Planting
One or two tomato crops can be planted in the greenhouse during the year. Planting, transplanting, and harvest dates will vary depending on location. As most tomato varieties will begin to ripen 100 days after planting.

Harvesting may be terminated at an earlier date if heating costs become extreme. Late spring harvest can be accomplished by delaying planting until late fall or early winter.

Plants are best started in individual containers (plastic pots, peat pots, or cubes) to reduce labor costs and reduce transplanting shock. Use of commercial sterile potting mixes will decrease the incidence of seedling disease problems. Custom soil mixes can be used, but must be pasteurized to eliminate insects, diseases, and weed seed. Heating the moist soil mixture to a temperature of 160°F for 30 minutes will kill most pests.

Sow two to three seeds per pot (1/4-inch deep) and water. Then cover pots with clear polyethylene and place in the shade (70°F) until seedlings emerge. Plastic should then be removed and the pots moved into full sun. Thin the seedlings to one plant per pot.

If possible, seedlings should be grown at daytime temperatures of 58-60°F (nighttime 52-56°F) for the first 10-14 days. This initial cold treatment should help seedlings develop larger cotyledons and thicker stems. Plants should also set more early fruit, increasing both early and total yields. Thereafter a daytime temperature of 70-75°F (nighttime 60-62°F) should be maintained. After the initial cold treatment, temperatures should not fall below 55°F, which may cause rough, irregularly shaped fruit and stunted plant growth. Temperatures can be reduced slightly during cloudy days.

Irrigation water may have to be heated in the winter before use. Water less than 50°F will chill the roots, causing poor growth. Plants should be fertilized weekly with a starter solution (1/2 ounce of 21-53-0 per gallon of water) in the irrigation water. As plants become larger, feeding can be increased to twice a week.

Transplants should be established in the ground beds approximately four to six weeks after seeding. Set transplants in the soil 1 inch deeper than previously grown. Space plants 15-18 inches apart in rows 3-3.5 feet wide. Water immediately after transplanting.

Training
Plants should be trained as single (main) stems by removing all side shoots or suckers that develop between leaf petioles and the stems. Remove shoots by snapping them off, not cutting, as diseases can be transmitted on the knife blade.

Vines can be supported by plastic or binder twine loosely anchored around the base of the plants (non-slip loop) and to overhead support wires (11- to 12-gauge) running the length of the row. Overhead wires should be at least 7 feet above the surface of the bed and be firmly anchored to support structures.

Twine should be wrapped clockwise around the vine as it develops, with one complete swirl every three leaves. The vine should be supported by the twine under the leaves, not the stems of the fruit clusters. Do not try to wrap the twine around the growing tip because the tip may break.

When plants reach overhead supporting wires, untie the twine and lower vines and twine at least 3 feet. After lowering, vines should all lean in one direction in one row. Vines in adjacent rows should lean in the opposite direction. Retie twine with the vines to the support wire. Be sure to leave at least 4-5 feet of extra twine for this purpose when initially tying vines. Remove any leaves that lie on the soil.

About 40-45 days before terminating harvest, plants can be "topped" by pinching out the terminal growing tip. Keep two leaves above the top flower cluster. Topping vines will force remaining food reserves into maturing fruit already present on the vines. Continue to remove any suckers that develop.As fruit mature on the lower part of the vine, pinch off older leaves below the fruit. This will provide better air circulation, which helps to reduce the incidence of disease and opens vines up for spraying and harvesting.

Growers should remove any deformed, immature fruit which will ultimately become culls. Removing excess fruit also will result in larger tomatoes at harvest that can be sold at a premium price.

Pollination
Mechanical pollination of tomato flowers is generally needed in the greenhouse due to limited air movement and high humidity. An electric or battery-powered vibrator can be used to vibrate flower clusters just above the area where they originate from the stem. The vibration will release pollen necessary for pollination. This can be done twice a day (around 10:00 am and 3:00 pm). Because all flowers on a cluster do not open at the same time, the same cluster will have to be vibrated again as new flowers open. Air from a mist-blower also has been found effective in pollinating tomatoes.

A number of factors can result in poor fruit set. The most common problem is temperature extremes (above 90°F during the daytime, above 75°F at night, or below 57°F at night). Other adverse conditions include high humidity, low light intensity, nutrient imbalances, pests, and water stress.

Plant Nutrition
Optimum soil pH for tomato production is 5.8-6.8. Depending on a soil analysis, phosphorous should be applied pre-plant incorporated at a rate of 200-400 lb/a of P2O5. Soils deficient in potassium may require similar quantities of potassium (K20). Both the phosphorous (treble-superphosphate) and potassium (potassium sulfate) should be incorporated to a depth of 8-12 inches. Approximately 50 lb/a of elemental nitrogen should be applied before planting. Additional nitrogen can be applied as a sidedressing or through the irrigation system as needed. Leaf analysis is the best way to determine additional nutrient requirements. Plants exhibiting deficiencies of minor elements such as iron or zinc can be treated with foliar applications of iron or zinc sulfates or chelates.

Mulching
A mulch of clean straw can be placed around plants to a depth of 3-4 inches. Mulches will help conserve moisture and keep soil from compacting between plants. Mulches are most effective when used in combination with drip irrigation.

Harvesting
Fruit should remain on the vine for as long as possible for maximum quality. However, market specifications will determine whether fruit should be harvested earlier (light red stage). Plants are generally harvested two to three times a week. Fruit should be snapped from the plant leaving a small portion of the pedicel and green calyx bracts attached to the fruit, a distinct trademark for greenhouse-grown tomatoes.

Ripe fruit should be cooled to 55°F for maximum shelf life, but never allow the temperature to drop below 50°F. Light-colored fruit can be held at 70°F until the desired color is achieved.

Pest Control
Diseases. Diseases are best controlled through prevention. Selecting a sunny site with a well-drained soil, sterilizing the soil, providing good air circulation, and monitoring your irrigation closely will help keep diseases to a minimum.

Nevertheless, keep a good supply of recommended fungicides on hand with an appropriate sprayer that will effectively cover all plant surfaces.

Seedling diseases include seed rot (failure of seed to germinate due to fungi), stem rot, and pre- and post-emergence damping-off. Damping-off refers to the attack of seedlings before and after emergence from the soil. Symptoms include the development of dry or water-soaked lesions at the soil line, resulting in stem constriction and plants toppling over. Seedling diseases are most commonly caused by soil-borne fungi like Pythium spp. and Rhizoctonia solani. Soil sterilization, seed treatment with appropriate fungicides, and good cultural practices are the most common control methods.

Root-knot nematodes cause plants to become stunted and wilt (diurnal wilting is common). Roots develop knots, galls, or swelling. Secondary symptoms of nutrient deficiencies may result from the inability of roots to take up the necessary nutrients. Soil sterilization is the most effective control measure.

Verticillium and Fusarium wilts cause leaves to become yellow along the margins and between veins. Plants become stunted and wilt severely during the day, but recover at night. Eventually the entire plant dies. Vascular tissue is streaked brown (streaking occurs high on the stem and into petiole scars with Fusarium wilt, and occurs on lower stems and is not evident in petiole scars with Verticillium wilt). For best control, use soil sterilization and plant resistant varieties.