When to Start Seeds Indoors Calculator
Enter your average last spring frost date and tick your crops — get the exact date to start each one indoors, the date to transplant it out, and honest "just direct-sow this outside" dates for the crops that don't want an indoor head start. Twenty common vegetables and herbs, offsets from university extension guidance, sorted into a printable season checklist. Everything runs in your browser — your plan is saved locally and never uploaded.
Your average last spring frost date
Southern Hemisphere? The math works from any last frost date (yours is typically Sep–Nov), but this page's seasonal wording — "spring", Jan–Apr framing — is written for the Northern Hemisphere.
Your crops
Your seed-starting plan
FAQ
Where do these offsets come from?
The weeks-before-frost windows are the typical ranges published by university extension services — e.g. University of Minnesota Extension and University of Maryland Extension: tomatoes 6–8 weeks before last frost, peppers 8–10, brassicas 5–7, cucurbits only 2–4, onions from seed 8–12. Each crop row shows the range this tool schedules within.
Why do some crops say "direct sow" instead of an indoor date?
Because for carrots, beets, beans, peas and sweet corn, starting indoors is not the norm — they germinate fine in the ground and most of them actively resent transplanting. Giving you a fake indoor date would be worse than telling the truth: sow them outside on the date shown.
Why do broccoli and cabbage transplant out before the frost date?
Hardened-off cool-season brassicas, onions, lettuce and parsley tolerate light frost, so they go out 2–4 weeks before the average last frost. Warm-season crops (tomatoes, peppers, eggplant, basil, melons) wait 1–2 weeks after it, until nights are reliably mild.
How exact are these dates?
They're planning dates, not promises. Your "average last frost" is an average — a real frost can land two weeks either side of it — and varieties, indoor light and local microclimate shift things by ±2 weeks. If your seed packet says something different, the packet wins: it's written for your specific variety.
Do my dates get uploaded?
No. The page is fully client-side — your frost date and crop picks are stored only in your browser's localStorage. There are no affiliate links; the extension and frost-lookup links are plain references.