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high tunnel

High tunnels are unheated, plastic-covered, solar greenhouses. Ventilation is passive through roll-up or roll-down side walls or curtains. Crops are grown in native soil under the high tunnel, which protects them from environmental extremes, such as wind, hail, rainfall, insects, and diseases and allows for significantly earlier and higher marketable yields.

Vegetables are the main crops grown in high tunnels around the world. The primary crops, in order of importance, are tomatoes, sweet peppers, cucumbers, muskmelons, lettuce, summer squash, and eggplants.

In Alabama, growers use high tunnels to gain the market advantage of having locally grown fruits and vegetables available for sale at a time when traditionally grown crops are not yet ready for harvest or traditional field production is completed.

While tomatoes are the most popular and potentially the most profitable crop grown in high tunnels, they should not be replanted without rotating to a crop from a different family. Growing the same crop in successive years can lead to an increase in disease, insect, and weed pressure. Crop rotation is used to break the cycle of the diseases and insects associated with specific crops. Several crops in different families can be grown in a rotation so long-term vegetable production can be sustainable in a high tunnel. Different vegetables, small fruits, and flowers are all suited to these growing systems and can be used in rotation. But the specific crops to be grown depend on marketing opportunities.

Crops in the Solonaceous family, such as tomatoes or peppers, can be followed the second year with cucurbit crops, such as cucumbers, squash, cantaloupes, and specialty melons. Early season melons are in strong demand, and many specialty melons are becoming increasingly popular with consumers. Specialty varieties include casaba melons, Canary melons, Crenshaw melons, honeydews, and Galia melons. Galia melons are light-green-fleshed cantaloupes with no sutures.

Galia melons are adapted to warm, dry climates that make them particularly suitable to high tunnel production. Other annual crops that could work well in a third year of rotation are strawberries, cut flowers, and herbs. Other crops specifically in demand in our region can also be produced in high tunnels. One is okra. The higher soil temperature in a high tunnel allows for an earlier harvest and a premium price on the local market. Greens and lettuce can be produced in certain parts of Alabama throughout the winter months when a high tunnel is used to moderate the environment.

All of these crops should produce faster, higher quality yields in high tunnels because of moderated temperatures and protection from harsh environmental conditions. However, growers using high tunnels may notice increased insect and mite pressure due to the lack of rainfall coming in contact with the crops. When growing melons in high tunnels, pay special attention to pollination—especially with all the cucurbit crops, which require insect pollination. Usually, proper timing of the raising and opening of side curtains and end walls will allow pollinating insects access to the crops. Additional beehives may be needed, however, if there is not enough bee activity when the crops are flowering. Bumble bees sold commercially by many vendors also provide excellent pollination for high-value crops.

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