Dig a hole to a depth of at least 8 inches. Radishes are fast growing, so plant them between rows of slower growing, cool-weather vegetables such as Brussels sprouts or cabbage.
Use a stick or your finger to make a 1/2-inch deep furrow for planting icicle radish seeds. Make each row 2 inches apart. Icicle radishes have long, narrow roots and can be grown close together.
Distribute seeds in the furrows, about 1/2 inch apart from each other. Cover with 1/2 inch of soil. Water lightly and keep the soil moist.
Thin the seedlings, when they come up in 7 to 14 days, to one every 2 inches. Allow these to grow for a total of three weeks, or until the root forms a bulb. Pull the radishes gently from the ground to harvest. Icicle radishes taste best when they are young, and the bulbs are 1 inch or less in diameter.
Stop planting subsequent rows three weeks before the weather in your area is expected to turn hot. Radishes do not grow well in heat, and the resulting vegetables are woody.