Two days ago, we got a sneak-peek at the future. Did you notice? The USDA released their newly updated Plant Hardiness Zone Map this Wednesday (click here to read the press release). Finally! The map hadn’t been updated since 1990, and things have definitely changed since then.
Don’t believe me? Compare the old map (below, top) to the new one (below, bottom). If you look closely (or click on the images to see the full-size maps), you’ll likely notice that most of the zone boundaries have crept north, or toward higher elevations. According to the USDA, most of us got a half-zone bump, which translates into a 5 degree temperature increase. Check it out:
Why the changes? Well, there are three reasons.
First, we’ve simply got better technology now. This new map is online, interactive and searchable by zipcode. It’s got terrain overlays, road maps and satellite imagery. It’s so zoomable that I can just about see my backyard. The old map? Yeah, it was nothing more than a static image. Doesn’t quite compare.
Hand in hand with better technology is better data. Scientists have access to better temperature data, and can translate that into a more finely resolved map. That’s the second reason. That’s what allows the map to show tiny patches of Zone 7b on the hills near my 7a-dominated hometown.
But, the third reason for these changes is absolutely the most important: climate change. It’s getting warmer out there.
That last thing — climate change: hotter summers, warmer winters, crazier storms — is something most of us gardeners have been noticing for years. The old map had my garden in 6b. Now, I’m a solid 7a. But, really, I’ve been gardening like a Zone 7 gardener for years. The new map simply confirms something I already knew. If you’ve been gardening in your region for a while now, then I bet you’re no more surprised by the new map than I am.
But, the map is just a snapshot. And, it’s not even a snapshot of today. These zone shifts are based on data collected between 1976 and 2005 (the old map used weather data from 1974 to 1986). So, this “new” map is already out of date. That’s not the USDA’s fault. The map is based on average temperatures, and there’s no other way to do averages. We need data, and for that data, we have to look to the past. The map doesn’t reflect where we are today. It shows us where we’ve been. Recently.
So, where does that glimpse of the future come in? Well… Even though the new USDA Plant Hardiness Zone Map reflects the recent past, it also does a great job of highlighting change. And, we better get used to this change. These zones are not going to hold still. In another 10 years, my 7a garden could be a 7b garden. Eventually, it could be an 8. Possibly even a 9.
Think I’m being extreme? That there’s no way my Northern Virginia garden will ever warrant a Zone 8 or 9 designation? Yeah, I wish I were wrong. But, here’s the thing. In their 2009 report, the US Global Change Research Program predicted that New Hampshire could have a climate similar to present-day North Carolina by 2070 or so. That’s a shift of two or three USDA plant hardiness zones over the next 60 years. That’s a zone shift every 30 years. Possibly faster. That’s an awful lot of change.
[Note: I’m way over-simplifying here. USDA zones are determined by average winter lows, and the US Global Change Research Program focused on summer highs for their New Hampshire prediction, for example. So, the USGCRP projections don’t correlate exactly with the USDA plant hardiness zones, but it’s still going to get an awful lot warmer in New Hampshire. Most everywhere else, too.]
I’ve always longed to grow citrus, but this is not the way I want to do it. I was dreaming of tall, beautiful greenhouses. Or, at least a properly sunny, south-facing window. This — climate change — may give me citrus, but could also rob me of blueberries, raspberries and apples. I’m not sure I want to make that trade.
According to Art DeGaetano, a climatologist at Cornell University and the director of NOAA’s Northeast Regional Climate Center, “By 2080, the hardiness zones that currently cover the area from southern Virginia to northern Georgia may replace those that we see across New York in the current update.” In other words, we’ve got a whole lot of change coming. This map revision is just the first of many. It’s a sneak-peek at the type of changes we can expect in the coming years.
Want an idea of what your garden might look like in a decade or two? Drive south for a few hours. Want to get a peek at 2080? Well, then pack a lunch. You’ll be driving south most of the day.
Of course, it’s not as simple as temperature. We use the term climate change because we’re talking about the entire climate. That includes things like precipitation, droughts, wind speed and season length. My Virginia garden won’t just be hotter in 20 or 30 years. It’ll also be drier in the summer and wetter in winter. Big extreme storms will probably be more frequent visitors. Summer droughts could become a regular thing. It’s going to be a very different garden than the one I’m planning for this summer.
If you want a better idea of how climate change might affect your garden, check out this piece I wrote for Organic Gardening in 2010: We’re Not in Zone 6 Anymore (pdf download).
And, don’t forget to check out your new USDA plant hardiness zone (click here to see the new map). Did your zone change?