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Green-house vegetable cultivation
By Dr Adnan Younis & Dr M. Aslam Pervez

Green-house vegetable production is a highly intensive enterprise requiring substantial labour and capital inputs. Because of this, potential growers should carefully consider all factors necessary for a successful enterprise.

In many ways, Green-house vegetable production is a 24-hour commitment. Its maintenance, crop production and handling emergencies require constant vigilance. Every 4,000 square feet of green-house space requires an estimated 25 to 30 hours of crop care and upkeep.

Green-house structures require constant maintenance and repair. Many of the selected Green-house covers must be replaced on a regular basis. Heating, cooling and watering systems must be maintained and routinely serviced.

In addition, contingency plans and backup systems must be in place in case any of these major systems should break down. Even a one-day loss of cooling, heating or water during a critical period can result in complete crop failure.

Along with the essential skills, capital and labour to build, maintain and grow a crop, producers must develop markets willing to pay the relatively high prices necessary to make the enterprise economically viable. Green-house-grown vegetables cannot compete with comparable field-grown crops based on price; therefore, green-house-grown vegetables often are marketed to buyers based on superior quality and off-season availability.

Finally, the personality and skills of the person or people involved in the enterprise should be considered. As mentioned earlier, this can be a 24-hour commitment. If you dont have the temperament to commit and to be available day or night as needed, then this is not for you. In addition, a successful green-house vegetable production operation requires mechanical aptitude, crop production skills and business acumen.

Although green-house production is an intensive undertaking, it can be very satisfying and rewarding. One advantage of green-house vegetable production is the relatively small amount of area required compared with field-grown produce. In addition, the return on investment can be good if the requisite markets can be found. Several vegetables have been successfully produced in a green-house, including cucumbers, tomatoes, peppers, lettuce, herbs and, by far the most important, tomatoes.

Cucumber: Cucumbers generally grow more rapidly than tomatoes and produce earlier. They also require high temperatures which mean they are generally grown as a spring or early summer crop. Daytime temperatures should be 80-85F and night-time 65-75F. Soil temperatures should be at least 65F. Lower temperatures will delay plant growth and fruit development.

Cucumbers are heavy feeders requiring 300-400 lb/acre of P205. Similar quantities of potassium are required. Weekly feedings with a balanced fertiliser (20-20-20) will be required for maximum production. Never stress seedlings for water or nitrogen.

Plants are best started in individual containers. As seeds are often very expensive, sow one seed per container (1/4 to 1/2 inch deep) in a sterile potting mix with the spiked end of the seed up (root will emerge facing down). Cover pots with clear polyethylene, and place in the shade. Plants will emerge in two to three days at 80-85F. Remove plastic coverings when plants emerge and place them in full sun.

After plants have formed at least two true leaves, transplant them to their permanent location in the growing bed. Cucumbers will require 6-8 square feet of space per plant. Plants are generally spaced two feet apart in rows three to four feet apart.

Tomato: One or two tomato crops can be planted in the green-house 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.

Tomato crops are generally planted in early July and transplanted to green-house 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. Plants are best started in individual containers (plastic pots, peat pots, or cubes) to reduce labour costs and 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 160F 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 (70F) 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 58-60F and night time 52-56F 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 70-75F and night time 60-62F) should be maintained. After the initial cold treatment, temperatures should not fall below 55F, 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 50F will chill the roots, causing poor growth. Plants should be fertilised 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 one inch deeper than previously grown. Space plants 15-18 inches apart in rows 3-3.5 feet wide. Watering should be done immediately after transplanting.

Lettuce: Lettuce is generally grown when light intensities are low and temperatures are cool. Plants prefer a daylight temperature of 60-65F and a night time temperature of 50-55F. High green-house temperatures will often result in spindly growth and seed-stalk development in some varieties.

A crop of lettuce can be scheduled between fall and spring tomato crops. Lettuce usually takes about one month from seeding to transplanting. Days to harvest from seeding may vary from 12-15 weeks in mid-winter and from 8-10 weeks in early spring.

Under poor light intensities a 9 x 9-inch spacing may be used, while a 6 x 6-inch spacing can be used in the spring as light conditions improve. Lettuce is a poor feeder, but requires a high level of nutrition. Apply a balanced fertilizer before planting with weekly nitrogen feedings as needed.


Courtesy: Dawn
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