Tomatoes grown in an unheated hoophouse were 30 days earlier and twice as productive as field tomatoes, according to trials the past two summers at the University of Missouri. Researchers found that 1,000 square feet of tomatoes (170 plants) would cost $1,073 to grow in a hoophouse (high tunnel). Yield was 10 pounds of marketable fruit per plant, or 1,700 pounds.
At a retail price of $2.50 per pound (a reasonable expectation for early tomatoes), net income from 1,000 square feet would be more than $3,100.
The research was conducted by Lewis Jett, state vegetable crops specialist at the University of Missouri in Columbia. Tomatoes were grown in Stuppy cold frames, 20×36 feet, with roll-up sidewalls for ventilation and a single layer of poly. On average, the tomato plants produced 7 pounds of #1 grade tomatoes, 2 pounds of #2s and 1 pound of lower grades per plant.
The researchers budgeted income based on averages obtained at a wholesale produce auction: $1.50 per pound for #1 tomatoes, $1 per pound for #2s and 50 cents per pound for others. At wholesale prices, total income from 170 plants was $2,210; net income was $1,136.
Growing tomatoes in unheated high tunnels is an exellent strategy for vegetable growers, Jett said. “Based on the results of this research, it is possible for a grower to have vine-ripe tomatoes from mid-June until October in the central Midwest by using high tunnels as a complement to field production,” he said.
Here are some of Jett’s recommendations for successful tomato production in the hoophouse. More detail can be found on the web site, www.hightunnels.org.
Tomatoes can be planted when the soil temperature at 2 inch depth is 60°F. For early tomatoes, plastic mulch can be used to warm the soil. Clear plastic will warm it most, but weeds will grow under it; black plastic will increase the soil temperature 5° and IRT plastic will increase it 5 to 10°. White or white-on-black plastic will significantly lower soil temperature, which makes it useful for late summer or fall tomatoes.
Floating row covers also should be used to protect against frost and to raise early spring temperatures. A medium weight row cover (.5 – .6 oz. per square yard) or a double layer of light row cover should be placed over the plants after planting. Row cover should be used when temperatures are below 50°F and can remain on the plants until the appearance of the first flower cluster.
Tomatoes will do best with drip irrigation to deliver water to the roots without wetting the foliage, which can lead to foliar disease. Tomatoes, which are 95% water, use a large volume of water, particularly during fruit sizing. From fruit set to harvest, 1.5 to 2 quarts of water per plant per day may be needed.
Tomatoes do not need a specific day length to flower. They are self-pollinated, but physical vibration either by shaking the plant, wind or insects will facilitate pollination. Optimum temperatures for pollination are 68-75° night and 60-90° day, so the hoophouse should be vented to keep the temperature within those ranges once the plants have flowers. For most cultivars, harvest is 45 days after flowering.

Planting and pruning
In Missouri, tomato plants were set out on March 24, a month before the average last frost date. Typical spacing is 18-24 inches apart in the row and 36-48 inches between rows. That allows for about 300 plants in a typical 20×96 foot hoophouse.
Plants should be trained in the stake and weave system, which allows more light to reach the plant and results in early fruit set. Drive a 4-foot wooden stake or piece of metal rebar between every other tomato plant. When the tomatoes are 12 inches tall, weave plastic twine down one side of the row, circling each stake, then back on the other side of the row, so the plants are captured between the two lines of twine.
Indeterminate varieties should be pruned to accelerate early harvest. Remove all suckers up to the one below the first cluster of flowers resulting in two stems per plant.