Last Updated on October 9, 2026
How to Start Celery Seeds Indoors
Start celery seeds indoors 10 to 8 weeks before your last spring frost. Press the tiny seed onto the surface of moist mix without burying it. It needs light to germinate. Keep it evenly moist near 68°F, or a fluctuating 85°F day and 70°F night (see below), and expect sprouts in about a week at that temperature. Then grow the seedlings under lights and transplant them 1 to 3 weeks after your last frost, not before, because young celery that sits in cold weather can bolt. Those windows are the ones the Plan My Garden planner uses. To turn them into dates, look up your last frost date by zip code or use my seed starting calendar.
The celery seed starting timeline
| Step | When |
|---|---|
| Sow seed indoors | 10 to 8 weeks before your last frost |
| Seedlings come up | About 7 days at 68°F soil, 12 days at 59°F, 16 days at 50°F |
| Thin to one per cell | Once the first true leaves show |
| Harden off | The 10 to 14 days before transplanting |
| Transplant out | 1 to 3 weeks after your last frost |
| Days to maturity | About 120 days, one of the longest on my days to maturity chart |
The sowing and transplant weeks and the days to maturity are from the Plan My Garden planner. Sow at 10 to 8 weeks before, plant out at 1 to 3 weeks after, and the seedlings spend about 9 to 13 weeks indoors. That is a long stretch, and it is why celery is on the short list in my seed starting calendar of crops people start too late; the calendar notes give them 10 to 12 weeks indoors. University of Minnesota Extension gives celery 12 to 13 weeks indoors too.
What you need
- Celery seed. It is tiny: Wood Prairie lists 68,800 seeds per ounce. My seed viability chart puts celery seed at about 3 years when stored cool and dry.
- A cell tray or flat with drainage holes, plus a plastic dome or plastic wrap. Soil blocks work too.
- Seed-starting mix, moistened before you fill the tray, and a little fine vermiculite.
- A spray bottle for watering the surface without washing the seed away.
- A grow light and a timer.
- Scissors for thinning.
How to sow celery seeds indoors, step by step
- Soak the seed. Utah State University Extension says celery germinates better if you soak the seeds in water and change the water every day, because the seed carries natural germination inhibitors that soaking leaches away.
- Moisten the mix. I put the seed-starting mix in a bucket in the sink, water it lightly and stir until it is evenly moist, then fill the cells.
- Sow on the surface. The note on my seed germination temperature chart says celery needs diffuse light for good germination, so do not bury it. My seed starting guide plants two seeds per cell. Press them lightly onto the mix. For seeds that need light, University of Minnesota Extension covers them with a thin layer of fine vermiculite, porous enough to let light through while it keeps the surface moist.
- Cover and keep it moist. Put on the dome or plastic wrap. The same chart note lists high moisture as part of the best conditions, and surface-sown seed dries out fast. Minnesota mists the surface gently with a spray bottle so the mix does not wash out. Take the cover off as soon as the seedlings come up.
- Keep it near 68°F. The temperature section below explains why warmer is not better for celery.
- Give the seedlings light. My step-by-step guide gives seedlings 14 to 16 hours of light a day. My seed starting guide keeps the grow light about 2 to 4 inches above them. Minnesota adds that the lights should not stay on around the clock, because many plants need a dark period each night.
- Thin to one. Once the seedlings have true leaves, Minnesota cuts all but the healthiest one off at soil level with scissors. Pulling them can damage the roots of the one you keep.
- Water from the bottom. After germination, pour water into the tray and let the cells soak it up through the holes, so the mix stays moist without getting waterlogged.
- Pot up if they outgrow the cells. With 9 weeks or more indoors, a small cell can fill up. Minnesota moves seedlings that outgrow cell packs into containers 1 to 2 inches wider.
Celery germination temperature and days to sprout
Celery is slow and it does not like heat. From my seed germination temperature chart, these are the days to emerge at each constant soil temperature:
| Soil temperature | Days to emerge |
|---|---|
| 41°F | 41 |
| 50°F | 16 |
| 59°F | 12 |
| 68°F | 7 |
| 77°F, 86°F and 95°F | Little or no germination |
The same chart lists 40°F as celery’s minimum and gives it no single optimum. Its note says celery needs diffuse light and a night temperature 10 to 15°F lower than the day, with the best results at 85°F by day and 70°F at night. The lab test held at one steady temperature did best at 68°F. A warm day and a cooler night also works. Either way, do not park celery on a heat mat running warm around the clock. Room temperature around 68°F matches the fastest steady reading, and a room that cools off at night matches the note.
