If you were wondering how to grow radishes from seed, you've come to the right place! These cool season crispers are more than bright red slices on a salad. Try roasting or pickling them for a new flavor, or use a more unique variety, such as daikon or Rat Tail. And because most radishes mature quickly, it's a perfect choice for kids learning to garden. However, stress from heat, improper spacing, or drought can cause them to bolt (flower), so follow the guidelines below to grow your best radishes.
Radishes are generally divided into two groups, Spring/Summer, and Winter. Spring/Summer radishes grow best in the cool weather of spring through early summer, and fall. It is usually small, can be globe shaped or elongated, and pungency ranges from mild to fiery spicy. Winter radishes are sown in mid to late summer because they require shortening day length to trigger root growth, need a much longer time to mature, and can overwinter in the ground in mild climates. Winter radishes may be long or round and are usually milder than spring/summer radishes, although some can be pungent. They store well in the refrigerator for up to a month, with tops removed.
When to sow outside:
Spring/Summer Radish RECOMMENDED. 4 to 6 weeks before average last frost, and when soil temperature is above 40°F, ideally 65°– 85°F. Successive Sowings: Every 1 to 2 weeks until late spring. Sow again in late summer until 2 weeks before average first fall frost. In mild climates successive sowings can continue until temperatures are below 40°F.
Winter Radish RECOMMENDED. 8 to 10 weeks before average first fall frost. Optimal soil temperature is 65°– 85°F. Successive Sowings: Every 10 days for about 3 weeks. In mild climates, successive sowings can continue until temperatures are below 40°F (60°F for Round Spanish) for germination.
When to start inside: Not recommended. Root vegetables are sensitive to transplanting.
How to sow
Space a group of two seeds 1"-5" apart depending on the variety (see packet).
Proper thinning is crucial for good radish development; thin soon after seedlings emerge.
Keep radishes weeded to prevent stress from crowding, light, or drought, which may cause them to bolt (flower).
Optimal Growing Conditions
Soil should be loose and light with a fair amount of organic matter, free of rocks and clods for up to a foot.
Radishes thrive in the cool temperatures of spring and late summer/fall.
Keep evenly moist. Too little water produces a small, spicy, bitter root. Too much water promotes excess foliage and small root. Uneven watering may cause radishes to crack or split.
Plant in full sun to part shade.
Is not necessary with fertile soil. Excess nitrogen can result in large greens and skimpy roots.
Radish plants thrive in cool temperatures, but the seeds require fairly warm temperatures to germinate. If you wish to help warm the soil, you can place black plastic sheeting on the growing area 3 days before sowing. Sow the radish seeds under the sheeting, and after 4 days, check daily for seedlings. Remove plastic immediately after seedlings have emerged.
To produce the straightest, whitest daikon, sow in trenches. As the radish grows, mound soil on top of its shoulder, keeping the shoulder covered to prevent greening.
Harvest before radishes reach the optimal size listed on the packet and before a hard frost. If allowed to grow larger than their optimal size, radishes can get spicy and pithy (spongy or hollowed core).
Store washed radish roots separate from their edible tops in a plastic bag or other container in the crisper of the refrigerator.
Common Pests and Diseases
Flea beetles can devour the green tops, which impacts formation of the radish root. If you live in an area where flea beetles are problematic, cover seeded area with row covers until harvest.