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Why Tomatoes Fail

By Sheri Hunter, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County

Tomato growers contemplating the upcoming gardening season may reflect on problems with last year’s crop. "Why did my tomatoes fail?" is one of the most frequently posed questions at our farmers' market Master Gardener booth.

Here are a few suggestions to help you plan for this year’s tomatoes.

Choose the Right Varieties

Many tomato plants fail because the selected plant is poorly suited to Colorado climate and soil or is susceptible to a soil-borne disease.

To avoid losing your plants due to these conditions:

  • Select plants resistant to fusarium wilt, tobacco mosaic virus, and nematodes.
  • Choose varieties with growing cycles of 65-75 days for best result. Colorado’s growing season is sometimes short. Varieties with longer maturity cycles may not ripen before the cold nights return.
  • Choose cold tolerant varieties if you expect a long cool spring.

Plant in the Best Environment

Tomato plants need to be planted under the right conditions to succeed.

  • If you are a tobacco user, wash your hands carefully before handling plants or seeds. Tobacco mosaic virus can be transmitted by cigarette handlers.
  • Locate plants in full sun. Less than full sun exposure results in spindly weak growth and few fruit. Rotate location of plants to minimize development of insects and diseases in the soil.  It's ideal to change planting sites so that tomatoes return to a growing location only once every three years.
  • Wait until all danger of frost is past and the soil temperature remains above 50 degrees Fahrenheit (late May or even early June). Cool temperatures slow growth, as will shorter days. Be patient.
  • Space plants widely (3-4 feet apart) to provide adequate sun exposure and air circulation. Tight spacing increases the incidence of disease and may reduce yields.
  • Cultivate the soil, testing it for adequate calcium, phosphorus and nitrogen. Adequate soil calcium helps to prevent blossom end rot. Adequate phosphorus
    ensures healthy flowers and fruit development.
  • Too much nitrogen causes abundant leaf growth at the expense of flowering and fruit formation. Overfertilizing can also cause a buildup of salts in the soil, interfering with normal nutrient uptake. With tomatoes, it’s best to fertilize at planting and then at midseason with low analysis fertilizer containing 5 or 10 percent nitrogen. Avoid high nitrogen fertilizers that promote excessive top growth at the expense of fruit development. Make sure the soil receives annual additions of compost. This helps to maintain good aeration and drainage. This is the best defense against disease and chemical imbalances.

Monitor Conditions

Inattention during the growing season can lead to plant failure. Periodic examination of your tomato plants can alert you to problems before it is too late.

  • The amount of water a tomato needs changes during the growing season but the need for consistent moisture remains the same. During the growth period, regular watering is important. Irregular watering often leads to blossom end rot, while underwatering to the point of wilting can weaken the plant and leave it susceptible to attack by pests and disease. Later in the growing season, when the hottest weather subsides and the fruit begins to ripen, adjust to the cooler weather by reducing watering while maintaining consistent soil moisture. Do this by feeling the soil for coolness, and indicator of adequate soil moisture.   Don't rely on your best guess and water without checking the soil. Both excessive and inadequate soil moisture lead to blossom end rot and other plant problems.
  • Protect plants from high wind whenever possible. A wind break is a frequently overlooked but may be well worth the effort as it saves your crop from severe stormy Colorado weather.

 Problems beyond your control

  • Poor pollination at blossoming can reduce fruit formation. Incomplete pollination can result in wildly misshapen fruits. The problem may have been overfertilizing (too few blossoms) or cool nights (less than 55 degrees) during fruit formation.
  • Uneven temperatures can cause cracking or "catfacing" as tomatoes ripen. Catfacing shows up as odd shaped fruits with deformed marks or lines. This is a normal occurrence as cooler temperatures return in very late summer.
  • Hail damage can be devastating. Protection from hail is a complex and expensive problem to solve. Most of us defer to nature, replanting if the damage is extreme and occurs early in the season.

Though not everything is in a gardener's control, regular care from a knowledgeable gardener markedly increases the chances for a successful tomato crop.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010