Vegetable · Apiaceae
Celeriac
Apium graveolens var. rapaceum
Give it a long season, rich soil, and water that never quits, and celeriac rewards you with a knob no store can match.
Full sun
Every 2–4 days
50–77°F · 10–25°C
100–120 days
Overview
Celeriac is celery grown for its root instead of its stalks. It belongs to the carrot family and shares its species with ordinary celery, but breeding has pushed all the plant's energy into a swollen, knobby base rather than crisp stems. Underneath the rough skin sits dense, ivory flesh that tastes of celery with a nutty, earthy edge.
This is a vegetable for the patient gardener. It runs slow from a fussy seed and needs a long season of 100 to 120 days, plus steady moisture the whole way through, before the knob fills out. Rush it or let it go dry and you get small, fibrous roots, which is why celeriac earns its reputation as demanding.
The payoff is a vegetable that stores for months and brings deep flavor to soups, mashes, and roasts. Get the basics right and one plant gives you a knob the size of a fist or larger, ready to keep well past the first frosts.
Care
The short version: full sun and rich, deep soil, water that keeps the ground evenly moist all season, a monthly balanced feed, and the patience to give it a full 100-plus-day run.
Light
Celeriac wants full sun to bulk up a good knob, though it will take a little afternoon shade where summers run hot. Skimp on light and the plant simply grows slower across an already long season.
Water
This is the make-or-break factor. Celeriac is a heavy drinker that needs the soil kept evenly moist for the entire season, often a deep watering every 2 to 4 days. Let it dry out even briefly and the knobs come up small, hollow, or cracked.
Soil
Plant in rich, deep loam packed with organic matter that holds water without turning soggy. A pH between 6.0 and 7.0 suits it well, and digging in plenty of compost keeps both the moisture and the feeding it craves close to the roots.
Temperature
Celeriac grows best in the mild range of 50°F to 77°F (10°C to 25°C). Cold snaps below about 50°F (10°C) on young plants can trigger bolting, so warmth at transplant time matters as much as warmth through summer.
Humidity
Ordinary garden humidity, somewhere around 40% to 70%, is all it asks for. Far more important is keeping the foliage from staying wet, since crowded, damp leaves invite the blights that plague this crop.
Feeding
Celeriac is a heavy feeder that wants a balanced fertilizer with steady nitrogen, fed about once a month right through the growing season. Rich soil and regular feeding are what carry the plant through its long run to a full-sized knob.
Pruning
There is little to do here. Pull off any lateral side shoots, and late in the season strip the lowest, oldest outer leaves to expose the crown of the knob. Never cut the central foliage, since that is what feeds the swelling root.
Repotting
Not applicable; grown in the ground or large beds, not as a container houseplant
Size & spacing
Plants reach 1.5 to 3 feet (46 to 91 cm) tall and 12 to 18 inches (30 to 46 cm) across. Set them close, about 6 inches apart in the row, which trials have shown actually produces the largest marketable roots.
When to plant
Celeriac asks for the whole growing season, so the calendar matters. Start seed indoors in late winter, set sturdy transplants out only after the last frost has passed and the soil has warmed, then harvest the knobs from late summer into fall before a hard freeze sets in.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 8-10 weeks before the last spring frost; seed is slow to germinate, surface-sow and keep warm and moist
- Plant: Transplant after the last frost once soil has warmed and seedlings are sturdy (late spring)
- Harvest: Harvest from late summer into fall once knobs reach 3-4 inches across, before a hard freeze
Hardiness
USDA hardiness zones: 4–9
Temperature: down to -34°C
Troubleshooting
Most celeriac trouble shows in the size of the knob or the state of the leaves, and the cause is usually water, cold, or crowding. Read the early signs below and match them to what you see. Catching a problem early is the difference between a fist-sized root and a fibrous dud.
A tall flower stalk shoots up and the knob turns woody
This is bolting, and it traces back to a cold spell that tricks the biennial into thinking a winter has passed. Once a plant throws up a seed stalk, the root stays small and fibrous and will not recover, so pull it and start over. The cure is patience at planting: keep transplants warm and don't rush them into cold ground.
