Tomato

Soils and Fertilization

Tomatoes grow on many soil types but all good tomato soils must drain well. On sandy soils, tomatoes mature early, but silt or clay loam soils are generally considered the most productive. Optimal soil pH is 6.0 to 6.5. Tomatoes are considered 'heavy feeders' because of their rapid growth and long production season. Production of one ton of tomato fruit removes 3 to 8 pounds N, 0.5 to 3.0 pounds P2O5, and 5 to 12 pounds K2O from the soil. The table below lists plant nutrient recommendations based on a soil test. See Soil Management for an example of the use of poultry litter in an Alabama tomato trial.

Nutrient deficiencies

Nitrogen: Tomatoes need N for vigorous growth, but it is easy to apply too much before fruit set. The resulting plants are thick stemmed and dark green. New leaves sometimes ball up rather than expand. Such plants are said to be 'bullish'. It is the ratio of nitrogen supplied to carbohydrates available from photosynthesis that is critical. If nitrogen and sunlight for photosynthesis are both adequate, then plants will grow and yield well. If N is high and plants are crowded or light is low, set will be poor because vegetative growth preempts all available carbohydrates. Such plants are sometimes described as 'viney'. The best solution is to provide as much light as possible and enough nitrogen to keep the plant growing steadily. Too little N is, of course, also bad because it stunts plant growth.

Other nutrient problems: Soft fruit and poor condition of skin are associated with low K; poor root growth and poor fruit development with low P, blossom end rot with low calcium availability, and fruit russetting, brittle stems and tip dieback wi th low boron.

Planting

Tomato seedlings require 5 to 7 weeks at 65 to 75 degrees F day and 60 to 65 degrees F night temperatures to be ready for transplanting to the field. If necessary, it is usually possible to use older or younger transplants successfully. In trials in Florida and Pennsylvania, transplants with ages ran ging from 3 to 11 weeks did not differ in marketable yields. Thus, if field planting must be delayed, transplants more than 5 to 7 weeks old may be used as long as they are growing well and have not been hardened for long periods by the withholding of water or nutrients. For staking of fresh market toma-toes, as described below, within-row spacings are 15 to 30 inches and between-row spacing are 54 to 72 inches.

Within-row spacing will depend on the vigor of the cultivar and on how severely it will be pruned. Some growers space plants widely (26 to 36 inches) in the row and prune very lightly or not at all.

Processing tomatoes and mechanically harvested fresh market tomatoes are often direct seeded by placing 4 to 7 seeds in clumps 7 to 12 inches apart in 5-foot double or single rows. At the second or third true-leaf stage, plants are thinned to single plan ts 6 to 9 inches apart or clumps of 2 to 4 plants 9 to 12 inches apart. No more than five plants should be allowed per foot or plants will be too small to be mechanically harvested.

Pruning and Staking

Trellising: In fresh market tomato production systems, plants are usually held off the ground with individual stakes or by a trellis strung along a row of stakes. In commercial fresh market tomato production, plants are usually trellised with two plants between each stake. With this system, they are pruned to remove all suckers except the one immediately below the first flower cluster. Then sturdy 4-foot stakes are placed between every two plants. Extra stakes brace the stake at the end of the row. Nylon twine is strung horizontally along the line of stakes, wrapping the stakes tightly and encircling the plants. Typically, the first stringing takes place 2 to 4 weeks after transplanting or when transplants are 12 to 15 inches tall. The first string is placed about 10 inches above the ground and is sometimes crossed between the plants to provide additional support. As the plants grow, additional strings are added at intervals of 6 to 10 inches up the stake. These additional strings are not usually crossed between the plants. Shorter determinate cultivars are used so only four strings are necessary. This system is variously referred to as the stake or trellis system and is widely used in commercial tomato production. Once the trellises are strung, the plants are generally not pruned again except to remove shoots growing from the base of the plant (ground suckers).

