You can buy transplanted crops from nurseries, but cultivar choices expand enormously when you grow celery from seed. You can choose standard varieties such as ‘Ventura’, experiment with self-blanching types such as ‘Golden Boy’ and ‘Tango’, or try red-stalked varieties such as ‘Redventure’. For a late-summer crop, sow seeds indoors 10 to 12 weeks before the last average spring frost. Soak the tiny seeds overnight to encourage germination. Fill a container with a mix of ½ compost and ½ sand, and plant in rows 1 inch apart. Cover the seeds with a sand layer ½ inch deep, then cover the flats with damp sphagnum moss or burlap until seeds sprout.
Place in a bright spot out of direct sun, and keep the temperature at 70° to 75°F during the day and about 60°F at night. Provide plenty of water and good drainage and air circulation. Transplant the seedlings into individual pots when they are about 2 inches tall. At 6 inches, harden off the plants for about 10 days, and then transplant them into the garden in a bed that’s high in organic matter (from a cover crop or added compost).
Space the plants 6 to 8 inches apart in rows 2 to 3 feet apart. Set them no deeper than they grew in pots. Water in each seedling with compost tea.
For a fall crop, also known as a second harvest, sow seeds indoors in May or June, and follow the same directions, transplanting seedlings in June or July. Provide shade in hot, humid weather.
Related: 10 Plants You Can Still Grow In The Fall