Radish (Raphanus sativus) is a plant species that represents a food staple in many cultures around the world. The radish has a wide range of variations, including variants that grow in the spring, summer and winter. The root is generally eaten raw and can be used in salads or as a garnish.
I. Appearance and Characteristics
The radish (Raphanus raphanistrum subsp. sativus) is an edible root vegetable of the mustard family, Brassicaceae, that was domesticated in Asia prior to Roman times.
Radishes are annual or biennial brassicaceous crops grown for their swollen tap roots which can be globular, tapering, or cylindrical. The root skin color ranges from white through pink, red, purple, yellow, and green to black, but the flesh is usually white. The roots obtain their color from anthocyanins. Red varieties use the anthocyanin pelargonidin as a pigment, and purple cultivars obtain their color from cyanidin. Smaller types have a few leaves about 13 cm (5 in) long with round roots up to 2.5 cm (1 in) in diameter or more slender, long roots up to 7 cm (3 in) long. Both of these are normally eaten raw in salads.
A longer root form, including oriental radishes, daikon or mooli, and winter radishes, grows up to 60 cm (24 in) long with foliage about 60 cm (24 in) high with a spread of 45 cm (18 in). The flesh of radishes harvested timely is crisp and sweet, but becomes bitter and tough if the vegetable is left in the ground too long. Leaves are arranged in a rosette. They have a lyrate shape, meaning they are divided pinnately with an enlarged terminal lobe and smaller lateral lobes. The white flowers are borne on a racemose inflorescence. The fruits are small pods which can be eaten when young.
The radish is a diploid species, and has 18 chromosomes (2n=18). It is estimated that the radish genome contains between 526 and 574 Mb.
Radishes are a fast-growing, annual, cool-season crop. The seed germinates in three to four days in moist conditions with soil temperatures between 18 and 29 °C (65 and 85 °F). Best quality roots are obtained under moderate day lengths with air temperatures in the range 10 to 18 °C (50 to 65 °F). Under average conditions, the crop matures in 3–4 weeks, but in colder weather, 6–7 weeks may be required. Homegrown varieties can be significantly sharper.
Radishes grow best in full sun in light, sandy loams, with a soil pH 6.5 to 7.0, but for late-season crops, a clayey-loam is ideal. Soils that bake dry and form a crust in dry weather are unsuitable and can impair germination. Harvesting periods can be extended by making repeat plantings, spaced a week or two apart. In warmer climates, radishes are normally planted in the autumn. The depth at which seeds are planted affects the size of the root, from 1 cm (1⁄2 in) deep recommended for small radishes to 4 cm (1+1⁄2 in) for large radishes. During the growing period, the crop needs to be thinned and weeds controlled, and irrigation may be required.
Radishes are a common garden crop in many parts of the world, and the fast harvest cycle makes them particularly suitable for children’s gardens. After harvesting, radishes can be stored without loss of quality for two or three days at room temperature, and about two months at 0 °C (32 °F) with a relative humidity of 90–95%.
II. How to Grow and Care
Sunlight
Radish thrives best under full sun conditions, receiving at least six hours of direct sunlight daily, which is crucial for optimal growth and root development. Though radish tolerates partial sun, where it receives four to six hours of direct sunlight, growth may be less robust, and the roots can become elongated and less flavorful. In low light, radish may exhibit legginess as it stretches towards the light source, which can lead to weak and spindly plants.
Outdoors, radish should be placed in a location that garners full sun exposure for vigorous growth and healthy root formation. Radish does not typically require indoor cultivation; however, if grown inside, a sunny windowsill that mimics outdoor conditions is suitable.
Temperature and Humidity
Radishes like temperatures between 40 and 70 degrees Fahrenheit, with temperatures in the low 60s being best. Hot weather can cause the plants to bolt and decline in quality. They can get tough and woody or spongy with hollow centers. Also, once a radish bolts, the bulb stops forming. Humidity isn’t an issue as long as adequate soil moisture is maintained and there is good airflow around the plants.
Watering
Radish plants typically need 1 inch of water per week. Soil that’s too dry can cause the plant to bolt (go to seed) and ruin the taste of the radishes, making it pithy, and soil that’s too wet can cause the roots to split and rot. A layer of mulch around the plants can help to maintain soil moisture.
Soil
Radishes do best in rich, loamy, or sandy, well-draining soil with a slightly acidic to neutral soil pH (6 to 7). The soil must not be heavy or compacted, as the roots won’t grow well in those conditions.
Fertilizing
If you’re already starting with rich soil, you typically won’t need to fertilize radishes. If you need to improve your soil, work in a few inches of compost before planting.
How to Grow in Pots
Container growing is a good option if you don’t have garden space or the loose soil that radishes need. Common radish roots are shallow, so they don’t require that deep of a pot. But it’s best to grow a round variety rather than a long one to ensure it has enough room to develop.
A container around 8 to 12 inches wide and deep should be fine. It also should have ample drainage holes. Unglazed clay containers are beneficial because they’ll allow excess soil moisture to evaporate through their walls, helping to prevent root rot. Use any high-quality potting soil. Containers dry out more quickly and need more watering than in-ground gardens. Monitor moisture closely.
If you consider planting in a 5-gallon container, you can evenly space the seeds, yielding about 10 radishes.
