Gardening

Seed Starting Calculator

Calculate when to start seeds based on your frost date

Enter your last frost date and select crops to get a personalized seed starting schedule — when to start indoors, when to direct sow, and when to transplant.

Seed Starting Calculator

Enter your last frost date to get a personalized seed starting schedule.

Find your average last frost date from local extension services

Select Crops

Enter your frost date and select crops to see your schedule.

How to Use

  1. 1
    Enter your last frost date

    Input the average date of the last spring frost for your area. Check your local extension office if unsure.

  2. 2
    Select crops to grow

    Pick the vegetables, herbs, or flowers you plan to grow this season from the searchable crop list.

  3. 3
    Follow the planting timeline

    Review your personalized calendar showing indoor start, direct sow, and transplant dates for each crop.

About

Timing is everything in vegetable gardening. Start seeds too early and you get leggy, root-bound transplants that struggle after planting out. Start too late and slow-maturing crops like tomatoes and peppers may not ripen before the first fall frost. The Seed Starting Calculator eliminates the guesswork by working backward from your local last frost date to generate a personalized planting schedule.

For each crop you select, the calculator shows three key dates: when to start seeds indoors under lights, when to direct sow outdoors (for crops that do not transplant well or germinate reliably in cool soil), and when to transplant hardened-off seedlings into the garden. The timing is based on each crop's weeks-to-transplant requirement and its frost sensitivity. Cool-season crops like broccoli, kale, and peas can be transplanted or sown before the last frost, while warm-season crops like tomatoes, peppers, squash, and basil must wait until frost risk has passed and soil temperatures have risen. The calculator also notes the hardening-off window and flags crops that benefit from succession sowing every two to three weeks for a continuous harvest throughout the season.

FAQ

How do I find my last frost date?
Your local cooperative extension office publishes average last spring frost dates based on historical weather data. In the US, the NOAA Climate Normals dataset provides frost probability dates for most weather stations. The date typically represents a 50 percent probability that the last freezing temperature has passed. For extra safety, many gardeners add one to two weeks to the average date before transplanting frost-sensitive crops like tomatoes and peppers.
Why start seeds indoors instead of direct sowing?
Starting seeds indoors extends the growing season by giving slow-maturing crops like tomatoes, peppers, eggplant, and broccoli a head start before outdoor temperatures are warm enough. Indoor starting also protects delicate seedlings from frost, heavy rain, and pests during their most vulnerable stage. Fast-maturing and cold-tolerant crops like lettuce, peas, radishes, and beans are usually direct sown because they germinate quickly in cool soil and transplant poorly.
What does 'weeks before last frost' mean on seed packets?
This notation tells you how many weeks before your average last frost date to start seeds indoors. 'Start 6-8 weeks before last frost' means if your last frost is May 15, you should sow seeds indoors between March 20 and April 3. The range accounts for variation in seed vigor and growing conditions. Starting too early produces leggy, root-bound seedlings; starting too late shortens the growing season and delays harvest.
When should I harden off seedlings before transplanting?
Hardening off should begin seven to ten days before your planned transplant date. Move seedlings outdoors to a sheltered, partially shaded spot for two to three hours the first day, then gradually increase sun exposure and time outdoors each day. By day seven, seedlings should be spending the full day outside including some direct sun. Bring them in if frost threatens. This process acclimates tender indoor-grown plants to outdoor UV intensity, wind, and temperature swings.
Can I start seeds in any container?
Seeds can be started in almost any clean container with drainage holes: cell trays, peat pots, yogurt cups, egg cartons, or soil blocks. The key requirements are drainage (waterlogged seeds rot), depth (at least two inches for most vegetables), and a sterile seed-starting mix (not garden soil, which harbors disease). Peat pots and soil blocks have the advantage of being transplanted directly into the garden without disturbing roots.