On November 17th the USDA updated the Hardiness Zone Map based on data from the past 30 years and many of us are now in new zones. So, what does that mean? Today on Just Grow Something we’re going to deep dive into the USDA Hardiness Zone Map; what the zone numbers and colors mean, how to use the map, what’s new and different with this version, what this means for perennials versus annual plants, and how it all ties into changes we may or may not want to make in our garden plans. Let's dig in!
Episode References and Resources:
2023 USDA Plant Hardiness Zone Map | USDA Plant Hardiness Zone Map
Ep. 117 - Growing Cut Flowers in the Home Garden with Kathy Gormandy
Just Grow Something Gardening Friends Facebook Group
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This is Positively Farming Media.
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Back in episode 167, when we were talking about frost
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protection measures and overwintering things in our
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gardens, we had a brief discussion about the USDA
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hardiness zone map. I mentioned at the time that we
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were due for a refresh on that map and that it wouldn't
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surprise me if things shifted just a little bit based on what
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I've been seeing in my own gardens in recent winters and
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what other gardeners were talking about in their areas.
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Lo and behold, last week the USDA updated those hardiness
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zones based on data from the past 30 years and many of us are
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now in new zones. I have gone from zone 6A to 6B.
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So what does that mean today on Just Grow Something, We're going
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to deep dive into the USDA hardiness zone map, what the
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zone numbers and colors mean, how to use the map, what's new
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and different with this version and how it all ties into changes
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we may or may not want to make in our garden plans.
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Let's dig in. Hey, I'm Karen and I started
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gardening 18 years ago in a small corner of my suburban
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backyard when we moved to A5 acre Homestead.
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I expanded that garden to half an acre and I found such joy and
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purpose in feeding my family and friends.
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This newfound love for digging in the dirt and providing for
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others prompted my husband and I to grow our small homestead into
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a 40 acre market farm. When I went back to school to
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get my degree in horticulture, I discovered there is so much
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power in food and I want to share everything I've learned
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with as many people as possible. On this podcast we explore crop
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information, soil health, pests and diseases, plant nutrition,
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our own nutrition, and so much more in the world of food and
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gardening. So grab your garden journal and
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a cup of coffee and get ready to just grow something before we
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get to hardiness zones. Remember back at the end of
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August when we were talking all about storing popular garden
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crops from the fall garden with just ambient cold storage?
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No canning or freezing or anything.
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That was episode 162, and I'll link to it in the show notes.
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But at the end of that episode, in the Q&A section on Spotify, I
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asked Are you planning to store any crops long term over the
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winter? If so, what?
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Well, Ashley Coats responded that she is storing winter
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squashes, sweet potatoes, and garlic, all favorites of mine to
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store each year, and that she hopes to try carrots next year
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too, which is another one of my favorites.
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But she also mentioned storing dahlias.
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Now, of course, she's talking about the tubers of the dahlia
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flowers, so popular in many gardens but not Hardy.
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In many regions, including my own, they're only Hardy to Zone
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8. So if you're in Zone 8 or
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warmer, you can simply cut them back at the end of the season
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and leave them in place and they'll come back naturally on
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their own without being damaged. But for gardeners in zones that
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are colder than that, Dahlia tubers need to be dug up at the
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end of the season and then put into storage so they can be
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replanted the next spring. You do this by lifting the
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tubers out of the soil, and you have to do it before the 1st
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frost in fall, otherwise they can actually be prone to rotting
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and then you remove most of the soil from the tubers.
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Some gardeners will dust the tubers with a fungicide just to
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prevent any fungal diseases. In either case, you put the
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tubers in a pot or a box of some sort and you cover it with dry
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compost, and then you just store them in a cool, dark dry spot
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indoors until it's time to plant them again in the spring.
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And this way you can replant the same tubers over and over again
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every year. Now, I know we generally focus
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on food gardening on this podcast because OK, that's what
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I'm most involved in, but it doesn't mean that I don't love
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some good florals and other landscaping.
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In fact, we had Kathy Gormandy from P&K Farms on as a guest
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last year. She is a flower grower and I'm
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thinking now would be a good time to have her back actually,
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because I know she's doing some really fabulous things in terms
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of opening a boutique and doing classes and stuff.
