edible gardening
When to plant tomatoes — US zone + UK timing chart
Plant tomatoes outdoors after your last frost: mid-March in US zone 9, late May in UK. Start seeds indoors 6 weeks earlier. Full zone-by-zone schedule.
When to plant tomatoes — US zone + UK timing chart
The single most important question in growing tomatoes is when to put them outside. Plant a week too early and a late frost wipes you out. Plant a week too late and you lose harvest weeks at the back end of summer. This guide is the regional timing chart plus the soil and weather rules that override the calendar.
Get your local timing: Growli ties the tomato planting reminder to your specific zip code or UK postcode + the current weather forecast — not just to a generic frost-date chart.
The rule
Plant tomatoes outdoors only after your last expected frost date. This is the single non-negotiable. Tomatoes are tropical plants — anything below 5°C (40°F) sets them back; below 0°C (32°F) kills them.
The dates below are statistical averages. A "last frost date of May 15" means in an average year, the last frost is around May 15 — but in any given year, you might get a late frost a week later. Track 7-10 day forecasts before committing.
US timing (by USDA hardiness zone)
| Zone | Last frost average | Indoor seed-start | Outdoor transplant |
|---|---|---|---|
| Zone 3 | Late May / early June | Mid-April | Early June |
| Zone 4 | Mid- to late May | Early April | Late May |
| Zone 5 | Mid-May | Late March | Late May |
| Zone 6 | Late April / early May | Mid-March | Mid-May |
| Zone 7 | Late April | Mid-March | Mid-May |
| Zone 8 | Late March / early April | February | Mid-April |
| Zone 9 | February / early March | January | Mid-March |
| Zone 10-11 | Frost-free | December-January | February-March |
Find your zone with our USDA hardiness zone map deep-dive, or the USDA hardiness zone lookup tool.
UK timing
UK hardiness uses the RHS H1-H7 system, not USDA zones — see our UK RHS hardiness ratings primer for what each rating means. For tomatoes, the practical timing is:
| UK region | Outdoor transplant |
|---|---|
| Channel Islands, Cornwall, south Devon | Early May |
| Southern England (London, Bristol, Brighton) | Mid- to late May |
| Midlands + Wales | Late May |
| Northern England (Manchester, Leeds, York) | Late May / early June |
| Scotland (lowland) | Early June |
| Scotland (highland), Northern Ireland | Mid-June or grow under cover only |
Start seeds indoors 6 weeks before transplant date. Most UK home growers buy starter plants in May rather than starting from seed — for the small number of plants a household needs, it's simpler.
How to count back from your last-frost date
- Find your last-frost date for your zone (charts above) or your specific zip/postcode.
- Subtract 6 weeks for indoor seed-start date.
- Subtract 1 week from the transplant date for harden-off start (gradually expose seedlings to outdoors).
Example: US zone 6 last frost = May 5. Indoor seed-start = March 24. Harden-off start = April 28. Outdoor transplant = May 5.
Don't trust the calendar alone — check three signals
Before you plant outdoors, verify all three:
- Frost-free 10-day forecast — no nights below 5°C (40°F) projected.
- Soil temperature 15°C (60°F)+ — measured 4 inches deep with a soil thermometer. Tomatoes refuse to grow in cold soil even when air is warm.
- No big swings forecast — a heatwave immediately after transplant is also bad. Aim for a settled 18-25°C window for the first week.
If any of the three is off, wait. Tomatoes transplanted in cold soil are stunted for the whole season.
Seed-starting timing details
If starting from seed, the indoor schedule (full setup guide: starting seeds indoors):
| Time before transplant | What you do |
|---|---|
| 6 weeks | Sow seeds in seed-starting mix |
| 5 weeks | Germination complete |
| 4 weeks | Pot up to 4-inch containers when first true leaves appear |
| 2 weeks | Start fertilising at quarter strength weekly |
| 1 week | Begin harden-off — set outside in shade for 1 hour day 1, increase daily |
| Day 0 | Transplant outdoors |
What if you missed the window?
If your last-frost date has passed by 4+ weeks and you haven't planted yet, you've lost about a month of growing time. Recovery options:
- Buy more mature transplants (12-18 inch plants from a garden centre) — skips the early growth phase.
- Choose short-season varieties — Sub-Arctic Plenty, Glacier, Bush Early Girl ripen in 50-55 days from transplant vs 75-85 for standard varieties.
- Use season-extension tools — row covers, walls-of-water, black plastic mulch to warm soil.
In US zones 8-10 and UK southern coast, a second crop is sometimes possible — plant out in late June for a fall harvest.
Related articles
- How to grow tomatoes — full growing guide
- When to fertilize tomatoes — feeding timeline
- What fertilizer for tomatoes — product comparison
- How to start a vegetable garden — beginner overview
- USDA hardiness zones explained — browse the full zone library
- Look up your zone by ZIP or postcode — fastest way to find your last-frost date
Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.
Frequently asked questions
When should I start planting tomatoes?
Outdoors: after your last expected frost — mid-March in US zone 9, late April in zone 7, mid-May in zone 5-6, late May in UK southern England, early June in UK Scotland. Indoors from seed: 6 weeks before your outdoor transplant date. Don't rush the season — cold-stressed tomato plants are stunted all summer.
When to plant tomato plants outdoors?
Wait until two conditions are met: (1) your last expected frost date has passed, and (2) soil temperature is 15°C (60°F)+ at 4 inches deep, measured for at least 3 consecutive days. The second condition matters as much as the first. Cold soil keeps tomato roots dormant even in warm air.
When to plant tomato seeds?
Sow indoors 6 weeks before your outdoor transplant date. For US zone 6 with a May 5 last frost, that's March 24. For UK southern England with a May 25 transplant, that's mid-April. Surface-sow on moist seed-starting mix and keep at 21-27°C; germination in 5-10 days.
When is the best time to plant tomatoes?
The best time is 1-2 weeks AFTER your last-frost date, when soil temperature has stabilised at 15-18°C. That margin protects against an unexpected late frost and ensures roots establish in warm soil. Planting exactly at the last-frost date is too aggressive — averages mean some years are colder than the chart.
When is a good time to plant tomatoes?
Same answer as 'best time' — 1-2 weeks after your last-frost date, with soil at 15°C+, and a frost-free 10-day forecast. In US zone 7 that's around the first week of May; in UK southern England it's late May to first week of June; in US zone 9 it's late March.
When to plant tomato seeds indoors?
6 weeks before your outdoor transplant date. The exact date varies by region — for US zone 5 (late May transplant), start seeds in mid-April. For UK southern England (late May transplant), start seeds in mid-April too. Use a heat mat to maintain soil temperature above 21°C for fastest germination.
When to cover tomato plants at night?
Cover when night temperatures forecast below 5°C (40°F) for the first 2-3 weeks after transplant. Use lightweight row cover, walls-of-water, or even an old bedsheet — anything that traps soil heat. Remove covers each morning so plants get full daylight. After 3 weeks of growth, tomato plants tolerate normal night temperatures.
How does Growli know when to plant tomatoes in my location?
Add your zip code (US) or postcode (UK) to Growli and the app ties the planting reminder to your local last-frost date from NOAA / RHS data, the current 10-day weather forecast, and your specific tomato variety's days-to-maturity. The reminder fires only when all conditions check out — not on a generic chart date.