Whether you start your celery bedding plants from seeds indoors or purchase bedding plants from your local nursery, plant the celery plants outdoors in early spring. Because celery plants require an extended and cool growing season, place them in the soil outside several weeks before the last spring frost. Approximately three to four months after transplanting, the entire celery plants will be ready to harvest.
Prepare the growing area in the spring as soon as the soil is workable. Cultivate the soil down to a depth of 4 to 6 inches with the garden spade. Add 1 to 2 inches of compost to the top of the soil and work this in carefully with the spade. Sprinkle the granular fertilizer over the soil (consulting the package for recommendations for amounts for the size of your growing areas). Work the fertilizer into the soil with the spade. Rake the soil surface smooth.
Harden off the celery bedding plants for one to two weeks before you transplant them outdoors. Place the bedding plants outdoors in a sheltered area for approximately three hours in the middle of the afternoon on the first day and then bring them back indoors. Gradually over the next week or two, lengthen the amount of time you leave the celery plants outdoors and also move them to an area where they are less protected from sun and wind. At the end of the hardening-off period, the celery plants should be inside only during the overnight hours.
Dig holes for the celery plants in the prepared growing area. Make the holes 8 inches apart and deep enough so the celery plants will be at the same depth as they are in the temporary containers.
Remove the celery plants from their temporary containers. As you hold the plants to transplant them, remove two or three of the outer-most leaves. This will encourage the celery plants to grow actively once you place them into their permanent location. Firm the soil gently around the celery plants to finish planting them.
Water the celery plants generously immediately after transplanting them. Never allow the soil around the celery plants to dry out over the course of the growing season. Celery plants need abundant water to ensure they do not become tough.
Place a 2-inch layer of mulch around the celery plants when they reach 6 inches high. The mulch will conserve soil moisture and prevent weeds from encroaching on the plants.
Pull weeds by hand when you see them. Celery roots are exceedingly shallow and you must weed carefully to avoid damaging the roots of the celery plants.
Fertilize the celery plants with the all-purpose fertilizer once per month starting one month after you transplant them. Mix the fertilizer with water according to package recommendations for the size of your growing area. Pour the fertilizer carefully around the base of the celery plants.
Harvest celery throughout the summer. Clip off the outer-most celery stalks as needed and leave the main plant to continue growing. At the end of the summer, pull the entire celery plant from the ground and remove the roots.