The Ultimate Guide to Plant Hardiness Zones

What are hardiness zones for gardening? 

When you’re ready to put your gardening hat on and figure out what special plants will grace your garden this season, the first thing you’ll need to know is your Plant Hardiness Zone. 
 
Specific to your region, and sometimes to your zip code, this zone tells you what plants will survive and thrive in the climate in which you are living. This is important to know when you are shopping for the new plants you will establish in your garden. What is more, it also determines whether a plant is an annual or perennial for your area.   

Plant hardiness zones range from Zone 1, which typically includes those closest to the North and South Pole, to Zone 13 for those who are closest to the equator. North America stays between Zone 1 and Zone 11.   

Zones are based on the average lowest temperatures over a 30-year period, as it is imperative for plants to survive your coldest winter in order to be considered a perennial. 

 

How to decide what to plant  

When you go to purchase a plant, whether online or in person, the plant will be tagged with the zone in which it survives all year round. For example, any plant tagged between Zone 3 and Zone 7 is considered a perennial for those zones, meaning it will survive the harsh winters and come back every season. 

On the other hand, plants tagged between Zone 8 and Zone 11 will be annuals for Zone 3 through Zone 7, and a perennial for Zone 8 through Zone 11.  

 

Why can a plant survive in one zone and not another? 

Plants that survive in warmer climates simply cannot survive the temperatures in lower climates. They often die once frost hits in those colder climates, which is why they are considered an annual for those colder zones. 

But, what about shrubs and perennials of colder climates? Why can they not survive in some warm climates?  

Like a bear that goes into hibernation, many perennials and shrubs do the same. They need a nice, long rest as a part of their natural growth cycle. This is so they can preserve their energy and use it to develop their roots beneath the surface as opposed to above ground. 

When some perennials and shrubs are planted in warmer climates, their biological clock may be completely thrown off! They might never take the time to rest and conserve their energy for below ground growth. These shrubs and perennials may not survive without this period of rest. That is why they may not be hardy in zones that do not experience a freeze. 

 

Microclimates 

Another thing to consider when learning about your zone is microclimate. This can be a small area within any zone that has slightly different zone characteristics. In some cases, there may be a small heat island, or a cooler area due to hills or valleys. It all depends on the surrounding geographical environment and structures like man-made objects like walls or fencing in your very own yard.  

Furthermore, your “zone” can change depending on what is on your property and how that affects plant protection from weather or sun exposure. It is up to every gardener to pay attention to the areas with which they can plant. This is all done through hands-on experience and will help inform which additional plants you can add to your garden because of this detailed knowledge. 

While many other factors play into the survival of perennial plants in your garden (like precipitation amounts, elevation, wind and freeze-thaw cycles), following the hardiness zone of your area is the first step in ensuring garden success.   

 

Planting Outside Your Zone – Right Plant, Right Place 

Proven Winners determines zone hardiness of plants through our extensive trialing throughout the United States. We determine plant hardiness based on overall health of the plant, vigor, disease resistance, and more. Yet, you may find success when planting a perennial that is one zone less hardy than your own.  

This is because there are spots in your yard or around your home that can protect perennials and keep them a few degrees warmer throughout the winter. Areas that are protected from wind, close to your home, or south-facing are good examples of where this can be true in your garden landscapes. 

So, if you really want to plant something that is hardy in zone 6, and you are in zone 5, find a spot in your yard that protects the perennial, and you may be able to enjoy its beautiful blooms for many years to come. 

Likewise, for warm climates, you may be able to place a shrub or perennial in a shady area that stays cooler than the rest of your yard. Therefore, you may find success planting shrubs and perennials that are hardy in one zone less than your own. 

For example, if a shrub is hardy up to zone 8 and you are in zone 9, you can plant it in a shady spot on the north side of your home.  

The trick to planting outside your zone is learning your unique yard and planting shrubs and perennials based on the elements of your yard. It is also understanding what a specific plant needs in order to thrive. All gardening is a learned skill and can take some time. That is perfectly okay and is exactly what makes it so fun!  

 

Planting in Containers 

The zone recommendations found on our plant tags refer to in-ground planting only. If you are interested in planting perennials and shrubs in your garden containers, you will need to pick plants that are two zones hardier than yours. 

Because there is less soil in a container than in the ground, plants in containers experience multiple cycles of thawing and freezing throughout the winter. This thawing and refreezing will cause many perennials and some woody shrubs to be less hardy. That is why you want to plant ones that are two zones hardier as they can withstand those cycles in your zone and survive the winters while placed in a pot. 


Interested in learning which zone you are in? Visit the USDA Plant Hardiness website and enter your zip code to find out!