Q&A With Sandy Feather: Tomato growth habits differ

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Q. I have been raising tomatoes for years. Instead of being bushy, they grow more than 6 feet tall, and the leaves start to turn brown as soon as the tomatoes begin to ripen. I don't think this is normal. Do you have any suggestions?

A. Tomatoes can be classified by their growth habits. Those that produce tall vines that continue to grow, blossom and set fruit up until frost are classified as having an indeterminate growth habit. They can easily grow 6 to 10 feet tall through the growing season. These tomatoes are the ones most likely to outgrow all but the tallest stakes and sturdiest cages. It sounds as if your tomato plants fall into this category.

Indeterminate varieties should be staked to keep the fruit off the ground to minimize problems with rot. Staking also allows better air circulation, which can reduce the incidence of disease problems. And staking allows more thorough coverage if fungicide or insecticide sprays are needed through the growing season. Examples of indeterminate varieties include 'Sweet 100' (cherry tomato), 'Big Boy,' 'Brandywine' and 'Beefmaster.' Indeterminate varieties can be used for fresh eating through the growing season, as well as canning and freezing.

Other varieties of tomatoes naturally have a bushier, more compact growth habit. They are classified as having a determinate growth habit. They grow to a certain size -- 3 to 3 1/2 feet tall -- then produce their flowers and fruit. Determinate tomatoes tend to ripen together, which makes them a good choice for gardeners who grow tomatoes for canning and freezing. They are good for fresh eating, too. Although many varieties are self-supporting, staking can help support a plant under a heavy load of fruit. Once they produce their main crop, production can fall off sharply, and the plants may go downhill quickly. Determinate varieties are much easier to grow in containers than indeterminate ones. Examples of determinate varieties include 'Roma VF' (many paste tomatoes have a determinate growth habit), 'Better Bush,' 'Bush Early Girl' and 'Mountain Spring.'

Still other varieties of tomatoes fall somewhere between these two growth habits and are called semi-determinate. They will grow larger than determinate varieties but are not as rampant as indeterminate ones. They typically grow 3 to 5 feet tall. They should be staked but are less likely to outgrow their stakes than indeterminate types. They will produce a main crop that ripens together but will also continue to produce up until frost. Examples of semi-determinate tomatoes include 'Celebrity' and 'Mountain Pride.'

You may be happier with varieties that are determinate or semi-determinate. Many seed catalogs include the tomato's growth habit in the description, and most catalogs can be found online nowadays.

The browning on the leaves is probably caused by one of several leaf spot diseases tomatoes are susceptible to. Early blight is one of the most common diseases that matches the description of your problem. The fungus that causes it overwinters on plant debris in the garden. Good sanitation -- removing all dead annual vegetable plants from the garden, cleaning up tomato stakes and ties, etc. -- is an important step in controlling early blight. The fungus can survive up to a year without a susceptible host. It can also be introduced to the garden on infected transplants.

It is always wise to practice crop rotation, even in small gardens. If you grow tomatoes in the same place year after year, you increase the likelihood of insect and disease problems becoming established in the soil. Be sure to rotate among plant families rather than just individual plants. For example, tomatoes, potatoes, peppers and eggplant are all in the nightshade (Solanaceae) family. A good alternate for tomatoes would be green beans or cucumbers because they are completely unrelated and are less likely to suffer from the same insect and disease problems. A three- to four-year rotation is recommended to allow diseased plant matter to decompose completely.

Early blight symptoms start close to the ground and work their way up the plant. The oldest leaves -- those closest to the ground -- are infected first as spring rain splashes up, carrying spores of the causal fungus that overwintered on bits of debris from last year's garden. The leaves develop dark brown spots characterized by dark concentric rings. Usually some yellowing develops around the leaf spots, too. Spots range from pinprick-sized to 1/2 inch in diameter. Early blight develops under a range of weather conditions, but it is favored by heavy dew and/or rainfall, moderately warm weather (75-85 degrees) and high humidity.

Mulching around plants with an organic mulch such as clean oat straw or shredded leaves, or a synthetic mulch such as black or red plastic, reduces the likelihood of spores splashing up from the soil to infect the lower leaves. Use drip irrigation or soaker hoses rather than overhead watering, if possible. You can also make fungicide applications to protect the plants from infection as they grow. Repeated applications are required through the growing season, at intervals recommended on the label. Organic gardeners can use a copper-based fungicide. Daconil 2787 (chlorothalonil) is also labeled to control early blight in the home vegetable garden.

Send questions to Sandy Feather by e-mail at slf9@psu.edu or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.


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