Space plants in trellised production system 18 to 24 inches apart. Stakes 4 to 4¸ feet tall should be driven about 1 foot into the ground. Begin stringing when plants reach 12 to 15 inches and space strings about 6 inches apart.

Growers sometimes elect to let more suckers develop in widely spaced plantings or on cultivars like 'Pikred' which are early maturing and not very vigorous vegetatively, producing relatively few leaves in proportion to the amount of fruit present. When this staking system is combined with black plastic mulch and drip irrigation, high yields of large excellent quality fruit result, assuming all other aspects of production are properly managed. Disadvantages are that trellises will sometimes fall over in high winds on wet fields and trellises and strings must be removed at the end of the season.

While the trellising system described above is widely used in the South for commercial fresh market tomatoes, greenhouse or home garden tomatoes are usually tied individually, and processing tomatoes are not tied at all. Procedures, and advantages and disadvantages of pole production and ground culture relative to trellising are discussed below.

Tying to poles: Individually tying each plant to its own pole or stake was once common, but this method is now mostly used in home gardens because it is labor intensive and expensive. In pole production, indeter-minate cultivars are pruned to a single st em which is tied or clipped to a 5-to-6-foot pole. As the plant grows, tying and removing side shoots from the main stem must be repeated every 7 to 10 days. To speed ripening, the main stem is usually cut off when it reaches the top of the stake . A variation of this method is used in greenhouses. The tomatoes are clipped to strings hanging vertically from a 6-to-7-foot high heavy gauge horizontal overhead wire which is secured to the greenhouse itself.

The advantages of this system include easy harvest, large, clean fruit, and little soft rot. In hot weather, however, the foliage offers little protection from the sun, resulting in sunscald and fruit cracking. It is also more expensive and labor-intensive than trellising.

Sprawling on ground: This method is used to grow mechanically harvested tomatoes such as those for processing and some mature green fresh market tomatoes. Generally plants are seeded rather than transplanted. There is little requirement for labor or mat erials but in wet weather, fruit rots on the ground even when grown on black plastic. Vines are more susceptible to foliar diseases because of poor air circulation. Yields are also lower because fruit are lost in mechanical harvest. In addition the vines are so damaged by mechanical harvest that the crop is generally harvested only once. However, research is underway to develop fresh market cultivars with a prostrate growth habit which will hold fruit off the ground without staking.

Water Requirements

There are many factors to be considered in determining water requirements for tomatoes in the south. Tomatoes have a high water requirement but also have an extensive root system. Summer rainfall in the south is unpredictable, and droughts can be locally and even regionally severe, reducing yield and fruit quality even though the plants themselves rarely die. With good growing conditions, plants should be given as much water as possible during vegetative growth. Under low light or high temperature con ditions, however, watering transplants excessively results in thin, leggy stems. For maximum yield, adequate water levels need to be maintained throughout fruit development. For maximal flavor, however, a slight water stress during fruit development 60 to 80 percent of the estimated requirement) is sometimes recommended. Probably the most important consideration in watering tomatoes is consistency. When water availability fluctuates or when it is too high or too low at critical stages, fruit disord ers develop. (See the section on physiological disorders.)

Mulches

Mulches such as black plastic and straw are widely used to reduce weed problems and conserve water. The decision of whether or not to use a mulch or what type of mulch to use is not easy, however. It is difficult to design and interpret experiments comp aring economic returns from the many possible combinations of mulching systems since not all costs and benefits have easily assignable economic values.

For example, black plastic warms the soil in the spring which will increase early yields, but it will also limit water penetration unless drip irrigation tubes are installed under the plastic. If drip tubing is not installed, growers sometimes punch holes in the black plastic to allow water entry, but this weakens the plastic and stimulates weed seed germination, especially where tearing occurs. Straw applied before soil warms up keeps soil temperatures low and early season plants become more susceptible to frost damage. Straw mulches allow sustained rains to penetrate but may intercept moisture from light rains. In western North Carolina, fumigation plus straw mulch increased yield and net returns compared to 1) fumigation plus plastic and herbicides, 2) fumigation plus herbicides or 3) fumigation plus cultivation. Current year costs were higher in the straw/fumigation treatment, however.

