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How to Choose the Right Plants for Your Climate

Not all plants are right for all regions. A plant’s suitability to your garden depends on several climate-related factors, including:

High and low temperatures during the summer and winter
Length of the growing season
Amount and timing of rainfall
Humidity
Number of daylight hours

Some of these factors apply more to some types of plants than to others. For instance, cold winter temperatures aren’t as important for annuals and vegetables, which live only through the summer. But climate in general is a crucial factor to take into account when you’re considering what plants to grow in your garden.

Resources for Choosing the Right Plants for Your Climate

To help select plants that will thrive in your region, you can:

Consult zone maps
Consider the length of the growing season in your area
Ask local gardeners and nurseries for advice

Zone Maps

In gardening, a zone map is a map that divides a country or continent into zones based on climate factors and the types of plants that grow best in those zones. In the United States, a number of different organizations have developed zone maps, each of which uses different climate factors to determine its climate zones. The zone maps you’re most likely to encounter are covered in this section.

USDA Plant Hardiness Zone Map

The U.S. Department of Agriculture (USDA) has developed the USDA Plant Hardiness Zone Map, which divides North America into 11 hardiness zones based on the average low temperature of each zone’s winter. The zones are numbered from 1–11, with 1 being the coldest and 11 the warmest. Because it’s based on winter low temperatures, the USDA Plant Hardiness Zone Map is used primarily for year-round (permanent) plants such as perennials, trees, and shrubs—not for annuals, which are meant to live only one season and aren’t expected to survive the winter.

Seed catalogs, plant encyclopedias, and nurseries label permanent plants with a number that indicates the zones in which they are hardy (can survive). For instance, a zone 5 perennial could survive the winter in zone 5 and all warmer zones, whereas a plant marked “zones 3–8” can tolerate those zones only—not the colder zones below zone 3 or the warmer zones above zone 8. Once you know the USDA hardiness zone of your area, you can be confident choosing plants that will be able to survive the winter in your garden. To find the hardiness zone of the place where you live, visit www.usna.usda.gov/Hardzone/ushzmap.html.

Sunset Zone Map

Many gardeners, particularly in the western United States, prefer the Sunset Zone Map to the USDA Plant Hardiness Zone Map for determining plant suitability. The Sunset Zone Map was created by Sunset magazine (www.sunset.com) and divides the United States into 45 climate zones. These regions are more precise than the USDA zones because they take into account climate factors beyond just winter temperatures. To see why this is important, consider the case of Austin, Texas, and Gainesville, Florida. Both cities are in zone 8 of the USDA Plant Hardiness Zone Map because their winter low temperatures are similar. But Gainesville’s climate is much wetter than Austin’s, which means that the specific plants that are likely to thrive in each region are quite different. The Sunset Zone Map captures this difference.

To access the Sunset Zone Map and find out which climate zone you live in, go to www.sunset.com/sunset/garden and look for the link to “Sunset Climate Zones.” Keep in mind, though, that most seed catalog and plant encyclopedias mark their plants with the USDA zone number, not the Sunset zone number. To use the Sunset Zone Map, you’ll have to do a little research and trial and error to figure out how your Sunset zone matches up with your USDA zone.

Heat Zone Map

The American Horticultural Society has developed a Heat Zone Map, which is similar to the USDA Plant Hardiness Zone Map, except that it separates the United States into 12 heat zones based on the number of days that an area experiences temperatures over 86°F (the temperature above which plants may suffer damage from heat). The heat zones are numbered 1–12, with 1 being the coolest and 12 the hottest. A growing number of garden centers and suppliers now code plants for heat zones as well as USDA hardiness zones. Unlike the USDA map, the Heat Zone Map applies not only to year-round plants, such as perennials, shrubs, and trees, but also to annuals, vegetables, and herbs as well.

Length of Growing Season

The growing season is the period between the last frost of winter/spring and the first frost of summer/autumn. Knowing the length of your region’s growing season is important when deciding what annuals and vegetables to buy. The growing season helps you decide:

What to grow: If a region’s growing season isn’t long enough to support the full growth and maturation of a single-season plant, then the plant probably won’t reach full maturity before the first autumn frost comes along.
When to grow: Instructions for growing plants often refer to the last frost rather than to a specific date. For example, the instructions might tell you to plant a flower two weeks after the last frost. It’s hard to follow these directions correctly unless you know when the last frost is.

Growing-Season Length and USDA Zones

The following table lists the average last and first frost by USDA hardiness zones and also provides the average length of the growing season in each zone.

Hardiness Zone	Last Frost	First Frost	Growing-Season Length
1	June 15	July 15	30 days
2	May 15	August 15	90 days
3	May 15	September 15	120 days
4	May 15	September 15	120 days
5	April 30	October 15	165 days
6	April 15	October 15	180 days
7	April 15	October 15	180 days
8	March 10	November 15	245 days
9	February 15	December 15	265 days
10	January 20	December 15	335 days
11	No frost	No frost	365 days

When buying seeds for vegetables or annuals, pay attention to the days to maturity or days to harvest number listed on the seed package. Look for annuals or vegetables that reach maturity within the window of your growing season.

Local Nurseries and Gardeners

If you’re not interested in poring over zone maps or researching growing season length, talk to experts at your local nursery or to nearby friends and acquaintances who garden to find plants that will grow well in your garden.

Local gardeners: They’ve learned from experience the kinds of plants that work in their garden. Plus, you may be able to visit their gardens to see what you like.
Nurseries: In general, if a plant is being sold at your local nursery, it’s probably hardy to your climate. Local nurseries generally sell only plants that will do well in the region.

Local nurseries and gardeners can also provide expert advice, opinions, and anecdotal knowledge that go beyond what any zone map can offer. Though zone maps can give you a general sense of your region’s climate, they can’t give you specific details abut the microclimate of your garden.

Microclimates

A microclimate refers to the specific climate of a very small area. Your garden’s microclimate can be affected by all sorts of factors—a nearby pond that keeps the air a little cooler and more humid, a building or tree on your block that throws shade across your garden for part of the day, or even a storm gutter that’s positioned so that part of your garden gets a lot of water when it rains. Because plants differ in their water and temperature needs and preferences for direct sun or shade, the microclimate in your garden will affect both the plants you choose to grow and the specific spots in which you plant them.

Acknowledgments & Disclaimer