7 Market Crops You Can Grow in a Greenhouse

Your farm income doesn’t have to drop just because the temperature has. Use your greenhouse to grow products for sale all winter-long.

by Jesse Frost
PHOTO: Rachael Brugger

When cold weather sets in, most farmers close up their market booth for the season and pack it in. However, a farmer looking to continue earning income in the off-season can turn to a greenhouse as a season extender, offering produce to hungry customers year-round. But what crops are best for greenhouse production? And what is the winter customer looking for? These are things you’ll need to identify before starting your greenhouse operation. While it will take a little bit of market research on your part, here are our favorite greenhouse crops, as well as how to maximizing your yields and get them into the hands of eager customers—though if we’re being honest, bring a fresh carrot to market in February and it will market itself.

1. Cut and Head Lettuce

Lettuce is a relatively hardy vegetable, and a popular one no matter what time of year. Grow a few different lettuce varieties for mixes, as well as some colorful lettuce heads, to draw customers in.

Grow It:

Sow seeds for leaf mixes thickly, preferably using a seeder, in tight rows 2 to 3 inches apart in 4-foot-wide beds. Cut leaves off one plant up to four times, tasting every time to make sure it hasn’t become too bitter. For head lettuce, sow or transplant seeds 10 to18 inches apart, depending on the variety. Succession-plant in early fall and late winter.

Market It:

Mix cut lettuce in plastic bags or enclosed totes, and display out of wind and sun. Dunk head lettuce in clean, cold water before market, and display on table. Keep both cut and head lettuce well-misted and prominent on the table. Few foods draw people in like fresh lettuce, especially the darker, redder varieties.

2. Spinach

Spinach is a classic greenhouse crop. It must stay watered and the farmer must avoid extreme temperature shifts by monitoring the greenhouse, but spinach can be cut from several times in a season and provide a dependable off-season income.

Grow It:

For full leaf spinach, sow seeds 1 to 2 inches apart, in rows 10 to 18 inches apart. For baby spinach, you can sow seeds in wider bands, in rows 6 to 10 inches apart. Succession-plant in early fall and late winter.

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Market It:

If growing full spinach leaves, harvest from the stem, wash and tie in large, attractive bunches. Bring a baby spinach harvest in a tote or in individual bags, or consider consider making salad mixes with your spinach and lettuce.

3. Other Leafy Greens

Leafy greens like kale, collards and Swiss chard are not only wildly popular but are a great fit for farmers wanting to extend the growing season. The flavor of some greens, like kale, even improves with a little cold. These crops are also ideal because unlike broccoli or cabbage, where you get one cut and that’s it, these greens can be picked off of all winter and provide months of income.

Grow It:

Whether you sow seeds or use transplants, leave at least 8 to 10 inches between plants and about 24 inches between rows. Plant into fertile soil in early fall and late winter, and water regularly for best leaf production.

Market It:

Tie or bag your greens in large, attractive bunches. Keep leaves misted and out of the wind to avoid wilting. Come to market with a full load—you’re sure to sell out!

4. Microgreens

Microgreens are tiny, tender versions of familiar vegetables like mustard, cress, radish, beet, basil and kohlrabi that pack a huge nutritional punch. You can grow microgreens from fall to spring, but because they are somewhat esoteric, also consider finding a buyer before they you plant. The good news is that restaurants tend to love these tiny bursts of green, especially when there aren’t a whole lot of other greens available. Also, the two- to four-week crop turnover and high price tag they garner make them a pretty attractive option.

Grow It:

Fill small flats with soil, and follow the germination requirements for your chosen microgreen. Sow seeds thickly, cover with a small layer of soil mix, and keep moist, preferably from underneath the tray, as to avoid splashing dirt on greens. Plant from fall to spring.

Market It:

Even though it’s wise to find a buyer (such as a restaurant or grocery store) before planting, microgreens will sell well in a busy market. Harvest when the first true leaves develop and when the sprouts are about 2 inches tall, after about two to four weeks. Wash the microgreens and bring to market in either a tote or in individual plastic bags, tied off with plenty of air.

5. Carrots

Carrots aren’t always considered the best use of greenhouse space because they grow so well in the open with a little row cover. But also consider this: Most winters are wet, and if the carrots are ready but the garden is mud, it’s a lot easier to dig them out of a space where you control the moisture.

Grow It:

Sow seeds thickly in rows 16 to 24 inches apart. As plants grow, thin to 1 inch apart, and keep well-watered. Plant in late summer and late winter.

Market It:

Harvest, wash and tie carrots in large, attractive bunches, with partial greens on. You can leave the entire greens on, and some customers enjoy that, but others will find the greens cumbersome. The greens may also take up a larger portion of your market display than you would like and hide the other bunches.

6. “Summer” Crops

Tomatoes, peppers, eggplants and cucumbers might not be the crops you want to sell at the winter market, but you can at least extend their season by growing them in a greenhouse. You can also grow starts of each of these plants to sell at market in the spring.

Grow It:

Following the basic growing guidelines for the summer crops you wish to grow, start them in late winter then plant in early spring, or start the crops in mid-summer and plant in the late summer. Also consider that these plants don’t typically tolerate temperatures below 35 degrees F, and need lots of sunlight, so they must be tended to and covered when temperatures drop.

Market It:

You will not need much help selling these items in the off-season. If you do want to improve their visibility, however, the fall is a great time for pickling and canning, so consider marketing these crops as “canning veggies.” Of course, being the first or last to arrive at market with tomatoes and peppers will make you a popular vendor no matter what.

7. Herbs

Whether it’s basil, cilantro, tarragon, rosemary or thyme, if you have good control over the temperature of your greenhouse, herb starts are another highly marketable product. Keep in mind that germinating and raising herbs requires a little more attention to detail but can be profitable under the right conditions.

Grow It:

Follow the growing guidelines for each herb you wish to grow, paying strict attention to temperature and water requirements. Try to have starts ready to sell for spring markets when gardens are being replanted and starts are most in demand.

Market It:

Selling herb starts can be a great business, especially in terms of perennial herbs, like oregano and rosemary, but even annual herbs do well. Bring them to market in attractive trays and consider growing them in or moving them into biodegradable containers that can easily be planted into the ground. Also, provide some simple growing tips for each crop––customers will definitely appreciate the extra effort.

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