Winter Growing & Season Extension

Greenhouse Growing • Basics & Advantages of Protected Culture

Why Grow in a Greenhouse?

Greenhouse Eggplant Trial
Greenhouse Eggplant Trial
Our greenhouse varieties undergo intense scrutiny in our trialing program; those we've selected demonstrate outstanding performance across multiple criteria.

Greenhouse Trial Criteria & Recommendations…

View All Our Greenhouse Performers…

Each year as the autumnal equinox passes us by, daylength dwindles to an increasingly noticeable degree. By the winter solstice, it becomes too cold and dark in many regions for much of anything to grow in the field. But greenhouse growers are gearing up to start tomato, lettuce, eggplant and pepper seeds, or other carefully chosen vegetables, herbs, and flowers. The seedlings may be started or transplanted into a heated or unheated greenhouse or hoophouse, with or without supplemental lighting, depending on the latitude, crop, and a host of additional variables unique to the greenhouse grower's operation.

If working in the greenhouse sounds to you like a way to banish the midwinter blues — as well as generate year-round income — then read on to learn more about how you might fit greenhouse production into your business plan.

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

The obvious reason to grow greenhouse vegetables, flowers, and herbs is to have crops at a time of year when they can't be grown outdoors. Out-of-season tomatoes, cucumbers, peppers, eggplant, lettuce, basil, and other vegetables command high prices in some markets.

It's important to note, though, that the cost of winter production of warm-weather crops like tomatoes is very high; prepare to jump into it only once you ascertain you have a market and a price point that will provide a return on your investment. Heating will be your biggest cost, followed by labor. And if you intend to remain in production through the very coldest, shortest winter months, you may also need to provide supplemental lighting — particularly during a long spell of overcast weather.

USDA Virtual Grower
USDA's Virtual Grower
Preliminary research to inform your greenhouse decisions and strategies is time well spent.

Virtual Grower allows you to run multivariate "what-if" scenarios for your geographic region.

Learn More…

If you have never attempted to grow greenhouse vegetables in winter, you should do a great deal of preliminary research to determine whether it can be profitable for you, given your climate, greenhouse structure, and projected fuel costs. Fortunately, there are many freely available resources to help you calculate costs and potential returns. A search online for greenhouse tomatoes enterprise budget, for example, will return a lengthy list of references to inform your research. Look for those published by your regional universities and cooperative extension agencies.

NOFA-VT's Cost-of-Production Resources
NOFA-VT's Cost-of-Production Resources
NOFA-VT worked with organic farms in Vermont to track and analyze their greenhouse costs of production, aggregating and presenting the data in a set of factsheets for growers to use, including the cost of production workbook developed as part of the project.

Learn More…

For predicting heating costs, a tool called the Virtual Grower is available through the USDA. It prompts the user to enter information such as nearest weather station, (from which it calculates average weather conditions), type of greenhouse structure, condition of the structure, type of heating system, and price of fuel. (Although the Virtual Grower is dated, it still holds utility; we hope this free software will soon be redeveloped.)

The Northeast Organic Farming Association of Vermont (NOFA-VT) offers several cost-of-production resources on their website for greenhouse crops, including a summary of metrics, crop-specific analysis, and a cost-of-production workbook.

Factors to Weigh for the Greenhouse Grower
Climatological / Geographical:
Circadian and seasonal variations in temperature, light, humidity, air circulation, pollination requirements, disease pressure and resistances

Cost Considerations:
Construction, maintenance, energy, tools, supplies, seed, human resources

Market Forces / ROI:
Supply chain management; demand for unique, high-end, and/or off-season products; collective/collaborative selling/transportation/marketing

As for timing, the broad rule of thumb for a beginning grower in the northern half of the US or Canada is to plant into a greenhouse until February 15, because the low light conditions earlier than that make the crop a riskier venture. More experienced growers and southern growers, however, can often produce all winter. By mid February, many crops can be grown with only minimal heat, and still provide a month or more of earliness compared to field crops.

If you have a market where you can sell vegetables in spring, greenhouse production can be profitable, especially when combined with early field crops. You may, for example, have field-grown spinach ready in April, but realize that's hardly enough to fill a market stand. If you can also bring head lettuce from the heated greenhouse, and arugula, radishes, and carrots from the unheated hoophouse, then you're able to put on a good display. Alternatively, think about the possibilities for Mother's Day: greenhouse tomatoes, cucumbers, cut flowers, and hanging baskets of flowers and fruiting strawberries, in addition to a full range of spring vegetables.

