Seed starting date calculator
Enter the average date of your last spring frost and pick a crop. The calculator counts back the usual number of weeks to give a window for sowing seeds indoors.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter your average last spring frost date.
- Pick a crop.
- Sow between the two dates shown.
How it works
The start window is the frost date minus the longest and the shortest number of weeks for the crop: tomato 6–8, pepper 8–10, eggplant 8–10, broccoli 6–8, cabbage 6–8, lettuce 4–6, onion 10–12, basil 4–6, cucumber 2–4, squash 2–4. These are general rules of thumb.
Worked example
Last frost 15 April, tomatoes at 6–8 weeks: 8 weeks back is 18 February, 6 weeks back is 4 March. Sow tomatoes between 18 February and 4 March.
Tips
- Warm-season crops should only go outdoors after the frost risk is over; harden them off for a week first.
- A heat mat helps peppers and eggplants germinate.
Frequently asked questions
Where do I find my last frost date?
Local extension services, gardening clubs and weather-service frost tables list an average last spring frost for your area. It is an average, so frost can still come later.
Are these numbers exact?
No. They are general guidance, as printed on many seed packets. Variety, warmth of your growing space and how big you want transplants to be all shift the best date, so follow your packet when it differs.
Why does cucumber start so late?
Cucumbers and squash grow fast and dislike root disturbance, so seedlings only need two to four weeks before they go outside after the frost has passed.
What about crops not listed?
Root vegetables and peas are usually sown directly outdoors. For other transplants, check the packet for “weeks before last frost”.