Celery requires a long growing season, lots of water and prefers cooler temperatures. It is a biennial plant (Apium graveolens) of the family Umbelliferae or parsley family, It was first cultivated for medicinal use, then (during the Middle Ages) as a flavouring and finally as a food, chiefly for soups and salads; the seeds are still used for seasoning.
As celery requires a great deal of water, it does best in soil, which is water retentive. The bed where celery is to grow should be prepared during December or January, if of course weather permits. Dig out a trench 1½ ft. (45cm) wide and 16 in. (406mm) deep. Put the soil on either side of the trench so that two ridges are formed. Smooth out the top of each ridge with the back of the spade and pat down slightly to make it firm.
The top of the ridges is the perfect place to sow a catch crop such as radish, lettuce or spinach, which will allow the vegetable garden to be made full use of the available space. Ridges should have at least 2½ ft (75cm) between them.
Into the bottom of the trench put a 6-inch layer of well-rotted manure and compost. On top add 5 in (127mm) of soil this should fill the trench to within 6 inches (15cm) of surface level. Apply fish manure over the soil at a rate of 4 oz. (120g) to the yard run. As the celery grows it will require several feeds with liquid manure to bust up the growth.
Always purchase disease-free seed that is resistant to blight because celery is particularly susceptible to this disease. Sow the seeds in the middle of February in trays of seed compost at a temperature of 60 to 65 deg F. (16 to 18deg C.) in a greenhouse. Cover the tray with a piece of glass which should be lifted each day and the underside wiped dry.
As soon as the seedlings are through the glass should be removed completely. When the seedlings are about ½ in. (12mm) high, prick them out and plant into 3 in (76mm) deep pots in potting compost.
The pots should remain in the greenhouse until late April early may when they can be taken outside and put into a cold frame to harden off. If it is not possible to start them in a greenhouse they can be sown outside under cloches in late March or early April. Leave the seedlings growing under the cloches until they are planted out into the trenches.
The plants should be about 3 or 4 in. (76mm-101mm) by early June, that is the time to plant them into the trenches. In the centre of the bottom of the trench, make holes with a trowel 1 ft. (30cm) apart then plant the young celery plants, firming in the roots. Half fill the trench with water after planting to ensure that the roots are in firmly.
If the weather is dry, soak the trench again in ten days after planting out; this will prevent the roots from drying out, as this must not be allowed to happen. After a month, start to use a liquid feed every ten days. Keep the area free from weeds and remove any side growths coming up from the base of the plants.
It is important to cover the tops of the plants with straw, then over the straw place cloches in readiness for winter protection; it will prevent water from trickling down into the celery hearts, as this will inevitably rot the celery from the insides.
Begin to earth up the plants in the middle of August when they reach about 1 ft. (30cm) high. Use the soil from the top of the ridges to add into the trenches to a depth of 6 in. (15cm). To avoid soil from falling into the centre of the plants between the stems, take hold of the plant in one hand, bringing the stems together, whilst pushing the soil around them with the other.
The next earthing up can be done about three weeks later. Pat the sides of the earthed up trench with the back of the spade so that they are sloping smoothly away from the plants. This will help the rain to run off without soaking the top. The third earthing up is done in October and again ensure that the sides are smooth and steep.
Water is required at the roots of the plants; therefore a length of pipe inserted into the ground close by each plant will allow the water when poured down the pipe to reach the roots.
Celery stems should be white before they are eaten. To achieve this, it will take about 8 weeks after earthing up has begun. When removing celery, make sure that soil is put into its place so that the ridge will not break up and so expose the adjacent plant.
Self-Blanching Celery This type of early celery has less flavour and is less hardy than the other. It is grown for use in September and October and must be cleared before any risk of frost. The seed is sown at the end of March, early April and it is ready to use at the end of August – October.