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Tomato Sow and Grow Guide

Tomato Sow and Grow Guide

By Botanical Interests
Photographs courtesy of Botanical Interests

With so many tomato varieties and uses in the kitchen, it's no wonder tomatoes are one of our most popular vegetables! We receive a lot of customer requests for additional tips and tricks on choosing, sowing, and growing the best tomatoes.

Choosing Tomato Varieties

Tomatoes are grouped into types according to growth habit and production. Determinate types 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 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. 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. 

Tomatoes are also grouped by use, shape, and size. Slicing tomatoes are large and juicy, while paste (sauce/roma/plum) tomatoes are drier (concentrated flavor), with fewer seeds, making them ideal for sauce but also excellent for slicing. Cherry tomatoes are bite-sized and come in several shapes like oblong, pear-shaped or round.

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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 temperature is at least 45°F, to avoid stunting growth. In mild climates/hot summer areas, like California and the South, transplant in December to April or July to February. Contact your county agricultural extension office or a local independent garden center for the best transplant time for your area. 


Use shallow, sterile containers with drainage (biodegradable pots or 4- or 6-packs at a garden center). Biodegradable, paperboard pots are the ideal size, easy to label, and easy to share with friends. If plant roots accidentally become dense and encircling ("root-bound") before potting up or transplanting, be sure to gently untangle some of the roots to discourage them from continuing the strangling pattern. Transplant into larger, 3"-4" containers once the true, scalloped leaves have emerged.

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. 

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Transplanting and Supporting

After plants are hardened off, it is time to transplant. Transplanting on a cloudy day or in the evening is best. 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 one to two sets of leaves above ground; or 2) set each plant almost horizontally in the ground leaving one to two 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 stakes, cages, or any other type of supports in the ground at transplant time to avoid root damage. While determinate tomatoes are usually stockier, you may still find a cage helpful in keeping them upright and supported when they are loaded with fruit. Indeterminate tomatoes can easily reach 6'.


Tomatoes need about 1"–2" of water per week, depending on the type of soil they are growing in. One or two deep soakings per week in mild weather, and two or three per week in hot weather should be sufficient. If tomatoes are cracking, reduce the water. Too much water can cause the fruit to burst and water down the flavor. 

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Tomatoes are medium feeders and may benefit from fertilizer during the growing season. Start out using a balanced (all three numbers are the same) or a mild grow formula (first number slightly higher) until plants are large enough to bear fruit. Then switch to a fertilizer higher in phosphorus to encourage flower and fruit set. This method ensures plants will get the nutrients they need to grow large and prolific. As always, a soil test of your growing area is ideal so you know what nutrients are actually needed. 

Growing Temperature

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). If you live in a high-heat area, choose heat-tolerant varieties. When transplanting, wait until night temperatures are at least 45°F. 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 tomato leaves take on a purple tinge soon after transplant it is a sign that 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. 

Special Care

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. 

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Each variety is different when it comes to color. Check your seed packet to know what color the tomato will be when 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 one 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, clean, and store them indoors in a single layer away from direct sunlight so they can ripen.

For a tomato comparison chart, visit Botanical Interests.

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