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What Are Planting Zones & What is Plant Hardiness?

What Are Planting Zones?

You've heard about planting zones, but what are they and why should you pay attention to them?

Planting zones are the areas on a grow zone map the show you exactly which plants have the ability to thrive in a specific area. When you are shopping for new plants or deciding which seeds to grow in your garden you'll hear the terms "growing zones", "planting zones", and "plant hardiness zone" which can all become a little confusing. Don't stress, it's all quite simple. To start, the three terms are interchangeable. Now that we've got that out of the way, let's talk about what a plant hardiness zone is. Simply stated it allows growers to identify which plants are most likely to survive the winter in their area. Using the plant hardiness zone map you'll have a great starting point in making the best planting decisions for your location. 

Referring to the USDA's plant hardiness zones will let a gardener in North Dakota know that he can't plant an orange tree. It's also important to know that when a plant is hardy in one zone it will typically do well in any hardiness zone with a higher number. So most plants that are hardy in Zone 2 will also perform well in zone 9, as long as all of the plant's other requirements are being met.

 Planting Zone Temperature Ranges 

You'll see from the graphic below that planting hardiness zones range in temperature from -60° - 70°F. The USDA has broken the planting zones into thirteen unique areas, also known as USDA zones, that cover all of the United States including Alaska, Hawaii, and Puerto Rico.  Each zone covers a 10-degree range with Zone 1 being the coldest and Zone 13 having the warmest winters temperatures. 

What is Plant Hardiness?

Plant hardiness describes their ability to tolerate growing conditions like cold, heat, wind, drought or flooding. Hardiness is generally measured by the lowest temperate a plant can withstand, which is determined by the plant's genetics.

Plant genetics can be quite complicated. What you need to know is the genetics determine the plant's ability to withstand cold temperatures without incurring damage. Even different parts of the same plant may have different hardiness levels. Your favorite perennial may die when winter arrives, however, the roots are are hardy enough to form new growth in the spring.

There are many plants that have very, very specific requirements in order for them to thrive. As a gardener, you can adjust many things, like how much light and water the plant gets, the soil type, and soil pH, but it's very hard to control the temperature. You will have the best chance of having success in your garden by selecting plants with hardiness levels appropriate for your planting zone.

What Planting Zone Am I In?

Finding out which planting zone you're in will allow you to focus your time, attention, and money on purchasing plants with the best chance of surviving your winters. 

Click here to find out which Planting Zone you live in. When you look up your planting zone you'll notice each zone is broken down into an "a" and "b" within the zone. These sub-zones cover a 5-degree range. For example, Zone 9 has a temperature range of 20° - 30°F, whereas Zone 9a has a temperature range of 20° - 25°F and Zone 9b has a temperature range of 25° - 30°F. Breaking the Zones down is another way for you to decide which plants to add to your garden.


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