Celery is a long, but persistent crop that takes attention and patience. Sow seeds indoors 8-12 weeks prior to the last average frost date. Use pre-moistened seed starting mix, with seeds covered 1/4-1/2 inch, watered in then placed on heat mat with 75°-85°F consistent bottom heat. Seeds need light for germination and some growers have found that providing 10°-15°F cooler temperatures at night is beneficial for germination. Once seedlings are up, place into bright indirect light off the heat mat, and as true leaves develop transfer into larger pots to grow on until hardening off for 7-10 days. Celery plants are semi-hardy with the ability to tolerate light frosts, so planting out early is helpful to get a jump on the season for this long-growing crop.
