Seed Starting Countdown Planner: Your Sowing Dates
Mat Caissy
Open the tool: Seed-Starting Schedule Calculator. For the full guide, read How to Start Seeds Indoors: A Schedule by Plant Type.
New to starting seeds indoors? Read the full guide: How to Start Seeds Indoors: A Schedule by Plant Type. This planner counts back from your transplant date to give you sowing dates by crop, with a hardening off window at the end.
Pick your transplant date and one crop, and you get a sowing window, not a single guessed date. It is free, it needs no account, and it saves nothing. Use the seed packet when its instructions differ from a general schedule, because variety and local conditions win over a general table.
How to use this tool
Primary action: choose Update schedule.
Result views: Timeline · Calendar.
- Enter the outdoor transplant date for that crop, not just your last frost date, because crops transplant at different times.
- Choose one crop, and read the sowing window, not a single date.
- Reserve the last one to two weeks before transplanting for hardening off, starting with a few hours in shade.
- Run it again for each crop, because a tomato and a cucumber do not share a start date.
- Check your seed packet last. If it differs from this general schedule, follow the packet.
What your result means
The sowing window is the indoor growing period counted back from transplanting. Sow at the early end if you want a larger seedling, and at the late end if you want a smaller, easier seedling to hold. The hardening off window is the gradual move outdoors, with more sun and time each day, so seedlings do not shock on transplant day. For the full vegetable and flower schedules, see How to Start Seeds Indoors: A Schedule by Plant Type.
If your transplant date moves because of weather, move the sowing window with it. A seedling held too long indoors is a common reason for leggy, weak transplants.
Frequently asked questions
Do I need an account?
No. This planner is free and needs no sign-up.
Is my data saved?
No. Your transplant date and crop are not saved.
Should I start all crops on the same date?
No. Count back from each crop's transplant date, using its own indoor period. Tomatoes need roughly 6 to 8 weeks indoors, while cucumbers and squash need only 2 to 3 weeks.
What if my seed packet differs from this planner?
Follow the packet. Variety, seed age, and local conditions can change the indoor period, and the packet is written for that variety.
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