OneTaskBy Tim King · Updated
Planting Date Calculator
When to Sow and Plant Out From Your Last Frost
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How the Planting Date Calculator works
This planting date calculator works out when to sow and plant each vegetable from your average last frost date. Enter the date and pick a crop, and it gives the window to sow seeds indoors, the window to plant seedlings out and, where it suits the crop, the window to sow straight into the ground outdoors.
Seed packets time everything from the last frost: tomatoes are sown indoors six to eight weeks before it and planted out a week or two after, while peas and broad beans go straight in the ground a month or more before it. Once you know your frost date, every sowing in the year follows from it. If you do not know yours, look it up in the frost dates table or ask a local allotment society or extension office.
How the planting date calculator works
The formula is sowing date = last frost date + the crop's offset in weeks, where a negative offset is before the frost. For example, with a last frost of 15 April, tomatoes are sown indoors from 18 February to 4 March and planted out from 22 to 29 April. A second example: with the same date, carrots are sown outdoors from 25 March to 1 April.
Tender crops (tomatoes, peppers, basil, squash, cucumbers, sweetcorn, beans) are killed by frost and go out only after it has passed. Hardy crops (peas, broad beans, spinach, kale, onions) tolerate light frost and are sown or planted weeks earlier. Half-hardy crops like lettuce and brassicas sit in between.
The frost date is an average, so there is still a real chance of a late frost after it. Keep fleece to hand for the first fortnight, and harden seedlings off for a week before planting out. To see how many successive sowings of lettuce or radish you can fit, repeat the outdoor sowing every two to three weeks.
Sowing and planting weeks relative to the last frost date, by crop
| Crop | Sow indoors | Plant out | Sow direct |
|---|---|---|---|
| Tomato | 8–6 weeks before | 1–2 weeks after | — |
| Pepper (sweet or chilli) | 10–8 weeks before | 2–3 weeks after | — |
| Aubergine (eggplant) | 10–8 weeks before | 2–3 weeks after | — |
| Lettuce | 6–4 weeks before | 2 weeks before to frost date | 4–2 weeks before |
| Cabbage | 8–6 weeks before | 4–2 weeks before | — |
| Broccoli | 8–6 weeks before | 2 weeks before to frost date | — |
| Cauliflower | 8–6 weeks before | 2 weeks before to frost date | — |
| Kale | 8–6 weeks before | 4–2 weeks before | 4–2 weeks before |
| Onion from seed | 12–10 weeks before | 4–2 weeks before | — |
| Leek | 12–10 weeks before | frost date to 2 weeks after | — |
| Peas | — | — | 6–4 weeks before |
| Broad beans (fava) | — | — | 6–4 weeks before |
| Spinach | — | — | 6–4 weeks before |
| Radish | — | — | 4–2 weeks before |
| Carrot | — | — | 3–2 weeks before |
| Beetroot | — | — | 3–1 weeks before |
| Potatoes | — | — | 3–2 weeks before |
| Swiss chard | 6–4 weeks before | 2 weeks before to frost date | 2 weeks before to frost date |
| Parsley | 10–8 weeks before | 2 weeks before to frost date | 3–1 weeks before |
| Basil | 6–4 weeks before | 2–3 weeks after | — |
| Sweetcorn | 3–2 weeks before | 2–3 weeks after | 1–2 weeks after |
| French or runner beans | — | — | 1–2 weeks after |
| Courgette (zucchini) and squash | 4–3 weeks before | 2–3 weeks after | 1–2 weeks after |
| Cucumber | 4–3 weeks before | 2–3 weeks after | 2–3 weeks after |
| Pumpkin | 4–3 weeks before | 2–3 weeks after | 2–3 weeks after |
| Melon | 4–3 weeks before | 2–3 weeks after | — |
FAQ
When should I plant tomatoes outside?
Plant tomatoes out one to two weeks after your average last frost date, once night temperatures stay above about 10 °C (50 °F). Sow the seed indoors six to eight weeks before the last frost so the plants are sturdy and about 15–20 cm tall when they go out.
How do I find my last frost date?
Use the frost dates table on this site, a national weather service's climate normals, or your local extension office or allotment society. Coastal and city gardens often have a last frost a couple of weeks earlier than the published regional average; frost pockets later.
Can I sow seeds before the last frost?
Yes, hardy crops. Peas, broad beans and spinach can be sown outdoors four to six weeks before the last frost, and radishes, carrots and beetroot two to four weeks before, as long as the soil is workable and not waterlogged. Tender crops must wait until after it.
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