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So I may reach out and see if we can get her back here again for
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you. I will leave a link to her
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episode in the show notes. And Kathy, if you're listening,
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expect an e-mail from me. But in any case, in that regard,
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I've been looking at expanding what we talk about a little bit
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in terms of florals and other more decorative aspects and how
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we can incorporate our edible plants into our landscapes so
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that we don't have to be strictly one or the other in our
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gardens. In our planting areas, we talk a
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lot about companion planting and getting away from mono cropping,
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and there's nothing that says a companion plant needs to be
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something edible. Yes, nasturtiums and marigolds
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can be helpful. And yes, they're pretty and
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they're edible, and there are loads of herbs that are both
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pretty to look at and also used culinarily.
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But what about using strictly decorative plants in and around
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our edible ones, and vice versa? Tucking those edibles in and
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around our other landscape? I have a large patch of irises
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smack dab in the middle of my kitchen garden area.
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And even though irises are actually like my least favorite
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flower and I really want to yank those suckers out so that the
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daffodils and the daylilies that are in there that are currently
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being choked out can actually come up and take over.
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But I do appreciate the burst of color those irises give me in
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the middle of all of my raised beds up there, and I would love
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to have that in some more areas in and around my gardens.
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And I really think I want more of them to be perennials.
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There's just something wonderful about having things pop up all
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on their own in the spring without any effort from me.
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When I'm in the middle of planning and seed starting and
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transplanting all of the annual vegetables that need to go in, I
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do put annual flowers out in containers.
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Like all over the place. But that really doesn't end up
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happening until like late May or even early June, because there's
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just no time for me to do it before then.
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So some pretty perennials would be greatly appreciated.
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So as I look at the topics to focus on for the next season of
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this show and for the articles and emails I'll be writing and
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sending throughout 2024, if there is a particular non edible
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plant you'd like me to focus on or a subject you'd like more
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information about, please let me know.
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And this goes for the other topics for next season 2 of
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course, whether it's a veggie or a soil question or what have
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you. What do you want to know more
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about? If you're in the Just Grow
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Something Gardening Friends Facebook group, feel free to
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post it in there or shoot me an e-mail from the for the website
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thatsjustgrowsomethingpodcast.com. You can use the link in the
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episode description of this episode to leave me a voice
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message. You can send me Adm on
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Instagram, wherever, whatever. Just reach out.
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Let me know what you really want to learn more about in 2024.
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So if you are a gardening friend in Canada, you have your own
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version of the USDA hardiness zone map.
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In fact, you actually have two. I will leave a link to those in
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the show notes. One is a hardiness zone map that
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combines information about a variety of climatic conditions
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across the entire country to produce a single map.
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It includes things like minimum temperatures in both the coldest
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and the warmest months of the year, the amount of rainfall
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June through November, wind gusts, snow depth, all kinds of
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stuff that is not represented in our USDA map.
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Really, really comprehensive stuff.
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The other map for Canada is the Extreme Minimum Temperature
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Zones map and that is patterned after our USDA version and it is
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literally only concerned with the average extreme minimum
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winter temperature for that area and it is aligned with our USDA
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version. So when I say zone 6B, that is
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represented in the same manner on our USDA hardiness zone map
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as it is on the Canadian Extreme Minimum Temperature Zones map.
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So just be aware of that when we're talking about different
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zones, you can also find hardiness zone maps for Mexico
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and also for other countries outside of North America.
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And most of them are going to have very similar indices as the
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USDA version. But in a lot of cases, this data
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actually may not be super important most of the time when
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we're planting our gardens. Let's talk about why.
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According to the USDA, the plant tardiness zone map is based on
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the average annual extreme minimum winter temperature for
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an area displayed as 10°F zones, ranging from zone one, which is
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the coldest, to zone 13, which is the warmest.
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Each zone is divided into half zones, designated as A or B.
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For example, 6A and 6B are 5°F increments, representing the
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colder and warmer halves of Zone 6.
