Celery fits into two groups: blanched and self blanching, and can be Pink, Red, or White.
White matures first, then pink then red.
Self-blanching white or green types that do not require earthing up are less hardy than the others and have a milder flavour.
Generally they perform best in a long cool damp growing season.
Sow seeds of blanching varieties in pots / trays of seed compost and germinate at a temperature of 16°C (60°F).
Pre-soak the seeds overnight prior to sowing.
Germination should take about two weeks.
Prick out the seedlings when large enough to handle into75mm (3") pots of potting compost.
Reduce the temperature to around 10°C (50°F) and grow the young plants in the greenhouse until well-established.
Pricked out Seedlings
Sow seed (under cloches) of self-blanching varieties directly into a pre-prepared seed bed.
Thin out seedlings to 200mm (8") apart when large enough to handle.
Place pricked out seedlings into a cold frame to harden off.
Plant out blanching celery 250mm (10") apart along the previously prepared beds, ensure that the root ball is set firmly then give a thorough watering in.
Surrounding the plants with a bottomless pots / buckets at this stage will offer some protection from the wind and later help to keep the plant/s compact which in turn will help blanching.
Keep the beds well watered, and remove any side-growths that appear from the base during the growing season.
Throughout the growing season feed the plants regularly with a 1:2:2 fertiliser.
When trench celery plants reach a height of around 300mm (12”) high they will need earthing up, or surrounded with tubes or some dark wrapping material to exclude light and assist blanching.
First remove all weed growth from the cropping area, taking great care not to get soil in the hearts of plants.
Soak the plants well if conditions are dry, remove any suckers, then loosely tie in the leaf stalks or wrap them in a paper collar (newspaper will do).
This will prevent the soil getting into the heart of the plant when earthing up.
Plants growing on
Draw up friable (crumbly) soil from either side of the trench to form sloping ridges up the sides of the celery.
Add more at intervals until soil reaches just below lowest leaves.
Allow an interval of about three weeks between each earthing up stage.
Protect the plants with slug bait.
The heads of trench-grown celery are usually sufficiently blanched eight weeks after the first earthing up.
Prepare trenches for planting out the following year's crop in an open sunny position.
Take out a trench 300mm (12") wide, and 600mm (24") deep, placing the bottom layer on one side of the trench and the topsoil on the other.
Fork soil at the bottom 150mm (6") deep and spread a layer of well rotted manure or garden compost.
Break up subsoil as you return it, mixing with it, a bucketful of farmyard manure to each metre (3ft) run and 2 oz of bonemeal.
Similarly when returning top soil, mix in well rotted manure, and add 1 oz. of bonemeal per metre run.
Rake bed over thoroughly in each direction, but don't do this if the surface sticky.
For self-blanching white and green varieties, it is sufficient to dig the plot one spit deep, and dig in liberal amounts of well-rotted manure or compost.