Caring for tomato plants throughout the season

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Tomatoes Part 1 covered how to select, plant and support tomatoes. Now that your tomatoes are planted (or they will be soon, it’s not too late!), it’s time to think about how to help them grow.

Tomatoes are heavy feeders and will deplete the soil of nutrients. They produce best when fertilized. Tomato-specific fertilizers are a great choice. Tonkadale carries Espoma Organic Tomato-tone, Organic Garden-tone and Miracle-Gro for Tomatoes, Fruits and Vegetables. With any fertilizer, be sure to follow label directions and be careful not to add too much nitrogen to the soil. This will result in vigorous green growth, fewer fruits, and higher susceptibility to disease.

Tomatoes also perform well with fish fertilizer such as Neptune’s Harvest Organic Fish Fertilizer (a Tonkadale staff favorite!) One good tip to know when using fish fertilizer: keep the dogs in for a little while after application because they like it, too!

As well as feeding tomatoes for growth, it’s important to watch for, and protect against, disease. Lack of nitrogen and phosphorous make tomato plants more susceptible to early blight, so feed plants to protect against disease. Early and late blight are two of the most common tomato problems, and the names are somewhat deceiving.

Early blight usually occurs near the end of the season. Black spots surrounded by yellowing occur on leaves, and sometimes lesions occur on stems and fruit, as well. Often the leaves will fall off completely, making the fruit susceptible to sunscald. The fungus that causes early blight (Alternaria solani) lives in the soil and is splashed onto the leaves by rainwater or overhead watering practices. Mulching around the base of plants can help protect them from soil splashing onto the leaves.

Late blight on tomatoes

University of Minnesota Extension photo

Late blight (Phytophthora infestans) is more common near the end of the season, but can occur any time if conditions are right. Cool, humid days and nights are ideal for late blight. Affected fruit may have brown, greasy spots and a white cotton-like substance. If late blight is suspected, apply a fungicide immediately or remove and destroy the plant.

If you determine you need to apply something to the plant for blight, Tonkadale recommends Bonide Fung-onil, Bonide Mancozeb, or organic Bonide Copper Fungicide as good options. Apply any of these as soon as blight is suspected.

Blossom end rot is another possibility. To protect against this problem, give tomatoes a consistent amount of water throughout their growing season (rain can make this difficult), mulch to conserve moisture, and don’t disturb the soil around the plant within a foot. Tonkadale also recommends Bonide Rot-Stop, which protects tomatoes after heavy rain and rapid growth, and Bonide Tomato and Blossom Set Spray, which helps plants set fruit even in bad weather conditions.

Tomato hornworm is a problem pest that will wreak havoc on leaves and fruit. Easy to identify, the caterpillar has a “horn” on the last section of abdomen. Hand pick and throw into soapy water for best results. If the infestation is large and the caterpillars are still small, effective chemicals include Captain Jack’s Dead Bug Brew, Bonide Insecticidal Soap, or Bonide Eight.

A good, overall product is Bonide Tomato and Vegetable, a three-in-one product that will protect against fungus, mites, and problem insects.

For more information on tomatoes visit the U of M Extension website at or stop in to Tonkadale to talk with a veggie expert.

Happy growing!

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