Pruning
You won’t have to do any pruning on your radish plants beyond thinning seedlings. If the radishes remain crowded, they won’t develop properly. Fortunately, you can eat the seedlings you thin. Snip them off at ground level rather than pulling up their roots to avoid disturbing the roots of neighboring plants.
Propagation
Radishes are typically grown from seed. Growing radishes from root scraps is possible, but that method is unreliable and not recommended. Seeds up to five years old are a much better bet.
The best time to plant seeds is in early spring and fall when temperatures average about 50 to 70 degrees Fahrenheit. Collect seeds from mature plants for future plants. Here’s how to harvest the seeds:
- Rather than pulling the radishes as they mature, allow the plant to remain in the ground. Eventually, it will send up a flower stalk and produce seed pods.
- Remove mature seed pods once they’ve turned brown and dried out. Crush the pods to release the seeds. Separate the seeds from the rest of the pods.
- Place the seeds in a paper envelope, and store them in a cool, dry spot. They should remain viable for five years.
How to Grow From Seed
Radishes germinate quickly from seed—usually three to five days—when air temperatures are between 50 to 60 degrees Fahrenheit. One seed yields one radish.
Plant them four to six weeks before you expect your last frost. You can succession sow every 10 days with another set of seeds until the air temperatures reach 65 to 75 degrees. You can also sow again in the late summer and early fall until the winter weather sets in. Remove any weeds around your seedlings to prevent competition for moisture and nutrients.
Here’s how to sow seeds:
- Direct-sow seeds outdoors about 1/2-inch deep.
- Cover loosely with soil. Space each seed 1 inch apart in rows 3 inches apart.
- Water seeds thoroughly, down to 6 inches deep.
- For larger varieties of radishes, like daikon, sow seeds slightly deeper than the small varieties. Gently firm the soil around the seeds, and keep it evenly moist but not soggy. Germination should occur in three to 10 days.
Overwintering
Radishes are annuals, meaning they complete their life cycle in one growing season. So no overwintering will be necessary.
Pests and Diseases
Cabbage maggots are common pests for radish plants, as they will tunnel into the radishes. Cutworms also feed on radishes. And flea beetles will feed on radish leaves but won’t injure the bulbs. Monitor to catch these insects before they destroy the whole crop. Growing your radishes under floating row covers can help to prevent pest issues. Wood ash mixed into the soil can help deter root maggots. Some radish plants’ diseases include downy mildew, black root, and scab. But maintaining proper growing conditions can prevent many problems with diseases.
III. Uses and Benefits
- Culinary uses
The most commonly eaten portion is the napiform or fusiform taproot, although the entire plant is edible and the tops can be used as a leaf vegetable. The seed can also be sprouted and eaten raw in a similar way to a mung bean.
The root of the radish is usually eaten raw, although tougher specimens can be steamed. The raw flesh has a crisp texture and a pungent, peppery flavor, caused by glucosinolates and the enzyme myrosinase, which combine when chewed to form allyl isothiocyanates, also present in mustard, horseradish, and wasabi.
Radishes are mostly used in salads, but also appear in many European dishes. In Mexican cuisine, sliced radishes are used in combination with shredded lettuce as garnish for traditional dishes such as tostadas, sopes, enchiladas and Posole stew.
Radish greens are usually discarded, but are edible and nutritious, and can be prepared in a variety of ways. The leaves are sometimes used in recipes, like potato soup or as a sauteed side dish. They are also found blended with fruit juices in some recipes.
In Indian cuisine the seed pods are called “moongra” or “mogri” and can be used in many dishes.
- Other uses
The seeds of radishes can be pressed to extract radish seed oil. Wild radish seeds contain up to 48% oil, and while not suitable for human consumption, this oil is a potential source of biofuel. The daikon grows well in cool climates and, apart from its industrial use, can be used as a cover crop, grown to increase soil fertility, to scavenge nutrients, suppress weeds, help alleviate soil compaction, and prevent winter erosion of the soil.
“Radi”, a spiral-cut radish, served with salt and occasionally chives, is traditionally served with beer at the Bavarian Oktoberfest.
- Culture
The daikon varieties of radish are important parts of East, Southeast, and South Asian cuisine. In Japan and Korea, radish dolls are sometimes made as children’s toys. Daikon is also one of the plants that make up the Japanese Festival of Seven Herbs (Nanakusa no sekku) on the seventh day after the new year.
Citizens of Oaxaca, Mexico, celebrate the Night of the Radishes (Noche de los rábanos) on December 23 as a part of Christmas celebrations. This folk art competition uses a large type of radish up to 50 cm (20 in) long and weighing up to 3 kg (7 lb). Great skill and ingenuity are used to carve these into religious and popular figures, buildings, and other objects, and they are displayed in the town square.
IV. Harvesting and Storage
Take note of when your radish variety should be ready for harvesting. In general, harvest when the roots are around 1 inch in diameter. You can often see the shoulders of the radish rising slightly above the soil line. You might have to pull one out to see whether it’s ready.
Don’t wait too long to harvest to ensure a pleasant flavor and tender texture. Left in too long, your radishes will taste too hot and pithy. Hot weather can also ruin this cold weather crop’s taste.
To harvest, pull up the plants, and cut off the tops and the thin roots. Leaving the leaves on will draw moisture and nutrients from the radish bulb. The greens can be stored in the refrigerator for a few days and eaten fresh or cooked. The bulbs can be stored in the refrigerator’s vegetable crisper for one to two weeks. They also are good fresh or cooked in salads, soups, and more.
