Almost every planting date in a seed catalogue is expressed relative to your last spring frost: "start indoors six weeks before last frost", "direct sow two weeks after". This calculator does that arithmetic for thirty crops at once, from the one date only you can supply.
There is no ZIP code lookup here, deliberately. Frost dates vary too much over short distances for a postcode to be a good answer, and the second question below explains why asking you is the more honest approach.
How to use it
- Enter your average last spring frost date. If you do not know it, the first question below lists where to find it for your country.
- Add your average first fall frost date if you know it. It is optional, and worth entering: it lets the calculator flag anything that will not ripen before frost, and tells you how long your season actually is.
- Pick your crops. Tap as many as you like; the calendar builds as you go.
Each row gives a date to start indoors, to transplant out, and to direct sow, plus a likely harvest window. Blanks are meaningful — a blank direct-sow date means the crop is not normally sown straight into the ground, not that the data is missing.
How it is calculated
Every crop carries three offsets in weeks, relative to the last frost date, and a days-to-maturity range:
start indoors = last frost - (weeks before last frost x 7)
transplant = last frost + (weeks after last frost x 7)
direct sow = last frost + (weeks relative to last frost x 7)
harvest = last planting step + days to maturity
Negative offsets mean before the frost date, which is why cool-season crops such as lettuce and kale show transplant dates earlier than the frost date itself — they take a light frost without harm.
All of this is computed in UTC and returned as plain calendar dates, so a shared result cannot shift by a day depending on the reader's timezone.
A worked example
A last frost date of 15 May, growing tomatoes:
- Start indoors: six weeks before, so 42 days back from 15 May = 3 April
- Transplant out: one week after, so 22 May
- Direct sow: not applicable — tomatoes are not sown outdoors in a temperate season
- Harvest: 60 to 85 days from transplanting = 21 July to 15 August
Radishes from the same frost date are direct sown three weeks early on 24 April and ready in 22 to 30 days, which is 16 to 24 May.
Typical offsets, in weeks from last frost
Every crop the calculator knows, with the same offsets it uses. Negative is before your last frost date, positive after it.
| Crop | Start indoors | Transplant | Direct sow |
|---|---|---|---|
| Tomato | 6 before | 1 after | Not usually direct sown — it needs a head start indoors to ripen in a temperate season. |
| Pepper | 8 before | 2 after | Not usually direct sown — it germinates slowly and needs the indoor head start. |
| Cucumber | 3 before | on the date | 1 after |
| Zucchini | 3 before | on the date | 2 after |
| Lettuce | 8 before | 3 before | 4 before |
| Spinach | Not usually started indoors — it goes in as soon as the ground can be worked, weeks before anything needs a windowsill. | Not transplanted — sow where it will grow. | 5 before |
| Kale | 8 before | 3 before | 3 before |
| Carrot | Not started indoors — moving a seedling forks the taproot, and the taproot is the crop. | Not transplanted — sow where it will grow. | 2 before |
| Radish | Not started indoors — it is ready in about four weeks, so a transplant only sets it back. | Not transplanted — sow where it will grow. | 4 before |
| Beet | Not usually started indoors — the root resents being moved. | Not transplanted — sow where it will grow. | 3 before |
| Onion | 12 before | 2 before | 2 before |
| Garlic | Garlic is planted in autumn, a few weeks before the ground freezes, and harvested the following summer — so no last-frost offset describes it. Work back from your first fall frost date instead. | ||
| Potato | Not started indoors — seed potatoes are chitted in a cool, bright place instead. | Not transplanted — seed potatoes go straight into the ground. | 2 before |
| Sweet potato | Not sown from seed — it is grown from rooted slips. | 3 after | Not sown from seed — set out rooted slips about three weeks after your last frost. |
| Bush bean | Not started indoors — beans grow fast and dislike root disturbance. | Not transplanted — sow where it will grow. | 1 after |
| Pea | Not usually started indoors — peas prefer cold soil and germinate readily in it. | Not transplanted — sow where it will grow. | 4 before |
| Sweet corn | Not started indoors — corn resents root disturbance and catches up quickly outdoors. | Not transplanted — sow where it will grow. | 1 after |
| Winter squash | 3 before | on the date | 2 after |
| Pumpkin | 3 before | on the date | 3 after |
| Broccoli | 8 before | 2 before | Not usually direct sown — transplants get ahead of spring weeds and of the heat that ruins heads. |
| Cabbage | 9 before | 3 before | Not usually direct sown — transplants get ahead of spring weeds and of the heat that splits heads. |
| Cauliflower | 8 before | 2 before | Not usually direct sown — it needs an unbroken start that a seedbed rarely provides. |
| Eggplant | 8 before | 2 after | Not usually direct sown — it wants a long warm run that an outdoor sowing rarely gives it. |
| Okra | 1 before | 2 after | 2 after |
| Basil | 6 before | 1 after | 1 after |
| Cilantro | Not started indoors — it bolts almost immediately after being moved. | Not transplanted — sow where it will grow, and sow again every few weeks. | 2 before |
| Parsley | 8 before | on the date | on the date |
| Dill | Not started indoors — the taproot resents being moved. | Not transplanted — sow where it will grow. | on the date |
| Strawberry | Not usually grown from seed — plant bare-root crowns or runners instead. | 2 before | Not sown from seed — set bare-root crowns out about two weeks before your last frost. |
| Watermelon | 3 before | on the date | 2 after |
| Asparagus | Not usually grown from seed — plant one-year-old crowns instead. | 4 before | Not direct sown — crowns are planted in a trench, not seed in a drill. |
| Blueberry | Not grown from seed in a home garden — buy a two- or three-year-old bush. | 4 before | Not sown from seed — a bush from a nursery fruits years sooner. |
| Marigold | 6 before | on the date | on the date |
| Swiss chard | 5 before | 2 before | 2 before |
Tips and common mistakes
Treat the last frost date as a coin toss, not a deadline. Half of years are later than the average. Anything tender wants a week or two of margin and a look at the forecast.
Soil temperature matters more than air temperature for sowing. Beans, corn and squash rot in cold wet soil rather than germinating. A cheap soil thermometer settles the question better than a calendar does.
Count back from the fall frost for autumn crops. For a late sowing, the useful arithmetic is days to maturity plus a couple of weeks of margin, subtracted from your first fall frost date.
Do not start seeds indoors too early. A tomato sown ten weeks before it can go out becomes a leggy, root-bound plant that never quite recovers. The offsets here are deliberately not generous.
Harden off before transplanting. A week of increasing time outdoors before planting out saves plants that would otherwise stall or scorch.