Originally posted by Wicked Cat:

When asking about how to plant tomatoes, the first question is how deep. Tomatoes have the ability to grow roots along their stems, so when planting tomato plants, plant deep; right up to the first set of leaves. This takes care of those leggy tomato seedlings. If the plant is too long and wobbly, dig a small trench and lay the plant on its side, gently bending it into a right angle. Bury the stem in this position leaving those first two leaves exposed. Some gardeners believe those leggy starters will form a healthier plant than those with a more compact form. Water your seedlings in with a weak solution of high phosphorus fertilizer.

Now is the time to choose your support: stakes, cages, or unsupported. How far apart to plant tomato seedlings depends on your chosen support. If you decide to use cages or stakes, place them now so you don’t damage the growing roots later.

Plants should be about 3 feet (1 m.) apart when tomato planting with cages. Staking only requires about 2 feet (0.5 m.) between plants. Loosely tie the plants to their stakes as they grow, but set the stakes when you set the seedlings. You’ll need 3 feet (1 m.) between the plants and 5 feet (1.5 m.) between the rows if you’re planting tomato plants to grow naturally.