Celery can be a little challenging to grow at home, since it requires a long, cool season and the tiny seeds must be started indoors and carefully tended until they go in the garden. But with a little knowledge and attentive care, you can harvest your own crunchy, tender celery stalks!
Celery should be started indoors in flats about 10-12 weeks before your last frost date. Soaking the seeds in water overnight immediately before planting can help boost germination. Sow the seeds on the surface of the moist soil and press them in gently. You may sprinkle a bit of soil loosely over the top of the seeds to help keep them moist, but do not press down any soil on top of the seeds. Celery requires light to germinate, so burying the seeds entirely will prevent them from sprouting. You’ll usually see sprouts in about a week, but germination can sometimes take up to three weeks.
Prepare a very nutrient-rich garden bed for your celery by mixing in about 4 inches of compost. While plenty of organic matter is a must, well-draining soil isn’t totally essential for celery - in fact, celery is one of few vegetable crops that can benefit from moisture-retentive soil. (Its wild ancestors were bog-dwelling plants.) Once the bed is ready, wait to transplant your celery seedlings into the garden until temperatures are consistently around 50 degrees F and will not drop below 40. Cold temperatures after transplant can trigger early bolting. Make sure to harden off the seedlings before transplanting as well. Space the plants 8 to 14 inches apart. It’s a good idea to keep the seedlings under row cover for the first few weeks to protect them from pests.
Throughout the season, keep your celery crop consistently watered. Be careful when weeding in the bed, since celery roots are very shallow. Mulching around the plants can help prevent weeds and keep soil moisture consistent. Once the stalks are large enough, you can begin harvesting by picking a few stalks from each plant as needed.
Celery (Apium graveolens) is an insect-pollinated biennial. In order to save pure seed, different varieties of celery and celeriac should be isolated from one another by 800 feet to 1/2 mile, depending on what kind of physical barriers are between crops. As a biennial, celery requires a period of cold (called vernalization) followed by warmer weather to trigger flowering. Sometimes this can be accomplished by planting out a crop early in spring, when temperatures are still regularly below 50 degrees F. A celery seed crop can also be overwintered in certain climates by thickly mulching and protecting the crop with row cover. Growers in very cold regions may have to pot up and store their celery plants in a root cellar to successfully vernalize them over the winter.
To harvest the seeds, cut whole flowering stalks once about two thirds of the seeds have turned brown, and bring them indoors to finish drying for up to two weeks. Once the seed heads are totally dry, gently brush the seeds out with your fingers. Mature seeds will detach easily. Store your seeds in a sealed container in a dark, dry, and cool location.