Radish

Origin & history

Radish and mooli are botanically the same species — the little radish is simply the small, fast-swelling selection from it. While the large mooli was already grown in ancient Egypt and Rome, the round red radish only turns up in French and German gardens in the 16th century. Its heat comes from mustard oil glycosides that are only released when the root is cut or chewed — the same group of compounds that gives cabbage and mustard their flavour.

Varieties

Alongside the round red varieties like “Saxa” or “Cherry Belle” there are red-and-white tipped ones like “French Breakfast”, long white ones like “Eiszapfen” and yellow and purple types; they differ less in taste than in looks. What matters is the sowing period printed on the packet: early varieties are bred for the cold frame and March, summer varieties stay firm longer and bolt later, autumn varieties are meant for the second sowing. An early variety sown in June will almost inevitably go pithy.

Care

Radishes need four to six weeks of uninterrupted growth — any check makes them hot and pithy, so water a little every day rather than a lot at once. Rows sown too densely give nothing but leaf: thin to 4–5 cm as soon as the first true leaf appears. Do not sow the whole packet in one go but a short row every ten to fourteen days, or everything comes ready at the same time. After heavy rain scratch open the crust that forms on the soil surface.

What can go wrong

Flea beetles punch fine holes in the seed leaves in dry warm weather and can bring a whole batch to a standstill; they avoid moist soil, so regular watering, shallow hoeing and fine-mesh netting from the day of sowing all help. Radishes are brassicas and belong in the cabbage rotation — do not sow them after cabbage, rocket or a mustard green manure, or clubroot builds up. Split or hollow roots come from harvesting too late or from a lot of water after a dry spell.

Harvest, storage & kitchen

Radishes are only at their best for a few days — pull them as soon as the shoulder shows 2–3 cm and do not wait for the neighbour to get bigger. Twist the leaves off straight away or they keep drawing water out of the root; wrapped in a damp cloth they keep about a week in the fridge. Young leaves can be used like a herb in soup or pesto. If you let a row flower you can pick the green seed pods — they taste as hot as the root and are eaten raw.

Frequently asked questions

Why are my radishes flowering instead of forming roots?

That is bolting: heat, long days and dry soil from June onwards push the plant straight into flower. The root stays small and woody and will not turn tender again. Pull those plants and wait until August for the next batch.

When can I harvest radishes?

From the spring sowings between mid-April and the end of June, and from the late-summer sowings between mid-September and late October. The first March batches need a good six weeks in cold soil; a May batch in warmth often takes only four.

Do radishes tolerate frost?

Light frost, yes — which is why sowing works from March under fleece or in a cold frame. They are not winter hardy though: sustained hard frost turns the roots glassy, so the last autumn pickings should be indoors by the end of October.

Do radishes work in a window box?

Yes, they are among the most rewarding crops for a box. Around 15 cm of compost depth is enough, sow 1 cm deep and thin later to 4 or 5 cm. In midsummer the box does better in part shade than in full southern sun.