Radishes are annual or biennial, cold-season cruciferous vegetables in the Brassica family (Brassicaceae), related to turnips, arugula, broccoli, and cabbage. Radishes are grown primarily for their mild-to-spicy taproots, but also for their edible leaves. Radish seed pods are also edible and can be surprisingly palatable, especially when very young, for eating fresh, in salads, steaming, sauteing, stir-frying, or pickling, with some radish varieties developed specifically for their edible pods. Radishes are grown commercially for oil production from the seeds.
The wild ancestor of the cultivated radish was probably native to Southeast Asia or China. The early history of its cultivation is unknown. By 300 B.C.E., radishes were being grown in Greece and around the Mediterranean.
Gardeners growing radishes have a huge array of varieties from which to choose. Cherry Belle is a popular moderately spicy variety that is tolerant of difficult soils and is also somewhat heat tolerant, while Champion, Crimson Giant, and Early Scarlet Globe are milder. Easter Egg radish, commonly sold in seed packets, is not a variety, but a collection of varieties in different colors, which can be an easy way to produce a successive or slightly staggered harvest from one seed packet or if you have time to seed only once.
French Breakfast and Icicle are more heat tolerant than other radish varieties, but they will still become overly spicy or tough if you wait too long to harvest. If you want to experiment with radishes in weather too warm for radishes to produce good-quality roots, you may wish to grow the heirloom Rat's Tail for its edible seedpods.
Daikon radish varieties such as Miyashige or Tokinashi (All Season) are biennial and typically mild-flavored with long carrot-like roots and fast-growing leaves that are often used in stir-frying. They need a longer growing season, usually 50 to 70 days, as opposed to 20 to 35 days for most smaller globe-type radish varieties.
Radishes should be seeded directly, either broadcasted or planted in rows, and are easy to grow from seed. GardenZeus recommends against transplanting radishes; even biointensive gardeners generally seed radishes directly. Some nurseries may happily sell you cell packs or transplants of lush-looking radish seedlings, but when transplanted these may tend to result in a disappointing harvest of lesser-quality roots.
Double-dig or loosen new, compacted, or clay soils and remove stones and obstructions to at least 6 to 12 inches shortly before planting. Radishes prefer reasonably fertile, uniform, well-drained soil with sufficient potassium and moderate-to-high organic matter to a depth of at least 12 inches (deeper for larger and carrot-shaped varieties), but will tolerate difficult soils. Preferred soil pH for radishes is 6.5 to 7.0. They may tolerate significantly more acidity and slight alkalinity, but may not produce quality roots quickly under these soil conditions. Daikon and other carrot-shaped and deeper-rooting radishes grow best in deep, loose soils, but are also often planted to break-up tough soils prior to planting other crops, and will produce edible roots that quickly become tough in compacted soils.
Radishes are unfussy and will generally thrive in any cool, sunny area with reasonably loose and fertile soil. They will grow in part shade, but produce smaller roots and a smaller harvest over a longer period of time when not in full sun, and if they do not receive enough sun, may fail to form bulbed roots.
Radishes are one of the easiest garden vegetables, and they come in a surprising and fun array of colors, sizes, shapes, and degree of mildness or spiciness. Generally they form edible if perhaps misshapen roots even in relatively compacted, poor soils. They are easy to germinate, and reach harvest size quickly, often within 20 to 35 days.
Because radishes grow so quickly, this may lead to what GardenZeus expert Darren Butler calls "radish syndrome," of which the primary and actually only symptom is having too many radishes at one time to eat or give away without awkwardness or spending a lot of time meeting new people. The phrase "How many radishes can a person actually eat?" becomes a common one when dozens or hundreds or radishes reach harvesting size at the same time. GardenZeus recommends spot planting of radishes here and there to mark other plantings (especially with other slower-germinating root crops), in bare areas after harvest or plant loss, and just about anywhere you can find a few inches of sun during cool weather, rather than dedicating larger bed or garden sections to radishes.
Radishes are highly recommended for new gardeners or those who have struggled with other crops, and are a fun and easy crop to grow with children.
Radishes need uniformly moist but not wet soil to produce good-quality edible roots. Radishes generally require regular watering, especially in sandy or light soils. In clay and heavy soils, water slowly over time to encourage infiltration to the full depth of the radishes’ roots. Do not allow soil to dry between waterings. Overwatering or wet soil may result in poor root formation, shallow rooting, and/or rotting or diseased roots. Underwatering or soil dryness between waterings, especially during the first several weeks after germination, may result in poor root formation, split roots, bolting, and tough or pithy roots.
Radishes should be seeded directly, either broadcasted or planted one seed at a time, and are easy to grow from seed. They germinate best at temperatures between about 60° and 85° F, and produce the best-quality roots at temperatures between about 50° and 65° F.
