Seed-starting timing is calculated backward from your last expected frost date, not a fixed calendar date — because frost dates shift significantly by region, every recommendation below is expressed in weeks before last frost, which you then map onto your own local date.
Find Your Last Frost Date First
Before using the calendar below, look up your local average last frost date — this is the single number every timing recommendation in this guide is calculated from. Gardeners in the UK, for instance, typically see last frost dates ranging from mid-April in milder coastal areas to late May in colder inland and northern regions.
Seed-Starting Calendar by Weeks Before Last Frost
| Weeks Before Last Frost | Start Indoors | Why This Timing |
|---|---|---|
| 10-12 weeks | Peppers, slow-growing herbs | Naturally slow germination and early growth |
| 6-8 weeks | Tomatoes, most flowering annuals | Standard lead time for strong transplant-ready size |
| 4-6 weeks | Zinnias, marigolds, cucumbers | Fast growers that don't need as much of a head start |
| 2-3 weeks | Lettuce (if starting indoors at all) | Very fast growing, often direct-sown instead |
| After last frost | Direct-sow beans, cucumbers, most root vegetables | Fast germination and dislike of transplanting |
Pro tip: Starting seeds too early is a more common mistake than starting too late. Seedlings held indoors well past their ideal transplant window often become leggy and stressed while waiting for outdoor conditions to catch up — following the weeks-before-frost window matters as much as not starting too late.
Worked Example: Using the Calendar
If your last frost date is May 15th: tomatoes (6-8 weeks before) should be started between March 20th and April 3rd. Peppers (10-12 weeks before) should be started between February 27th and March 13th. Zinnias (4-6 weeks before) fall between April 3rd and April 17th.
What Happens If You Start Too Early or Too Late
| Timing Mistake | Likely Result |
|---|---|
| Started too early | Leggy, stressed seedlings outgrowing indoor space before it's safe to transplant |
| Started too late | Shorter growing season, delayed harvest, less time to recover from any setbacks |
Shop by Starting Window
Get a head start on the season with our tomato seeds and herb varieties from our herb collection — both benefit from the longer indoor lead time. For fast growers better suited to direct sowing, browse our zinnia and marigold collections.
Frequently Asked Questions
How many weeks before the last frost should I start tomato seeds?
Tomatoes are typically started indoors 6-8 weeks before the last expected frost date in your area.
What happens if I start seeds too early indoors?
Seedlings started too early often become leggy and stressed while waiting for safe outdoor transplant conditions, which can weaken the plant compared to timing the start correctly.
Can I find my exact last frost date online?
Yes, searching your city or postal code alongside "last frost date" typically returns a reliable average based on historical local weather data.
Plan your full growing season with our complete seed collection.
