When to Start Seeds Indoors in Zone 6: Full Schedule
Published: October 21, 2026 · 8 min read
A zone 6 garden with an April 20 last frost starts its first seeds on February 2 and finishes indoors by April 1. Onions and celery lead, peppers and eggplant follow at mid-February, tomatoes at the start of March, cucumbers and squash at the end of March.
Zone 6 runs from southern Ohio to the Hudson Valley, plus most of Missouri and the high desert outside Santa Fe. Last frost moves from about April 10 in 6b to May 10 in 6a, so these dates assume April 20 and shift with your own. The Frost Date Calculator turns a ZIP code into that date.
Most zone 6 seed starting fails early, not late. A tomato sown February 1 is a 14-inch plant with pale lower leaves by April 1, root-bound and stalled, out-yielded by one sown March 5.
The Zone 6 Indoor Schedule
Dates assume an April 20 last frost; the Seed Starting Date Calculator applies the same offsets to your own date.
| Crop | Start indoors | Set out | Weeks before frost | Note |
|---|---|---|---|---|
| Onions, from seed | Feb 2 | Apr 1 | 11 | Long-day cultivars only |
| Celery | Feb 2 | Apr 1 | 11 | Needs light to germinate |
| Peppers, eggplant | Feb 17 | May 5 | 9 | Soil at 80°F |
| Tomatoes | Mar 2 | May 5 | 7 | No earlier than Feb 24 |
| Broccoli, cabbage, cauliflower | Mar 2 | Mar 23 | 7 | Out 4 weeks before frost |
| Lettuce | Mar 16 | Apr 6 | 5 | Bolts if started late |
| Basil | Mar 9 | May 1 | 6 | Waits for 60°F soil |
| Cucumbers, squash, melons | Mar 30 | May 12 | 3 | Three weeks is plenty |
| Peas | Direct sow Mar 20 | 4 before | Resent transplanting | |
| Carrots, beets, radishes, spinach | Direct sow Mar 20 – Apr 5 | 2 to 4 before | Root crops fork in trays | |
Two rows carry the risk. Onions need 11 weeks because they put on an inch a month under lights; wait until March and you plant sets. A six-week cucumber is a vine wrapped around its own tray.
Zone 6 Is Not One Date
Two zone 6 gardens 60 miles apart can be three weeks apart on frost. Cold air drains downhill and pools in valleys, so a plot at the bottom of a slope runs colder than one 40 feet higher. A south-facing wall buys 10 to 14 days at each end of the season; black plastic over a raised bed warms soil 5 to 8°F above the ground beside it.
Your anchor date is a coin flip
Published frost dates are probabilities: the date with a 50 percent chance of a later frost. Planting tender crops then is a wager. Market growers wait 7 to 14 days past the average, which is why their first tomato ripens before a neighbor's.
6a against 6b
Zone 6b clears its last frost between April 1 and April 20; 6a runs April 21 to May 10. If your date lands late, push every row back three weeks and start nothing before Washington's Birthday.
February: The Slow Crops
Onions from seed want 11 weeks
Seed sown February 2 is ready around April 1, when transplants are pencil-thick and carrying four leaves. Order long-day cultivars. Zone 6 sits between 36 and 42 degrees north, and short-day onions bulb at 10 to 12 hours of daylight, which this latitude does not reach until late March. Long-day types start at 14 to 16 hours, in June. A $4 packet holds 250 seeds.
Onion seedlings take frost to 20°F once hardened, so they go out three weeks before frost. Trim tops to 3 inches and set an inch deep. A 10-foot row at 4-inch spacing holds 30 plants and yields about 25 lb.
Peppers and eggplant want bottom heat
Both germinate at 80 to 85°F in 14 to 21 days. At 70°F the same seed can sit a month and rot. Start nine weeks out, pot up once at four weeks, keep nights above 60°F; pepper flowers abort below 55°F.
March: Tomatoes, Brassicas, Basil
Tomatoes at seven weeks
Sow March 2 for a May 5 set-out: a quarter inch deep, soil at 75 to 80°F until the first loop shows, then lights 2 inches above the leaves for 14 to 16 hours. Seven weeks transplants without a check; ten weeks produces a plant that flowers in the tray.
Brassicas go out before the last frost
Broccoli, cabbage, and cauliflower take 6 to 8 weeks, then go to the garden four weeks before last frost, around March 23, at three or four true leaves. Older transplants button, the head forming at 2 inches. They shrug off 25°F once hardened. Row cover for the first month keeps cabbage moth off.
