Why knowing your USDA hardiness zone is critical to keeping plants alive – CNET


Chris Monroe / CNET

At first glance, gardening seems easy. Dig a hole, plant a seed and water it. However, a little planning goes far and you should consider the size of your garden, the wealth of your soil and the hardiness zone of the region in which you live.

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What are hardiness zones?

A winter hardiness zone is a geographical zone in which certain plants grow best in this particular climate. The USDA Hardiness Zone Map divides the United States and Canada into 13 zones, with Zone 1 being the northernmost and Zone 13 being the southernmost. In winter, each zone is on average 10 degrees warmer or colder than the zone next to it.

Most zones have very different weather conditions than the others. For example, zones 4a and 4b in the United States will almost always get snow each year, while zones 8a and 8b are unlikely to see snow.

The hardiness of a plant is largely measured by how well it can withstand cold winter temperatures. Something that can survive the minimum temperature in zone 5 would feel zone 4 too cold.


The USDA 2012 Plant Hardiness Zone Map


Many plants, fruits, and vegetables sold at your local nursery or hardware store contain a winter hardiness zone suggestion on their labels based on this card. The USDA Plant Hardiness Zone Map 2012 is the latest version developed by the USDA Agricultural Research Service (ARS) and the PRISM Climate Group of Oregon State University (OSU).

There are maps for Great Britain and Australia, but they are not as up to date as those for the USA. Still, they can be a useful resource for deciding what to plant in your garden.

Why do i need it

You can adjust to many factors in your garden, such as shade, water drainage or soil quality. What you cannot control is the weather.

This is where the Plant Hardiness Zone Map comes into play. It helps experts and hobby gardeners to recognize which plants have the highest chance of success in their climate and to avoid planting something that would never survive the winter or a spring frost. If you want a plant, vegetable, or tree to survive and grow year after year, it must be able to tolerate the conditions in your area.

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The map is also a great way to compare your climate with the ideal climate for a particular plant you want to grow. That doesn’t always mean that you can’t grow this plant near you. It just means that you should pay special attention to responding to its sensitivities. For example, if a vegetable grows better in a warmer climate, you should cover it every time there is a frost warning in your area.

Inconsistencies and exceptions

The USDA card is a good guideline, but not a strict rule. The National Gardening Association notes that while the map does a good job of protecting the climate in the eastern half of North America, it does have some shortcomings, especially in the west, where the climate is much more diverse.

For example, Seattle and Tuscon are both in Zone 8, although there is a big difference between the rainy coastal climate of Seattle and the drier Tuscon inland.

Zones are a helpful guide, but you should also consider the direction and amount of sunlight your garden receives during the day. The orientation of your garden towards sun and shade plays a major role in the life cycle of your plants.

Hardiness zones can vary between cities and even within the same city.

Screenshot by Sarah Mitroff / CNET

If you want to view the zone for your region, you can use the USDA’s interactive map to find the plant hardness zone exactly where you are. And yes, winter hardiness zones can be different in the city.

My neighborhood is in Zone 6b, but the part of the city a little further west is classified as Zone 7a. While you may not find much of a difference where plants can survive in two such similar zones, it is still important to know where your garden is on the map. For my region, vegetables like radishes, lettuce, peas, and tomatoes will probably thrive if they are properly cared for.

With knowledge of your home’s hardiness zone, you can safely sow, grow and harvest the plants that are best suited for your part of the country this season.

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