Guide
Two systems shape when and what you can grow: USDA hardiness zones and frost dates. Gardeners often confuse the two, but they answer different questions. Understanding how they work together is the foundation of a reliable planting schedule.
The USDA Plant Hardiness Zone Map divides North America into zones from 1 through 13, based on the average annual minimum winter temperature. Each zone spans a 10°F band and is split into "a" and "b" halves of 5°F each. Zone 5, for example, has average winter lows of −20°F to −10°F. The map is used mainly to judge whether a perennial, tree, or shrub can survive winter in your area.
Here's the crucial distinction: hardiness zones tell you what can survive winter, while frost dates tell you when it's safe to plant in spring and when to harvest before fall. For annual vegetables — tomatoes, beans, lettuce, squash — frost dates are far more useful than your zone number.
| Hardiness zone | Frost dates | |
|---|---|---|
| Measures | Winter minimum temperature | Timing of first/last freeze |
| Best for | Perennials, trees, shrubs | Annual vegetables & flowers |
| Answers | "Will it survive here?" | "When do I plant?" |
A good planting schedule anchors every crop to your frost dates:
The frost date planner generates all of these dates automatically for 50+ crops when you enter your zip code — spring sowing, transplanting, and fall planting windows in one view.
Two gardens in the same hardiness zone can have very different growing seasons. A coastal zone 8 and an inland zone 8 share winter lows but may differ by weeks in frost timing and summer heat. That's why relying only on a zone number leads to mistimed plantings. Pair your zone with local frost dates — and your own microclimate observations — for the most accurate schedule.
The USDA periodically revises its hardiness map as climate data accumulates; the most recent update was released in 2023, and some regions shifted half a zone warmer. It's worth rechecking your zone every few years, especially when choosing long-lived perennials. Frost dates, likewise, drift gradually and are refreshed from ongoing NOAA climate records.