Tools · Seed starting
Seed starting calculator: when to start seeds indoors
Enter your average last spring frost date. The table shows when to sow each crop indoors and when it can go out into the garden.
| Crop | Start seeds indoors | Plant out | Weeks indoors |
|---|---|---|---|
| Pepper | 6–8 weeks before last frost | 1 week after last frost, soil 60°F+ | 6–8 |
| Eggplant | 6–8 weeks before last frost | 1 week after last frost, soil 60°F+ | 6–8 |
| Tomato | 5–7 weeks before last frost | 1 week after last frost, soil 60°F+ | 5–7 |
| Broccoli | 9–12 weeks before last frost | 4–6 weeks before last frost | 4–5 |
| Cabbage | 9–12 weeks before last frost | 4–6 weeks before last frost | 4–5 |
| Kale | 9–12 weeks before last frost | 4–6 weeks before last frost | 4–5 |
| Cucumber | 3–4 weeks before last frost | 1 week after last frost, soil 60°F+ | 3–4 |
| Summer squash and zucchini | 3–4 weeks before last frost | 1 week after last frost, soil 60°F+ | 3–4 |
| Melons | 3–4 weeks before last frost | 1 week after last frost, soil 60°F+ | 3–4 |
How the dates are worked out
Each crop needs a certain number of weeks from sowing to a transplant ready for the garden, plus a week of hardening off: moving it outdoors a little more each day. The calculator counts back from the day each crop can safely go outside.
- Hardy: plant out 4–6 weeks before your last frost, after hardening off. Broccoli, cabbage, and kale tolerate light frost once they are hardened off.
- Tender: plant out after your last frost, once soil is at least 60°F. The calculator plans for one week after your last frost date. If the soil is still cold, wait; cold soil stalls warm-season crops.
A last frost date is an average, not a promise. In a typical year there is still a real chance of frost after it. For transplants you cannot replace, the seasonal planner explains how to use a safer, later date.
When to adjust the dates
- Check the seed packet. Varieties differ, and some peppers take longer than others.
- Give seedlings enough light. On a windowsill, seedlings often stretch and grow slowly, which throws off the schedule. Under grow lights they stay compact and on time.
- Don't start too early. Seedlings kept indoors too long get root-bound and leggy, and they settle into the garden more slowly than younger plants.
For containers, seed-starting mix, temperatures, and grow lights, read how to start seeds indoors. For which crops to sow directly in the garden instead, see the March guide.
Sources
- Iowa State University Extension: Guide to starting seed indoors — weeks from sowing to transplant, plus a week for hardening off.
- University of Minnesota Extension: Planting the vegetable garden — planting hardy crops four to six weeks before the frost-free date, and tender crops after it.
- University of Maryland Extension: Planting vegetable transplants — warm soil for tomatoes, peppers, and eggplant.
- University of Minnesota Extension: Starting seeds indoors.
- Illinois Extension: Don't get started too early on planting seed — why overgrown transplants struggle.