With so many tomato varieties and uses in the kitchen, its no wonder tomatoes are one of our most popular vegetables! We receive a lot of customer requests for additional tips and tricks on sowing and growing the best tomatoes.
When to start tomatoes
Start tomatoes indoors 4 to 6 weeks before average last spring frost. Ideal soil temperature for germination is 70-90°F. Transplant seedlings when air temperatures are at least 45°F, to avoid stunting growth. In mild climates/hot summer areas, like California and the South, tomatoes are transplanted in December–April or July–Feb. Contact your county extension office or a local independent garden center for the best time for your area.
Use shallow, sterile containers with drainage (4- or 6-pack at a garden center). Transplant into larger, 3”–4” containers once the true, scalloped leaves have emerged. Biodegradable paperboard pots are the ideal size, easy to label, and easy to share with friends. If plants accidentally become thick and encircling (“root-bound”) before potting up or transplanting, be sure to massage some of the encircling roots apart to discourage the strangling pattern.
Seed Starting Mix
Use a lightweight seed starting mix/media, and sow seeds at a shallow, 1/8”–1/4" depth. Seed-starting mix is sterile (unlike garden soil) and lighter than potting mix, allowing for the ideal air-to-moisture ratio.
Transplanting and Supporting
The method for planting tomato seedlings is quite different than any other plant. When covered with soil, the stem will develop additional roots. More roots increase the uptake of nutrients and water resulting in a healthier, more resilient plant with improved drought tolerance. When transplanting seedlings outside, either 1) plant them deeply, burying the stem leaving 1–2 sets of leaves above ground; or 2) set each plant almost horizontally in the ground leaving 1–2 sets of leaves above ground. The buried part of the stem will sprout roots and develop a strong, extensive root system. The top of the seedling above ground will naturally reach toward the sun and right itself. Place any stakes, cages, or other type of supports in the ground just after transplanting to avoid root damage. While determinate tomatoes are usually more squat you may still find a cage helpful in keeping them upright and the branches supported when they are loaded with fruit. Indeterminate tomatoes can easily reach 6’. Here is a tomato support system we tried and loved last year.
Tomatoes are medium feeders and may benefit from fertilizer during the growing season. Start out using a balanced (all 3 numbers are the same) or a mild grow formula (first number slightly higher) until plants look large enough to bare fruit. Then switch to a fertilizer higher in phosphorus to encourage flower and fruit set. Using this method plants will get the nutrients they need to grow large, giving them more potential to provide more fruit. As always, a soil test of your growing area is ideal so you know what nutrients are actually needed.
Do not mulch too early when weather is still cool; the roots of young plants need to be in soil that is warmed by the sun. When the weather warms up (over 55°F at night) and plants are established, mulch to a depth of 2” or 3” with a material such as straw, leaves, or compost. Mulch helps to conserve moisture and reduce weed growth.
Temperatures above 55°F at night are required for fruit set. Night temperatures above 75°F in the summer inhibit fruit set and can cause blossom drop (no fruit production). Wait until night temperatures are at least 45°F before transplanting. If your spring warm-up is lagging, use plastic mulch or season extension products like hot caps or walls-of-water to warm the soil. If your tomatoes take on a purple tinge soon after transplant it is a sign the cool temperatures are preventing phosphorous absorption. They will grow out of this deficiency as temperatures warm. Fertilizing with kelp or seaweed can help plants with stress from heat, drought, or transplanting.
Tomatoes need about 1”–2” of water per week, depending on the type of soil they are growing in. 1 or 2 deep soakings per week in mild weather, and 2 or 3 per week in hot weather should be sufficient. If tomatoes are cracking, back off on the water. Too much water can burst tomatoes and water down the flavor.
Common Pests and Disease
Diseases are usually caused by fungus or bacteria. Once you have a disease you can generally only manage the spread of the disease. This is why early identification and treatment is key. Most fungal or bacterial diseases can be organically treated using copper or sulfur. Your local extension office can help identify a disease with an infected sample. Proper crop rotation (at least 3 years before replanting crops from the same family), clean-up of infected material, proper air circulation, and following other good cultural practices are key to preventing and eliminating disease.
BLOSSOM END ROT is a common problem with tomatoes. The good news is that it is caused by a fixable deficiency and not a disease. The main cause is drought stress followed by excessive moisture; this fluctuation reduces the plant’s uptake of calcium. The most obvious symptom is a dark area at the blossom end (bottom) of the tomato, resulting from a lack of calcium in the fruit. Avoid blossom end rot by watering deeply on a regular basis, and mulching after the weather warms up and plants are well established.
