Seeding tomatoes directly into the field is not recommended due to the high cost of hybrid seed and the specific conditions required for adequate germination. Most tomatoes are transplanted to the field from greenhouse-grown plants.
Direct seeding has other disadvantages:
(1) Weed control is usually much more difficult with direct seeded than with transplanted tomatoes;
(2) Direct seeding requires especially well made seedbeds and specialized planting equipment to adequately control depth of planting and in-row spacing;
(3) because of the shallow planting depth required for tomato seed, the field must be nearly level to prevent seeds from being washed away or covered too deeply with water-transported soil; and
(4) Spring harvest dates will be at least 2 to 3 weeks later for direct seeded tomatoes.
At 59, 68 and 77 degrees F soil temperature, tomato seed require 14, 8 and 6 days, respectively, for emergence when planted ½ inch deep. Typically, 5- to 6-week old tomato seedlings are transplanted into the field. As with most similar vegetable crops, container-grown transplants are preferred over bare root plants. Container grown transplants retain transplant growing medium (soil-substitute) attached to their roots after removal from the container (flat, tray).
Many growers prefer this type transplant because,
(1) They are less subject to transplant shock,
(2) Usually require little, if any, replanting,
(3) Resume growth more quickly after transplanting, and
(4) Grow and produce more uniformly.
Tomato plants produced in a 1-inch cell size tray are commonly used for transplanting. Many growers will use a 1.5-inch cell tray for transplant production in the fall when transplant stress is greater.
Tomato transplants should be hardened off before transplanting to the field. Hardening off is a technique used to slow plant growth prior to field setting so the plant can more successfully transition to the less favourable conditions in the field. This process involves decreasing water for a short period prior to taking the plants to the field. Research shows that reducing temperatures too drastically to harden tomato transplants can induce cat facing in the fruit.
For maximum production, transplants should never have fruits, flowers or flower buds before transplanting. An ideal transplant is young (6 inches to 8 inches tall with a stem approximately ¼ inch to ⅜ inch in diameter), does not exhibit rapid vegetative growth, and is slightly hardened at transplanting time. Rapid growth following transplanting helps assure a well-established plant before fruit development. In most cases, it is more economically feasible to have transplants produced by a commercial transplant grower than to grow them on the farm. When purchasing transplants, be sure the plants have the variety name, have been inspected and approved by a plant inspector, and they are of the size and quality specified in the order.
Set transplants as soon as possible after removing from containers or after pulling. If it is necessary to hold tomato plants for several days before transplanting them, keep them cool (around 55-65 degrees F if possible) and do not allow the roots to dry out prior to transplanting. When setting plants, place them upright and place the roots 3 to 4 inches deep. Setting plants at least as deep as the cotyledons has been shown to enhance plant growth and early fruit production and maturity. Completely cover the root ball with soil to prevent wicking moisture from the soil. Tomatoes grow best if night time soil temperatures average higher than 60 degrees F.
At transplanting, apply an appropriate fertilizer starter solution (see Fertilizer Management section). After transplanting (especially within the first 2 weeks) it is very important that soil moisture be maintained so that plant roots can become well established.