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Across most of North America, December is down time for market farmers. Days will keep getting shorter until the winter solstice on Dec. 21 and, in most places, it’s too cold for much of anything to grow. Greenhouse growers, though, are gearing up this month. It’s time to start tomato, lettuce, and pepper seeds for transplanting into a heated greenhouse, followed shortly after by transplant production for the unheated greenhouse. If working in the greenhouse sounds like therapy for the mid-winter blues — not to mention a way to make some cash earlier next year — then read on to learn more about how greenhouse growing might fit into your business plan.
The greenhouse advantage
The obvious reason to grow greenhouse vegetables and flowers is to have crops at a time of year when they can’t be grown outdoors. Out-of-season tomatoes, cucumbers, 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, so don’t jump into it unless you are certain you have a market and a price that will provide a return on your investment. Heating will be your biggest cost, followed by labor. And if you happen to have a long spell of overcast weather, you may also need to provide supplemental lighting.
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 fuel costs. Fortunately, there are many free resources to help you calculate costs and potential returns; do an internet search for “greenhouse tomatoes enterprise budget” and you’ll find plenty of reading material to help with your research. An invaluable tool for predicting heating costs is Virtual Grower software, which is free from 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. You can download the software here. http://www.ars.usda.gov/services/software/download.htm?softwareid=309
As a broad rule of thumb, a beginning grower in the northern half of the country should not plant into a greenhouse until Feb. 15 because the low light conditions earlier than that make the crop a riskier venture. Experienced growers and southern growers 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 combined with early field crops. For example, you may have field-grown spinach in April but that’s hardly enough to fill a market stand. But if you can also bring head lettuce from the heated greenhouse and arugula, radishes, and carrots from the unheated hoophouse, you’re ready to put on a good display. Or 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 and supplies for the greenhouse
Greenhouse vegetables and flowers can be grown in two systems: in-ground soil culture, or container culture. 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, 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 and cucumbers require trellising onto vertical lengths of twine. Vines can be attached to the trellis with individual trellis clips or with the Duratool, a device (formerly called Ty’mup) that wraps a flexible band around the stem and trellis string. Other greenhouse crops such as basil and cut flowers may need to be held upright with a horizontal trellising system such as Hortanova netting.
For in-ground cultivation of salad mix, a seeder speeds up planting greatly. And a greens harvester makes short work of cutting baby lettuces.
What to grow
You can grow virtually anything in a greenhouse, but that protected space is prime real estate, so you should choose crops carefully to maximize profits and produce crops that don’t do well outside for you. Tomatoes are the Number 1 greenhouse crop grown in the U.S., probably because demand is high and consistent year-round. Cucumbers are the second most popular greenhouse crop, followed by head lettuce and salad mix. Cut flowers can be profitable in a greenhouse, particularly bulb crops such as Oriental lilies and Dutch iris. 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. 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.
Whatever 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, greenhouse varieties don’t require insect pollination. You can find a complete list of suggested greenhouse crops here, or look for the greenhouse symbol next to variety names in the catalog.
As the days get shorter this month and you find yourself inside more frequently, spend some time reviewing the possibilities for greenhouse production. If you decide to go for it, now is the time to buy seeds and schedule sowing dates for a mid February to mid March planting. By April or May, you could have a greenhouse full of crops ready for market.
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Reprinted from JSS Advantage