The best time to plant celery is indoors in March, with most gardeners sowing seed from mid-March to early April. You then move the young plants outside about 10 weeks later, once the last frost has passed in your area. March is the sweet spot for a spring crop in most temperate zones.
Celery takes a long time to mature, and that single fact drives the whole schedule. A full crop needs 130 to 140 days from seed to harvest. That is more than four months in the ground. If you wait for warm soil to direct sow, the season runs out before the stalks ever fill in. Starting early indoors buys you the weeks you need, and it lets the plant do its slow early growth in a spot you control.
There is another reason to know when to start celery seeds indoors. The seed is tiny and slow to sprout, often taking two to three weeks to show. Celery seed also needs light to germinate, so you press it onto the surface and barely cover it. Bury it too deep and it may never come up. A warm windowsill or a grow light handles this far better than cold spring ground, where the seed can sit and rot.
After germination, the seedlings grow slow and steady on a sunny sill or under lights. Give them strong light so they stay stocky instead of stretching tall and weak. You harden them off over a week or so, then set them out only after frost danger passes for good. Celery is a cool-season plant, but a late frost will still check its growth or kill a tender transplant. Patience here saves the crop.
To pin down your own sowing month, count back 10 weeks from your last frost date. If your frost ends around mid-May, that math lands you on early March for sowing. A gardener with a late April frost would start in mid-February instead. Your local frost date matters more than any fixed calendar month. A quick search for your zip code or postal area gives you that date, and the whole schedule flows from there.
Look up your average last spring frost, then back up 10 weeks to set your sowing week.
Press seed onto moist mix and leave it uncovered so light can reach it. Keep it warm and damp.
Once sprouts appear, hold them near 55 to 65°F (13 to 18°C) under bright light for stocky plants.
Ease seedlings outside over a week, then transplant once the last frost has passed for good.
Temperature in those early weeks decides whether you get tender stalks or a plant that bolts. Keep your seedlings near 55 to 65°F (13 to 18°C) while they grow indoors. Cold after they sprout is the real danger. A stretch below 55°F (13°C) can trick celery into flowering early. The plant thinks winter has come and gone, so it rushes to seed. You end up with bitter, stringy stems instead of a crop. This is why a warm March start beats setting plants out too soon.
A fall crop follows the same logic in reverse. You start seed in summer, often June or early July, so the plants mature as the weather cools down. Celery sweetens in cool fall air, and this second sowing suits cool-climate gardeners who want a long, mild finish. Just give it enough lead time before your first hard frost. Count back the same 130 to 140 days from that frost date to find your summer sowing window.
So your celery planting timeline comes down to one habit: find your last frost date, back up 10 weeks, and sow that month. For most gardens that means a March indoor start and a transplant in late May, with an optional summer sowing for fall stalks. Get the timing right and the rest of the season takes care of itself.
Read the full article: Celery Plant Guide: Grow, Care, and Eat
