Celery takes around five months to mature. During its long growing season, it doesn’t tolerate high temperatures or frosts – a fussy customer indeed. In the cooler, southern parts of the country, spring until midsummer is the best time to sow celery, while in the warmer, northern regions avoid the hottest summer months and sow from late summer until spring.
The seed is best started in trays (but, in late summer, can be sown in situ, in warmer regions). To get away to a quick start in cooler areas and to maximise the growing season, start seed around eight to 10 weeks before the last expected frost. As seed is fine, mix it with sand to make sowing easier, and cover very lightly with seed-raising mix. If the weather is particularly cold, trays might need to be placed in the airing cupboard or on a heat pad. Germination normally takes between two to three weeks.
Ensure seedlings are well hardened off before planting out, and temperatures are consistently above 12°C. Celery plants need plenty of sun to develop, but, in summer, do best in a site that doesn’t receive the hottest midday sun. Space seedlings 30cm apart, in rows also spaced 30cm apart. Continue to sow at three-weekly intervals for a succession of plants.
If you missed the boat on seed sowing, help is at hand. Punnets of celery are available from garden centres throughout the growing season. Ensure you transplant seedlings carefully or the plants will bolt to seed.
Be vigilant against slugs and snails. They will polish off seedlings quickly, and can lodge between the stems of mature plants and eat into the stalks.
To provide plants with the well-drained, rich, alkaline soil they need, dig in well-aged compost and apply lime, and blood and bone prior to planting, then side dress with blood and bone or apply a nitrogen-rich liquid fertiliser regularly during the season. Firm soil down around the base of plants because they become top-heavy as they mature.
The next task is watering. Celery is a shallow-rooted plant, which, true to its bog plant ancestors, needs to be kept constantly moist. Even a short period drying out will result in a harvest of tough, stringy, dry stalks. A mulch around the base (clear of the stalks) helps keep soil cool and moist in summer. Celery grown in pots needs to be watered at least twice a day in warm weather.
As harvest approaches, varieties of celery with green stalks (such as ‘Elne’) should be blanched (hidden from light to inhibit chorophyll production) to avoid stalks developing an unpleasant, bitter taste. There are a few common ways to do this. One way is to plant the celery in a 20cm deep trench and, starting around three weeks before harvest, fill the trench to about a third of the way up the stem, then cover another third of the stem each week (leaving the leaves uncovered). A second way is to plant celery in a block so plants shade each other’s stalks, then place boards around the outside of the block to shade the outer plants. Probably the easiest approach is to tie newspaper or cardboard around the stems three weeks before harvest. Easier still is to grow a self-blanching type (such as ‘Utah’) with a golden stem, though some gardeners will still blanch such varieties.
If you love the taste of celery, but not its demanding ways, lovage or parcel might be better options. Lovage is a tall-growing perennial in the celery family and its leaves can be substituted for celery in salads and soups, while parcel is a small, mild-tasting variety of wild celery.