With a tough winter and a seemingly unending Polar Vortex cold snap, it’s pretty hard to imagine what it must be like for some of our poor perennial plants, shivering their way through the winter under a layer of snow. While we are endlessly thankful for inventions like furnaces and space heaters, we don’t envy the lives of our tough perennials these days!
When you’re buying plants it’s easy to forget just how diverse they are. In the Garden Center, you can find a tropical monstera just steps away from a desert cactus. Different plants are made to be resilient to different types of conditions - and when we have harsh winters like this one it’s a reminder of how important it can be to choose plants that are tough enough to cut it in the worst of our annual conditions.
WHAT’S A ZONE?
We want to pick perennials that will be able to make it through our deepest freezes, but how can you know just from looking at a plant if it’s going to be tough enough? The US Department of Agriculture (USDA) created a “Zoning” system that breaks it down for us - and every plant has a zone number.
North America is incredibly diverse, stretching from Arctic tundra to lush tropical forests and everything in between. The USDA has broken the whole continent into 13 zones (originally 11), all based on the coldest expected winter temperatures. Plants rated for each zone can easily handle their zone’s coldest temperatures or warmer, but will struggle or not make it in weather any cooler. Each zone is further divided to narrow down the temperature expectations.
WHAT’S OUR ZONE?
Our area of Indiana is in zone 5b, and some southern parts of the state are in zone 6a. Plants suited to zone 5b can tolerate temperatures as cold as -10 or -15°F regularly. Keep in mind that cities are usually at least a few degrees warmer than open areas thanks to all of the buildings and roads.
WHAT DOES OUR ZONE MEAN?
The zone in your area tells you the coldest you can expect conditions to get, so you know which plants are tough enough to make it through the winter. Fortunately, you only have to be careful about the zones of plants you expect to keep outside over the winter. In the spring and summer, you can plant perennials rated for any zone as a summer annual and enjoy it for that one season, just like any other annual.
For a surefire garden that doesn’t require a lot of extra work or stress, you’ll want to make sure all of your perennials are designed for your zone or colder so that you know they’ll make it through the whole winter without any work. Don’t worry though, there’s a surprising number of absolutely gorgeous plants that will tough out the worst of our Indiana winters and still dazzle your garden during the growing season.
You can plant outside your zone, but within limits. Of course, sometimes you just fall in love with a plant and have to have it at home - and sometimes they aren’t in our zone. Anything quite far from our zone will only work as an annual or will need to be wintered indoors, but many gardeners find ways to make something rated for one zone warmer (zone 6 for us) work. If you take a shot at this, be warned - you will need to put a little more work into babying your out-of-zone plants and setting them up with mulch over the winter for protection. Plants rated more than one zone warmer than ours are unlikely to survive the winter, no matter how much effort you put into keeping them alive.
Zones are a handy description of how hardy your plants are. They give you insight into your plants’ needs and whether they’ll survive the winter before you commit to buying and planting. Paying attention to your plants’ zones is like reading a cheat sheet to your garden’s survival.