It may look like a plain white root vegetable on the outside but inside, the watermelon radish is bursting with colour. Watermelon radish is an heirloom variety of Asian daikon radish. The crisp texture and colour complement the slightly sweet taste. Watermelon radishes are round and grow from 1 to 5 inches in diameter. Plant watermelon radish seeds in the spring and summer. This fast-growing vegetable crop adds colour to spring and summer salads as well as fall vegetable dishes.
Work the soil in the garden bed early in the spring. Turn over the plot and remove weeds, sticks and rocks. Amend poor soil with 2 to 4 inches of compost or manure dug into the top 8 inches of the garden bed.
Sow watermelon radish seeds directly into the garden bed early in spring. Radish seeds are not frost sensitive and can withstand some light frosts after planting. Space the seeds 3 inches apart and cover with a quarter inch of garden soil.
Look for signs of the emerging seedlings in seven to 14 days. Once the watermelon seedlings grow 2 inches tall, thin them to a spacing of six inches.
Water once or twice a week to keep the soil consistently damp around the developing seedlings. Consistent moisture is important when radish seeds are in the germination process.
Plant a second set of watermelon radish seeds in mid- to late spring and a third planting in late summer for continued harvest into the fall.
Harvest watermelon radishes 55 to 60 days after planting. Dig under the radish with a garden fork and lift it out of the soil. Shake off the dirt and wash the root.
Pull a few watermelon radishes early, after 25 to 30 days. The immature roots are crisp and tender, perfect for salads and raw vegetable dishes.