Jan 16, 2014
Greenhouse tomatoes can pay dividends

A primary reason for growing tomatoes in greenhouses is to reach higher levels of quality and value.

That was a takeaway message from Richard Snyder, professor and vegetable specialist with Mississippi State University. He was a speaker at December’s Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Mich.

Greenhouse tomatoes can pay dividends for growers because the locally grown, vine-ripened nature of the crop leads to uniform size and shape, along with good red color and flavor, Snyder said.

The advantages of greenhouse tomato production allow for environmental modification, including temperature, light, insects, diseases and weeds, as well as control of air pollutants and water supply.

While structures such as greenhouses, high tunnels, row covers and plastic mulch can be more costly than traditional growing methods, the value of the crop tends to be significantly higher, he said.

“It also allows crop production at a time when it would otherwise be impossible,” he said. “We can raise cold-sensitive plants in the winter months in a greenhouse, which we could not do in the field at the same time of year.”

Snyder listed some key aspects of tomato production in greenhouses:

Be sure to get your water tested before starting in the greenhouse tomato business. Your state university, state department of agriculture or a private lab can test your water. Submit a gallon of the water you plan to use in a clean (i.e. not a milk jug) bottle and tell the lab that the water will be used for greenhouse tomatoes.

Tissue analysis is the only way to know if your fertilizer program is optimized. Send in 10 to 12 full-sized leaves taken randomly from the greenhouse. Leaves should be chosen from the same location on each plant so they are all the same physiological age – either the eighth fully expanded leaf from the top, or the leaf opposite a golf-ball sized fruit.

Use a vented heater only. Heaters must have a stack through the roof or the end wall to remove exhaust gases from the greenhouse. Tomatoes are extremely sensitive to ethylene and carbon monoxide, and flower abortion will result from contamination of the greenhouse air.

“Don’t even think about growing greenhouse tomatoes unless you have a market to sell them,” Snyder said. “If you are a small grower, you can sell locally. Always have alternative buyers.”

Snyder stressed doing research before moving ahead with greenhouse tomato production. In addition to “learning the language” of the craft, resources include conferences and workshops, Extension publications, books, newsletters, visits to other growers and online information.

For those considering getting into the business, Snyder suggested attending the Greenhouse Tomato Short Course, which attracts growers from more than 20 states. In its 24th year, the short course is held in Jackson, Miss. The next one will be March 4-5.

When establishing a greenhouse, Snyder said growers should determine its size, location and whether sales will be conducted on site. Drainage is a factor, with the best approach being a 1 percent to 2 percent slope.

A relatively small start is recommended; one or two bays, as opposed to several bays or acres of greenhouse area.

Labor is a constant variant, he said.

“There is an average of 20 hours per week, per bay over the life of the crop. You need to determine whether you can do it by yourself, how much labor may be needed and making sure it is available when you need it.”

Temperature control within the greenhouse is a tricky element. Heaters must be able to raise the temperature to a minimum of 64˚ F, with fans available to keep conditions below 90˚ F.

Snyder suggests a plant population area of 5 square feet per plant, which would allow for 460 plants in a 24-foot by 96-foot area.

A strong support system includes wire height at an average of 7 feet – higher for a taller grower, lower for a shorter grower.

“Be sure it has good support,” Snyder said. “Those 600 plants with fruit load can weigh 3 to 4 tons. The wires should be 3 feet apart in a V-formation over the row. Tie strings to the wire above and clip to the base of the plant.”

A preferred greenhouse tomato variety must include good yield and size, red color, excellent disease resistance and be free of physiological disorders. Two types of tomato plants could be pursued.

For a determinate type, height is genetically determined to be a short plant. The top of the plant ends with a flower cluster. It has an earlier first harvest and will produce for a short season.

An indeterminate type allows for height that is not genetically determined, yielding a tall plant; the top of the plant is a vegetative shoot, it will grow and produce over a long season and bring higher total yield.

“In most cases, for greenhouse production, red indeterminate is preferred with a concentration of beefsteak, or smaller types if a good market exists,” Snyder said. “Greenhouse varieties should not include field or home garden types that are not well adapted to greenhouse conditions. Again, you may deviate from this based on market demands.”

Some recommended tomato varieties include Trust, Big Dena, Geronimo, Torero, Heritage, Starbuck and cluster types such as Success and Tradiro. Some older types could include Caruso, Laura and Tropic, Snyder said.

Choosing a good growing medium is essential, he said. Some elements that factor into that mix include pine bark, perlite, coconut coir, rockwool, peat-lite mixes, soil, sand and any newer alternatives.

Some important “tools of the trade” for greenhouse growers include a pollinator or bumblebee hive (Class A, B, C), ph meter, EC meter and a high/low thermometer.

Designing a good greenhouse irrigation system is “not as simple as it sounds,” Snyder pointed out.

“You should get help from an irrigation engineer, choose proper emitters, use filters and plan for fertigation, including the use of a bulk tank and injector,” he said.

Insects and diseases “will get into your greenhouse,” Snyder said. “Insects do not know if you are organic. Prevention works best. Greenhouse structures do not prevent insects and diseases from getting in. Consider a double-door entry. And always consult with your pest management specialists.

“Do not use Roundup in the greenhouse and don’t use it outside the greenhouse when plants are inside. Do not use any herbicides in the greenhouse, or outside when the plants are inside.”

Pruning and training plants the proper way in the greenhouse will make a big difference, he said.

“Train to one stem. Remove every sucker once a week. Tie the top of the string to horizontal wires overhead. Tie or clip the bottom of the string to the base of the plant. Attach it under a leaf – not under the flower cluster or fruit that can cause damage. Once per week, either add a plant clip or twist string around the stem, always in the same direction.”

Equipment maintenance should be near the top of the list for greenhouse growers, said Snyder, who said heaters, fans, vents, emitters, injectors and pumps “should always be ready in advance of need.”

Being meticulous in their oversight is a good idea for growers, Snyder said.

“Check your work, use pH and EC meters to check nutrient solutions daily and after mixing. Use a gallon jug to check volume per day. Walk the greenhouse every day, looking for wilting plants and critters.”

Gary Pullano

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