When to start seeds indoors, without guessing
Sowplot has one tool and four guides. The tool turns your last frost date into a sowing schedule for fourteen crops; the guides cover the setup that decides whether those seeds survive.
Start here
Know your last frost date? Open the seed starting calendar and it will build the table for you.
Why the frost date, and not the calendar month
"Start tomatoes in March" is wrong somewhere in the country every single year. Gardening advice tied to a month only works in the zone it was written for; the date that actually matters is the average last spring frost where you garden, and everything else counts back from it. A tomato needs six to eight weeks indoors, a pepper eight to ten, a cucumber three to four — those weeks are the plant's biology, the frost date is yours.
The calendar here does that arithmetic for fourteen common crops and shows the window as a range, because a range is honest: sow early in the window with strong light and heat, late in the window if your setup is a windowsill.