Fix:
- Pull and discard bolted plants; the root will not improve
Knobs come up small, split, or hollow inside
Almost always this is thirst, since celeriac drinks hard across its long season and a dry spell stalls the swelling for good. A shortfall of boron can also hollow and brown the center, and crowding or too short a season leaves the roots stunted. Water deeply and steadily, feed well, and give each plant about 6 inches of room.
Fix:
- Maintain even deep watering
- Ensure adequate fertility and balanced micronutrients
- Allow the full long season and proper spacing for bulking
Brown and gray spots spread across the leaves
A fungal leaf blight, usually Cercospora or Septoria, takes hold when the foliage stays wet and crowded. Strip off the marked leaves, open the planting up so air can move, and water at the base instead of over the top. Rotating where you grow celeriac each year keeps the spores from carrying over.
Fix:
- Remove affected foliage
- Improve spacing and air flow
- Water at the base rather than overhead
Leaves turn chewed, curled, or sticky to the touch
The sticky shine points to aphids and the honeydew they leave behind, while ragged holes usually mean celery worm, slugs, or earwigs working the tops. None of this touches the root you are after, so hand-pick the caterpillars and slugs and hose the aphids off. A vigorous, well-watered plant shrugs most of it off.
Fix:
- Hand-pick caterpillars and slugs
- Hose off or treat aphids as needed
Toxicity
Celeriac is a food crop and carries nothing that poisons pets, livestock, or people. The root is safe for everyone, and the only mild catch sits in the leafy tops: their natural furanocoumarins can leave sensitive skin sore after handling them in bright sun. Slip on gloves for that one job and you have nothing to worry about.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
No toxins here. A cat that nibbles a leaf might get a brief stomach upset from the unfamiliar greens, nothing more.
Dogs None
Safe for dogs, leaf and root alike. Plain cooked celeriac even shows up in some homemade dog meals.
Horses Safe
Horses can graze or be fed celeriac without worry, since the plant carries nothing that harms them.
Rabbits Safe
Both the leafy tops and the root are fine for rabbits in sensible amounts, offered as part of a mixed diet.
Livestock Safe
Cattle, goats, and sheep handle celeriac with no trouble; it is grown as food, not a hazard to the herd.
Birds Safe
Backyard chickens and other birds can pick at the tops and trimmings safely.
People Safe
The root is a fine food cooked or raw. The one small catch is the foliage, which holds furanocoumarins that can leave sensitive skin sore after handling the tops in bright sun, so wear gloves and wash up afterward.
Like other Apiaceae (celery, parsnip), the foliage contains furanocoumarins (psoralens) that can cause mild phytophotodermatitis in sensitive people who handle the tops in bright sun. This is milder than parsnip and is a minor handling note, not a pet-poisoning risk.
Varieties
Celeriac cultivars differ mostly in size, smoothness, and how cleanly the flesh stays white inside. A few names turn up again and again in gardens and trials.
Balena
A vigorous, heavy-cropping pick that grew the largest marketable roots in University of Maine trials, especially when set at a close 6-inch spacing.
Brilliant
A solid mid-season grower with smooth, rounded roots that resist the internal browning celeriac is prone to.
Diamant
Smooth-skinned roots that show little browning inside and keep well in storage.
Giant Prague
The classic heirloom, prized for large, globe-shaped roots carrying relatively few of the side rootlets that make peeling a chore.
How to propagate
Celeriac is grown one way, from seed, and that seed is the hardest part of the whole crop to coax along.
SeedModerate
Start indoors 8-10 weeks before the last spring frost · Roughly 2-3 weeks to germinate and about 10 weeks to reach transplant size before setting out
Celeriac is grown from seed, and it tests your patience from the start. The seed is tiny and slow, taking 2 to 3 weeks to sprout, so surface-sow it with light, keep it warm and evenly moist, and start a full 8 to 10 weeks before your last frost. Count on about 10 weeks to reach transplant size, then harden the seedlings off before they go out.
Myths
Celeriac is a completely different plant from celery.
They are the same species, Apium graveolens, just bred for different parts. Celeriac is the root-grown variety rapaceum, while the familiar stalk celery is variety dulce, so the two are close kin rather than strangers.
The knobby edible part is a true root.
That swollen knob is mostly an enlarged hypocotyl and stem base, not a single taproot. The actual fibrous roots are the stringy bits trailing off its underside.