At a glance
- Sow in succession: a short row every 10 to 14 days, from CW 12 to CW 36. That way you harvest steadily instead of all at once.
- Keeping the soil evenly moist is the whole trick. Water stress makes the roots woody, spongy and sharp.
- Radishes need about four weeks, daikon eight to fourteen depending on the variety. Both want to grow without a pause.
- Flea beetles arrive in dry, warm weather. A fleece straight after sowing and moist soil keep them in check.
- Both are light feeders. Too much nitrogen drives leaf instead of root and encourages black, hollow bulbs.
Few vegetables reward impatience as quickly as the radish. Four weeks after sowing you pull the first crisp bulb out of the soil, and that is exactly what makes it the perfect start for children and for anyone who wants to watch their bed grow. Its big brother, the daikon, takes longer and grows larger, but follows the same rules. And they are surprisingly simple: no water stress, no crowding, no excess of fertiliser. Follow that and you harvest mild and juicy instead of woody and fiercely hot.
Why radishes turn woody or sharp
Woody, spongy, hollow, fiercely hot: those are the four disappointments radish growers know. All four share the same root cause, namely a growth stall. A radish is a sprinter. When it grows quickly and without interruption, the tissue stays tender and full of water. But the moment it stalls, because the soil dries out, because it gets too warm or simply because it stays in the ground too long, the plant lays down fibres and the sharpness rises.
The sharpness itself is not a flaw but a mustard oil called allyl isothiocyanate, the same principle as in mustard and cress. In moderation it is what makes a radish interesting. Too much of it forms under drought stress and heat. The practical takeaway is wonderfully simple: keep the plant moving. Evenly moist, not too tight, not overfed, and harvested in good time.
A radish that goes thirsty defends itself with heat.
Old gardener's rule
Sow in succession: never too much at once
The most common beginner's mistake is to broadcast a whole packet at once in April. Then thirty radishes are ready at the same time, half of them bolt before you eat them. Succession sowing is better: a short row every 10 to 14 days. From CW 12 (mid March, earlier under fleece) to CW 36 (early September) you can sow almost continuously.
Loosen the soil
Radishes like loose, humus-rich soil. Rake the bed fine and remove stones so the bulbs turn out round instead of twisted.
Sow shallow
Draw a drill half to one centimetre deep. Seeds sown deeper germinate poorly and form long, misshapen bulbs.
Space thinly
Lay the seeds 3 to 5 cm apart, with rows 10 to 15 cm apart. Sow too densely and you will have to thin later, otherwise the bulbs crowd each other and stay small.
Firm and water in
Press the soil down, water with a fine rose. At 12 to 15 degrees the seeds germinate in about a week.
Sow again in two weeks
As soon as the first batch germinates, mark the next sowing date. A steady supply is the secret of a full radish summer.
For early sowings from CW 10 to 12 a fleece does double duty: it keeps off the night chill and warms the soil, so the seed germinates faster. Radishes tolerate light frost down to about minus three degrees, but under fleece they establish noticeably quicker.
The watering rhythm decides it
If you remember a single thing from this article, let it be this: even moisture. Not soaking wet, because waterlogging rots the bulbs. But never bone dry either, because every dry spell brings fibres and heat. On sandy soils that means daily watering in high summer, morning or evening.
- Evenly moist
Better a little every day than a lot once a week. Swinging moisture makes the bulbs split.
- Barely feed
As light feeders they only need a little ripe compost before sowing. Too much nitrogen drives leaf and turns the bulbs black and hollow.
- Part shade in high summer
Above 25 degrees radishes bolt quickly. A spot with midday shade or sowing between taller crops helps.
- Harvest in time
Do not wait until the bulb is huge. Smaller and young tastes milder, overgrown it turns spongy.
A widespread myth is that plenty of fertiliser makes big radishes. The opposite is true. Radishes and daikon are light feeders, they draw their strength from a well-prepared soil. On a bed freshly dressed with manure you get magnificent leaves and puny, often black-spotted bulbs. Save the nitrogen for the hungry feeders and give the radishes only a little compost.
