Black radishes are low-maintenance, fast-growing vegetables that require only a small patch of ground and a generous dose of sunshine. Although black radishes are rather odd in appearance, they are snow white under the thin outer layer. Plant them as soon as the ground thaws in the spring, and you'll have radishes in less than a month. Plant a small crop every two weeks until midsummer for a continuous supply.
Prepare a sunny spot to plant black radishes. Use a hoe to remove any weeds, and loosen the soil to a depth of 8 to 10 inches. Rake some well-rotted manure or compost into the top of the soil.
Create a shallow trench with a stick or the corner of the hoe. Plant the radish seeds an inch apart, and cover them with a half inch of soil. If you are planting more than one row, space the rows 12 inches apart.
Water the radish seeds with a watering can, or use a spray attachment on a hose. Be careful not to wash the seeds away.
Thin the radishes to 3 inches apart when the seedlings appear. Use the tiny radish seedlings for salads, and let the larger radishes grow for a few more days.
Harvest the black radishes as soon as they're ready. Leaving them in the ground too long will cause the texture to be woody, and the flavor will be hot. If you aren't ready to eat them, they'll keep in the refrigerator for a few days.