by Colleen Kennedy, Extension Master Gardener
The tomato (Solanum lycopersicum) is one of several New World crops introduced to the Old World by the Spanish conquistadors in the 1500s. From Portugal and Spain tomatoes were introduced to the Far East and Africa. Tomatoes were originally desert plants that were domesticated by the Aztecs and Mayans in Central America. The Nahuatl word “tomatl” evolved into the Spanish word “tomate,” from which the English word “tomato” is derived. Tomatoes were not in common culinary use in the United States until the mid-to-late 1800s. Before that, they were ornamental and thought to be poisonous.
Despite its botanical identity as a fruit (a seed-bearing structure arising from and replacing the ﬂower of a plant), the Supreme Court has ruled that the tomato is in fact a vegetable. In 1893 the Court arbitrated a trade dispute, Nix v. Hedden, and decreed tomatoes vegetables because they were eaten as part of a main course and not dessert.
Second only to the potato, another New World crop, the tomato is the most-consumed vegetable in the world. China, India, and the US, in that order, are the major producers of an annual world crop of 161.7 million metric tons. About 20–25 pounds are consumed per person annually. Tomatoes are rich in vitamins A and C, low in calories, and rich in lycopene, which gives the fruit its red color and is a strong anti-oxidant.
Tomato cultivation requires answers to several questions. What do you like to eat? Cherry tomatoes are good for snacks and salads. Beefsteaks or slicers make tasty sandwiches, and paste tomatoes shine in sauces. How much growing space do you have and where will you locate your tomato crop? Will you be using containers, raised beds, or a garden plot? Determinate, or bush, tomatoes are best for containers. They rarely surpass four feet in height, produce their fruit early and at the same time, and then decline. Indeterminate, or vining, tomatoes can grow as long as ten feet, require staking and more space, and will continue to grow and produce until frost, disease, or poor conditions kill them.
Another decision is whether to start your tomatoes from seed or to purchase plants. Starting tomatoes from seed gives you the option to grow exactly the kind of tomato you prefer, including heirloom or rare varieties. Heirloom tomatoes are open-pollinated and originated before 1950. Purchased plants are generally hybrids and standard varieties. Hybrids are crossbred, which will show the dominant characteristics of each parent. The ﬁrst famous hybrid was Big Boy, created in 1949. In either case, choosing seeds or plants resistant to common diseases (septoria, early blight, late blight, fusarium wilt, and verticillium wilt) is an advantage.
Seedlings may be started any time between 1 March and 1 May. You will need seed-starting soilless growing medium, containers, a source of heat, moisture, and after germination, light. A fan, to keep air moving and strengthen the stems, is also helpful. There are many commercially available seed-starting mixes. Most contain peat moss, perlite, and limestone. Some contain coir or mild fertilizer. The mix should moisten easily and stay ﬂuﬀy. Using garden soil is a bad idea. It is too heavy and may contain insects, weeds or disease.
Any container which is clean and can drain from the bottom is suitable. Fill with the seed-starting mix. Place a few tomato seeds on top and then cover with a thin layer of the mix. The container should be watered initially from the top, covered with plastic, and placed on a heating pad, radiator, or warm appliance to encourage germination. Watering from the bottom is ideal after the first watering. Soil temperature between 70° and 80° Fahrenheit is ideal for germination. Once germination occurs, seedlings must be placed in a south-facing window or, preferably, under grow lights, and the plastic cover should be removed. Grow lights should be positioned about one inch above the plants and adjusted as they grow. Seeds germinate in 5–12 days. Seedlings usually require transplanting to larger containers 3–4 weeks following germination. At this stage they have 5–7 true leaves. They may be fertilized with dilute ﬁsh emulsion. Water frequently, but allow to dry out between waterings. They will be ready for planting out when they are 3–6 inches tall, about 5–8 weeks after planting.
