How the schedule works
Most seed packets give a number of weeks to start seeds indoors before transplanting — for example 6–8 weeks for tomatoes and 8–10 for peppers. The calculator counts back from your plant-out date by that many weeks. It suggests potting up or thinning to one seedling per cell once seedlings have their first true leaves, and starting to harden off a week before planting: put plants outside in shade for an hour or two and lengthen the time and sun each day.
Choosing a plant-out date
Tender crops go out one to three weeks after your last frost date, when nights stay above about 50°F. Cold-tolerant brassicas and onions can go out two to four weeks before. With your ZIP entered, we fill in the date from the crop’s timing and your frost dates; you can always type your own.
Questions gardeners ask
When should I start tomato seeds indoors?
About 6–8 weeks before you plan to plant out, which is usually 1–3 weeks after your last frost date.
Can I start seeds too early?
Yes. Seedlings held indoors too long get leggy and root-bound and often establish worse than younger transplants.