wake up babe, the new hardiness map just dropped 💁🏻♀️
are you in a new zone? what zones can & can't tell you
Big news in the gardening world this week! 🗞🗞🗞
My zone changed! 😱
For some gardeners, zone is part of your identity. “What zone are you?” is the first question I ask when people across the country ask if I’m able to help them, and it’s the first question I’m asked when I call on others for support. Zones help ground gardeners in a sense of place and reality — it’s how we make facebook groups and find commonality between ourselves and people growing thousands of miles away from us.
If you are on your gardening journey, it’s important to understand what a Zone can tell you, and what it can’t.
🤔 WHAT A ZONE TELLS YOU 🤔
A zone is meant to tell you which perennial plants are likely to thrive in a typical year, based on the average coldest winter temperature across the last 30 years. When you purchase a perennial or shrub, it should say “hardy to zone X” — with the average lowest temperature in that zone typically being the coldest temp it can tolerate.
Critics of the USDA Zoning system are correct in that there are so many other factors that can determine if the new shrub you bought will make it — Is it cold but never snows? Without snow insulation, the soil may chill deeper! Do you have long, dry heat waves? This may be what kills it, not the cold. Do you get long heavy rains and have a prairie native plant in a low zone? Long term wet roots can suffocate it.
When I was beginning to garden, it stressed me out to hear criticism of the VERY few tools we are given to guide us — and so I say, ignore them! Know your zone, practice the lifelong skill of observing weather around you, and carry on.
🙅🏻♀️ WHAT A ZONE DOESN’T TELL YOU 🙅🏻♀️
❌ How cold it will get any given winter. For example, I am now in 8a, and it absolutely has gotten below 10° here. 10-15° is the average lowest temp across the last 30 years of data.
❌ What fruit trees will fruit in your location. Fruit trees are based on average number of chilling hours (between 32-45°) per winter. This merits its own newsletter, you can read more here.
🗺 CHANGES TO THE MAP 🗺
Our USDA map was created in 1960, revised quickly in 1965, and re-issued with ‘a’ and ‘b’ distinctions in 1990 — when I was three years old. 22 years later, in 2012, they re-issued it again, using 30 year learnings from data from 1976-2005.
And then, this week, we got a new one! And it is amazing.
**Make sure you look at your location by typing in your zip code on desktop and then zooming to your location — NOT mobile, and NOT the static jpg map. This will show you the detail. Without zooming to your exact location, the zip code-based zone may be incorrect depending on how ‘big’ your zip code is. I am actually in 8a now!
Our new version was built using data from 13,625 stations — compared the 7,983 used for 2012.
The biggest improvement is being able to see 30 year averages for your neighborhood, rather than just your city or general region. This is a meaningful difference for people living in a city (where it’s warmer) or a valley (where it’s colder) or any other unique terrain/microclimate location.
🌎 LIMITATIONS & CLIMATE CHANGE 🌎
The two hardest parts of my job as a full-time gardener are (a) giving watering instructions and (b) explaining that our weather is more volatile than it’s ever been so plants and gardens may behave in unexpected ways.
Each year there seems to be some ‘never before’ weather event that dramatically effects a group of plants. The average person is unaware of the event’s damages, and often takes the affected plant’s failure as their own.
Last December we had a historical Polar Vortex event that caused temps to drop 40-50+ degrees in an 18 hour window, which killed even resilient plants like hollies, boxwoods, figs, etc. This event helps explain the limitations of our Zoning system. The low temperature last December is not what killed them — it was the ability of a plant’s vascular cell tissue to retract water and protect itself in one day, rather than the normal slow drop over several weeks.
The year prior it was a historically late freeze in the spring, which zapped everyone’s hydrangea buds, and made new gardeners think they couldn’t keep hydrangeas alive.
Your zone will tell you the average low temp, at a time when averages are becoming a less reliable form of prediction. We are seeing higher highs, lower lows, and pretty dramatic changes in the way water moves across the globe. This means more heavy snows and rains, and more long stretches without.
Gardening is an art form, an act of creation and self-expression, a practice of nurturing, and our hand at playing god as we collect plants from across the street or across the world for our little backyard.
It is for this reason that I say all gardens are high maintenance, and gladly so.
As we create our mini dream planets, we must be prepared to water, to shield, to share, to guide, to feed, to observe and learn. This is how great gardens have always been, and how they will continue to be.
Note: With the 1990 update, about half the country moved into a warmer zone, and with this week’s update, the same thing happened again. The USDA has been clear to distinguish that climate change markers are based on 50-100 year temperatures while our Hardiness maps are on 30 year averages. Our USDA Hardiness maps are meant for relatively short lifespan plants (crops, perennials) while climate change is affecting larger scale changes with forests, wildlife, grasslands, etc — as we see these slowly dying or traveling to new regions over decades. Essentially, yes climate change is happening but we have evidence of this through a thousand other markers; our Hardiness maps are sort of irrelevant to this.
🏴 WHAT DO OTHER COUNTRIES USE? 🇨🇦
It is very interesting to see what other countries use to help guide their gardening efforts. Canada publishes both their own and USDA maps, and the Canada formula is AMBITIOUS:
England (which is generally inside of our Zones 6-9 range) has unsurprisingly produced another reminder that they are superior gardeners with their RHS Hardiness Ratings. This system functions quite differently in that the plants are assigned a rating, with a more detailed definition that helps inform you how to care for it.
I like looking at hardiness maps around the world because it reveals how many more climates America has than nearly any other country — and what a difficult job we have as professionals and industry staff to help guide, teach, or provide relevant materials the entire country.
If you have any epiphanies or crazy findings about the new map and how it’s impacted you, please comment to share. 👩🏻🌾
“You are lost the instant you know what the result will be.” Juan Gris