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These designations serve as convenient labels and shorthand
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for communicating and comparing the extreme winter temperatures
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within the United States and Puerto Rico.
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Zone numbers are typically listed with the descriptions of
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perennial plants in catalogs and other sales information produced
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by commercial nurseries and plant suppliers.
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The sequence of colors assigned to the zones mimics the
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chromatic spectrum produced by a prism red, orange, yellow,
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green, blue, indigo, and Violet, providing A graphical
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representation of the plant hardiness zones.
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The overlay of colored zones on the map provides a convenient
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tool for understanding and comparing plant cold hardiness
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across the United States and can facilitate the selection of
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appropriate perennial plants based on their observed
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performance in other regions of the country.
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Notice I said perennial plants, the plant hardiness zone maps
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serve as general guidelines for growing perennials.
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They are based on the average lowest temperature, not the
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lowest temperature ever. Zones in this updated edition of
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the map are based on 1991 to 2020 weather data.
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This does not represent the coldest it has ever been or will
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ever be in an area. It is the average lowest winter
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temperatures for a given location for this particular 30
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year span. This map was updated by the USDA
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Agricultural Research Service Technical Plant Hardiness Zone
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Map Review team say that five times fast and the PRISM Climate
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Group at my alma mater, Oregon State University.
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So the previous map was updated in 2012 and it covered the 30
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year period from 1976 to 2005. The update that occurred before
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that was in 1990 and then the very first version was in 1960.
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Now to give you an example of how things have changed in that
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first version, my area of Missouri was listed as Zone 6A.
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In 1990 we were redesignated as Zone 5B.
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In the 2012 version, we were pushed back into Zone 6A and
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drumroll, please This year we have been redesignated as Zone
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6B, which means the average low temperature in winter in my area
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over the past 30 years is about 5 to 10°F warmer than it was
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before. So rather than an average low
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temperature of -10 to -5 Fahrenheit, we're now looking at
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an average low of -5 to 0 Fahrenheit.
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That would be -20.6 to -17.8 Celsius.
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Now, this change may not seem significant since I'm still
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considered Zone 6, just the warmer edge of Zone 6, But I've
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already heard from some of you that you've moved from the warm
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edge of one zone up into the next zone up.
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Does this mean you should immediately start putting
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perennials in the ground that are for a warmer zone?
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Well, if you're growing perennial fruits or vegetables
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or decorative plants that are sort of riding the line of the
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coldest temperatures in your zone and an extreme cold snap
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hits colder than usual for your area and it lasts for just a
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full day or two, Perennials that have happily grown in your
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garden for years could suddenly be lost if they're susceptible
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to those colder temperatures. We as gardeners need to
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understand that these past weather records cannot guarantee
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a forecast for future variations in our weather.
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So if I'm in zone 6B and I plant a fruit tree that says it's
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Hardy to zone 6, and we have an extraordinary cold winter where
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temperatures are regularly dipping lower than usual, will
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that tree may not make it, especially if it's not well
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established. If I wanted to hedge my bets, I
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would plant a variety that's Hardy down to zone 5 to give
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myself some wiggle room. Mother Nature is unpredictable,
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so if you suddenly find yourself in a warmer zone than you were
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before, air on the side of caution When it comes to
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planting perennials, we also have to remember that there are
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so many other factors that go into the success or failure of
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perennial plants. The frequency and speed of the
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wind are soil type. The level of soil, moisture,
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humidity, and pollution are all factors.
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Just because something says it's Hardy in your zone does not
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automatically mean it's a great choice.
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You may need to do a little more research.
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Let's look at light, for example.
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Plants need to be planted where they'll get the proper amount of
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light during each part of the season.
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So if you have a plant that requires partial shade and
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you've got it planted under a tree, it may do fabulously well
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for most of the year. But if you live in an area that
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gets lots of sunshine in the winter and suddenly the tree
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that plant has been relying on for shade has dropped all its
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leaves, well, that little plant may now be getting too much sun
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at a very inconvenient time of the year.
