Early radishes germinate in three to seven days, marking your garden rows. This allows you to cultivate early with confidence when you interplant radishes with other slower-growing vegetables. Radishes act as natural cultivators because their thick, round roots leave holes in the soil when harvested. Long, white icicle radishes are ideal for this, especially if you have heavy clay soil or if you want to grow long carrots or parsnips. The remaining plants will expand and thrive in the newly created spaces.
Radishes are also trap crops for some garden insects.
If there are hungry root maggots, leafhoppers or flea beetles around, they'll usually go for the first plants they find, and radishes are one of the earliest crops. You may even find them doing double duty with both their tops and bottoms acting as hosts for insects. Just pull and destroy the half-eaten radishes and you'll destroy the insects, too. Radishes are great planted by themselves, but interplanting them with other crops is more space efficient, and will still provide you with plenty for fresh eating. Try growing them with lettuce or late-maturing crops such as cucumbers or squash.