By Sheri Hunter, Colorado Master
GardenerSM, Colorado State University Cooperative Extension, Denver
Tomato growers contemplating the upcoming gardening season
may reflect on problems with last years crop. "Why did my tomatoes fail?"
is one of the most frequently posed questions at our farmers' market Master Gardener
Here are a few suggestions to help you plan for this
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. Colorados 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
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
- Cultivate the soil, testing it for adequate calcium,
phosphorus and nitrogen. Adequate soil calcium helps to prevent blossom end rot. Adequate
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, its 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.
Inattention during the growing season can lead to plant
failure. Periodic examination of your tomato plants can alert you to problems before it is
- 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
- 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
- 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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