Tips for Tomato Growers

Tomatoes are America's most popular garden crop, but they are not necessarily the easiest crop to grow. Even the most experienced gardeners occasionally find themselves at a loss as to why their tomato plants fail. Here are a few helpful guidelines for understanding tomatoes. The more you know about their needs and growth habits, the easier it will be to cope with their sometimes puzzling behavior.

Developing a Fertilizing Schedule

Tomato plants have a heavy workload, so their soil needs to provide them with a good supply of nutrients. To produce a crop of fruit successfully, they require moderate levels of nitrogen and phosphorus and moderate to high levels of potassium and calcium. Before planting seedlings, mix 1 cup of kelp meal and 1 cup of bone meal into the bottom of the planting hole. This will provide your plants with the necessary potassium and phosphorus. As long as you are starting with good soil, no additional feeding should be necessary until fruit is set.

Once fruit is set, feed plants monthly with an organic fertilizer that is low in nitrogen and high in phosphorus and medium to high in potassium. If your plants are starting out in poor soil, water your plants weekly with 1 cup of a fish emulsion solution (1 Tbsp. fish emulsion per gallon of water). Continue this from planting until the first blossoms form.

Uniform Watering is Key

In the early stages of growth, before fruit has set, it is a good idea to put the plant under slight stress by stretching out the length of time between watering. After fruit has set, however, it's important to maintain uniform soil moisture. Fluctuating wet and dry spells can bring on stunting of plants, blossom-end rot and a host of other problems.

• Fruit crack: If soil moisture varies too much- if the soil gets too dry and then it rains, for example - the fruit can experience a growth spurt, which may cause the skin to split and crack. If droughts are common to your area, plant crack-resistant varieties.

Failure to Set Fruit

• Prolonged moisture: Rain or prolonged humid conditions hamper fruit set. Gardeners growing tomatoes in cool, humid climates have found that fruit set can be increased by shaking the plant (or tapping the stakes of trained plants) to release pollen. Do this in the middle of the afternoon when the temperature is highest and the humidity is low.
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• Temperature: Tomato plants are quite fussy when it comes to air temperature (especially at night). They won't set fruit when temperatures fall below 55 degrees or rise above 100 degrees F. In many cases the plants will flower, but the blossoms simply drop off before they are fertilized. One way to avoid this problem is to start the season with early maturing varieties, which have been bred to set fruit at lower temperatures.

  Once the weather warms up, plant your main season varieties. Row covers can also provide a bit of protection from weather that is too cold. Use them in the spring until the weather warms up.

• Too much nitrogen: Tomato plants sometimes fail to move from the growing stage to the fruiting stage of growth if they are given too much nitrogen early on in their development. Excess nitrogen and lots of water encourages young plants to keep on producing foliage at the expense of fruit. You can help the plant switch over to the fruiting stage by pinching out some of the terminal shoots, or by withholding water to check growth.

Sun Scald

When temperatures rise above 86 degrees F and the sun is at its most intense, fruit that is exposed to direct sunlight can fail to develop good, even red color. In climates where high summer temperatures are the norm, try to select varieties known for having a good dense foliage cover that will help protect developing fruit.

Leaf Curl

• Hot weather: During midday summer heat or after a prolonged period of wet weather, a certain amount of leaf curl and wilt is normal- some varieties showing more sensitivity than others. For tomatoes growing in containers, wilted, droopy top-growth is their way of signaling the need for more water. Heavy pruning also seems to encourage leaf curl in some varieties.
• Tobacco mosaic virus: This is a disease spread on seeds and by contact - not contact by insects, but by way of contaminated tools or even a gardeners own hands (smokers can spread it because it is often present in cigarette tobacco). Affected plants will have leaves that are curled and/or mottled, with discolored pale green or yellow fruits.

Misshapen Fruits, Dropped Leaves, & Other Evils

Tomato problems are usually caused by nutrient deficiencies, viruses, fungi, or insects. Some tomato varieties are more resistant to problems than others, and as always, good cultural practices can go a long way in reducing or eliminating many problems.

• Blossom-end rot: Blossom-end rot appears as a large, leathery scar (rot) on the blossom end of the fruits. It can occur at any stage of development, and is usually caused by a lack of calcium. The calcium may be present in the soil, but it's not being transported to the fruits where it's needed, usually as a result of uneven watering. Blossom-end rot can also affect the inside of the fruit. When this happens, the outside of the tomato appears normal, while the inside is rotten and fuzzy.
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• Catfacing: The fruits are misshapen with bulges, crevices, scars or holes at the blossom ends. Catfacing is caused by anything that damages the fruit as it begins to develop within the flower. This includes heat, dry soil, excessive nitrogen, and especially, cold temperatures.
• Fungal diseases: Early blight and tomato late blight are fungal diseases that are active during periods of warm, moist weather. The spores are usually spread by wind, splashing water, or contaminated tools. Early blight appears as irregularly shaped spots on lower leaves with a subtle bull's-eye pattern, and then gradually infects higher sets of leaves. Eventually, the infected leaves turn yellow and drop off, and the fruits develop dark, sunken blemishes.

  Late blight appears as dark green or brown patches on leaves and stems. Gray fuzz may appear on the undersides of leaves, while the stem ends of the fruit develop slimy brown patches.

• Wilts: The other two major tomato diseases are fusarium or verticillium wilt. Plants may become affected early in the season, while the symptoms show up later - often just as the fruit starts to ripen. One day your tomato plants look fine, and the next day they are suddenly yellow and wilted.

The best ways to avoid tomato problems is to follow good cultural practices and start with disease-resistant plants. In catalogs and on plant tags, initials given after the variety name indicates kinds of resistance. Double initials indicate resistance to more than one strain of that type of disease.

V = verticillium wilt; F = fusarium wilt; T = tobacco mosaic virus; A = alternaria (early blight).