Know Your Climate

Your USDA Plant Hardiness Zone is based on the 30-year average of the single coldest temperature recorded each winter where you live (the current map uses 1991–2020 data). The map splits the US into 13 zones, each 10°F colder than the next, and each zone divides into an “a” and “b” half that are 5°F apart — so Zone 6b averages a winter low of −5 to 0°F, and 7a averages 0 to 5°F.

Its job is to tell you whether a perennial — a tree, shrub, or plant meant to live for years — can survive winter in your area. When a plant tag says “hardy to Zone 5,” it means that plant can take a Zone 5 winter.

This trips up a lot of new gardeners: your hardiness zone says nothing about your growing season. It ignores summer heat, how long your warm stretch lasts, snow cover, wind, and soil. Two gardens in the same zone can have very different seasons — a Zone 6 garden in the Midwest may have far fewer frost-free days than a Zone 6 garden on the Pacific coast.

For annual vegetables — the tomatoes, beans, and lettuce you replant every year — what actually matters is your frost dates, not your zone.

Two dates frame your year: the average last spring frost and the average first fall frost. The stretch between them is your frost-free growing season. In a Zone 5b–6a area, for example, the last frost might fall around April 8 and the first fall frost around October 23 — roughly a 197-day season.

These are averages, not guarantees, so a late cold snap is always possible. They tell you when it’s safe to set out tender plants and how many growing days you have before cold returns — which decides whether a long-season crop will even finish in time.

Cool-season crops — peas, lettuce, spinach, beets, radishes — can go in as soon as the ground can be worked in early spring, weeks before the last frost, and many shrug off a light frost. They bolt and turn bitter in summer heat, so they’re spring and fall crops.

Warm-season crops — tomatoes, peppers, beans, cucumbers, squash, melons — are frost-tender. They wait until after your last spring frost, once the soil has warmed. The longest-season heat lovers (melons, watermelon, winter squash) often wait until the soil is reliably warm, around a couple of weeks past the last frost.

Many cool-season crops can also be started indoors or direct-sown a set number of weeks before the last frost — your seed packet and each plant’s profile spell out the timing.

You don’t have to memorize any of this. Set your zip code in Account settings (the ☰ More menu) and HomeSown looks up your USDA zone and local frost dates for you.

From there, every plant in the Library shows a planting calendar tuned to where you live — when to start seeds indoors, when to plant outside, and when to expect harvest — and your My Garden tasks follow the same schedule. Set it once and the timing follows you around the app.