Celery

Light and exposure

Celery wants light and mild warmth, without excess. A sunny to lightly shaded spot during the hottest hours suits it well, all the more so because scorching full sun quickly dries out a soil that must be kept moist. Allow at least five to six hours of daylight a day.

Avoid overly confined corners where the air does not move: foliage that stays wet encourages leaf diseases. Look for the compromise, a bright but cool spot where the earth does not bake at the first July ray.

Watering

This is the crucial point. Celery descends from a marsh plant and demands soil that never dries out, from transplanting to harvest. A shortage of water, even brief, is paid for dearly: the ribs of stalk celery turn stringy and hollow, and the root of celeriac stays small and fibrous. Water generously and regularly, every day in strong heat if need be.

A good mulch at the base works wonders here: it holds the moisture, limits evaporation and spares you some of the trips with the watering can. In cool clay ground, nature helps you, but keep an eye on the dry spells of high summer all the same.

Soil and repotting

Celery is one of the hungriest vegetables in the garden. It calls for deep, rich, humus-filled soil that above all can hold water. Work in a good dose of ripe compost or well-rotted manure the previous autumn or at planting: it asks for more.

Heavy, cool ground, which would keep any other vegetable too wet, suits it perfectly. On light, sandy soil that dries fast, you have to make up for it with generous additions of organic matter and steadier watering. Aim for a neutral pH and a loose structure at depth, especially for celeriac, which must swell without obstacle.

Temperature and humidity

Celery likes coolness and mildness, between 15 and 20 degrees it feels at home. It dreads both dry heat, which makes it bolt, and the sharp cold of early season. A young plant exposed too soon to low temperatures, below 10 degrees for several days, takes a hit and risks flowering prematurely instead of forming ribs or a root.

That is why you do not put it out too fast. Wait until the nights warm up for good, above 10 degrees and the last frosts past, to transplant into open ground. At the other end, celery withstands the first autumn colds and is harvested before the hard frosts, which do damage the ribs and the root.

Pruning and upkeep

Celery is not pruned as such, but stalk celery calls for a particular gesture if you want tender, pale ribs: blanching. As harvest approaches, you deprive the base of the stalks of light so it stays pale and loses its bitterness. The simplest method is to earth up soil around the base, or to wrap the ribs in a sleeve of cardboard or paper, two to three weeks before harvesting.

For celeriac, the work is different: gradually clear the soil around the ball as it swells and remove the lateral roots that appear on the sides, to obtain a fine, regular root. In both cases, remove the yellowed outer leaves as the season goes on.

Pests and diseases

The disease to watch closely is septoria leaf spot, a fungus that covers the foliage with small brown spots ringed with yellow, sometimes speckled with black dots. It explodes in mild, damp weather, the profile of a cool oceanic summer and autumn, and can strip a plant bare if you let it run. To hold it back: space the plants, water at the base without wetting the foliage, remove and destroy affected leaves, and practise rotation.

Other troubles complete the list. The celery fly lays in the leaves where its larvae dig pale galleries; an insect-proof mesh protects effectively. Rust and boron deficiency, which hollows and browns the heart of the root, also occur. Slugs and snails, finally, love young plants freshly transplanted.

Propagation

Celery is propagated from seed, and it is the stage that demands the most care. Its seeds are tiny, slow to germinate, and they need light to come up: never bury them, lay them on the surface and press them barely into the compost. Sow early, from February or March, indoors in the warm between 18 and 20 degrees, because the crop is long and emergence can take two to three weeks.

Keep the sowing constantly moist and well lit until emergence, a transparent cover helps hold the air humidity. Then prick out into individual pots, harden the plants off gradually, and set them in open ground only after mid-May, once all risk of a cold snap is past. Space them 30 to 40 centimetres apart. For stalk celery, plant level with the soil without burying the heart.

Month-by-month care calendar

Green Hub tips

• Never cover celery seeds: they need light to germinate, lay them on the surface and press them barely in.
• Water is everything: soil that dries out gives hollow, stringy ribs and a stunted root. Mulch and water without ever letting thirst set in.
• Do not transplant before the nights stay reliably above 10 degrees: a cold snap on a young plant makes it bolt instead of forming ribs or a root.
• Blanch stalk celery by earthing up or sleeving the plants two to three weeks before harvest, for pale, mild ribs.
• Against the septoria that damp weather loves, always water at the base, air the plants and quickly remove leaves spotted with brown.