Hardiness Zones are Shifting With Climate Change

Posted In: , ,
microburst thunderstorm clouds on the horizon as a pefect analogy for changing hardiness and climate zones

We will have to deal with climate zone map changes in the near future. Climate shifts have already begun to affect our everyday lives in ways even scientists can’t always predict. For example – many expert analyses suggest that plant hardiness zones have shifted in the past couple of decades; if nothing is done, they are only set to move further in the future. We will explore the causes and repercussions of this phenomenon below.

Hardiness Zones Basics

So, what are hardiness zones in the first place? Basically, these are specific geographic zones with relatively distinct climates; at least from the point of view of plant growth. With this in mind, Canada and the United States are divided into 13 zones; the thirteenth zone is the one that’s the furthest to the south. Each of these zones is, generally, colder or warmer by about 10 degrees compared to its adjacent ones.

As you may imagine, most of the zones house varying weather conditions. For example, Zone 8B in the US is almost guaranteed to get snow every year; unlike Zone 4A. And the actual “hardiness” of the plants found in these zones indicates how well the plants are able to withstand extremely cold seasons.

Climate Zone Maps Worldwide

Canada’s Plant Hardiness Zone Map –> Click Here

US Plant Hardiness Zone Map –> Click here

UK Hardiness Zone Map –> Click here

European Hardiness Zone Maps –> Click here

Asian Climate Zone Maps –> Click here

World Climate Zone Map — > Click Here

Video Explaining Plant Hardiness Zones

Paradigm Shifts

Most maps conducted by the relevant authorities in the past few decades indicate that the climate zone maps are shifting. Analyses show that the last 40 years have seen a change occur at a hitherto unprecedented speed. And the correct definition of these zones is absolutely crucial for any kind of plant growth; from casual gardening to large-scale agriculture. Judging by these zones – growers and gardeners can determine what plants will be able to survive where, and which won’t be able to withstand the cold of the winter.

Experts from the National Centers for Environmental Information indicate that the hardiness zones are moving north, “creeping up” to higher elevations and latitudes. So, while you may not be able to grow bananas in Central Park just yet, don’t count this possibility out in the future. These days, you can already successfully grow plants farther north than half a century ago.

Important Factors

Considering this, just what are the factors that determine how far north you may grow a certain plant, and which plants can survive winter? Naturally, the single biggest factor is the cold. That’s why lemon trees are traditionally a “southern” fruit; they’re extremely sensitive to cold and frost. Their ideal zones are generally between 11 and 9, as they don’t go below 20 degrees on average. Conversely, sweet cherry trees are far less sensitive to cold winters; being able to thrive as far north as zone 5. Apart from that, there are other factors to think about; like soil type, precipitation, and light; all of these influence whether a plant will be able to survive in a given location.

But these days, all of this is changing. Many people have reported that they are forced to alter their planting schedules and habits due to an increasingly balmier climate during the winter. They’re able to grow perennial plants that were, up until a couple of years ago, a few temperate zones to the south; they’re also overwintering plantations that were protected and dug up before.

Governmental Stances

This isn’t just empty talk and citing of empirical cases; the Department of Agriculture also maintains a hardiness zone map. And while this federal agency won’t mention climate change, their detailed maps of hardiness zones have been altered in the past decades; climate change being the only way that, well, changes to the climate could happen. For instance, their mapmaking process is quite different for the 2012 map than it was for the one in 1990, making it nigh impossible to rule out global warming as the culprit.

The National Climate Assessment, constructed by several different government agencies, attributed the global warming evident from changes in hardiness maps to fossil fuel emissions. In other words, this is a confirmation of man-made climate change.

What This Means For Growers

It should be noted that hardiness maps present a general, overall look at zones of plant growth; not an absolute that guarantees success. For instance, researchers from Oregon State University that have worked on the 2012 map of hardiness zones also talk about cold snaps. Even though they do confirm that growing zones are gradually going northward; quick cold snaps reminiscent of the old days can still easily wipe out all of the less-hardy seedlings. All in all, these maps show the average changes due to global warming; not the extreme volatility in weather that can happen from year to year.

Still, if you want to study the correlation between local vegetation and global climate change; such maps are a decent place to start. And sure, these changes might mean that you can grow some plants up north with fewer risks. But this also means that you will see new naturally occurring species in these areas. And these can be potentially invasive plant species; causing havoc to the local ecosystem!


Emma is a gardener, a bookkeeper, writer, and mother of three. She is spending her time mostly in her garden. When she is not there, you will find her working on developing her own line of homemade natural skincare products. 

Share with Friends and Family

More of Interest