Radish Plant Growth Stages: Seed to Seed in Six Weeks

Six stages in about five weeks. Knowing which one a plant is stuck at is how you work out what went wrong, which is usually one of three things.

The six stages

Germination, 3 to 7 days

Among the fastest of any garden vegetable, and reliable enough that radishes are commonly sown as a row marker alongside slow germinators like carrots and parsnips — they mark the line within a week and are harvested long before the carrots need the space.

Cotyledons, 5 to 10 days

Two heart-shaped seed leaves, bright green and smooth. These are not true leaves; they are the seed’s own food reserve unfolding, and they look nothing like the adult plant.

This is the moment to thin. Everything that goes wrong with radishes later is decided here.

True leaves, 7 to 14 days

Oval, rough or bristly to the touch, often lobed. These do the actual photosynthesis, and once they are established the plant starts building a root.

Root swelling, from about day 10

Technically the swelling is the hypocotyl — the stem section between the seed leaves and the root proper — rather than the root itself. It pushes up slightly as it expands, which is why you can scrape a little soil away and see the shoulder.

Harvest, 21 to 30 days

About 2.5 cm across for round salad types. The window is short — days, not weeks — and in warm weather a perfect radish becomes a pithy one inside a week.

Bolting, from around day 35

A central stem rises, the root goes spongy and hollow, and the flavour sharpens considerably. This is the plant moving on, and nothing reverses it.

Why “all leaves and no root” happens

In order of how often it is the cause:

1. Overcrowding. Radish seed is small and easy to sow thickly, and unthinned seedlings compete for light and space, producing a mat of foliage with nothing underneath. Thin to about 2.5 cm apart as soon as the seedlings can be handled. This is the job everyone skips.

2. Too much nitrogen. A bed that has just had a nitrogen-rich feed, or fresh manure, pushes leaf growth at the expense of root storage. Radishes want modest fertility.

3. Heat. Above about 25°C the plant heads for flowering rather than building a root, which is why spring and autumn sowings succeed where midsummer ones often do not.

4. Not enough light. Long, pale, weak leaves and no root means the plants are too shaded.

Timing by type

Winter radishes behave like a different vegetable: slower, far more forgiving of being left in the ground, and storable.

Using the whole plant

Worth knowing, because it changes what a bolted row is worth:

• Leaves — edible at every stage. Hairy raw, excellent wilted, in soup, or as pesto
• Roots — usable as soon as they are worth pulling; mildest when young
• Seed pods — crisp and peppery, formed after flowering. Rat-tail radish is grown specifically for them
• Flowers — edible, and good for hoverflies

A bed that has bolted has not failed. It has moved on to a different crop, and the pods are genuinely good.

Succession, which is the real technique

Salad radishes go from perfect to pithy within a week, and no household eats three metres of them in that window.

Sow a 60 cm row every two weeks rather than one long row at once. That single habit converts radishes from a crop people grow once and give up on into one that produces continuously from early spring to late autumn.