Raphanus sativus var niger (or longipinnatus)
Introduction: Winter radishes are most often associated with Japan, where a quarter of all vegetables grown are radishes. However they were actually popular in Europe before the familiar small radishes were introduced. Like the turnip they were an important winter food for peasants.
The roots get much larger than ordinary radishes and sometimes reach 3˝ diameter and 18˝ long. They are called winter radishes because (like winter squash) they were stored for winter use. They are treated a lot like turnips.
Climate: Radish is a cool weather crop, growing best at a cool 60°F and with moist conditions. Hot weather causes them to develop a very pungent flavor, similar to the related horseradish.
Germ temp: 45 (70 – 80) 95°F
Germination time: 3 – 10 days
29 days / 41°F
11 days / 50°F
6 days / 59°F
4 days / 68°F
4 days / 77°F * Optimum
3 days / 86°F
Seed viability: 5 years
Germination percentage: 75+
Growing temp: 45 (60 – 65) 75°F
Plants per person: 20
Plants per sq ft: 16
Fall: 7 – 12 wks before first frost
pH 5.5 – 6.8
The soil needs to be more fertile than for other radishes and should be rich, loose and friable (ideally a rich, sandy loam). Most soils will benefit from 2 – 3˝ of organic matter (compost or aged manure), incorporated into the top 6” of soil (also remove any rocks or debris you come across. The roots go much deeper than other radishes, so you need to loosen the soil to a greater depth (ideally 12˝), especially in heavy clay soil). In very poor soil you can dig a special trench and fill it with a mix made from compost, sand and soil.
When: If you plant winter radish in warm summer weather they will merely produce leaves and bolt, without producing a large swollen root. The plants appreciate the warm weather, but need cool nights to produce large roots.
The plants need a minimum of 65 days to produce roots, so plant them in late summer, about 60 – 90 days before the first autumn frost is expected.
Direct sowing: There is no reason to start radishes indoors, because they germinate easily in cool soil and the plants grow rapidly. Like most roots they don’t transplant well.
The seed is sown directly into the garden ½ – 1½˝ deep and 1˝ apart. A deeper planting may give you slightly larger roots, especially if you give them a slightly wider spacing (1½˝). Bigger seed may also result in larger roots.
Spacing: Space the plants 6 – 18˝ apart, depending on soil and variety.
Sowing: Sow the seed ¾ – 1˝ deep and 2˝ apart.
Thinning: Proper thinning is essential if you are going to grow good radishes. If the plants are crowded they won’t produce useful roots. You can eat the thinnings in salads.
Weeds: These small plants don’t compete with weeds very well, so should be hand weeded regularly. Don’t use a hoe too near the plants as their shoulders are easily damaged.
Watering: The plants need consistently moist soil for good growth. Too little water can result in woodiness and excessive pungency (often such roots are also pithy and have marked growth rings). Too much water may encourage top growth at the expense of the roots. Irregular watering can cause them to crack.
Mulch: This keeps the soil cool, which is important in warm weather. It also retains moisture and keeps down weeds.
Though radishes are one of the easiest crops to grow, beginners often have problems.
Pests and diseases: Radishes are susceptible to the usual host of Brassica pests.
Flea beetles: These will commonly eat small holes in the leaves, but this isn’t usually a major problem. You can protect your plants against many pests by using floating row cover.
Cabbage root maggot: This is the big pest of the radish and is most problematical in spring and late summer. See Cabbage for ways to deal with it.
Radishes are sometimes planted as a trap crop, to lure the little worms away from more valuable Brassicas.
Seed saving: The flowers are cross-pollinated by insects, so only one variety should be flowering at a time (or they should be caged or isolated by a half mile).
The usual method of obtaining seed is to plant it in late summer, protect it over the winter (inside or outside) and allow it to flower in spring. It should be planted in a block so insects are likely to visit many plants without going to other plants nearby. Collect the dry pods when they are ripe (they shatter easily so watch carefully), sift out the seeds, dry further and store.
Harvest: The flavor of the root can be improved by frost, so don’t harvest too early.
Some radishes are grown for their edible leafy tops, which are eaten like turnip greens.
Storage: When possible the roots are left in the ground until needed (a thick mulch will protect them from cold weather). If this is not possible they can be stored in moist sawdust, or sand, in a root cellar at 32 – 40°F. The harvested roots will keep in a plastic bag in the refrigerator for several weeks.
Unusual growing ideas
Compact soil: Daikon radishes have a very strong and deep penetrating root and are sometimes planted to loosen compacted soil, as an easy alternative to digging.
Varieties: Some varieties have very beautiful roots.
Giant Luo Bo: Large oval roots are sweeter than many. 80 – 100 days
Myashige: The medium spiked roots are often pickled. 60 days
Tokinashi: Is quite pungent. 60 days.
Shogoin: This turnip shaped radish is usually cooked. 70 days
Sakurajima: This variety can get very big. 80 days
Wayakama White: Long white roots. 70 days
April Cross F1: A giant spiked root, slow to bolt. 60 days
Minowase summer cross F1: Another giant spiked root, heat tolerant and does better in warm weather. 60 days
Leaf radishes: In Asia some varieties of radish are grown for their edible leafy tops, rather than their roots. These include:
Four season F1
Pearl leaf F1
Kitchen use: The roots are peeled and eaten raw, cooked like turnips, pickled (very popular in Japan), stir-fried and dried. The grated root is often used in sauces in Japan.
The immature seedpods are good in salads or pickled. The ripe seed is sprouted like alfalfa.