A high tunnel is a type of temporary greenhouse that allows commercial gardeners to extend their growing season. This type of greenhouse is similar in construction to a hoop house. During warm weather, growers can roll up the plastic sidewalls of the house to ventilate it. Thanks to the use of high tunnels, commercial farmers can grow tomatoes in cooler climates, and can grow tomatoes year-round in warm climates.
Plant the tomato transplants in 5-gallon containers. Space each container far enough apart to promote good circulation in the high tunnel.
Water the plants when the soil becomes slightly dry, using a garden hose. The soil of each container should remain as damp as a wrung-out sponge. Water your plants consistently to prevent blossom end rot. Add a balanced liquid fertilizer (10-10-10), using a hose-end applicator.
Examine each plant as you water it for signs of mold or mildew. Mold and mildew problems in a high tunnel are more pronounced than in the open air because of the presence of water and absence of circulation. If you see a tomato plant infected with mold or mildew, remove the plant from the high tunnel. Do not return the plant to the high tunnel until it is free of mold and mildew. Space your plants further apart to increase circulation throughout the high tunnel.
Drive stakes into the ground between tomatoes, using a mallet. Weave two lengths of twine between the stakes and the tomato vines to hold the vine upright. As the tomato vine grows, weave more twine between the stakes and the tomato plants.
Shake each tomato plant gently to force the tomato blossoms to self-pollinate.
Remove any secondary shoots, known as suckers, as you trellis the tomatoes, using pruning shears. Suckers are vigorous new growth found at the base of the leaves. Suckers will steal a tomato’s energy and will prevent it from producing healthy fruit.
Place a thermometer in the high tunnel. Keep temperatures between 75 and 80 degrees Fahrenheit during daytime hours and above 50 degrees at night. Lift the sides of the tunnel wall when temperatures climb above 80. Add a gas space heater and use it to heat the interior of the high tunnel when temperatures drop below 50 degrees. Tomatoes only thrive in these temperature ranges.