When to Plant Tomatoes: Using Your Frost Dates
When to start tomato seeds indoors and when to transplant outside, based on your average last frost date, plus how to check the planting window for your ZIP code.
Last updated 2026-10-01
Tomatoes need warmth, not just the absence of frost
Tomatoes are frost-tender and grow poorly in cold soil. Even after the last frost passes, cool nights slow them down, so transplanting a little after the average last frost date usually pays off.
The University of Maryland Extension planting calendar, built for central Maryland's April 15 average last frost, schedules tomato seed starting indoors from mid-March and transplanting outdoors from May into early July. On each ZIP code page, those windows are shifted to your own frost dates.
A simple plan
- Look up your ZIP code and note the average last frost date and the safer 10% date.
- Start seeds indoors about four to eight weeks before you plan to transplant.
- Harden seedlings off outdoors for a week or so, increasing their time outside each day.
- Transplant after your 10% last-frost date, or earlier only if you are ready to cover plants on cold nights.