How to Grow Celeriac

Start early or don't start

Celeriac's season is long — UC Master Gardeners plan on 100 to 150 days to maturity — and it will not tolerate being rushed. Sow indoors about 10 weeks before the last frost (the RHS starts in March in a heated propagator around 15°C / 59°F).

Germination is the first test of patience: erratic and slow, up to three weeks. Keep the sown surface lit, warm, and moist, and do not resow in a panic at day ten.

Harden off and transplant once frost danger has passed — late May or early June in the UK — spacing plants about 30 cm (12 inches) apart in rows 40 to 45 cm apart, into soil enriched with compost or rotted manure. Keep young plants above about 50°F; extended early cold pushes celeriac to bolt instead of building a root.

Water is the crop

Celeriac is shallow-rooted and a heavy feeder, and the swollen base only sizes up with unbroken moisture. Keep the top few inches of soil consistently damp all season; UC's guidance is even, regular watering, never letting the root zone cycle between soaked and dry.

The RHS adds the recovery rule: if the soil does dry out temporarily, give one good soaking rather than watering little and often. Mulch helps hold the moisture that this crop refuses to do without.

The hilling question, and harvest

Old guides often say to hill soil over the swelling root to blanch it, and UC's Sonoma County Master Gardeners still describe snipping side roots and hilling up soil over the bulbous root. The RHS advises essentially the opposite: gradually remove the outer leaves when they fall to horizontal, exposing the crown so it can develop, and take off side-shoots as they appear. Exposing the crown is the mainstream modern practice; burying it is optional tradition, not a requirement — and the root swells fine without it.

Harvest begins around October, once roots reach a usable 3 to 4 inches across or larger — lift with a fork. There is no rush: the crop is hardy, the RHS harvests from October through the following March, and flavor strengthens in cold weather (UC notes it improves after a light frost).

For storage out of the ground, trim the tops and pack roots in damp sand somewhere cold — or simply leave them in the bed and lift as the kitchen requires.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• RHS — How to grow celeriac — Start seed in March at 15°C (59°F); germination erratic and slow, up to three weeks; transplant after frost, late May/early June, 30cm apart in rows 40-45cm; keep soil consistently damp and give a good soaking rather than little-and-often if it dries; gradually remove outer leaves when they fall horizontal to expose the crown (rather than earthing up) and remove side-shoots; harvest October through the following March; hardy, flavor develops in ground.
• UC Master Gardener Program of Sonoma County — Celeriac — Plan on 100-150 days to maturity; sow about 10 weeks before last frost; transplant 10-12 inches apart; shallow-rooted, requires even regular watering with top inches of soil kept moist; describes snipping side roots and hilling soil over the swollen root to blanch it; lift roots at 3-4 inches across or larger; flavor increases following a light frost.

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