Why celery goes out after your last frost
Celery is rated semi-hardy in the planner and on my frost tolerance chart, yet the planner transplants it 1 to 3 weeks after the last frost, later than most cool-season crops. The reason is bolting. Utah State says the minimum temperature for celery is 36°F, but plants exposed to cool temperatures for several weeks will flower.
Oregon State University’s celery guide, aimed at commercial growers (it gives per-acre fertilizer rates and yields), protects transplants from mean daily temperatures below 55°F for 10 to 14 days, and below 45°F for even short periods, because that exposure preconditions celery to bolt. UMass Amherst’s celery fact sheet puts the line at 40°F for 10 to 14 days. Either way, these are field numbers, not backyard trials, but keep young celery warm.
- Do not rush it out, or hold it too long. Oregon State moves transplants out when temperatures are above 55°F, and says larger transplants are more prone to bolting and transplant shock.
- Bring them in at night while hardening off. Minnesota brings seedlings back inside before the temperature drops each evening.
- Cover after a cold snap. Utah State says hot caps, plastic tunnels and fabric covers protect young transplants from frost and cooler temperatures.
Hardening off and transplanting celery
- Harden off first. My transplanting guide starts this about 10 to 14 days before planting out: a few hours outdoors out of direct sun at first, then more time and more sun each day.
- Size. Utah State plants transplants that have 3 to 4 mature leaves and a well-established root system. Oregon State’s commercial transplants go out at 4 to 5 inches tall.
- Spacing. The planner sets 2 celery plants per square foot, on the diagonal about 6 inches apart, which fits up to 32 plants in a 4×4 bed. My square foot gardening chart allows 4 per square for thinner stalks. The details are on how many celery plants per square foot.
- Water in and mulch. Water the transplants thoroughly once they are in the ground, then mulch. Utah State says celery needs at least 1 to 2 inches of water a week and has a small, shallow root system, so soak the soil each time.
Where to get celery seed
Wood Prairie’s organic celery seed includes Ventura, a Utah Tall type at 80 to 100 days. Utah State’s own guide separately names a variety it calls Utah as one of its two finest-quality picks, a different cultivar of the same type. Wood Prairie’s lineup also includes cutting celery, an 85 day herb grown for its celery flavor in salads. Each packet is about 200 seeds, far more than the 32 plants a 4×4 bed holds at the planner’s spacing. Code PMG5 takes 5 percent off.
Quick questions
When should I start celery seeds indoors?
10 to 8 weeks before your last spring frost, the window the Plan My Garden planner uses, then transplant 1 to 3 weeks after the last frost. That gives the seedlings about 9 to 13 weeks indoors.
Does celery seed need light to germinate?
Yes. The note on my seed germination temperature chart says celery needs diffuse light for good germination. Press the seed onto the surface of the mix instead of burying it, or cover it with a thin layer of fine vermiculite that lets light through, as University of Minnesota Extension does for light-needing seed.
How long does celery seed take to germinate?
About 7 days at 68°F soil, 12 days at 59°F, 16 days at 50°F and 41 days at 41°F, from my seed germination temperature chart. At a steady 77°F or warmer the chart shows little or no germination, so skip the hot heat mat.
Should I soak celery seeds before planting?
Yes. Utah State University Extension says celery germinates better if you soak the seeds in water and change the water every day, because soaking leaches away natural germination inhibitors in the seed.
Why did my celery bolt?
Usually cold. Utah State University Extension says celery exposed to cool temperatures for several weeks will flower. Oregon State University’s commercial guide warns that mean daily temperatures below 55°F for 10 to 14 days precondition celery to bolt, which is why the planner transplants it after the last frost.
Get your celery sowing week
Celery is one of the first seeds of the year and one of the last transplants, so both dates matter. Plan My Garden is free to start: enter your zip code and it finds your frost dates, draw your beds, pick celery and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors, transplant and direct sow dates) from your frost dates.
