How to Read Your SowWhen Planting Calendar
Updated June 2026 · SowWhen
When you enter your ZIP code or pick your USDA hardiness zone, SowWhen builds a month-by-month schedule for every crop it covers. The schedule isn't a generic seed-packet suggestion — it is calculated from your zone's average last spring frost and first fall frost, the two dates that govern almost everything in a vegetable garden. This guide walks through what each row of your calendar is telling you to do, and when.
The four actions on every calendar
Each crop shows up to four windows. "Start seeds indoors" is the range to sow into trays or pots under a light or on a windowsill, giving frost-tender, slow-growing plants a head start before it is safe to be outside. "Transplant outdoors" is when those seedlings, once hardened off, can go into the ground. "Direct sow" is the window to plant seeds straight into the garden bed. "Harvest" is a projection — days-to-maturity counted forward from planting — so you know roughly when to expect food, and, just as usefully, whether a crop still has time to finish before your fall frost.
Not every crop has all four. Carrots and beans are direct-sown only, because their roots and fast growth make transplanting pointless or harmful. Tomatoes and peppers are almost always started indoors and transplanted, because they need weeks of a head start that the season won't give them outdoors. SowWhen only shows the windows that actually apply to each plant, so an empty column is information too.
Reading the timing: it's all relative to frost
The reason two gardeners in different states get different dates for the same tomato is frost. A packet that says "start indoors 6–8 weeks before last frost" means late February in a mild zone and late April in a cold one. SowWhen resolves that math for you: it takes each crop's rule, applies your zone's frost dates, and prints real calendar weeks. You never have to count backwards from a date you had to look up yourself.
Because these are averages, treat the windows as a planning range rather than a hard deadline. If your spring is running warm, lean toward the early end; if a late cold snap is forecast, wait. The single most important habit is to not put tender plants out before your last-frost window — a single frost undoes months of work.
A simple weekly routine
The calendar rewards checking in rather than reading once. Early in the year, your only jobs are indoor sowings — a tray of tomatoes here, peppers there. As your last frost approaches, transplanting and direct-sowing windows open in waves. Through summer, harvest windows arrive and fall sowing windows open for a second season. Save your zone (SowWhen remembers it) and glance at the current month whenever you have a free weekend; the "what to do now" view keeps you a step ahead instead of scrambling.
If you want the calendar off-screen, you can export it to your phone's calendar as reminders or print a clean one-page version for the shed. However you use it, the logic is the same: know your frost dates, act within the windows, and let the projected harvest tell you whether there's still time.
Build your planting calendar →