Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Looking for a little variety in your radishes? How about daikon radishes? They are larger and milder than the usual spicy red radishes.
What are Daikon Radishes?
Daikon radishes (Raphanus sativus var. Longipinnatus) are a cultivar of radish that is native to Southeast Asia. They have long, thick taproots that can range in size from eight inches to 24 inches. The roots are generally white, although the Korean variety of Daikon can be partly green. A popular Chinese variety is called watermelon. The outside of the roots are green while the insides are a bright pink like watermelons. These larger radishes have a milder flavor than the smaller, more familiar red radishes.
Many Southeast Asian cuisines use both the root and the foliage. The roots are eaten raw, pickled, stir fried, cooked in soups or shredded and dried. The foliage is most often served as a green vegetable.
Why are Daikon Radishes Called "Tillage Radishes"?
Daikon radishes are also referred to as “tillage radishes” when they are planted as a cover crop. The long thick taproots penetrate dense soils creating openings that can be used by other crops whose roots cannot easily penetrate dense soils. The long roots are also able to access soil nutrients that are too deep for more shallowly rooted crops to access. Then the taproots are left to decay in the soils so that they can release those nutrients into the soil to nourish spring crops.
Tillage radishes are especially effective when planted in rotation with potatoes. The taproots are left to decay in the soil over the winter. The following spring, when the potatoes are planted, the openings in the soil created by the decayed taproots allow the potato plants to form more and larger tubers.
The tops (foliage) of the tillage radishes are also used as fodder for farm animals.
How to Grow Daikon Radishes
Because of their root size, when planting Daikon seed, it’s a good idea to loosen the top eight inches of soil and amend it with compost. Sow your seeds directly into your garden in late summer. You can sow the seeds in the spring when the soil is as cool as 40⁰F, but they will take longer to germinate and could possibly rot before they have a chance to germinate. When the soil temperature is warmer, 60⁰F to 85⁰F, germination will occur in 3 to 6 days.
The seeds should be sown 2 to 3 inches apart in rows that are 8 to 12 inches apart. Cover with ½ inch of soil. When your seedlings develop their first set of true leaves, thin them to 5 to 6 inches apart. You can compost the seedlings or use them in salads.
Flea beetles love radishes! In fact, radishes are often used as a trap crop for flea beetles, attracting them away from other cruciferous crops such as cauliflower, broccoli and cabbage. The theory is that radishes are grown for their roots so it’s okay if the flea beetles consume their foliage.
Daikon radishes take longer to mature than their smaller, red cousins. Those long taproots need their foliage intact to grow. To prevent flea beetles from consuming the foliage and stunting the growth of the roots, cover your seedlings with floating row covers until they are established plants. With nothing to eat, the flea beetles will have moved on in their search for a meal.
How to Harvest Daikon Radishes
You can begin harvesting your Daikons when the roots are 8 inches long and continue harvesting until the foliage is killed by frost. At that point, you should harvest all the remaining roots in your garden. If you leave them in the ground over the winter, they will rot.
When harvesting, it’s best not to just grab the plants and pull. The foliage will separate from the roots. You should carefully loosen the soil around the roots, then reach into the soil, grasp the root and pull.
The Japanese heirloom, Minowase, is the largest of the Daikons. The roots can be 24 inches long with a 3 inch diameter. They need 50 days to reach maturity and maximum size.
How to Store Daikon Radishes
After harvest, brush the soil off the roots and cut off the foliage. Do not wash the roots until you are ready to use them. They can be stored, unwashed, in a cool, dry place for 2 to 3 weeks.
Questions & Answers
Question: How cold does it need to get to kill a radish?
Answer: Temperatures of 32 degrees Fahrenheit will kill the foliage. Mature roots left in the ground over the winter will rot. They should be harvested when the foliage has been killed by the frost.
Question: How do you apply the fertilizer to grow Daikon radishes?
Answer: I am an organic gardener so I do not use commercial fertilizers. Instead, when I make a hole to plant a seed or plant, I mix compost into the soil I use to cover the seed or plant. Compost provides nutrients and texture to the soil, feeding plants and making it easier for water to reach the roots.
Question: The daikons I grew this spring had many smaller roots coming out of the main radish, I had prepared the soil with cow manure and bone meal, did I just over do it?
Answer: It sounds like the cow manure and bone meal combined together to create a very dense soil which your daikon radishes had difficulty penetrating. When a tap root can't go straight down, it sends out offshoots. Try using manure only or bone meal only.
© 2018 Caren White
Caren White (author) on August 28, 2019:
Yup! Harvest away.
Daikondan on August 23, 2019:
I am growing daikon (first tyme ) and the root has burst out of the ground and about 4” of the root is exposed
Is it time to harvest?
Caren White (author) on February 19, 2019:
Rebecca, I think that it is the lack of water rather than the temperature that is the stumbling block here. Make sure that you water well while you are at your wummer home during July, mulch heavily and cross your fingers. October may be too late to seed them. Unfortunately, the ideal window to seed daikon radishes is August/September.
Rebecca on February 19, 2019:
I would like to grow daikon radish as a cover crop to rot in the ground, but it is at our "summer home" where we will be visiting in July and later in October. The temperatures average 26/14 degrees C in July, 18/9 degrees C by October, and in November 13/5 degrees C. I should add that summers are usually quite dry, and when we leave the property the plants have to fend for themselves. We will be mulching heavily though. My concern about leaving it until October is that it will be too cool for the radishes to mature. I would appreciate advice! Thanks