Celery has shallow roots and a shallow container that is 8-10 inches deep works best. Make sure the container has sufficient bottom drainage holes, then place a paper coffee filter over each drain hole to prevent soil from leaching our during watering.
Choose a good quality potting soil mix and fill container halfway with it. Add one cup of compost to the potting soil and mix in well. Plant celery seedling in early spring and/or late summer.
Don’t cover the crown or outer stalks of the celery with the soil, and don’t bury the roots too deeply. Water seedling thoroughly. Add two inches of organic compost on top of soil.
Celery does best when placed in full sun. It also must be kept well-watered and never allowed to to dry out. If the soil dries out, the stalks will be stringy and pithy. Since the plant does require a steady supply of water, placing the container near a water source makes care easier.
In addition to daily watering, use a water soluble fish emulsion, compost tea or other liquid fertilize once a week. To encourage the development of a pale, mild-flavored celery heart you will need to secure the stalks into a bunch for the last two weeks prior to harvesting. A soft hair scrunchie does this job quite well or a strip of pantyhose. By bunching and binding the stalks together, light is prevented from entering the heart of the stalk and they become naturally blanched, creating a paler stalk with a mild flavor.
Cut stalks 2 inches up from ground level with a sharp knife. A new stalk will sprout from the stump left behind. Trim away excess leaves and tough outer stalks, then store celery in refrigerator for up too 2 weeks.