Not sure? Most of southern New Hampshire and coastal Massachusetts falls around May 10–20; northern New England and higher elevations often push into early-to-mid June. Check your county's exact average via the Farmers' Almanac frost date lookup.
Your Seed Starting Timeline
Why Timing Actually Matters
Too early is worse than too late. Seedlings started too far ahead of your transplant date get root-bound in their trays, stretch and get leggy reaching for light, and go into transplant shock harder than seedlings started right on schedule. When in doubt, start a few days later rather than earlier.
"Weeks before last frost" assumes a normal transplant date — right around or shortly after your last frost, once nights are reliably above the crop's minimum tolerance. Cold-hardy crops like broccoli and kale can go out a couple weeks before last frost; heat-lovers like peppers and tomatoes should wait until nights are consistently above 50°F.
Some crops are marked "direct sow only." Root vegetables like carrots, radishes, and beets don't transplant well since disturbing the taproot stunts or forks the root — they go straight into the garden bed as seed, no indoor head start needed.