How to Use Plant Hardiness Zones to Decide What to Grow

Let's say you've just heard about a gorgeous perennial or a spectacular shrub you want to add to your garden. Will it survive in your region? This dilemma is why the USDA Plant Hardiness Zone Map was created. A glance at it, and you can figure out your Zone. Terrific, now what?

Most hardy plants have a zone rating to indicate where they will survive the winters from year to year. Maybe the plant you have your eye on is hardy in Zones 5-9, and you live in Zone 4. That could be iffy, but you could try it if you don't mind a little risk for the thrill of growing something that usually wouldn't survive in your region. You could also play it safe and find another plant that can withstand your area's coldest temperatures. Either way, here's how you can use USDA Plant Hardiness Zones to guide your decision.

What Is the USDA Plant Hardiness Zone Map?

You've probably run across the USDA Plant Hardiness Zone Map or references to it in garden magazines and books, as well as on seed packets or in plant catalogs. This map divides the United States into 13 Zones (each of which is then divided into two subzones labeled "a" and "b"). Each Zone is 10°F warmer (or colder) in an average winter than the adjacent Zone. The lower the Zone number, the colder the region. The two subzones in each Zone represent 5°F increments.

Although factors other than temperature affect a plant's ability to survive in a particular climate, the USDA map is a good starting point when you're deciding what to grow. However, in many areas of the country, elevation and precipitation can have more of an effect on plant survival than only the temperature.

What You Can Grow in Your Hardiness Zone

For annual flowers, such as petunias, and vegetables, such as zucchini, you don't need to pay attention to hardiness zones because these plants usually complete their life cycle (seed sprouting to seed producing) in a single season. You might see these plants given a zone rating of 0 to indicate they aren't hardy anywhere. However, when you're dealing with perennials, vines, shrubs, and trees that typically live for many years, you want to know the coldest temperatures a species is expected to survive and compare that to the zone you're in.

When considering the hardiness zones a particular plant is rated for, think of that information as a guideline, not a guarantee that it will survive in your climate. The list below provides examples of plants that can take the cold in each USDA Plant Hardiness Zone. Only the coldest zone for each listed plant is considered; some plants won't thrive in substantially warmer areas, but some will. Check with the source of your plants for information on whether they are well-suited to your area.