Flea beetle: the little jumper in the dry bed
Anyone who finds tiny round holes in radish leaves in early summer has a visit from the flea beetle. These beetles, a few millimetres small, spring away when touched and love exactly one kind of weather: dry and warm. On freshly germinated seedlings they can stall whole rows, because a perforated seed leaf grows slowly, and slow growth is a problem we already know.
The good news: flea beetles hate moisture. A bed you keep consistently moist is unattractive to them. That handles two things at once, because the same moisture keeps the bulbs mild. Lay a fine-mesh insect net or fleece straight after sowing and you simply shut the beetles out before they ever land.
On young seedlings a heavy infestation can cost you a whole sowing. Act early: hose the bed down in the evening, mulch and lay a net while the plants are still small. Later, once the foliage is strong, the feeding does little damage.
Daikon is the radish's big brother
Botanically radishes and daikon are the same species, Raphanus sativus. The difference lies in size and pace. While the radish is done in four weeks, a white summer daikon needs eight to ten weeks, a winter or beer radish up to fourteen. In return it grows to the size of a hand and keeps for weeks in a cellar or a box of sand.
Because daikon stands in the bed longer, the even watering rhythm matters even more with it. It also needs more room: allow 10 to 15 cm between plants and 25 to 30 cm between rows. Sow summer daikon from CW 16 to 24, and the storable winter radish such as Radish 'Runder Schwarzer Winter' only from CW 26 to 30, so it grows into the shortening days and does not bolt.
Both get along well with lettuce, carrot and pea, so they make ideal gap fillers. What you should avoid is neighbouring and rotating them with other brassicas. Radish, daikon, cabbage and mustard belong to the same family and share the disease clubroot. So keep a four-year break on the same bed.
Harvesting at the right time
Radishes tell you themselves when they are ready: the bulb pushes visibly out of the soil and, depending on the variety, reaches about coin size. Pull them promptly then, because every extra day costs tenderness. Harvest in the morning if you can, when the bulbs are plump with water. The leaves, by the way, are edible and make a peppery soup or pesto.
Harvest daikon as soon as the shoulder reaches the expected variety size. A simple test: press a thumbnail lightly into the skin. If it gives juicily, it is ripe. If it feels spongy, it stayed in too long. Winter radish keeps for several weeks in moist sand in a cool cellar.
Raphanus sativus var. sativus
- Familie
- Brassicas (Brassicaceae)
- Standort
- Sunny to part shade, loose and humus-rich
- Saison
- Sowing CW 12 to 36, harvest after about four weeks
- Wasserbedarf
- Evenly moist, light feeder
- Frosthärte
- Frost-tender, briefly takes about minus 3 degrees
Common questions about radishes and daikon
Why do my radishes turn hot and woody?
Both are signs of water stress and too slow growth. When the soil dries out in between, it gets too hot or the bulb stays in the ground too long, the plant lays down fibres and forms more mustard oils. Keep the bed evenly moist and harvest young rather than large.
Why do my radishes make only leaves and no bulbs?
This usually has two causes: too much nitrogen in the soil or too little light. Radishes are light feeders, a freshly fertilised bed drives lush foliage instead of bulbs. Crowded stands and shade have a similar effect. Sow more thinly, in a sunny spot, and feed only with a little compost.
What helps against flea beetles on radishes?
Flea beetles love dryness. Keep the bed consistently moist, hose it down in the evening and mulch shallowly. Most effective is a fine-mesh insect net straight after sowing, which shuts the jumping beetles out before they reach the young seedlings.
How often can I re-sow radishes?
From CW 12 to CW 36, a short row every 10 to 14 days. This succession sowing gives you fresh bulbs over months instead of everything ripening at once. In high summer choose a part-shaded spot, otherwise they bolt quickly in the heat.
How do radishes and daikon differ?
It is the same species. Radishes are the small, fast form, ready in four weeks. Daikon grows much larger, needs eight to fourteen weeks and can be stored as winter radish. The care is the same, only daikon needs more room and even steadier moisture.
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