When planning your garden it is important to think about what type of plants will thrive in your climate. Your garden will be easier to care for if you consider factors like rainfall, temperature, and amount of daylight hours before choosing what types of plants to include in your garden. Luckily, there are a few tools that can help you with this, and they are known as hardiness zone maps. These include the USDA Hardiness Zone Map, the Sunset Garden Climate Map, and a number of international maps.
USDA Hardiness Zone Map
This map was developed by researchers from the U.S. Department of Agriculture (USDA). In the United States this map is generally accepted as the standard by which to gauge plant hardiness. Most gardening books will refer to the USDA hardiness zones, and seed packets will also usually classify plants according to this standard.
How does it work?
The USDA hardiness zone map is based on average minimum winter temperatures, which were used to delineate 11 zones across the United States. Zone 1 is the coldest and Zone 11 is the warmest; plants will generally survive the winter in their zone and warmer zones. For example, a plant that is classified as Zone 6 will survive the winter in zones 7 though 11 as well.
How do I use the map?
It is important to remember that the USDA hardiness zones are only a guide, and that many factors besides winter lows will impact the ability of plants to thrive in your climate. It is often a good idea to cross-reference plant encyclopedias to assure that you have an accurate idea of how well any particular plant will do in your garden. Asking gardening experts in your area, such as university extension agents and nursery workers, may also give you a better idea of how to care for a particular plant.
Online Hardiness Map Resources:
- US Arboretum
This web version of the USDA map provides information on how the map was created and how to use it.
- National Gardening Association
Here you will find a useful online USDA map that allows you to locate your region and research plants appropriate for your zone.
- The National Arbor Day Foundation
For a quick reference, use this search engine to determine your hardiness zone by zip code.
Sunset Garden Climate Zone Map
There are many climate factors other than the USDA minimum winter temperatures that can impact a plants survival in any given region. That is why Sunset Magazine developed an alternative plant classification system nearly 40 years ago, which takes into account factors such as: rainfall, humidity, summer highs, and the length of the growing season. The drawback to using the Sunset Map is that, although it is popular in many Western states, it is not generally used as a reference point in gardening encyclopedias or plant catalogues.
Canada Plant Hardiness Zone Map (The Atlas of Canada)
South American Plant Hardiness Zone Map (Backyard Gardener)
Online European Climate Map (Garden Web)
China Hardiness Zone Map (Backyard Gardener)