If you want plants that grow well in your area – or heirlooms or anything other than the generic plants sold by the big box stores and most garden centers, you’re going to have to start them yourself. Here are the basics related to tomato care.
The easiest thing for home gardeners to do is sow seeds directly into small pots of soilless mix. (Promix or similar).
Figure two seeds per pot (and thin the seedlings to the strongest one after 3 weeks).
Too tall and spindly seedlings – not enough light
Grow as many pots as you need plants. This will give the transplant enough room to grow and develop a thick top and full root system.
A plant that has been grown in its own pot will not suffer transplant shock when it is moved to the garden as much as a smaller cell-pack plant. (essentially, they have bigger roots)
Giving adequate space is particularly important if you do not have full outdoor light levels with a greenhouse or large grow light system.
Crowded seedlings tend to be long and thin.
Grow light systems will be needed if you donʼt have a greenhouse or full south-facing window (and maybe even with the window too).
Keep the lights about 4-6 inches above the seedlings as they grow (move them upwards but keep them close or your seedlings will get spindly)
If you need a LOT of seedlings, you can sow them in a flat by keeping the seeds approximately 1-inch ( 2-3 cm) apart. Then transplant them into growing cells. The problem here is that unless you have adequate light levels you will produce inferior transplants.
The soil temperature for germinating tomato seed should be around 72-73F (23C) . Use a heating cable or mat to produce this heat because room temperatures will only give sporadic germination.
When seedlings break the soil around the 10-day mark, reduce the temperature to 64F (18C) and then when they have 4 true leaves, reduce the temperature again and grow on at 59F (15C) .
Too high temperatures produce spindly plants.
Feed seedlings twice a week with a quarter-strength fish emulsion or other liquid plant food. A lack of fertilizer will create a tall spindly plant.
Lack of light, too much heat and not enough fertilizer can create the same spindly condition. You have to identify which one is the culprit.
Get them all right for short, blocky, dark green, fast-growing transplants.