🌱 Seed Starting Date Calculator

Enter your area's average last frost date and select a crop to see when to start seeds indoors for transplanting after the frost risk passes.

Average Last Frost Date

Crop

Counting back from the frost date

Each crop carries a fixed head start in weeks, subtracted from the date you enter:

sowing date = last frost date − (weeks × 7 days)

pepper, eggplant 8   tomato, marigold 7   broccoli, cabbage, basil 6
lettuce 5            cucumber, squash 3

With a last frost of 15 May, tomatoes come out at 27 March, peppers a week earlier on 20 March, and cucumbers not until 24 April. The figures are midpoints of the ranges catalogues quote: a packet saying 6–8 weeks for tomatoes is the 7 here.

The frost date is the shaky input

Find yours from freeze data, not a hardiness zone. The USDA Plant Hardiness Zone Map — revised in November 2023 on 1991–2020 normals, moving about half the US half a zone warmer — describes average winter minimum temperature. It says nothing about when spring frost ends; for that, use NOAA freeze-date probabilities or your county extension service.
An average is a coin toss. A 50% date means frost has arrived later than it in half of all years. NOAA also publishes 10% and 90% dates; tender crops are safer planned against the later, low-risk one.
Your garden is not the weather station. A frost hollow or north slope can run a fortnight behind a sheltered plot in the same town, and a city runs warmer than the fields around it.

The single indoor sowing date does not suit every crop listed. Cucumbers and squash dislike root disturbance and are often direct sown instead; hardened broccoli, cabbage and lettuce can go out weeks before the last frost rather than after it.

Frequently asked questions

When should I start tomato seeds indoors?

Seven weeks before your average last frost by this tool's figure, with catalogues saying six to eight. Starting too early gives you leggy, root-bound plants waiting on a cold garden.

How do I find my last frost date?

Look up freeze-date probabilities for a nearby station through NOAA or your extension office, then adjust for your site. Do not read it off a hardiness zone, which covers winter lows only.

Can I plant out on the last frost date itself?

For tender crops it is a gamble, since roughly half of years see a frost after it. Wait a week or two, watch the forecast, and harden plants off first.