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's 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 Pole, to zone 13 for those who are closest to the equator. North America encompasses every zone, while the contiguous United States (All states with the exception of Alaska and Hawaii) contains zone 3 through 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.
If you'd like to take a deeper dive into your (or any other) zone specifically, check out our blogs on each of the individual zones! We highlight the main areas and characteristics of the zone, any important information about the zone, and go over what plants tend to thrive there.
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 perennials and shrubs that are native to colder climates are planted in warmer ones, their biological clock can be completely thrown off— depriving them of the dormancy that many plants need for survival (let alone growth).
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 extensive trialing throughout the United States. It's based mainly on overall health of the plant, vigor, disease resistance, and so on. However, 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 how to read the conditions of your yard, and planting shrubs and perennials based on the elements you've noticed. It's equally important to understand what a specific plant needs in order to thrive.
We must note: when planting outside of the recommended zone range, you are running the risk of losing the plant. It often takes trial and error to be successful with it— don't plant anything outside of its zone range if you're not willing to potentially lose it. With that being said, it can be a very rewarding experience to grow something that most others in your area have not. It can be tough depending on what you're trying to grow, but it will undoubtably improve your skills as a gardener and bring you closer to the garden that you've created.
Like most others, gardening is a learned skill, and thus will take some time to perfect. That's 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! Then check out our individual blogs on each zone, and our favorite plants for them!
Happy planting!