Celery is often regarded as a tricky crop to grow, usually because the more traditional types need a lot of work and attention. They need to be planted in deep trenches and require layers of soil added regularly to blanch the green stems. Fortunately modern plant breeders have developed strains that do not need earthing up to produce tender white stems due to developing self blanching types. Plants can be grown from seed sown in early spring, although its often easier to buy plugs. Young plants can be planted out in May or June.
Preparing the soil
As Celery has specific needs then preparation is key. Start off by digging over the soil in early spring well before planting, make sure you remove any large stones as well as weeds and add in a generous amount of compost or well-rotted manure (make sure its well rotted as fresh will burn the plants).
About a week prior to planting planting out, hoe in a general purpose granular fertiliser into the surface layer of the bed, follow the manufacturers instructions about the amount needed.
Celery seed is very small, lightly sow the seed across the surface of the seed tray. As the seed is small place the tray in a larger tray of water to wet the soil rather than by watering from above as this will disturb the seeds. Finally cover the seed with a thin layer of vermiculite and place on a windowsill or if you have one in the greenhouse. Remember not to let the soil dry out.
Once the seeds have germinated, these can be pricked out into individual pots once the first adult leaves have grown. Keep the pots watered and about 5 or so weeks later they should be about 8-10cm tall and will now be ready for planting out.
As with all seedlings grown in doors or a green house they need to be toughen up first by placing in a cold frame or if you dont have one take them out during the day and bring them back in at night.
Plant them out into the prepared ground about a foot apart (30cm), Celery grows better if they're planted in a grid-pattern, instead of long rows.
Keep the plants well watered and weed free, additional plant food can be added during the season.
Your celery should be ready for harvesting from August until the first frosts, lift plants as required using a small hand fork, making sure you don't damage nearby plants.