TOMATO HORNWORM hummingbird-sized hawk/sphinx moth. They bore into fruit and strip away foliage leaving just the middle vein. Tomato hornworm can be organically controlled using Bacillus thuringiensis (Bt) or spinosad and/or hand picking. Bt and spinosad kill all caterpillars so avoid spraying unaffected plants or butterfly host plants.
FLEA BEETLES These tiny, hopping pests can skeletonize leaves rapidly, especially in spring when they are most active. They eat a number of crops, but prefer eggplant, tomatoes and brassicas (alyssum, mustard, broccoli, cauliflower, kale, cabbage, radishes, etc.). Organic controls include: protecting young plants with row covers immediately at transplanting or sowing, making a spray with garlic or hot peppers and applying frequently, planting trap crops such as nasturtiums or mustard, and doing fall cleanup/tilling to help reduce their numbers.
THRIPS cause tiny beige stippling on leaves and spots on fruit where they have fed. Thrips also spread disease. Spinosad is an organic control for thrips. Apply organic pesticides in the evening, night, or early morning and avoid spraying flowers. Using these practices help keep your garden safe for bees.
CUTWORM the larvae of the Black Cutworm Moth, feed on stems of vegetable and flower seedlings at night, severing the plants at ground level. During the day, they rest just below the soil surface, curled beside plant stems. As there is usually one generation per year, peak damage tends to occur in the spring; setting out transplants later in the season could avoid damage. Protect transplants with collars made of paper, foil, cardboard, plastic, or tin cans with both ends removed; push collar an inch into soil. A week before planting, scatter moist bran mixed with Bacillus thuringiensis var. kurstaki (Btk) and molasses over surface of beds, or apply neem (an extract of the tropical tree Azadirachta indica) or parasitic nematodes to soil. Weed control, fall clean-up, and fall and spring soil cultivation are all-important means of avoiding cutworm problems.
APHIDS are among the most common and troublesome garden pests. They feed by sucking plant sap, which causes distorted leaves, buds, and flowers, sometimes spreading plant viruses in the process. Aphids excrete a sticky honeydew which attracts ants, and is a host for black, sooty mold. Knock aphids off plants with a strong stream of water—repeat frequently as needed. There are many native predators and parasites which can control aphids; attract them by planting pollen and nectar plants. For heavy outbreaks, spray insecticidal soap, neem, or homemade oil sprays. Oil sprays work by smothering the insects and mites they come in contact with; thus, thorough coverage is important.
Each variety is different when it comes to color. Check your seed packet to see when the tomato is ripe. Tomatoes may also be picked at the “first blush” stage, when colors just begin to change, and ripened at room temperature without decreasing flavor or nutrition. Picking often and early increases yield, and decreases the risk of cracking and pest damage. Another tip to prevent cracking is to pick near-ripe and ripe tomatoes ahead of rain, as excess moisture causes cracking.
At the end of the season, about 1 month before the average first fall frost, clip all blossoms and any undersized fruit off the plant. This will steer all the plant’s remaining energy into ripening what’s left. If you have a lot of unripe tomatoes near the end of the season and a frost is approaching, pick, sanitize, store them indoors in a single layer away from direct sunlight to ripen.
Tomato Types Tomatoes are grouped into two main types according to growth habit and production. DETERMINATE types (e.g., Ace 55, Glacier, Italian Roma) grow in a compact, bush form, requiring little or no staking. Fruit is produced on the ends of the branches; most of the crop ripens at the same time. One or more successive plantings will ensure an extended harvest period. Determinate types are often the choice of those who want a large supply of ripe fruit at once for canning. INDETERMINATE(e.g., Better Bush, Sun Gold, Black Krim) varieties continue to grow and produce fruit all season until first frost. Tomatoes in all stages of development may be on the plants at one time. The plants set fruit clusters along a vining stem, which grows vigorously and long. Under optimum conditions, some can grow over 15’, but in most home gardens they generally reach about 6’. Some indeterminates have a bush form with stockier vines, which set fruit clusters closer together. In between these two types are the SEMI-DETERMINATE (e.g., Lizzano). The plants will grow larger than determinate varieties, but not as large as indeterminate. They produce a main crop that ripens at once, but also continue to produce up until frost.