How to Grow Celery in Australia

Celery (Apium graveolens) belongs to the carrot family, Apiaceae. It is grown for crisp stalks, aromatic leaves and, in celeriac, a swollen stem base. One species gives all three: stalk celery, leaf celery and celeriac. It is a slow crop, often four to five months from sowing to whole plants. What trips most gardeners up is water: celery that goes dry turns stringy and bitter.

Three mistakes that matter

1. Letting the soil dry out. Celery has a small, shallow root system, and any water stress makes the stalks stringy and strong-flavoured. Soak the soil thoroughly at every watering and keep a thick mulch over the bed.
2. Chilling young plants. Young plants held below about 13°C for ten days or more can later run to seed (bolting, early flowering that ends the crop). Plant out once nights stay above 10°C, and cover young plants in a cold snap.
3. Burying the seed. Celery seed is tiny and needs light to germinate, so seed sown at the usual depth often never appears. Press it onto the surface of the mix and cover it with no more than a dusting.

When to plant

Celery grows best while days run between 12°C and 24°C, so the cue is mild weather at both ends of the crop. Seed needs at least 15°C to germinate, which is why it starts in trays at least six weeks before planting out. Most gardens fit one or two sowings a year.

In Melbourne and the cool zone, Melbourne Cup weekend is a sound marker for planting out spring-raised seedlings. At the hot end of any window, pick outer stalks early rather than waiting for full-sized plants.

Site, soil and setup

Follow a four-year rotation, keeping celery out of beds that recently grew celery, celeriac, carrots or parsnips.

Container growing

Celery does well in a large pot, and self-watering pots or a wicking box take care of its thirst. Allow at least 20 L and 30 cm across for each stalk celery or celeriac plant, filled with premium potting mix. Leaf celery 'Amsterdam', 'Light Green' and 'Tender Crisp' suit pots best, since none needs blanching.

• Water: pots dry out much faster than beds, so check them daily in warm weather and never let the mix dry.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly from two weeks after planting.
• Position: full sun in winter; afternoon shade on hot days.

Sowing Seeds

Raise celery in trays or punnets and plant out seedlings at about six weeks from emergence.

Choosing a variety

Starting in trays

• Fill punnets or cell trays with fine seed-raising mix and water it first.
• Sprinkle seed on the surface, press it in, and dust it with mix no deeper than 3 mm.
• Stand the punnet in a tray of shallow water until seedlings appear, then lift it out so roots do not rot.
• Keep it warm, ideally 15°C to 25°C; seedlings usually emerge in 14 to 21 days.
• When seedlings have two true leaves, prick them out into individual cells or small pots.

Planting out

• Plant out at about six weeks from emergence, when seedlings have three or four true leaves and stand near 10 cm.
• Harden them off first (gradually getting seedlings used to outdoor life). Cut back water for 7 to 10 days, but never chill them; see hardening off seedlings.
• Space plants 20 to 30 cm apart in a block rather than a single row, so they shade each other's stalks.
• Set the crown at soil level, not buried, and water in with seaweed solution.

Care by growth stage

Steady moisture and regular feeding decide the crop, because celery is a heavy feeder with a small root system. Weeks count from planting out.

If you prefer a conventional feed, mix a controlled release granular (NPK 12-3-8 to 14-5-10) into the soil at planting. During leafy growth, use an all-purpose soluble (NPK 23-4-18 to 27-5-9) fortnightly. As stalks fill, change to a higher-potassium soluble (NPK 15-4-26 to 15-5-20), also fortnightly.

Hilling and Mounding

Blanching, which means shading the stalks from light, makes them paler, milder and more tender. It is optional: unblanched celery is stronger in flavour and suits soups and stock.

• Start once plants stand about 30 cm tall, usually two months after planting out.
• Gather the stalks and tie them loosely, so no soil falls into the heart.
• Wrap each plant in a collar of cardboard, thick paper or a milk carton with both ends cut off, leaving the leaves in the light.
• Alternatively, mound soil up around the stalks for the last 3 to 4 weeks before harvest.
• Skip blanching for 'Tender Crisp', 'Light Green' and leaf celery.

Celery sap can cause a skin rash, especially on sunny days. Wear gloves and long sleeves while tying, wrapping and picking.

