If you only need a small amount of celery, simply snip off single ribs one at a time as needed. Be careful not to damage other ribs, as damaged areas could introduce bacterial or fungal infections into the plant. You can also pull ribs away from the plant, but be careful not to uproot the plant as you do so.
Not only will you have less waste when you harvest only what you will use, but the plant will also have the opportunity to grow additional ribs through the growing season. This could double your production from the same growing space.
For celery that will be used immediately, cut plants off at ground level close to the roots. Leave a portion of the base of the plant to hold stalks together. If you intend to store celery for a longer term, pull the plants up by the roots. The roots will help the plants last much longer in storage.
Many gardeners prefer to blanch their celery before harvesting. This lightens the stalks, making them tender and delicately flavored. Some bank soil around celery, but this can lead to slug infestation. Others wrap the plants in bands of newspaper or tar paper and secure with rubber bands.
For long-term storage, stand celery bunches with roots in boxes of damp sand. Keep the boxes in a dark place at a cool temperature. You can also store celery inside a trench dug in the ground. In colder climates, the trench should be under a cold frame where the soil will not freeze. Keep stalks dry, but moisten the roots regularly.