Gardening: Go undercover

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Greenhouses are useful additions to any garden, especially those that experience temperature extremes.

When building a greenhouse, consider the following:


Choose a level site free of debris, stones, tree roots or other hard-to-remove materials. Avoid locating a greenhouse beneath large trees with overhanging limbs that could fall and cause damage. Unless a greenhouse, such as a lean-to, is attached to a building, distance it from structures. Buildings often cast large shadows, which could cause the greenhouse to become overly shady and cool. If possible, position the greenhouse to protect it from harsh elements, such as wind or hot western sun.


Most greenhouses require some type of adjustable shade devices. These might include a combination of blinds, shade cloth, screens or specially treated glass.


Aside from using solar heat and electrically powered heaters, you may warm plants with all manner of devices. One easy, inexpensive method involves surrounding plants with items that hold heat, such as large containers of sun-warmed water. As the containers give off heat, the plants are kept warm.


Build your greenhouse within reach of utilities, such as electricity and water. The sun will warm your greenhouse during most of the year, but you will need to provide additional heat or air conditioning during extreme weather. You may also decide to equip your greenhouse with electrically controlled vents, lights, grow lamps, fans, humidifiers, grow lights, sprinklers or propagating equipment. Hoses, misters or other irrigation devices are a must in a greenhouse.


Stagnant air can occur in a greenhouse if it holds heat without ventilation. This type of environment encourages insect pests and disease. Open vents daily if possible and keep them closed only when weather is extremely harsh.


Water plants according to their needs. Be aware that a closed, heated environment will affect moisture loss and retention. Water trays or capillary matting may be useful for increasing humidity. Experiment with potting mixtures to determine which soils wick water or hold moisture best for your plant or propagation endeavors. To discourage fungal diseases, do not allow water to pool on foliage or greenhouse surfaces.

Resources:, American Horticultural Society, The Garden Book

For answers to your horticulture questions, please call the Texas AgriLife Extension, Hood County at 817-579-3280 and ask to speak to a Master Gardener or visit the website at