Basil and lettuce
Basil germinates in a week at 70°F and sulks below 50°F; six weeks is enough, then out a week after frost. Lettuce needs five weeks and takes a light frost, so April 6 is safe. Past mid-April, long days push it to bolt before it heads.
Light, Heat, and the Electricity Bill
| Crop group | Soil temp to germinate | Days to sprout | Weeks indoors | Night temp after |
|---|---|---|---|---|
| Tomatoes | 75–85°F | 6–10 | 6–8 | 60–65°F |
| Peppers, eggplant | 80–85°F | 14–21 | 8–10 | 65–70°F |
| Broccoli, cabbage | 65–75°F | 5–10 | 6–8 | 50–60°F |
| Onions, celery | 65–75°F | 10–21 | 10–12 | 50–60°F |
| Cucumbers, squash | 80–85°F | 5–10 | 3–4 | 65–70°F |
Light is where the cheap setup gives out. One 4-foot shop light covers two 1020 trays, nothing more. Two 40-watt LED tubes for 16 hours a day over ten weeks pull about 90 kilowatt-hours, roughly $15 at 17 cents. A south window is no substitute: glass cuts a third of the light.
A heat mat holds soil 10 to 20°F above room air, the gap between a 68°F kitchen and the 80°F peppers want. Pull it at germination; seedlings left on bottom heat grow soft, stretched stems.
Turn your frost date into 25 start dates
Enter your last spring frost and the calculator returns a start date, a transplant date, and a week count for every vegetable on this page.
Open the Seed Starting Date Calculator →Potting Up and Hardening Off
A 72-cell tray holds a seedling about four weeks, then roots circle the cell and top growth stops. Move tomatoes, peppers, and eggplant into 4-inch pots at the fourth true leaf, set deeper than they grew.
The schedule has slack for one lost week, not for a plant that spent nine weeks in a cell. If April turns cold, hold seedlings at 60°F and 12 hours of light.
What the Starts Cost
| Item | 2026 price | What it covers | Per plant |
|---|---|---|---|
| Tomato seed, 25 seeds | $4.50 | 25 plants | $0.18 |
| Nursery six-pack | $5.49 | 6 plants | $0.92 |
| 72-cell tray with dome | $9 | Five seasons or more | — |
| Seed starting mix, 16 qt | $14 | Three trays | — |
| Heat mat, 10 by 20 in | $25 | Ten seasons | — |
| 4-ft LED shop light | $30 | Eight seasons | — |
Twelve tomato plants from one $4.50 packet cost about $6 once mix and a share of the tray count. The same dozen as six-packs run $66. Gear pays back the first spring you would otherwise buy 20 transplants. Under a dozen plants, buying is cheaper.
The Fall Window Zone 6 Also Gets
First frost lands between October 5 and October 31, and that date sets a second calendar nobody uses. Fall cabbage and broccoli go into trays in late June, 12 to 14 weeks before frost. Kale for October starts late June to early July, lettuce for September in late July. Fall brassicas size up in heat and head in cool air, and cabbage worms taper off after Labor Day.
The Garden Yield Calculator converts row feet into pounds, and the printable planting calendar takes the dates to the shed wall.
Frequently Asked Questions
When should I start tomato seeds in zone 6?
Between February 24 and March 10 for a last frost near April 20, 6 to 8 weeks of indoor growth. March 2 is the safest single date. Earlier starts flower in the tray and yield less.
Can I start seeds indoors in January in zone 6?
Only onions, leeks, shallots, and celery, which need 10 to 12 weeks and grow slowly enough to stay in a tray. January tomatoes run out of light and root space before the garden is ready.
What is the last frost date in zone 6?
Roughly April 1 to April 20 in zone 6b and April 21 to May 10 in zone 6a. Every published date is a 50 percent probability, so tender crops usually wait another 7 to 14 days. Use your ZIP code rather than the zone number, since two zone 6 towns can be three weeks apart.
Do I need a heat mat to start seeds in zone 6?
For peppers and eggplant, yes. They need 80 to 85 degrees Fahrenheit to germinate and can sit 30 days at 70. Tomatoes sprout fine at 75 to 80, and brassicas, lettuce, and onions need no bottom heat. Pull the mat at germination.
Start With the February Tray
Buy onion and celery seed now and sow both February 2. Add peppers two weeks later, tomatoes on March 2, brassicas that same week, and hold cucurbits until the end of March. About $90 of reusable gear covers a zone 6 garden.
The exception is the late-frost corner of 6a, where April 20 is a hope, not an average. There, move every date three weeks later and accept first tomatoes in August. Run your own dates through the Seed Starting Date Calculator first, and see the seed starting calendar guide for setup. The Plant Spacing Calculator settles how many of each fit.