By Susan Perry
CSU Master Gardener in Larimer County
With warm weather arriving, it’s time to start your tomato garden. With the right weather conditions and a little luck, these tips will help you grow a great tomato crop. Here are 14 suggestions for success:
Select healthy, VFN resistant plants. VFN stands for Verticillium wilt, Fusarium wilt, and nematodes. Nematodes are not a problem in Colorado, but both wilts are potentially deadly threats to your tomatoes.
When selecting tomatoes, keep in mind our short growing season when checking the plant label for days to maturity. Most home gardeners select indeterminant vines, which grow until frost.
Harden tomato plants before planting. Most tomatoes are kept in greenhouse conditions until purchase. Planting them immediately is a shock from which many cannot recover. Hardening gradually accustoms the plant to the outdoors by putting it outside in full sun (and wind) for a few hours a day. To encourage hardening off, allow the plant to barely wilt before watering. Extended wilting can result in plant death, so use caution. After a week, the plant will be tough enough to endure most outdoor weather conditions.
Select a location with a minimum of eight hours of sunlight. Tomatoes thrive on sun and heat. Temperatures above 90 degrees before 10 a.m. or below 60 degrees at night may affect blossom development and fruit set, causing poor tomato production. Pay attention to nighttime temperatures in May and early June, and protect your plants by covering them until the danger of cool nights has passed. A week of 55 degree temperatures, day or night, can significantly stunt growth.
Amend soil with organic matter, and loosen an area larger than you need. Warm the soil with a piece of black plastic for the week prior to planting. Cool soil can slow growth.
Space tomato plants at least two feet apart. Many diseases affecting tomatoes spread because of lack of air circulation or crowding.
Before planting, remove any blossoms that have developed in the greenhouse to encourage better root system development. This may seem counter-intuitive, but it eliminates any competition for crucial energy and nutrients during root development.
If your tomato plant is root-bound, gently tear the root ball apart from the bottom to encourage the root system to generate new roots that will spread away from the plant.
Remove several inches of lower leaves to prevent soil-borne disease transmission. Add a narrow band of aluminum foil to protect from tomato cutworm.
Mulch your tomato plants for more consistent moisture and to reduce weeds. Organic mulch like grass clippings should be at least two inches deep. Several layers of newspaper or UV-resistant black plastic at least six millimeters thick can also be used as mulch. Whichever you select, be sure none of it touches the plant.
Provide consistent, even moisture to reduce blossom end rot.
Drip or hand water — overhead watering can spread disease. The best time to water is in the morning.
Apply a starter fertilizer when you first plant, and then fertilize with a general purpose fertilizer every two weeks until blossoms form. Cut back to monthly fertilizing for the remainder of the summer to improve yield and reduce nitrogen stress, common in our clay soils. Symptoms of nitrogen stress include yellowing of lower leaves and higher susceptibility to Early Blight.
In August, as tomatoes begin to ripen, prune leaves (particularly the leaves at the ends of the main stems) and small fruit that will not have time to mature. The remaining fruit will be larger and ripen earlier. Speed the ripening by gradually reducing water slightly. The result will be fewer green tomatoes to ripen inside.
The author has received training through Colorado State University Extension’s Master Gardener program and is a Master Gardener volunteer for Larimer County.
Larimer County is a county-based outreach of Colorado State University Extension providing information you can trust to deal with current issues in agriculture, horticulture, nutrition and food safety, 4-H, small acreage, money management and parenting. For more information about CSU Extension, Larimer County, telephone (970) 498-6000 or visit www.larimer.org/ext 
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