How to grow radishes

This is the radish complaint, and it has three separate causes. Most guides name one.

The first is crowding. Radish seed is large enough to handle and small enough to over-sow, and a crowded row makes leaves competing for light instead of roots. They need about two inches each, which looks absurdly generous when the seedlings are up and is not. Thin at the seedling stage — within a week or so of emergence — and eat the thinnings.

The second is heat. Radish is a cool-season crop, and above about 75°F it stops making a root and runs to flower instead. A summer sowing produces exactly the tall leafy plant people describe, no matter how well thinned. This is why the crop belongs to spring and autumn, and why sowing every fortnight from midsummer is wasted seed.

The third is nitrogen. Ground freshly manured or heavily fed produces lush foliage at the expense of the root, in a crop where the root is the point. Radishes want ordinary, unenriched soil, and they are one of very few things that genuinely do better in ground you have not improved.

So the fix is: thin properly, sow in cool weather, and do not feed them.

Direct sow only — a radish is a root and it will not transplant.

Sow half an inch deep, about an inch apart, in rows ten inches apart, and thin to two inches. Our figures sit close to the 1912 hand-cultivation column, which gives rows twelve to eighteen inches apart at eight to twelve plants to the foot.

Sow a short row every ten days or two weeks from early spring, and stop when the weather warms. A radish row that all matures at once gives you far more radishes in one week than anybody wants, and they do not hold in the ground.

Start about four weeks before your last frost — they tolerate real cold — and resume in late summer for an autumn crop, which is often better than the spring one because the plants size up as the weather cools rather than as it heats.

The old trick of sowing radish along a row of slow-germinating carrots or parsnips is worth doing. The radishes come up in days and mark the row, and they are pulled and gone before the carrots need the space.

A radish has a narrow window. Left in the ground past its size it turns woody, hollow, unpleasantly hot, and eventually splits.

Check by scraping soil from the shoulder of one rather than pulling at random. Spring types are best at about an inch across, and there is nothing to gain by waiting.

Heat and drought both make them hotter. A radish grown fast in cool moist soil is mild and crisp; the same variety grown slowly in dry summer soil is fierce. If yours are too pungent, the answer is a cooler sowing date and steadier water, not a different variety.

Do not throw the tops away. Radish leaves are edible, peppery, and good cooked like any other brassica green — which is worth knowing given how much leaf the crop makes.

And if a few bolt, let them. The seed pods that follow are crisp, hot and excellent raw, and some varieties are grown for the pods alone.

Flea beetle is the one you will see: tiny black beetles that jump when disturbed and pepper the leaves with small round holes, exactly as in the photograph at the top of this page. On most brassicas that is a real problem. On radish it usually is not — the crop is so fast that the plant outgrows the damage, and the part you eat is underground. Heavy attack on seedlings can check them, and floating row cover from sowing prevents it entirely.

Cabbage root fly is the one that matters, because its maggots tunnel the root itself. The damage is invisible until you pull a radish full of brown channels. Fine mesh from the day of sowing is the effective control, along with rotation away from where brassicas grew.

Slugs take seedlings in a wet spring, which in a maritime climate is most springs.

Rotation deserves a note that beginner guides skip: radish is a brassica. It belongs in the same rotation group as cabbage, kale, broccoli and turnip, and following one with the other concentrates exactly the pests both share. It is easy to forget because radish looks nothing like a cabbage.

Everything above is about the small fast spring radish. There is a second group, and it is a genuinely different crop.

Winter radishes — Black Spanish, daikon, the large Chinese sorts — are sown in mid to late summer, take two or three months, grow to the size of a parsnip, and store for months in damp sand or in the ground under mulch. They are milder and denser than spring radishes and are used cooked, pickled and grated as much as raw.

Burr treats them as their own category in 1863, splitting his twenty-eight varieties into spring-and-summer and autumn-and-winter groups. Eight of his are winter types. They quietly left American gardens over the following century and never left Asian ones, which is why a daikon is easier to buy than to find on a seed rack.

They are worth trying for a practical reason as well as a historical one: sown in late summer, they occupy the gap after an early crop comes out, and they are one of very few things that will give you a substantial root harvest from an August sowing.

Daikon is also grown as a soil crop — a deep-rooting cover that punches through compaction and then rots in place over winter, which is the tidiest use of a vegetable most people never eat.