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Tomato Tips 2020

Your tomato plants survived the spring’s extreme and variable weather and are now dark-green, vigorous, and full of promise. You may have even started picking a few ripe fruits of early-maturing cultivars, especially if you garden on the Eastern Shore or in Southern Maryland.

Despite the challenges of diseases (plant and human), climate change, racism, and loved ones who don’t quite get our “tomato devotion,” we are ever hopeful about the upcoming harvest season. Here are some tips to help you navigate the challenges and pick loads of delicious fruits:

First, don’t sweat the small stuff. Tomato plants will be in the ground for 4-5 months. Even when plants are quite healthy and productive you will likely see some insect feeding, leaf spots and discoloration, dead lower leaves, pinched and torn foliage, broken stems, fruit drop, and some blossom-end rot. This can be alarming, but they can tolerate these minor, temporary issues when their basic needs are being met.

Catfaced fruits should be removed while small and green (“small stuff”).

Container tomatoes have no weeds and fewer pest problems but require closer monitoring. Your plants are relying on a relatively small amount of growing media and you to supply the necessary water, nutrients, support, and protection. You may need to water daily and fertilize every two to three weeks. Open any drainage holes that get clogged with roots and growing media. If possible, move containers from very hot, sunny locations (especially if on hardscape) to a cooler spot that receives late afternoon and early evening shade. Full-sized cultivars need at least 5-gallons of growing mix to grow well.

Water and nutrients go together like tomato and basil. Soil water contains the plant-available nutrients taken up by plant roots. If you have fertile soil with a high organic matter content (>5% as measured by a soil testing lab) you may not need to fertilize. Commercial growers and many gardeners apply a high-nitrogen fertilizer when the first fruits start to form. Applying a dry fertilizer around established plants is called “side-dressing.” Pull mulch back, sprinkle the fertilizer evenly in an 8-inch diameter circle around the plant base, replace the mulch, and water in the fertilizer. Side-dressing example: apply ¼ – 1/3 cup of cottonseed meal fertilizer (6-2-1) per plant when green fruits appear. Follow soil test report recommendations and fertilizer label directions. See last month’s blog post on this subject.

Fruiting plants need more water. Plan to give each plant 1-2 gallons once or twice per week depending on rainfall, temperature, soil texture, mulch, and plant size. The root zone should be moist at all times so that plants can take up all the water they need. Water around the base of each plant.

A water breaker nozzle with a wand is a good investment.

Regular, deep watering will help prevent blossom-end rot and cracking. Tomato skins thicken and harden as they enlarge and ripen. They crack easily (see below) with rapid and large changes in fruit temperature and water availability. Excess nitrogen is another contributing factor. Significant cracking can occur after heavy downpours. Fruits with poor leaf coverage are especially susceptible to cracking.

Mulching plants will help minimize weeds, conserve soil moisture, and maintain a stable soil temperature. Cover black plastic or landscape fabric with grass clippings if high soil and air temperatures begin to stress plants causing blossom drop and wilting.

Grass clippings (no lawn herbicides) can be spread 4-inches deep. They recycle nutrients and feed the soil food web as they decompose.

A strong support system will keep your vines from crashing down due to storms and heavy fruit loads. Continue to secure vines to your support structure as the plants get taller. Remove suckers from vigorous stems to reduce crowding and improve air circulation around foliage. You can also lop the tops off vigorous stems to make them easier to support and manage.

These three commercial cages were twisted and flattened in a storm. They aren’t designed to support large plants loaded with fruit.

You probably have a support system in place. If not, check out these options:

The “stake and weave” support system holds tomato stems upright between pairs of parallel runs of string. Newspaper sections covered with straw makes a reliable organic mulch.
Simple trellis system using 7-ft. T-posts, connected by five strands of #17 electric fence wire. Plant stems are tied to the horizontal wires.
Strong but labor-intensive bamboo structure. Uprights must be buried 15-18 inches in the soil.

Foliar diseases of tomato thrive during warm, wet, humid summers (just like tomato plants!) Early blight and Septoria leaf spot are the two main diseases that can defoliate plants and reduce yields in Maryland.

Irregular lesions with a yellow halo and target pattern are classic early blight symptoms.
Septoria leaf spot appears as small distinct lesions with dark borders and tan centers.

Symptoms of these leaf spot diseases are first seen on lower leaves. The infection moves up the plant, spreading rapidly during humid, wet weather. They often co-occur and are managed the same way:

  1. Provide adequate spacing to increase air circulation and remove all suckers that emerge from the plant base.
  2. Keep plants well mulched to minimize soil splashing.
  3. Water plants at their base. Avoid wetting the foliage.
  4. Prune off the lowest 3-5 leaf branches once plants are well established and starting to develop fruits. This increases air circulation and slows down infections.
  5. Remove infected leaves during the growing season and remove all infected plant parts at the end of the season.
  6. Apply a synthetic fungicide or an organic fungicide (fixed copper) according to label directions, early in the season, when symptoms appear to slow the spread of the disease. This may be helpful where the disease causes severe blighting each year leading to reduced yields.
  7. Diseased plant parts can be composted if hot composting” techniques are used (pile temperatures should exceed 120° F throughout and piles should be turned two to three times).
Sunscald is caused by a loss of leaves, usually due to foliar diseases.

Insects pests: several caterpillars such as tomato fruitworm and tobacco/tomato hornworm are common fruit pests, but the damage is seldom severe. By the time signs of the problem are seen it’s too late to anything but compost the infested fruits. Search for and dispose of caterpillars found on foliage and fruit.

Scraping and tunneling damage caused by a yellow-striped armyworm larva.

Several different stinkbug species feed on tomatoes. They feed using piercing-sucking mouthparts and leave behind white to yellow corky spots. Stinkbugs are widespread and difficult to handpick and control. Minor damage can be cut out with a sharp knife.

Minor stink bug injury (left), Southern green stink bug (right)

Pick fruits when they first begin to change color (“breaker stage”) from green. This allows you to get your fruits off the vine before problems strike, greatly increasing the number of usable fruits. Ripen them indoors on a counter (never refrigerate!) I think you’ll find they taste just as good, and have the same desirable texture, as fruits that fully ripen on the vine.

Fruit picked when first turning color (left) Four days later (right)
Concentric cracking (eft) Longitudinal cracking (center) Cuticle cracking (rain checking) (right)
Anthracnose (one of several fruit diseases of ripening tomatoes)

Years ago, when I grew tomatoes commercially I sold “seconds” and “thirds” (fruits with splits, nicks, soft spots, and stink bug stings) at greatly reduced prices for canning. Think about what you can quickly do with your “seconds” and “thirds”- salsa, gazpacho, cooked or cold tomato sauce, tomato juice, etc. Above all, share the harvest this summer and pass on your gardening knowledge.

By Jon Traunfeld, Extension Specialist. Read more by Jon.

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