How to Grow Radishes
Radishes are quick and easy to grow, and are a tasty addition to salads and roasted vegetable plates. Some radish varieties mature in one season, while others are over-wintered and produce seed in the second season.
Time of Planting
Plant radishes outdoors as soon as soil can be worked, in early to mid-spring and early fall.You can plant every 3-4 weeks for a continual harvest throughout the season.
Sow seeds ½ inch deep in rows 2-3 inches apart.
Time to Germination
When growing annual radishes for seed, increase spacing to 4-6 inches between plants in rows 24 inches apart. When growing biennial radishes for seed, increase spacing to 12-18 inches between plants in rows 24-48 inches apart.
Common Pests and Diseases
Radishes can be affected by flea beetle, cabbage fly, and slugs.
When and How to Harvest
Fast-maturing varieties can be harvested in as little as a month after planting. Harvest when leaves are 6 inches tall. Gently pull on the base of the stem to dislodge radishes from the soil.
Radishes are often included in salad plates or roasted vegetable dishes.
Radishes can be stored in the refrigerator for about a week.
How to Save Radish Seeds
Growing radishes for seed poses some challenges for seed savers. Radishes readily cross-pollinate, so you have to be sure to isolate your radish crop from other radish varieties, including wild radish.
Annual or biennial, depending on the variety
Recommended Isolation Distance
Separate varieties by 800 feet to ½ mile.
Recommended Population Sizes
To ensure viable seeds, save seeds from at least 5 plants. When maintaining a variety over many generations, save seeds from 20-50 plants. If you’re saving seeds for genetic preservation of a rare variety, save seeds from 80 plants or more.
Assessing Seed Maturity
Radish fruits do not split open at maturity and can be left to dry in the field without fear of shattering. Fruits should be harvested when they turn brown and become brittle. In most areas this occurs between early and late summer.
Fruiting branches can be cut as they mature or all at once, when approximately two-thirds of the planting is seed mature. Although losing seeds to shattering is not a concern, seed quality can decrease if pods are left in the field for too long after maturity. After they are cut, the mature seed stalks should continue to dry on row cover or landscape fabric in a sheltered location. Threshing is easiest when pods are completely dry, usually after one to five days of drying.
Cleaning and Processing
Radish seeds do not shatter, so their seeds must be extracted by a method more forceful than threshing by hand. On a small scale, plants can be threshed by placing the harvested material on a trap or in a large container and treading upon it until the siliques break apart. Radish pods may not release their seeds easily even when broken open, and it may be necessary to crush fruits completely during the threshing process. On a larger scale, plants placed between two tarps can be driven over with a car or truck. Radish seeds are generally much heavier than the chaff and are easy to clean by screening and winnowing.
Storage and Viability
When stored under cool, dry conditions, radish seeds can be expected to remain viable for six years.