How to Grow Celeriac (Celery Root): Planting & Harvest

Celeriac (Apium graveolens var. rapaceum), also called celery root or knob celery, is the homely cousin of stalk celery grown for its swollen, knobbly, flavor-packed root rather than its stems. That gnarled base hides creamy white flesh with a mild celery-and-parsley taste that is superb roasted, mashed, or shredded raw into winter salads. Celeriac has a reputation for being fussy, but the truth is simpler: it is just slow. With a very long growing season of 100 to 120 days or more, the single biggest key to success is starting seed early and never letting the plants check their growth. This guide covers the long season, starting and transplanting, watering and feeding, and bringing in a clean harvest that stores for months.

Understanding the Long Season

Everything about growing celeriac well comes back to one fact: it is one of the slowest vegetables in the garden, needing roughly 100 to 120 days from transplant — and even longer from seed — to swell a usable root. In most of North America that long window means you cannot simply sow it in the garden in spring and expect a harvest. You must start it indoors early and give it a continuous, unchecked growing season, because any stall from cold, drought, or transplant shock can permanently stunt the root.

Celeriac is grown as a cool-season annual. It loves the cool, moist conditions of spring and fall and tolerates light frost, but it has two temperature traps. Prolonged exposure to cold below about 50°F early in life — for instance, transplanting too soon into chilly soil — can trigger premature bolting, where the plant flowers instead of forming a root. At the other extreme, hot, dry summer weather stresses the plants and produces tough, fibrous roots. The ideal plan is to start early indoors, transplant only when the weather has truly warmed and settled, then carry the crop through summer and into the cool of fall when the roots size up nicely. For another slow, rewarding root crop, compare notes with our guide to growing sorrel.

Starting Celeriac From Seed

Because of that long season, start seed indoors 8 to 10 weeks before your last expected spring frost. Celeriac seed is tiny and slow, sometimes taking two to three weeks to germinate, so patience starts here.

1. Sow seed on the surface of a moist seed-starting mix and press it in lightly — celeriac needs light to germinate, so do not bury it.
2. Keep the mix warm (around 70°F) and consistently moist; a humidity dome or plastic cover helps until sprouts appear.
3. Once seedlings emerge, give them bright light to prevent leggy growth and grow them on at slightly cooler temperatures, around 60–65°F.
4. Thin to one strong seedling per cell, and pot up if they outgrow their starting tray before it is warm enough to plant out.

Roughly a week or two before transplanting, harden the seedlings off by setting them outdoors for gradually longer periods, but protect them from cold snaps — remember that too much chilling now can cause bolting later.

Soil Preparation and Transplanting

Celeriac is a hungry, thirsty crop that rewards rich ground. Choose a site in full sun, or part shade in hot climates, with deep, fertile, moisture-retentive soil. Before planting, work in 2 to 3 inches of compost or well-rotted manure to feed the long season and help the soil hold water. A neutral to slightly acidic pH around 6.0 to 7.0 is ideal. If your soil is sandy and dries quickly, add extra organic matter, because celeriac will not tolerate drought.

Transplant outdoors only after all danger of frost has passed and the soil has warmed to at least 50°F — rushing this step invites bolting. Set plants 8 to 12 inches apart in rows about 18 to 24 inches apart. Plant them at the same depth they grew in their pots; unlike tomatoes, celeriac should not be buried deeply, as the developing root needs to sit at or just above the soil surface. Water them in well and keep the bed consistently moist from day one.

Watering and Feeding Through the Season

If you remember only one care instruction, make it this: celeriac must never dry out. Even moisture is the difference between fat, smooth roots and small, woody, cracked ones. Aim to provide at least 1 to 1.5 inches of water per week, and more in hot or windy weather, keeping the soil evenly damp throughout the long season. A 2- to 3-inch mulch of straw or compost around the plants conserves moisture, moderates soil temperature, and suppresses weeds that would otherwise compete with the slow crop.

To fuel that 100-plus-day push, feed regularly. Work a balanced fertilizer or plenty of compost into the bed at planting, then side-dress with a balanced or slightly nitrogen-rich feed, or water with a diluted liquid feed such as fish emulsion, every 3 to 4 weeks through summer. Steady feeding keeps the foliage lush and the root swelling without interruption. As the season progresses, some growers gently pull soil and old outer leaves away from the crown to expose the top of the root, which encourages a rounder, cleaner bulb — though this is optional.

Common Problems

• Small or woody roots: the classic symptom of too short a season, inconsistent watering, or poor soil. Start earlier, water steadily, and enrich the bed.
• Bolting (flowering instead of rooting): usually caused by a cold spell early in life. Don’t transplant into chilly soil, and protect hardened-off seedlings from cold snaps.
• Cracked or hollow roots: erratic watering — long dry spells followed by heavy soaking. Keep moisture even.
• Hollow or soft heart: can result from boron deficiency in some soils; maintain fertile, well-balanced soil.
• Slugs, celery leaf miner, and carrot fly: the usual celery-family pests. Manage slugs, remove mined leaves, and use row cover early if carrot fly is a known problem in your area.

Harvesting and Storing Celeriac

Celeriac is ready in fall, typically 100 to 120 days after transplanting, once the roots reach 3 to 5 inches across — about the size of a baseball or a bit larger. There is no rush to pull them the moment they size up; in fact, celeriac flavor improves after a light frost or two, and the roots can stay in the ground well into cold weather. In mild-winter areas you can mulch heavily over the row and harvest as needed, while in cold-winter regions it’s best to lift the crop before the ground freezes hard.

To harvest, loosen the soil with a fork and lift each root, then trim off the leafy tops and the long fringe of side roots beneath. Don’t wash off all the soil if you plan to store them — a little clinging earth helps prevent moisture loss. Stored in a cool, humid spot near 32–40°F, such as a root cellar or a perforated bag in the refrigerator, trimmed celeriac roots keep for several months, making it one of the best winter-keeping vegetables you can grow. For another storage-crop project to round out the fall harvest, see our guide on growing vegetables in the Plants & Flowers section.

Celeriac asks for patience and steady moisture more than any special skill. Start it early, never let it dry out, feed it through its long season, and you’ll dig a crop of richly flavored roots that carry the taste of the garden well into winter.