets and hanging strawberries, along with all your spring vegetables.

A longer season is only one benefit of a greenhouse. Crops under cover suffer less damage from wind, rain and hail, so more of the harvest is saleable. Yields are often higher too when you can give each crop ideal conditions. Greenhouses shield crops from many diseases, especially soilborne ones splashed up by rain, and from many field pests. Greenhouse crops do have their own problems, such as leaf diseases, aphids and whiteflies, so keep a close eye on them.

Tools & Supplies for the Greenhouse

Greenhouse vegetables, herbs and flowers are grown in three main ways:

1. In the ground
2. Container culture
3. Hydroponics

Growing in the ground is easiest for beginners, since watering and feeding are less exacting. Containers mean no weeding and fewer soilborne diseases, though. Often your greenhouse decides for you: on a concrete or gravel floor you'll need containers such as grow bags, bulb crates or large pots, while a soil floor lets you choose.

Either way, unless you're growing hydroponically, drip irrigation is the way to go: it saves labor, waters more evenly and avoids problems from overhead watering such as soil splash and wet leaves. Plastic mulch can keep weeds down and hold moisture. An inner layer of row cover on hoops over the crop can keep the soil warmer without burning more fuel.

Tomatoes, cucumbers, peppers and eggplant need to be trained up vertical twine. Clips attach the vines to the twine, and Rollerhooks save time and space in a lower-and-lean system. Crops like basil and cut flowers may need horizontal support such as Hortonova netting to stay upright.

For baby greens and salad mix grown in the ground, a seeder sows more precisely, saves seed and makes planting much faster, and a greens harvester makes quick work of cutting baby lettuce and other greens.

What Crops to Grow in Your Greenhouse, Hoophouse, or Poly Tunnel

Almost anything can be grown in a greenhouse, but that protected space is valuable, so choose varieties carefully to maximize profit and grow crops that struggle outdoors where you are. Many varieties are bred, trialed and selected specifically for greenhouse growing. To see what we look for and which varieties do well under cover, read our article on how we evaluate greenhouse varieties.

Vegetable Crops

The most popular greenhouse crops are usually those in steady demand year-round with a fairly high return, such as:

• Tomatoes
• Cucumbers
• Lettuce and Salad Mix
• Peppers
• Microgreens

Cut Flower Crops

Cut flowers can pay well in a greenhouse too. Among seed-grown flowers, the best picks are those that suffer outdoors in wind and rain, such as:

• Campanula
• Dianthus
• Lisianthus
• Snapdragons
• Sweet Peas

Herbs

Of the herbs, basil can be grown earlier and later in a greenhouse and is always in demand. Tender perennial herbs such as rosemary and thyme can be kept as stock plants in the greenhouse and propagated in late winter to sell in spring as potted plants or fresh-cut herbs.

Fruits

Strawberries are another valuable greenhouse crop and can grow in hanging containers to keep floor space free.

Whatever you grow, choosing the right varieties is key to greenhouse success. Varieties are labeled suited to greenhouse growing for many reasons: they may resist common diseases better or grow better in a greenhouse's lower light. Many greenhouse cucumbers are parthenocarpic, which means they set fruit without insect pollination, and gynoecious, which means all their flowers are female, so yields are higher because every flower can become a fruit. Look for the greenhouse note in each variety's description on our website. To see what we look for and which varieties do well under cover, read our article on how we evaluate greenhouse varieties.

Opening up to Year-round Possibilities

As days shorten and winter brings you indoors more, take some time to explore greenhouse or hoophouse growing. If you decide to try it, now is the time to plan production and schedule purchases and sowing dates. Wherever you are, you could fill a greenhouse with crops for market through winter and early spring!

Learn More About Greenhouse Growing

• How we evaluate greenhouse varieties Article
• Top grafting tomatoes: benefits, supplies, technique PDF tech sheet
• Side grafting tomatoes: benefits, supplies, technique PDF tech sheet
• Trellising tomatoes in a hoophouse Article
• Figuring ROI for greenhouse cucumbers Blog
• Growing greenhouse cucumbers PDF tech sheet
• Cucumber types and terms (PDF)
• Growing greenhouse eggplant PDF tech sheet
• Growing greenhouse bell peppers PDF tech sheet
• Growing fruit under cover Article
• Greenhouse vegetables Products
• Greenhouse fruit Products
• Greenhouse flowers Products
• Greenhouse herbs Products
• All greenhouse varieties Products