Enrichment · Cultural Studies · Gardening

One frost date,
a whole season
of sowing days.

Type the average last spring frost where you garden. The calculator counts the weeks back and forward for each crop and hands you a sowing calendar, from the first onion seeds in winter to beans and corn after the frost.

Make the calendarWhat you get

The seed starting calculator

The worked example is a made-up school garden with an April 15 last frost and an October 20 first frost. Nothing you type leaves this browser.

Loading the calculator. If nothing appears, turn on JavaScript.

What you get

Enrichment · Cultural StudiesFree

What you finish with
A sowing calendar for 20 crops: when to sow indoors and when to plant or sow outdoors, the first seeds to start, and the frost-free season. It prints as a calendar and downloads as a spreadsheet.
Who it is for
Home and school gardeners, garden clubs, teachers running a school garden, and families growing vegetables.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a calendar; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Cultural Studies space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Find your average last spring frost date from a local weather station or extension office.
  2. Type it, and the first fall frost if you know it.
  3. Filter to the crops you grow.
  4. Read the indoor and outdoor windows.
  5. Print the calendar and hang it by the seed trays.

Make the calendar

How the dates are worked out

Weeks before and after one date.

The worked example: tomatoesLast frostApr 15the average date− 8 to 6 weeksFeb 18to Mar 4: sow tomatoes+ 1 to 2 weeksApr 22to Apr 29: plant outSeason188 daysApr 15 to Oct 20The worked example: tomatoesLast frostApr 15the average date− 8 to 6 weeksFeb 18to Mar 4: sow tomatoes+ 1 to 2 weeksApr 22to Apr 29: plant outSeason188 daysApr 15 to Oct 20
Every date hangs off one number: the average last frost. Seeds go in a set number of weeks before it so the plants are the right size when it is safe to set them out.

Why the frost date

Frost kills tender plants, so the average date of the last spring frost is the hinge of the garden year. Slow crops such as onions and peppers are started indoors 10 to 12 weeks ahead so they are sturdy transplants by planting time; fast ones such as cucumbers need only 3 or 4 weeks. Cool-season crops such as peas, lettuce and cabbage go outside before the frost; warm-season crops go out after it.

Typical, not exact

The windows here are the ranges commonly published by university extension services. Varieties differ, so where the seed packet gives its own timing, use that. The frost date itself is an average: in roughly half of years the last frost comes later, which is why warm-season transplants wait a week or two past it.

Sources

  1. University of Minnesota Extension. Starting seeds indoors (extension.umn.edu).
  2. Penn State Extension. Starting plants from seeds and Vegetable garden planting guide (extension.psu.edu).
  3. National Oceanic and Atmospheric Administration, National Centers for Environmental Information. U.S. climate normals, including freeze dates (ncei.noaa.gov).
  4. Colorado State University Extension. Fact sheet 7.061, Vegetable planting guide (extension.colostate.edu).

The worked example is made up. Weather varies from year to year; watch the forecast at planting time. Your dates stay in this browser. Support: team@caveatacademic.com.