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This needs to be factored in. Another factor is the soil
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moisture. Plants have different
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requirements for soil moisture and sometimes these requirements
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change with the seasons. So if the soil is too moist or
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too dry in the fall as the plant is entering dormancy, some
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plants can suffer from that moisture stress and end up being
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damaged. Another consideration is air
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temperature. Most of our plants grow best
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within a range of optimal temperatures from high to low.
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That range might be really wide for some varieties and some
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species, but it could also be very narrow for others.
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Does that plants temperature range match the range for your
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area? Zone 8 in North Carolina can be
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very different from Zone 8 in Texas the same way that zone 5
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in Wisconsin can be very different from Zone 5 in
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Colorado. Take that into consideration.
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Another consideration is duration of exposure to the
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cold. There are a lot of plants that
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can survive a short period of exposure to cold that may not be
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able to tolerate longer periods of that same cold weather.
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So just like some of our annuals can handle freezing temperatures
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for like 2 hours, but maybe not 12, many perennials have the
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same tolerance issues. And then the last consideration
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would be humidity. High relative humidity limits
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cold damage by reducing moisture loss from the plant.
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So if you're in an area that is usually pretty humid, your
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plants may be able to withstand colder temperatures, whereas
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cold injury can be more severe if you're in an area where the
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humidity is usually low. Now we've been referencing
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perennials this whole time. What does this mean for the
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annual plants in our gardens and landscape?
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Does this seemingly warmer winter weather have any effect
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on those? Likely not?
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Frost sensitive plants are simply that, frost sensitive.
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The date that frost appears may or may not be any later than
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you've been experiencing. Any of you who have been
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gardening for more than a few years, and especially those that
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keep a garden journal, know whether or not your area has
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been getting warmer or not. I know that on average our frost
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dates have been within about a week or two of usual, but the
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temperatures immediately following that first frost have
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been getting warmer and staying warmer for longer into the late
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fall. Now that has changed how and
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when I have my frost protection on hand, but it's not changing
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what I plant or when I plan for those crops to be mature.
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And the fact that my zone has now shifted is also not an
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indication of anything actually being any warmer.
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In fact, the USDA has some very important points they want to
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make when it comes to this. Climate changes are usually
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based on trends in overall annual average temperatures that
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are recorded over 50 to 100 years.
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Now, because the USDA hardiness zone map represents only 30
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years of averages of the coldest temperature of the year, the
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USDA was very specific to say that changes in zones are not
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reliable evidence of whether there has been global warming.
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Yes, zone boundaries in this edition of the map have shifted
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in many areas compared to the previous two versions.
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The new map is generally about 1/4 zone warmer than was
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reported on the 2012 map throughout much of the US, and
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part of this is as a result of just having more recent
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averaging period. So the first averaging period
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was from 1976 to 2005 and the current averaging period is now
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1991 to 2020. But the USDA is very quick to
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point out that some of the changes in the zones are
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actually the results of additional data sources and
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improved estimation methods. These zones shifts can sometimes
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result in locations actually being classified into a cooler
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zone rather than a warmer one. They said the most substantial
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changes produced by additional data sources and improved
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interpolation methods were seen in upland areas of Alaska.
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I will link to the USDA maps in the show notes and they are
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really simple to use. The maps are now interactive so
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you have two options. The 1st way is to enter your zip
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code into the search box and find your location within the
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map. Click on the map at that
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location of interest and you will see the zone classification
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there. The 2nd way is to download the
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digital map for your state and then just find your county.
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There is a Maps Downloads tab at the top of the page.
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This is also the only way you can get a physical print out of
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the maps. The USDA no longer makes any
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physical copies. It's all digital, so if you want
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one, you'll have to print it yourself.
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Until next time, my gardening friends, keep on cultivating
00:21:10
that dream garden and we'll talk again soon.
00:21:12
You just finished another episode of the Just Grow
00:21:14
Something Podcast. For more information about
00:21:16
today's topic, go to justgrowsomethingpodcast.com
00:21:20
where you can find all the episodes, show notes, articles,
00:21:23
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I'd also love for you to head to Facebook and join our gardening
00:21:28
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Facebook group. Until next time, my gardening
00:21:33
friends keep learning and keep growing.