GardenZeus recommends against transplanting radishes; even dedicated biointensive gardeners generally seed radishes directly. Avoid planting radishes in soils or beds where other cruciferous vegetables, such as turnips, cabbage, kale, broccoli, cauliflower, and brussels sprouts, have grown within the past 2 years (the longer the better).
Radish seeds are large enough to plant one at a time, which has worked well for GardenZeus expert Darren Butler over many years. Who can eat more than 50 or a hundred radishes within a few weeks anyway? Even when planting for a large family, it’s best to stagger seeding every week or 2, and GardenZeus recommends not planting more than 50 or so radish seeds within any 2-week period unless you’re absolutely certain that you want to cope with that many radishes all at once when they mature.
Spacing and planting depth varies by type. Small globe radishes can be planted an inch apart and thinned to a final spacing of 2 to 3 inches. Daikons and other radishes with larger carrot-shaped roots need about 6 inches final spacing, but this may vary by variety from 4 to 12 inches; refer to your seed packet for recommended spacing. Fodder radishes need final spacing of 10 to 18 inches, and Sakurajima Daikons growing to maturity will need a final spacing of at least 2 to 3 feet.
3 to 8 days to seed germination, often longer in cool or cold temperatures below 60° F.
20 to 35 days from germination to root harvest for small globe types.
45 to 85 days or longer for Daikon, long-rooted, and large-rooted types.
Because we most-commonly eat the roots of radishes, we generally prefer slow flowering (slow bolting), and are generally not concerned with pollination unless growing for edible seedpods or saving seeds.
Radish seeds are traditionally planted at the same time with carrot seeds or other root crops to mark rows as the radishes sprout and are harvested earlier than the other slower-germinating root crops. GardenZeus recommends spacing radish plantings at least a few inches from carrots to avoid disturbing young carrot roots when harvesting the earlier radishes. Other traditional companions for radishes include leaf lettuce, chervil, nasturtium, cucumbers, peas, and beans.
Avoid planting radishes in soils or beds where other cruciferous vegetables, such as turnips, cabbage, kale, broccoli, cauliflower, and brussels sprouts, have been growing within the past 2 years (the longer the better).
Radishes are unfussy and will generally do well in most loose soils with reasonable organic matter and sufficient potassium. Use caution with application of nitrogen. GardenZeus recommends adding nitrogen in the form of diluted urea or a cup of chicken manure diluted in 4 gallons of water (half cup if fresh manure) and mixed thoroughly, applied as a soil drench once when radish sprouts are 1 to 2 inches tall. For longer-season varieites such as daikons and fodder radishes, repeat application of nitrogen about once per month throughout the growing season. Excessive nitrogen in soils may result in poor root-bulb formation.
Use a quarter-inch fine mulch for small starts when they reach 2 to 3 inches in height; increase to half-an-inch or more of fine-to-medium mulch after plants are at least 4 to 5 inches tall.
GardenZeus does not recommend cutting back or pinching radish leaves except for harvesting a minimal number of leaves for use as greens in salads, soups, and other dishes.
From seed. GardenZeus recommends open-pollinated, untreated, organically grown seeds.
GardenZeus recommends a soil mix of at least 50% sand when growing radishes in containers, with some organic matter or compost but not too much. Potting soils with high proportions of organic matter tend to shrink and collapse over the course of a growing season as soil microbes and macro organisms like insects digest or decompose the organic matter, which results in falling soil levels and possibly insufficient soil depth for some varieties of radishes to form full taproots. Standard globe-type radishes are well-suited to growing in containers of 12 inches or more in depth. Daikons and other long-rooted radish varieties need deeper soil and should be grown in the ground or in containers of at least 18 to 24 inches in depth.
Radishes are a cool-weather crop that forms the best roots at temperatures between 50° and 65° F.
In warm weather inland valleys of California, radishes are generally grown in the fall through spring. In cool coastal areas, radishes are often grown year around. In cold winter areas of California, radishes are an ideal summer crop, as they quickly reach maturity during the short growing season.
Generally the longer a radish is in the ground and the larger the root in proportion to normal harvest size for the radish variety, the spicier, tougher, and/or pithier the root will be. You may want to harvest radishes when they are on the small side for their variety to enjoy the crispest, crunchiest, and mildest roots.
Common problems with radishes include roots that are misshapen, small, or tough as a result of poor soil, compacted soil, overcrowding, not enough thinning, uneven watering; or too much heat. Radish bulbs failing to form at all may be the result of overcrowding, warm or hot weather, too much soil nitrogen, or not enough sun. Overly spicy roots are generally the result of waiting too long to harvest.
Many radish roots that are oddly shaped still taste fine, especially if harvested early. Cracked or split roots can be the result of uneven watering, but many radish varieties crack naturally as roots get larger and older. Harvest early for the most attractive and mildest roots.
Radishes are affected by a number of diseases, including soil fungi such as damping off (usually in cold, wet soils), Rhizoctonia and Fusarium (usually in warm, wet soils), leaf spot, and mildews.
