Tomato Cultural Practices
Plant Spacing and Density
The object in a tomato production greenhouse is to utilize all the growing space to maximize light interception and provide sufficient space between rows to service the plants. However, there is an ideal plant spacing pattern best suited for every growing system. The extent of shading can be varied by altering the plant spacing pattern. With the physical arrangement of plants being normally in double rows, the space between the rows and the plant spacing within the row can significantly affect light penetration through the canopy. In a plant spacing of 2.5 plants per square meter in a plant spacing configuration of 45 by 45 cm., about 60-70% of the solar radiation during the 1-hour period of solar noon will reach the greenhouse floor. By increasing the plant spacing to 3.5 plants per square meter, 60-70% of the solar flux is intercepted by the plant canopy. Suggested optimum spacing of plants in double rows at 80-cm spacing within the row and 1.2 meters between the double rows, while some suggest 4 ft2 per plant for a population of 10,000 plants per acre. The arrangement is double rows about 4 feet apart with 14 to 16 inches between plants in the row.
A two-crop season is the common practice in the northern latitudes in order to avoid the cold low light intensity months (January and February). Plants are set in late August and harvesting of fruit continues through December, and then plants are set in March and harvesting of fruit continues into June or July. In the lower latitudes where the period of cold and low light intensity is less, a single crop is commonly used with plants set in September and the crop is carried through until June or July. In Colorado greenhouses, a staggered schedule of transplanting and replacing plants every 8 months in a two-row planting system ensures continuous production of fruit year-round. Variations of these various planting schedules are practiced based on consumer demand and price obtained for fruit.
Pruning and Training
Maintaining a plant through a long growth period can be a challenge to the grower. The plant is trained up a single vertical plastic twine with suckers removed to maintain a single stem. When the top of the plant reaches the horizontal support wire to which the vertical support twine is attached, the plant can be either topped (terminating further extension of the plant) or lowered (allowing plant growth to extend up the lowered twine).
Careless management of the plants in the greenhouse can be costly in terms of lost yield and low fruit quality. Daily attention is required to ensure that plants are kept upright on the suspension growing system and suckers and vegetative stems from the fruit trusses are promptly removed when appearing. Abnormal looking plant material should be promptly removed. Fruit clusters are pruned to the desired number and abnormal fruit removed when first appearing. Any abnormal growth or plant appearance should be carefully evaluated. Questionable-looking plants should be removed from the greenhouse, and steps taken to determine the cause for any plant abnormality that appears.
Although all current tomato cultivars/varieties are self-pollinated, the transfer of pollen to the stigma under greenhouse conditions may not occur in order to ensure complete pollination. Incomplete pollination results in poorly shaped fruit. If the flower blossoms are hand pollinated, flower vibration using a mechanical vibrator must be done daily based on a preplanned program, following the procedure needed to keep from damaging emerging fruit. If bumblebees are being used for pollination, hive placement and size of the hive will be determined by the stage of plant development and number of plants. If few flowers are ready to pollinate, repeated visits by bees to a flower may result in damage to the flower. Flowers that are not pollinated will fall from the fruiting truss whereas incomplete pollination results in misshapen fruit.
Cluster pruning, practiced to maintain fruit size, is the removal of flowers or small fruit to keep a set number of fruit per cluster. However, severe fruit pruning can result in blossom-end rot (BER). Any fruit that is not normal in shape or has been physically damaged should be removed from the plant when first observed. Fruit removed from the lower trusses results in an increase in fruit size on the upper trusses. A single green fruit should not be left on a harvested truss in the hopes that it will eventually mature.
Plant Culture Systems
The demands of the marketplace, the growing environment (such as light intensity and duration) and outside air temperatures will dictate to a considerable degree which tomato plant culture system can be efficiently employed. A single initial planting and fruit harvesting over a long period of time is one system; also there are several variations of multi-cropping systems in which the tomato plant is allowed to develop to a certain point, then topped allowing already set fruit to mature, and then the plant is removed from the greenhouse and replaced by a mature seedling. This cycle of planting, topping, and replanting can be used to sustain a continuous supply of high quality fruit over a long period of time. It should be remembered that the first three set fruit trusses are those that contribute the highest fruit weight and quality.