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, seed should be planted so the fruit begin to ripen soon after first frost for fall crops.
In cooler areas of New Mexico, tomato crops are generally planted in early July and transplanted to greenhouse beds in mid-August. Harvest will begin in October and may continue until early March. 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. Planting dates in southern New Mexico should be delayed until mid-August or later due to hot weather in mid-summer.
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.
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. Also wrap twine in the same direction, using clips or tape to keep vines from slipping down the twine. 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.
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). If tobacco mosaic virus has been a problem, the vibrator should be wiped after each use with a clean cloth or sponge moistened in a 5 percent chlorine solution. 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.
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.
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.
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.
Tomatoes should be graded using USDA standards. Most buyers prefer U.S. No. 1 fruit. The best market for greenhouse-grown tomatoes in New Mexico is between November and April.
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.
Greenhouse tomatoes are generally marketed in 8- to 10-pound baskets or cartons. Some two-layered cartons may hold 16-20 pounds of fruit. Cartons should be sturdy enough to prevent mechanical damage when handling. Fruit and packaging should be distinctly labeled with decals or other identification to distinguish them as greenhouse-grown tomatoes.
'Tropic' - very popular; very firm, large, red fruited type (8-9 oz); resistance1 to Fusarium wilt (race 1), Verticillium wilt, early blight, gray leaf spot, and some leaf molds; tolerance1 to blotching and some races of tobacco mosaic virus (TMV).
'Jumbo' - similar to 'Tropic'; excellent yields; more USDA #1 fruit (8 oz); resistance to Fusarium wilt (races 1 and 2) and Verticillium wilt; not resistant to TMV.
'Floradel' - 6-oz fruit; resistance to Fusarium wilt, gray leaf spot, and some leaf molds.
'Floralou' - excellent fruit quality and color; vigorous and productive plants; medium-size fruit; resistance to Fusarium wilt and gray leaf mold; resistance to fruit cracking.
'Vendor' - develops good red color; medium-large fruit (4-8 oz); uniform ripening fruit; moderately firm; resistance to TMV (race 1), Fusarium wilt, and several races of leaf mold; fruit resist cracking.
'Pole King' - 8- to 9-oz fruit; sturdy vines; resistance to Fusarium and Verticillium wilts.
'Michigan-Ohio' hybrid - medium-large fruit (8 oz); resistance to Fusarium and Verticillium wilts; adapted to low light conditions.
'Tuckcross O and V' - excellent fruit quality and color; very productive; small to medium-size fruit; minimal fruit cracking; resistance to leaf mold (one strain) and Fusarium wilt.
'Trend' - high yield potential; large, smooth, red fruit; good crack tolerance; resistant to Fusarium crown rot.
'Furon' - red, medium size, beef-steak type; good tolerance to cracking and russeting; resistant to Fusarium crown rot.
'Husky Cherry Gold' - golden-yellow cherry type; vigorous vines up to 6 ft long; more compact and larger fruit than other cherry varieties; resistance/tolerance to Verticillium and Fusarium wilts.
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.
Leaf mold (Fulvia fulva = Cladosporium fulvum) is the most common and destructive disease in greenhouse-grown tomatoes, and is particularly severe under conditions of high humidity. Lower leaves develop pale green spots on their upper surfaces and eventually turn yellow; spots become covered with patches of olive-green to brown mold on the bottoms of leaves. Maintaining humidity below 90 percent by providing good air circulation will help control this disease. Use appropriate fungicides, resistant varieties, and soil sterilization for maximum results.
Gray mold (Botrytis cinerea) is a grayish, powdery, moldy growth on fruit, leaves, and stems. Use similar control measures as for leaf mold; resistant varieties are unavailable.
Early blight (Alternaria solani), which may occur at any time in the season, causes collar rot of seedlings and spotting on leaves and fruit. Note that concentric rings on leaves create a target pattern. Use similar controls as for leaf mold.
Bacterial wilt (Pseudomonas solanacearum) causes diseased plants to wilt and die rapidly (with no yellowing or leaf necrosis). The pith in the stem near the soil line will become water-soaked and dark. Best controls include good sanitation and soil sterilization.
Tobacco mosaic virus (TMV) disease reduces fruit set and quality. A mosaic or mottled appearance of the leaves is the most common symptom. Plants infected as seedlings are usually stunted and slightly yellow; the leaves also may be curled, small, or deformed. Greenhouse workers should wash their hands carefully with soap and water after using tobacco products. Remove any diseased plants as they appear.
Fruit rots are caused by fungi like Alternaria, Phytophthora, and Botrytis. Maintaining optimum temperature and humidity are critical for good control. Use of registered fungicides can help to reduce the incidence and severity of fruit rots as can good greenhouse sanitation. Handle fruit carefully to prevent bruising.
Physiological diseases that can cause problems with greenhouse-grown tomatoes are blossom-end rot and sunscald. Blossom-end rot occurs when tomatoes are stressed for water and calcium, resulting in the formation of a sunken, brown, leathery spot on the blossom-end of the fruit. Monitoring soil moisture and mulches will help prevent this problem. Over-exposure of the fruit to sun can result in sunscald. Training of vines and leaves to cover developing fruit should solve this problem.
Insects. Aphids are small, soft-bodied insects that insert piercing-sucking mouth parts into tomato plants to extract plant juices. Heavy populations can cause leaf curling and plant stunting. Aphids also serve as vectors for several plant diseases. Sticky honeydew produced by aphids may result in growth of black sooty mold.
Whitefly adults are small, winged, white insects 1/16" long. They suck juices from plants and, like aphids, whiteflies are vectors for some diseases. Honeydew produced by whiteflies also will support growth of black sooty mold.
Thrips are very small insects with piercing-sucking mouth parts that feed on plant juices. They can spread tomato spotted wilt viruses and cause premature blossom drop.
Spider mites are non-insect pests (related to spiders) that feed on plant juices on underside of leaves. Leaves may become stippled (gray) and covered with a fine web; defoliation can occur with heavy infestations. Mites are yellowish to greenish with a dark spot on either side.
Other insect and non-insect pests that can cause occasional problems include cutworms, earwigs, snails, slugs, and various caterpillars. Sanitation, soil sterilization, screens on ventilation fans, and appropriate insecticides should be used for maximum control of pests.