Radish

Direct-sow spring radishes as soon as the soil can be worked

Loosen the bed at least six inches deep, then sow seed a half inch deep with about an inch between seeds and rows 10 to 12 inches apart. Sowing can start once soil reaches 40F, and seed comes up in 5 to 10 days. Sow a short row about every 10 days instead of one big planting, so you get a steady supply rather than a glut. Radish can be sown once soil reaches 40F and germinates best at 55F to 75F, and roots mature 25 to 45 days from seeding depending on variety, so the crop has to size up while the weather is still cool. Stress during the first six weeks of growth often leads to premature flowering and low yields, and roots that finish in heat turn hot and bitter.

Sow daikon and winter storage radishes in late summer

Sow the long and storage types from midsummer to late summer for a fall harvest, planting the larger-rooted kinds up to an inch deep and thinning them to four to six inches apart. They take considerably longer than the three to five weeks a spring garden radish needs, so count back from your first hard frost. Winter radishes need a long cool finish, so they are timed to mature as temperatures fall rather than rise; radishes pushed into heat run to flower and seed before the root fills.

Water regularly and evenly - never let the bed swing from dry to soaked

Water radishes regularly. How much depends on your soil type, so judge by the bed rather than a fixed weekly number - check that moisture is reaching root depth and stays steady. Use drip irrigation if possible, and mulch around the plants to conserve soil moisture. Never let the bed dry to the point of wilting and then flood it. Moisture fluctuations cause root cracking, slow leaf development, and contribute to hot, bitter roots - the flavor growers usually blame on the variety. Stress during the first six weeks of growth also often leads to premature flowering and low yields, and a crop this fast has no time to recover.

Thin about a week after each sowing, before the roots start to swell

Once the seedlings are up and a couple of inches tall, thin salad types to 1 to 2 inches apart and daikon or winter types to 4 to 6 inches. Do this for every sowing, spring or fall. It feels wasteful and it is the single step most gardeners skip. A radish root has to have room to expand sideways; crowded plants stay stringy and shriveled no matter how well they are watered, and thinning too shallowly is a leading cause of roots that never fill.

Check seedlings for flea beetles until they reach 4 to 5 leaves

Look at the seedlings every few days for shallow pits and rounded holes smaller than an eighth of an inch. In a home garden, treat only if you find more than five beetles per plant or 10 to 30 percent of the seedling leaves have been lost. Past the 4 to 5 leaf stage the plants outgrow the damage and need nothing. Adult flea beetles do nearly all the damage and only matter while the plant is small - a seedling with half its leaf area gone cannot photosynthesize enough to fill a root, while a larger plant shrugs the same feeding off.

Flea beetle: spinosad on seedlings only if scouting says so

If seedlings pass the threshold and covering the row is not an option, spray spinosad, and confirm radish is named on the label of the product you buy. Kaolin clay is a non-toxic alternative that works by coating the leaf. Do not spray plants that have outgrown the seedling stage. Spinosad kills the adult beetles doing the chewing and is one of the softer materials labeled for radish, so it protects the seedling window without wiping out the ground beetles and parasitoids that keep other pests down.

⚠ Spinosad on radish carries a 3 day pre-harvest interval - on a 25 day crop that is a real constraint, so count back from your pull date. Spinosad is toxic to bees while the spray is still wet; spray in the evening. Always follow the label on the container you are holding.

Cover the row at seeding to shut out cabbage maggot and flea beetles

Lay spunbonded row cover over the bed the day you seed and seal the edges with soil so no fly can walk under. Leave it on through harvest - a radish is pulled before it flowers, so pollinator access is not a concern. Do not plant where a brassica grew last year. The cabbage maggot fly lays eggs at the base of young seedlings and the larvae tunnel straight into the root, and flea beetles chew shotgun holes in the first true leaves; both are excluded outright by a cover put on before they arrive, and the maggot overwinters as pupae in soil where brassicas grew.

Pull salad radishes young - under an inch across

Start pulling spring types about three to four weeks after seeding, when the roots are the size of a large marble and still under an inch in diameter. Pull at usable size rather than waiting for bulk. Storage radishes come out around 60 days and keep three to four months at 32F and 95 percent humidity; topped bunching radishes hold three to four weeks at the same conditions. A radish left in the ground past its size goes pithy and turns fiercely hot as the root fibers lignify - the sharp flavor people dislike is almost always a timing failure, not the variety.