Most radish disease problems can be avoided by planting during cool times of year in well-drained, reasonably fertile soil with an active soil ecosystem; rotating crops or avoiding planting where other cole crops were grown within the past 2 years; avoiding excess application of nitrogen; and otherwise meeting the plants' cultural needs, especially with uniform and sufficient watering without overwatering.
Common pests of radishes in your zone include flea beetles, thrips, cabbage maggot, bagrada bugs, harlequin bugs, ground squirrels, gophers, rabbits, and deer.
To maintain uniform soil moisture for radishes it may help to keep a full watering can near your radish patches and give them small amounts of water every 1 to 3 days, especially if they are planted here and there in odd areas throughout your garden near plants that need less-frequent watering.
Radish leaves are edible but often ignored because of their slightly furry texture, and radish leaves can be downright prickly in some varieties and with older leaves. GardenZeus expert Darren Butler recommends young and non-prickly radish leaves for salads; and steaming larger and slightly prickly leaves, or using them in soups or stews. Radish leaves will not be to everyone's taste, but they are so easy and quick to grow, and to some gardeners add such an interesting flavor and texture to many dishes, that they are well worth using as an occasional or even staple kitchen green.
While most seed-saving guides insist that to save quality seeds, radish varieties must be separated by 600 feet to a half-mile or more, in practice, GardenZeus expert Darren Butler has found that reasonably to perfectly true-to-variety radish seeds are generally produced over at least a few generations as long as only one variety of radish is allowed to flower and seed in a given garden. This may be the result of few gardeners allowing their radishes to flower and set seeds near where Darren has gardened, but the abundant seed production of radishes makes it worth a try, and the careful gardener can harvest or rogue out off-variety radishes in subsequent generations without letting them flower or set seeds.
When allowed to bolt and go into full flower, the unobtrusive everyday radish we know from our gardens and supermarkets becomes something almost grand. Bolting radishes reach about 2 to 4 feet in height and width for most globe varieties in reasonably fertile soil, and set many small flowers that attract bees and beneficial insects. After flowering, many varieties of radish will set large numbers of edible seedpods that are best enjoyed when young and tender, and are ideal for salads, steaming, sauteing, stir-frying, pickling, and other dishes. Seeds allowed to mature and dry on the plants may be harvested for seed saving, or left to feed birds and other wildlife. Annual varieties of radish usually begin to bolt within a few weeks of the onset of warm-to-hot weather, with their flowers and seeds an important addition to an insectary or bird-garden.
Try using fodder radishes and daikons as a cover crop, or to break up the top layers of compacted soils in your garden. Broadcast seeds in an area with tough soil, cover with 1/4 to 1/2-inch of sand mixed with compost or fine organic matter, and keep moist for at least 7 to 10 days until a large percentage of the seeds germinate. Harvest roots, leaves, and young seedpods as desired for eating during the windows when these plant parts are palatable. The aboveground radish plant and roots can be harvested as a compost crop, or left in the ground to feed bees and beneficial insects when it blooms, and set seeds for feeding birds and seed-saving.
Radish cover crops can be used in low-till or no-till gardening, and are especially effective in creating root channels in tough soils for crops that follow. GardenZeus expert Darren Butler recommends allowing radish cover crops to go to maturity when possible, saving seeds, then cutting down the expired plants at soil level to use as woody compost material or mulch, and leaving the roots undisturbed to rot in place, feed the soil, and provide root channels for crops that follow.
Radishes store reasonably well; radishes of average size can be expected to last for up 28 days under ideal the conditions of 32° F and high humidity. Larger radishes, such as the Daikon radish, may last up to three months. Rapid cooling is essential: radishes are iced-topped by farmers to maintain proper temperature and moisture. Consider icing your radishes immediately after harvest, or at least moving them out of the sun and placing them in a cool, inside location until washing. To optimize the storage life of radishes, brush off all dirt, then wash and dry thoroughly. Unless you are using the radishes right away, remove the green tops by cutting through the green foliage and place in a plastic bag. Radishes with tops still attached can be expected to last only from 7 to 14 days, even in optimal storage conditions.
Humidity in refrigerators is too low for radish storage. To store radishes in your refrigerator, do so in a humid produce drawer with humidity turned up to full, or with an open bowl of water, and/or in a cloth or paper bag to reduce drying. Over-mature or improperly stored radishes tend to be pithy or spongy and may develop harsh flavors.
Radishes are not sensitive to the ethylene gas given off by most fruits; however, bunched radish tops may become yellow with prolonged storage and ethylene exposure.
Radishes make an ideal garnish for salads and platters. Use as a layer in sandwiches, or rub them with butter, dip them in sea salt and serve them with some artisan bread for an ideal late afternoon snack.
Radishes are often dismissed as having low nutritive value, but they do provide significant amounts of fiber, Vitamin C, Folate, and Potassium, as well as small amounts of other vitamins and minerals.