On Gardening Home Greenhouses And Vegetables For Winter

University Park, Pa. -- Incorporating solar greenhouses into modern home design has prompted questions about the possibilities of using these structures for producing food along with heat for the home. To do well, plants must have adequate light, correct temperatures, water, nutrients and air to survive inside in a greenhouse. If you plan to use a solar greenhouse used for both purposes, you often have to make decisions that favor heating the home or higher food production.

Full sun for 6 to 8 hours a day is needed for good vegetable production. Light intensities of about 4,000 foot-candles will produce good growth, but winter sun through a double-glazed greenhouse may yield only about 900 foot-candles. To increase light levels for good plant growth, recommendations are that all surfaces be painted a highly reflective color, such as white. However, to enhance solar absorption for use during the night, it is suggested that heat storage masses (walls, drums of water, cement blocks, etc.) be painted black. To reduce the problems associated with dual demand, use building methods that allow for optimum light penetration and locate your plants with high light demands in areas with full exposure.

If the greenhouse is going to provide adequate household heat at night, you will need to select crops that survive night temperatures between 40 and 45 degrees F. Most root crops like onion, beet, carrot, radish, and chive will do well at those temperatures. Leaf crops like chard, kale, spinach, lettuce and parsley will survive cooler temperatures. Cool season plants like broccoli, cauliflower, cabbage and peas can also be used. Fruiting plants such as tomato, pepper, eggplant and melons have minimum temperature limits between 60 and 65 degrees F. for optimum production.

Soil management inside a greenhouse is also different from what it is in the garden. Soil should be light textured, richer and better drained than a garden soil. Greenhouse soil needs to be mixed specifically for indoor use, and it should be changed each season.

Good drainage in the growing container is as important as light textured soil. There should be adequate drain holes in pots and benches that hold the interior crops. Watering and fertilizing techniques will also have to modified according to the growth rate of the plants, which is directly related to the available light and temperature levels.

As a rule, fewer pests are encountered in a greenhouse garden. However, any pests that do develop must be controlled. The closed system doesn't allow for natural predators to impact any problem, and with the interrelated ventilation, and the closeness of family and pets to the plants, nonchemical control methods are essential.

Good air circulation is also critical to prevent fungus diseases. If natural air flow is not possible between the greenhouse and house you will need to use small fans to move the air. The fans are also helpful for maintaining the heating efficiency of the greenhouse. During the hottest parts of the summer months, shade will also be needed to keep indoor conditions cool enough for optimum plant growth.


**Dr. Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor's, master's, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.