Season extension is just one of the advantages gained from greenhouse growing. Protected crops are less apt to be damaged by wind, rain, and hail so the percentage of marketable products is higher. Yield is often higher as well, if you can provide optimum growing conditions for each crop. Greenhouses protect crops from many diseases, particularly those that are soilborne and splash onto plants in the rain. And greenhouse crops may be protected from common field pests. Of course, greenhouse crops have their own particular problems, such as foliar disease, aphids, and whiteflies, so vigilance is still required.

Tools & Supplies for the Greenhouse

Trellising & Crop Supports
Trellising & Crop Supports
Learn how to maximize efficiency with tutorials, tools and supplies expressly designed to facilitate greenhouse tasks, such as trellising and supporting your vining crops.

See Resources below to learn more…

Greenhouse vegetables, herbs, and flowers can be grown in three main systems:  in-ground soil culture, container culture, and hydroponics. The first is easiest for beginners because watering and fertilization requirements are not as exacting. Growing in containers, though, has the advantages of no weeding and reduced incidence of soilborne diseases. So the determining factor may well be the type of greenhouse you own. If you have a transplant house with a concrete or gravel floor, you will have to grow in containers such as grow bags, bulb crates, or large pots. If you have a soil floor, you can choose which system to use.

In either case — unless you're using hydroponics — drip irrigation is recommended to reduce labor, improve watering consistency, and prevent problems caused by overhead watering such as soil splash and wet foliage. Plastic mulch may be used to prevent weeds while also conserving soil moisture. An inner layer of row cover held above growing crops by hoops may be used to keep soil warmer without increasing fuel usage.

Tomatoes, cucumbers, peppers, and eggplants require trellising onto vertical lengths of twine. Vines can be attached to the trellis with clips, and Rollerhooks can provide maximal time-saving, space-conserving trellising in a lower-&-lean system. Other greenhouse crops such as basil and cut flowers may need to be held upright with a horizontal trellising system such as Hortonova netting. Take time to learn about the various crop support tools and accessories available, to select the system best for your application.

For in-ground cultivation of baby leaf greens and salad mix, using a seeder affords greater precision, conserves seed, and speeds up planting greatly. And a greens harvester makes short work of cutting baby lettuces and other greens.

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

Greenhouse Tomatoes
Always in demand and offering the grower a wide range of sizes, shapes, colors, flavors, and production methods, tomatoes are the number-one greenhouse crop in the U.S.

You can grow virtually anything in a greenhouse, but that protected space is prime real estate — with careful variety choices, you can maximize profits and produce crops that don't do well outside for you. At Johnny's, we breed, trial, and select seed specifically for greenhouse culture. To learn more about what we look for and recommended greenhouse performers, read our article on Greenhouse Trial Criteria.

Tomatoes are the number-one greenhouse crop grown in the US, probably because demand is high and consistent year-round. Cucumbers are the second most popular greenhouse crop, followed by lettuce and salad mix. Greenhouse peppers are also extremely popular in the US, and offer diverse options though more exacting in their cultural needs. Microgreens, too, are in steady year-round demand, and offer several advantages, including short turnaround time, relative ease in growing, tremendous diversity, and appreciable ROI.

Cut flowers can also be profitable in a greenhouse. Among seed-grown flowers, the best choices are those that don't do well outside in the wind, such as delphinium, lisianthus, and snapdragons. In cool climates, heat-loving flowers such as celosia are good candidates for greenhouse growing.

Hortonova Flower Trellising
Hortonova in the Hoophouse
Horizontal trellising helps provide correct spacing, as well as support, for premium cut-flower production.

Learn More About Crop Supports…

Among the herbs, basil can be grown earlier and later in the year in a greenhouse, and there is a consistent demand for it. Tender perennials herbs such as rosemary and thyme can be kept in the greenhouse as mother plants, then propagated in late winter to sell as container plants or culinary cut herbs in spring. Strawberries are another valuable greenhouse crop, and can be grown in hanging containers to keep floor space free for other crops.

Whichever crops you choose, variety selection is important for greenhouse success. Varieties are identified as good for greenhouse production for many reasons. They may have increased resistance to common diseases, or grow better in the lower light conditions of the greenhouse. In the case of cucumbers, many greenhouse varieties are parthenocarpic, meaning they don't require insect pollination to set fruit — and gynoecious, meaning all flowers are female, resulting in a higher yield since every flower has the potential to turn into a fruit. Remember to look for the red greenhouse symbol next to variety names here on our website and in our catalogs.

Opening up to Year-round Possibilities

As the days get shorter with the approach of winter and you find yourself indoors more frequently, spend some time reviewing the possibilities for greenhouse or hoophouse production. If you decide to go for it, now is the time to lay out your production plan and schedule purchases and sowing dates. Wherever you live, you could grow a greenhouse full of crops, ready for market through winter and earliest spring!