Garden soil should be tested several weeks before transplanting. Tomatoes prefer a pH of 6.2–6.8, slightly acidic. Tomatoes are heavy feeders but should not be over-fertilized. For good fruit quality and yield, adequate potassium is required, which can be supplied by organic matter, wood ash, or fertilizer. Too much nitrogen will result in abundant foliage but much less fruit. Absent a soil test a good rule of thumb is to work 2.5 pounds of 5-10-10 (nitrogen-potassium-phosphorus) into 100 square feet of soil.
Before planting outside, which can occur 1 May to 15 June, the seedlings or purchased plants must go through the process of “hardening oﬀ.” This means toughening them up to withstand outside conditions. One or two weeks before planting out, cut back on watering and fertilizing to slow plant growth. On warm days (at least 45°F), put plants outside in a shady, protected location. A little bit of wind will not harm the seedlings. Bring them back indoors at night. Each day increase the amount of sunlight they receive. On the ﬁnal day they should be left in a sunny spot and remain outside overnight. They should be ﬁnally situated in a site that receives at least 6–8 hours of sunlight per day.
When seedlings or plants have been hardened oﬀ they are ready to be planted outside. This is best performed in the afternoon with expected evening temperatures of at least 50°F and no high winds or heavy rains. Soil temperature should also be at least 50°F. A hole, or preferably, a shallow trench should be dug, deep enough that the plant can be “trenched,” or buried up to the top 2–3 sets of leaves while positioned almost horizontally. Once planted, indeterminate plants will need to be supported with stakes, tomato cages, or trellises. Tomatoes may be interplanted with other crops like lettuce, which is more shallow-rooted, and carrots, which are more deep-rooted.
Best management practices in caring for tomatoes include: choosing disease-resistant cultivars, testing the soil for pH and nutrients, soil aeration, and adding organic matter to the soil. It is best to water in the morning with soaker hoses or drip irrigation, delivering at least one inch of water per week. Watering from the top can drench leaves and encourage disease. It is important to avoid injury to the plants or their roots, which can be entry points for disease. Plants should be mulched, both to retain water and to prevent soil and soil-borne diseases from splashing on plants. Mulches could include salt hay, straw, compost, or even plastic. Plants should be spaced so there is plenty of room for air circulation, usually 18–30” apart with rows 30–48” apart. For container growing, the minimum size container should be 14”. Larger containers are better. Containers should be ﬁlled with a soilless mix, usually containing peat moss, perlite and pine bark. The mix might also contain coir or peanut shell. More than in-ground plantings, containers require vigilant watering and fertilizing, since water and nutrients leach out more quickly.
For many gardeners, raised beds are an advantage. They warm faster in the spring, provide better drainage, and no tilling is involved, since compost and amendments are placed on top. It is easier to keep out critters, and plants may be spaced closer since there is looser soil with good root spread. Weeds are not as proliﬁc, and are easily removed.
Tomatoes can usually be harvested 70–90 days after planting. Hopefully, after all your gardening eﬀort, a delicious tomato will be your reward.
- Early Blight on Tomatoes: Cornell University.
- Early Blight – Vegetables. Home & Garden Information Center, University of Maryland Extension
- Fusarium Wilt of Tomato – Vegetables, Home & Garden Information Center, University of Maryland Extension.
- Late Blight of Tomatoes, Home & Garden Information Center, University of Maryland Extension.
- Gao, Gary et al. Growing tomatoes in home garden, Ohioline. Ohio State University Extension.
- Heiser, Charles. The Fascinating World of the Nightshades: Tobacco, Mandrake, Potato, Tomato, Pepper, Eggplant, Etc. 1987 Dover
- Plant Disease Diagnostic Form. Publication 450-097. Virginia Cooperative Extension.
- Reif, Diane, et al. Tomatoes, VCE publication 426-418
- Septoria leaf spot: Missouri Botanical Garden, Cornell Department of Plant Pathology
- Vegetable MD Online, Department of Plant Pathology, Cornell Univ. Ithaca NY.
- Tomato Love presentation, April 2020 by Extension Master Gardeners