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Radishes can be sown in both spring and fall, but the fewest failures come from a late summer to early fall sowing. As the weather cools, insect pressure drops and the roots fill slowly and firmly, which gives a good round shape. Sown in the heat of summer, they put everything into leaves and the roots never swell.
In spring, start about four weeks before your last frost date, once the soil can be worked. In fall, sow from late summer until about a month before your first hard frost. For a first year, stick to those two windows and you will get a feel for the three to four week rhythm before trying summer or winter crops.
| Sowing time | Days to harvest | How it goes |
|---|---|---|
| Early spring | 25 to 30 days | Slower while the soil is still cold |
| Late spring into early summer | Around 20 days | Pests build up, so a net is needed |
| High summer | Sometimes under 20 days | Roots struggle to swell. For experienced growers |
| Late summer to early fall | Around 25 days | The easiest and most reliable sowing |
Sow in a drill, one seed every half inch
Radish seed is round and fairly large, so you can place it one seed at a time. Make a drill about a third of an inch (1 cm) deep and drop a seed roughly every half inch (1 cm). Sown thickly, the roots crowd each other and grow long and thin instead of round.
Leave 6 to 8 inches (15 to 20 cm) between rows. On a narrow bed, two rows is plenty. Skimping on the spacing here cannot be made up for later at thinning time.
- Make the drill Press the edge of a board or a stake into the soil to make a straight drill a third of an inch (1 cm) deep, with a level bottom.
- Drop seed half an inch apart Pinch the seed and set it along the drill one at a time. Where several land together, spread them with a fingertip so the spacing stays even.
- Cover and firm Push soil in from both sides to cover the seed by about a quarter inch (5 mm), then press lightly with your palm so seed and soil make contact.
Leftover seed keeps well in a sealed jar in the refrigerator. It still germinates well into its second year.
A quarter inch of cover, and never let it dry
Too much soil on top and the seedling uses up its reserves before it reaches the light. Too little and the seed dries out and dies. Aim for a quarter inch (5 mm), just enough to hide the seed, and firm it so water can reach it.
For the three or four days before germination, keeping the surface damp is everything. If it looks pale and dry in the morning, water gently that day. Any stretch that dries out once will leave a gap in the row.
- Water well on sowing day Use a fine rose turned upward so the water falls like rain. A hard stream washes seed together into clumps.
- Lay row cover over the bed A light row cover laid loosely over the drill slows drying and keeps insects off. Take it off once the seedlings are up evenly.
- Look for seedlings from day three At around 68°F (20°C) they show in three days. If a stretch of row has nothing after four days, resow just that part.
A container only needs to be six inches deep
Radish roots are shallow, so a container 6 inches (15 cm) deep is enough. They do well on a balcony or patio, and sowing every two weeks keeps a steady supply. An ordinary vegetable potting mix works straight from the bag.
A shallow container dries out fast, so watering needs more care than in the ground. Letting it dry hard and then soaking it is the usual cause of split roots.
| Container | How to sow | Roughly how many |
|---|---|---|
| Standard 26 inch (65 cm) window box | Two rows | 20 to 30 radishes |
| Round pot, 10 inches (24 cm) across | Five spots, a few seeds each | 5 to 8 radishes |
| Deep foam or plastic tote | Three rows | About 30 radishes |
Use fresh potting mix for each crop in containers. Reused mix tends to produce small galls and misshapen roots.
Sorting out patchy germination
Nothing comes up, it comes up in clumps, or seedlings appear and then fall over. The cause is nearly always water, covering depth or pests, and you can usually tell which by looking. The sooner you decide whether to wait or resow, the less your harvest plan slips.
- One stretch of row is empty That stretch dried out or was covered too deeply. Dig with a finger to find the seed; if it is not swollen and white, resow.
- Nothing at all comes up The soil is too cold or too hot. Below about 40°F (4°C) or above 86°F (30°C) germination stops, so shift the date and resow.
- Seedlings fall over right away Either damping off or something chewing at the soil line. Pull one and look at the stem; a clean, sharp cut points to a cutworm.
- Seedlings are thin and leggy Not enough light. They are stretching toward the sun, so move the container somewhere brighter or resow in a sunnier spot.
Sow every two weeks so you never run out
Radishes work best when you do not sow too many at once. Sow the whole packet in one go and they are all ready the same week, more than you can eat, and the ones left in the ground split. Small sowings every two weeks is the basic pattern for a home garden.
Divide a bed into three and sow each part in turn, or use the gaps before another crop goes in. Because the crop takes only three to four weeks, it never gets in the way of what comes next.
- Split the bed into three Sow one section, then the next two weeks later, then the third. Three sections give about six weeks of harvest.
- Write the date on a label Push a dated label in at the end of each section. You will know when to start checking, and where to sow next.
- Sow 10 to 15 per round Decide first how many your household eats in a week. The more you sow, the more get left too long and split.
Sown between other crops, radishes also mark the row and help you keep your spacing straight.