Every seed-starting date is calculated the same way: take your average last frost date, then count backward using the number of weeks printed on the seed packet under "start indoors." The regional dates below assume typical last-frost dates for each zone band.
Cold zones (3–4, last frost late May)
Start tomatoes and peppers indoors in mid-March, six to eight weeks before transplanting outdoors in late May or early June once nights stay reliably above 50°F.
Moderate zones (5–6, last frost mid-to-late April)
Start peppers in early February (they need the longest lead time of any common vegetable), tomatoes in early March, and squash or cucumbers indoors only three to four weeks before your last frost — they resent being started too early and transplant poorly once root-bound.
Warm zones (7–8, last frost mid-March)
Start peppers in mid-January, tomatoes in early February. Many warm-zone gardeners skip indoor starting for squash and beans entirely and direct-sow instead, since the soil warms fast enough that transplanting offers little advantage.
Hot zones (9–10, minimal or no frost)
Timing shifts around summer heat rather than frost. Start tomatoes and peppers in December or January for a spring harvest before summer heat shuts down fruit set, and again in July for a fall crop.
