Sacrificing the weak so that the strong may survive
The amount of space needed between plants depends on how large each plant is expected to grow. Most smaller-sized mature plants should have 3 or 4 inches between them, whereas larger plants may need 10 to 12. When plants are small you can thin them by pulling the entire seedling out of the soil. If you are thinning older plants, or plants mixed with other plants with established root systems, thin by cutting the plant off at the base.
Be careful not to thin out too many seedlings too soon, in case any plants should be "thinned" later by a ruthless snail or clumsy pet. If you wait too long to thin, however, you could cause root damage to surrounding plants. Thinning your seedlings gradually as they become crowded will ease the pain of the sacrifice, while still appeasing the green goddess of growth.