by Dr. Vern Grubinger, Extension Vegetable and Berry Specialist, University of Vermont
BURLINGTON – A vegetable garden is not complete without tomatoes. Local farm stands will soon be offering a wide selection of tomato transplants for your garden. Try a few different varieties.
Most modern tomato varieties are hybrids. They’re vigorous, tolerant of some diseases and with fruit that are uniform in size and shape. Open-pollinated varieties, including heirlooms, offer a wider range of flavors and colors although they may be more vulnerable to diseases, yield less fruit than hybrids and can be prone to splitting.
Determinate tomato plants are bushy. They grow and flower until they reach three to four feet tall then stop. That condenses the harvest period and limits the need for pruning. You can use small stakes to support them.
Indeterminate varieties grow all season, producing fruit for months. They benefit from early season pruning and tall stakes. Semi-determinate varieties are in-between. They don’t sprawl, but they aren’t bushy either.
Before planting, a soil test will reveal whether you should add lime and how much fertilizer. You can have your soil tested through the University of Vermont Agricultural and Environmental Testing Lab (go.uvm.edu/soiltest).
Many garden soils already contain plenty of phosphorus from previous compost, manure or fertilizer use. It’s common to find that only nitrogen and potassium are needed. Tomatoes are heavy feeders of both those nutrients.
Good drainage is important. If your soil tends to be wet, making raised beds can help. Water-logged soil promotes diseases such as Phytophthora that cause root rot.
Crop rotation helps avoid plant diseases. Moving your tomato plot a long distance each year is ideal, but even moving over a few rows can help. If root or leaf diseases are severe, you can skip a year of tomato growing to allow diseases to die off.
Be patient. Planting early usually doesn’t have much benefit, since tomatoes grow slowly when it’s under 70 degrees Fahrenheit. If nights get into the low 50s, the crop may be injured, which shows up as light-colored blotches on the leaves.
Set tomato transplants deeply in the soil, especially if they’re leggy. Roots will form along the stem, so you can bury plants up to the lowest leaves if necessary. Plant late in the day or during cloudy weather to limit transplant shock. Water in well and use small stakes if it’s windy.
Watering whenever needed in the summer promotes good growth and helps avoid blossom end rot of fruit, a calcium deficiency. Since calcium moves with water through the plant, dry soil can lead to a calcium shortage when fruit is forming.
Wet the soil deeply when it doesn’t rain. Sandy soils need watering every few days. Those with a lot of silt and clay retain moisture longer. Put your hand in the soil to see if it’s drying out. Don’t wait until your plants wilt to irrigate.
Straw, wood chips or plastic mulch reduce evaporation from soil, so less irrigation is needed. Mulch also reduces soil blowing and splashing, which helps prevent leaf diseases such as early blight and Septoria leaf spot. These are promoted by leaf moisture.
Staking, pruning and wide spacing of plants encourage good air movement to keep leaves dry. When watering, don’t wet the foliage.
Prune indeterminate plants to avoid a tomato jungle. Aim for two main stems per plant by pinching off suckers at the base, up to the one below the first flower cluster. Remove suckers when they’re a few inches long to avoid making large wounds.
Late in the season, cutting plant tops off will allow green tomatoes to finish ripening before frost, but stop most new growth. Determinate plants usually don’t need pruning, but you can keep plants smaller by removing the lowest suckers if you wish.