Celery is usually planted at the beginning of the year under cover. It needs to be sheltered from the wind, have continual moisture and very rich conditions and it must be protected from frost. A good idea is to put a box around it and fill it with sharp sand or leaf mould, which should keep it protected from frost. Another method would be to create a raised hot bed. Dig but some of the soil and put some well rotted horse manure in the bed followed by the soil on top, then plant the celery and place a fleece on top, this will induce some heat and keep some moisture off, helping the celery grow.