Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
One of my fondest memories as a child is sneaking into my father’s vegetable garden and eating the radishes. I loved pulling them out of the ground, washing the soil off of them using the sprinkler that was watering the garden and then eating them right in the garden!
What Are Radishes?
Radishes (Raphanus sativus) are a cool season root crop that is a member of the brassica family which includes broccoli, cauliflower and cabbages. Radishes are thought to be native to China and have since spread throughout the world. The plants are grown for their swollen tap root but the leaves and the seed pods are also eaten in some cultures.
There are many types of radishes, but they fall into two main groups: round and oriental. Round radishes are familiar to most gardeners. The color of the root can be red, pink, purple, white or even black. They are usually 1 inch in diameter. Oriental radishes are shaped like carrots and are usually white. Daikon radishes are a good example of oriental radishes. In both cases, the interior of the root is white.
Radishes make excellent trap crops attracting flea beetles away from your peppers. The beetles chew holes in the foliage of the radishes but most gardeners don’t mind because they are growing them for their roots, not their leaves. The damage to the foliage does not affect the quality of the root.
They also make excellent companion plants. Their pungent foliage repels pests such as ants, aphids, cucumber beetles, squash bugs and tomato hornworms so plant them amongst your tomatoes, cucumbers and squash.
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How to Grow Radishes From Seed
Radishes can be grown in either the spring or the fall. They do better in the fall because the soil is cooling down. In the spring, sow your radish seeds in your garden 4 weeks before your last frost date. Make bi-weekly sowings while the soil is between 65⁰F and 75⁰F. For a fall crop, plant your seeds 8 weeks before your first expected frost. You can continue to sow seeds every 2 weeks up until 3 weeks before your first frost date.
Plant the seeds ½ inch deep and 1 inch apart in rows 12 inches apart. You don’t need to devote a separate space to your round radishes. They germinate and mature quickly so they can be sown in between other slower growing root crops such as carrots or parsnips. Germination will occur in 5 to 7 days. When the seedlings are 2 inches tall, thin them to at least 3 inches apart. Crowded plants do not develop the desired round roots. Instead, they will be thin and inedible. Oriental radishes which have larger roots should be thinned to 6 inches apart. Keep your plants well-watered. The roots will dry out and crack if they do not receive enough water. Radishes grow best in temperatures between 50⁰F and 70⁰F.
How to Harvest Radishes
Keep a careful eye on your round radishes. They mature quickly, 3 to 4 weeks after germination. If they are left in the ground too long, the roots become cracked and woody. Harvest them when the roots are larger than a grape but no more than an inch in diameter. Oriental radishes take longer to mature, 2 to 3 months. Oriental radishes that have been sown in the fall can be left in the ground until the soil freezes.
How to Store Radishes
When harvesting in warm weather, pull the roots from the ground and immediately immerse them in cool water. Cut the foliage off and store the roots at room temperature for 2 to 3 days or in the refrigerator in plastic bags for up to 3 weeks. The foliage is also edible. It should be stored separately from the roots.
Common Pests That Attack Radishes
Flea beetles, cabbage root maggots and cutworms often attack radishes. Cover your plants with floating row covers to prevent the insects from getting to them. Be sure to anchor the sides of the row covers with pins, soil or even rocks so that the insects can't get underneath the cover. You don't need to remove the cover for pollination because you are growing radishes for their roots, rather than for fruit so pollination is not necessary.
© 2018 Caren White