How to Build a Planting Calendar From Your Frost Dates

Seed packets rarely give you a date. They give you an instruction like "start indoors 6 to 8 weeks before last frost" or "direct sow 2 weeks after last frost", because the right calendar day depends entirely on where you garden. Everything in a vegetable season is measured from two anchors: the last spring frost and the first fall frost.

Fix those two dates and the rest of the schedule falls out of them arithmetically.

Start From Your Hardiness Zone

The quickest way to both anchors is your USDA hardiness zone. Our garden planting calendar generator takes a zone from 3a to 10b and works out a full crop schedule from the frost dates typical of that zone: start indoors, plant out, and an approximate harvest window for around twenty common vegetables.

One caveat worth stating plainly, because it changes how you should read the output: those frost dates are zone averages. A zone spans a wide band of country, and elevation, slope and how close you are to water can move your real last frost by two weeks in either direction. Treat the generated dates as a starting frame, then adjust them with a local figure from your county extension service or from your own records.

Work Backwards for Transplants

Long-season crops -- tomatoes, peppers, eggplant, onions -- have to be started indoors, and the start date is counted backwards from last frost. Peppers at eight weeks before last frost usually means sowing in a tray while there is still snow outside. Miss that window by three weeks and you do not get three weeks less growth; you get a plant that is still setting fruit when the fall frost arrives.

Work Forwards for Direct Sowing

Cool-season crops go out before last frost. Peas, spinach and radishes tolerate cold soil and resent heat, so the risk is sowing them too late rather than too early. Warm-season direct sows -- beans, corn, squash -- wait until after last frost, when the soil has actually warmed.

Check the Harvest Against Fall

Add days to maturity to your plant-out date and compare the result with your first fall frost. If a hundred-day pumpkin does not finish before frost in your zone, you either start it indoors, choose a shorter-season variety, or accept that it is a gamble.

Put It Somewhere You Will See It

A planting schedule is useless in a drawer. Print the season's dates onto a monthly calendar for the months that matter, or mark the whole run of them on a yearly calendar so the sowing weeks are visible from across the room.