Celeriac

Celeriac grows like celery until late in the season, when the stem base swells. Its care differs in a few ways:

Companion planting

Good neighbours for celery come from other plant families, which share neither its leaf diseases nor the soil problems of the carrot family.

Grows well with

• Cabbage and other brassicas, which belong to a different family and want the same rich, moist bed.
• Onion, from another family again, which carries neither celery leaf spot nor celery mosaic virus.
• Tomato, from a different family, so it carries none of celery's leaf spots.

Keep apart

• Carrots, parsnips and parsley, carrot-family relatives best kept to their own rotation so family pests and diseases do not build up.
• Sweet corn, whose tall growth shades low celery plants.

Harvesting Stalks

Pick outer stalks once they reach about 30 cm, usually 12 to 14 weeks after planting out. Take whole plants at around four to five months from sowing, before stalks turn pithy or the outer leaves yellow.

• Snap outer stalks off at the base with a sideways pull, leaving the heart to keep growing.
• For a whole plant, lift it with a fork once the base is 7.5 cm or more across.
• Cut leaf celery and 'Light Green' sprigs as needed, leaving the centre to regrow.
• Lift celeriac with a fork and trim the leaves to 2 to 3 cm.
• Pick in cool weather where you can: stalks picked in hot, dry spells can be tough and bitter.

Celery keeps in the fridge for up to two weeks. Air-dry leaf celery sprigs to keep their flavour for longer. Celeriac lasts several weeks in a perforated bag in the fridge, or 4 to 6 months in damp sand at 0°C to 5°C. Eat stalks raw or braised, use leaves to flavour soups and stews, and mash or grate celeriac.

Common problems

Slow start after planting out. Celery puts on most of its growth in the last third of its life, so small plants for the first two months are normal.

Black heart. The youngest centre leaves die and blacken when calcium cannot reach them, which follows uneven watering; keep soil moisture steady.

Cracked stalks. Splits across the leaf bases, with the tissue curling back, point to boron deficiency; a soil test confirms it before any correction.

Pithy stalks. Stalks left too long on the plant turn pithy, so pick them while they are still solid and juicy.

Flower stalks. A bolting plant has usually been chilled when young, as described in Three mistakes. A biennial, celery also flowers after a cold winter.

Pests and diseases

Most celery troubles start small and spread in wet or crowded conditions, so check plants weekly. Use only sprays whose label names celery, and keep to the withholding period.

Green peach aphid (Myzus persicae). Colonies under the lower leaves suck sap and spread celery mosaic virus. Hose them off with a strong jet or spray insecticidal soap, and encourage ladybirds and lacewings. Read more

Cotton bollworm (Helicoverpa armigera). These caterpillars, also called heliothis, are the main insect pest of celery; native budworm looks alike and is managed the same way. Spray a Bacillus thuringiensis (Bt) product while caterpillars are small.

Cutworm (Agrotis species). Young plants are cut through at ground level overnight. Scratch the soil around the stump to find the curled caterpillar. Read more

Celery leaf spot (Septoria apiicola). Small brown spots, dotted with tiny black specks, spread up the plant in wet weather and can strip it. The fungus travels on seed and splashing water, so remove spotted leaves and water the soil, not the leaves.

Early blight (Cercospora apii). Yellow spots on older leaves enlarge into grey-centred patches that dry and turn papery in wet weather. Space plants widely and clear old crop remains after harvest.

Celery mosaic virus. Leaves show a light and dark green mottle, turn narrow and crinkled, and plants stunt with a flattened top. Sprays do not cure a virus, so pull infected plants and keep aphids down. Read more

Prevention first

• Raise seedlings in fresh seed-raising mix and clean trays.
• Water at the base in the morning so leaves dry quickly.
• Pull wild celery family weeds and old celery plants, which can carry the virus.
• Bin spotted leaves and finished plants rather than composting them.

Tips

1. Sow a second tray three or four weeks after the first, so the harvest runs on for longer.
2. Stalk celery, leaf celery and celeriac are one species and cross when they flower, which happens after several weeks of cold. To save seed that comes true, let only one kind flower.
3. Plant celery near a tap or beside a path you use every day. A crop this thirsty does best where watering is never forgotten.