The difficulty of comparing net returns from mulch production systems was also shown by a Pennsylvania study. In this study, the 'conventional' system consisted of overhead irrigation, no mulch or staking, soil-applied chemical fertilizers, and IPM pest control using synthetic chemicals. The 'hybrid' system consisted of trickle irrigation, several applications of soluble fertilizers in the drip lines, plastic mulch, staking, and IPM procedures for pest control using synthetic chemicals. The 'biological' system consisted of trickle irrigation, compost and manure fertilizers, straw mulch, stakes, and IPM pest control using biological materials. Tomatoes from all three systems were assumed to have the same market value. Using this assumption, the conventional system netted the highest returns, and the biological system the lowest.

Although current year returns from the biological system were relatively low, an added but not easily economically quantifiable benefit was an increase in the soil water-holding capacity. Plants grown in the biological system plots needed half the water of the hybrid system and a quarter the water of the conventional system. Additional benefits of higher water-holding capacity of the soil were apparent during the following year, which was very dry. Sweet corn was grown on all three plots without irrigation. Because of the increased soil water holding capacity, sweet corn in the biological plots produced much more than sweet corn in either of the other two systems.

Physiological Disorders

Blossom end rot (BER): Calcium moves only in water-conducting tissues of the plant. When water movement into the tomato fruit is restricted, a localized calcium deficiency often develops at the blossom end. This area fails to fill out and eventually appears sunken and black. A number of environmental and cultural problems can cause BER in tomatoes. The most common of these and some preventative measures are summarized below.

Growth cracks: There are three types of growth cracks. With all three types, there is considerable variation between cultivars in susceptibility.

1. Concentric cracking: Rings of brown scar tissue encircle the stem end of the fruit. A form called rain or weather checking results when poor foliage cover exposes water droplets on the shoulder of the fruit to full sun.
2. Radial cracking: Susceptibility to this type of cracking increases with ripening. Deep v-shaped openings start at the stem end and sometimes extend almost to the tip. Typically this disorder appears after rain when plants grown in dry soil suddenly experience high moisture levels. In the greenhouse, however, radial cracking can also result from overwatering.
3. Russetting: Brownish scar tissue (callus) develops over microscopic tears in the tomato skin, giving the fruit a rough, clouded appearance. Russetting most often develops in very humid greenhouses.

Puffiness: Poorly pollinated fruit may be angular on the outside and the end is somewhat pointed, giving the fruit a triangular appearance. The walls 'give' when squeezed rather than feeling firm. When cut open, there are few seeds and little lo cular material (gel). Although eating quality is poor because of the lack of gel, some cultivars have been bred to be puffy so they can be stuffed more easily.

Anther scarring: Zipper-like lines along the side of the fruit appear because of abnormalities in early flower development. Although sometimes attributed to high humidity, the exact cause is unknown.

Edema or oedema: Under humid, cloudy conditions, if tomatoes are over-watered, areas develop on the leaves with undifferentiated, green callus growth. These areas eventually scab over and turn brown. There are no particular adverse effects from these patches of callus tissue, but growers often become concerned because they suspect a pathogen.

Sunscald: Fruit exposed to direct sun in hot weather develop bleached areas. Eventually these areas become dry and papery. The best prevention is to protect against defoliating diseases, but less severe pruning and closer spacing will also incre ase foliage cover.

Catfacing: The female part of the flower (pistil) develops abnormally because of low temperatures (below 60 degrees F), resulting in misshapen fruit. Usually fruit are large with scaly scar tissue covering gaps between the irregular lobes.

Blossom end rot: problems and prevention.