A planting calendar by USDA zone

The USDA hardiness zones on every plant tag answer one question, winter cold, and planting calendars borrow them because cold sorts the year’s work better than anything else. A zone tells you when your ground thaws, roughly when it closes, and where your average last frost sits. The table below turns that into windows for the planting seasons this guide covers. Treat it as a frame, not a verdict: the soil thermometer and your own notebook always outrank a table.

What a zone actually says

Each USDA zone is a band of ten degrees Fahrenheit in average annual extreme minimum temperature, the cold of a typical worst winter, and each band splits into a and b at five degrees. That is all a zone says. It says nothing about summer heat, rainfall or soil, which is why a zone 7 in the humid Southeast grows a different garden from a zone 7 in the dry Mountain West. It is also why the same zone number makes one column of a planting calendar workable everywhere: thaw, ground closure and frost dates all hang off winter cold, loosely enough to argue with, tightly enough to plan with.

The windows by zone band

Bare root trees, roses and hardy perennials ride the first column: ship windows, explained in the shipping guide, follow it almost exactly. Tender perennials and vegetables wait for the second column plus a soil reading above their threshold. The third column is the fall planting window for woody stock, which opens fully two months before it closes, and which most gardeners leave empty.

How to bend the table to your garden

Three corrections cover most gardens. Elevation and cold air pockets move you half a zone colder; south slopes and cities move you half a zone warmer, so measure rather than argue. A low spot that gathers frost is a month late for tender stock whatever the zone says. And mulch left in place over winter keeps soil cold well into spring, which is why it is pulled back a fortnight before planting to let the sun work. Your own records beat everything else: a notebook of last frost, first frost and soil readings, kept honestly for two years, is a better calendar for your beds than this one, which is exactly what this one is for.

Ordering against the calendar

The calendar runs the mail order trade from its far end. Specialty nurseries build winter catalogs for spring ships, and the varieties that sell out are gone by late winter, so the ordering checklist is simply the calendar read backward:

• Order in deep winter, while every variety on the list is still dug and in stock.
• Bare root and hardy stock: ask for the earliest sensible ship slot in your zone band.
• Tender stock: book the slot after your average last frost, not before it.
• Fall planting: order in summer for the autumn reopening of container shipping.
• Write the expected ship week beside each order, and unpack on arrival day.

Mistakes to avoid

Calendar mistakes repeat every spring. Planting by date instead of soil, when two gardens in one town can be a fortnight apart in readiness. Trusting the zone number to cover summer heat, which kills more first year plants than winter does. Forgetting the fall column, and cramming the whole year’s woody planting into one frantic spring. Buying tender plants the first warm week of April and holding them on a porch through three cold nights. And treating an average frost date as a promise, when the word average means the frost will be early about half the years of your life.

The calendar in one habit

Order in winter, plant hardy stock as the soil reaches the mid forties, plant tender stock after your frost date and a warm soil reading, plant woody stock again in the two months before the ground closes. Everything else is weather. Use the table to choose the week, the thermometer to choose the day, and the notebook to correct both next year, and the season stops being a guess.