Garden & Water Utilities
When to start seeds indoors.
Enter your average last spring frost date and get the week to sow tomatoes, peppers, brassicas, cucumbers and more indoors, plus the earliest sensible date to plant them out. Runs in your browser.
Your frost date
Sow and plant-out dates
Fill the form and press Calculate.
Worked example
Last frost on 10 May 2026. Tomatoes go in 6 to 8 weeks before that: sow indoors between 15 March and 29 March. They go outside about a week after the last frost, 17 May. Broccoli, which tolerates light frost, is sown 4 to 6 weeks ahead (29 March to 12 April) and planted out 2 weeks before the last frost, 26 April.
How it works
Each crop has a window of weeks before the last frost to sow indoors and a planting-out offset relative to that frost. The tool subtracts those weeks from your date using plain calendar arithmetic. Cool-season crops (broccoli, cabbage, kale, lettuce, onions) go out before the last frost; tender crops (tomato, pepper, eggplant, basil, cucumber, squash, melon) go out after it, when nights stay mild.
What this is not. The weeks are typical ranges and vary by variety, light, heat and how big you want transplants. Your seed packet and local advice come first. A last frost date is an average, not a guarantee. Harden seedlings off for a week or so before planting out.
Sources and basis (checked 2026-10-06): the default weeks before last frost are typical ranges, not a published schedule for each crop. For one published example, Penn State Extension says you can sow most summer annuals indoors 6 to 8 weeks before the last frost (Sowing Annual Seeds). Find your own last frost date from a local frost table, for example the Old Farmer’s Almanac frost date lookup.
FAQ
When should I start tomato seeds indoors?
Six to eight weeks before your average last spring frost. With a last frost on 10 May that is 15 to 29 March. Starting earlier gives leggy, root-bound plants that are hard to keep alive until it is warm enough to plant out.
When do peppers and eggplants go in?
Eight to ten weeks before the last frost. They germinate slowly and need warmth, so a heat mat helps. They go outside about two weeks after the last frost, once nights stay mild.
How do I find my last frost date?
Look up a local frost table by postal or zip code, or ask your regional extension office or garden club. The date is an average, so there is still roughly a 50 percent chance of frost after it.
What if I am not sure of my frost date?
Pick the later of the dates you find. Seedlings kept a week longer indoors cost you little, while a frost on seedlings you planted too early can kill them.