Pascal Giant
Celery in the US

Right then, starting celery from seed is where the challenge often begins. The seeds are tiny, so you want to sow them thinly, just barely covered with a sprinkle of fine compost, indoors, usually around 60-70°F (15-21°C). My GrowMore CookMore app shows timing for zones 5-7, but you'll need to adjust for your local climate; for example, folks in zone 3 might sow May-June, while those in zone 9 could start as early as January or as late as October for a later crop. It takes about 100 days from sowing to harvest, so an early start is key. You won't find many plug plants of celery, so it's best to grow your own from seed.

Once your seedlings have a couple of true leaves, they'll need pricking out into individual pots. Handle them gently, they're a bit delicate. Keep them watered and once they're sturdy enough, usually 4-6 inches (10-15 cm) tall, it's time to harden them off properly for a week or two. Don't rush this bit, you know. Plant them out after all danger of last frost has passed, spacing them about 10-12 inches (25-30 cm) apart in rich soil. They do quite well in large containers too, if you're short on space.