Growing tomatoes from seed is one of the most rewarding things you can do as a gardener. There’s something deeply satisfying about nurturing a tiny seed all the way through to a plant bursting with ripe fruit. But timing is everything — start too early and your seedlings will be leggy and rootbound before the soil is warm enough outside; start too late and you’ll miss the best of the growing season.
The principle is simple: tomatoes should be started indoors 6 to 8 weeks before your last frost date, once all risk of frost has passed and soil temperatures have reached at least 60°F (15°C). Here’s exactly when to do it, depending on where you live.
When To Start Tomato Seeds Indoors in United States 🇺🇸
| Region | Start Seeds Indoors | Transplant Outdoors |
|---|---|---|
| Zone 3–4 (Minnesota, Montana, northern Wisconsin) | Mid-March – Early April | Late May – Early June |
| Zone 5–6 (Ohio, Pennsylvania, Missouri, New England) | Late February – Mid-March | Late April – Mid-May |
| Zone 7–8 (Pacific Northwest, Virginia, Tennessee) | Late January – Mid-February | Late March – Mid-April |
| Zone 9–10 (California, Texas, Florida, Arizona) | December – January | March – April |
To find your exact last frost date, use the Old Farmer’s Almanac frost date tool and simply enter your zip code. Count back 6–8 weeks from that date to get your seed starting window.
When To Start Tomato Seeds Indoors in United Kingdom 🇬🇧
| Region | Start Seeds Indoors | Transplant Outdoors |
|---|---|---|
| Scotland & Northern England | Late March – Early April | Late May – Early June |
| Midlands & Northern Wales | Mid-March – Early April | Late May |
| Southern England & Southern Wales | Late February – Mid-March | Early – Mid-May |
Note for UK growers: Because British summers can be cool and short, many gardeners grow tomatoes under cover in a greenhouse or polytunnel. If that’s your plan, you can start seeds a week or two earlier than the dates above. Early-ripening varieties like Gardener’s Delight or Sungold are particularly well-suited to British conditions.
General Tips for Starting Tomato Seeds Indoors
Use a quality seed-starting mix. Avoid heavy garden soil — a light, fine-textured compost gives seedlings the best start.
Keep it warm. Tomato seeds germinate best at 20–25°C (68–77°F). A heat mat under your seed trays can speed things up considerably.
Maximise light. Seedlings need 14–16 hours of light per day. A south-facing windowsill can work, but a grow light is ideal in darker regions, especially the UK in early spring.
Harden off before transplanting. Two weeks before your transplant date, begin moving seedlings outside for a few hours each day to gradually acclimatise them to outdoor conditions.
Happy growing! 🍅