The USDA just released a revised Plant Hardiness Zone Map, the first update since 1990. Based on average low temperatures in a region, boundaries have shifted across much of the country and two new were added. The new interactive online map is meant serve as a guide for gardeners on which plants will thrive best in their area, and is far more precise than the last version. Tune in to find out what the changes mean for your own backyard.


  • Phil Normandy Plant collections manager, Brookside Gardens
  • Diane Vogel Managing Producer, The Kojo Nnamdi Show; gardener
  • Christopher Daly Founder and director, PRISM Climate Group at Oregon State University


  • 13:06:46

    MR. KOJO NNAMDIFrom WAMU 88.5 at American University in Washington, welcome to "The Kojo Nnamdi Show," connecting your neighborhood with the world. They are familiar sights in grocery stores, but does it surprise you to know bananas can now grow in Maryland, figs in Boston and pomegranates in Virginia? Warmer average temperatures around the globe are opening up new possibilities for gardeners and farmers everywhere. Perfect timing, you might say, for the folks responsible for redrawing the plant zone map. A map relied upon by many of America's 80 million gardeners.

  • 13:07:31

    MR. KOJO NNAMDIWe're here to find out how to know what plants will and won't survive in your neck of the woods. But first, today's chilly weather finally makes it feel like winter after weeks of unseasonably warm weather. Our local trees and plants, not to mention birds and insects, seem a bit confused. Daffodils are sprouting here, crocuses are coming up there. What's blooming in your neighborhood? Call us now at 800-433-8850. It is your turn.

  • 13:07:59

    MR. KOJO NNAMDIYou can also send us a tweet @kojoshow, email to or simply go to our website, Tell us what's blooming in your neighborhood. How does it affect your gardening plans or, for that matter, your allergies? And what do you think it will mean for springtime, usually the prettiest time in our region? 800-433-8850 is the number to call. It's your turn.

  • 13:08:25

    MR. KOJO NNAMDIJoining us in studio is Phil Normandy. He's a horticulturist and plant collections manager at Brookside Gardens in Wheaton, MD where he oversees all outdoor and indoor displays. Phil Normandy, thank you very much for joining us.

  • 13:08:39

    MR. PHIL NORMANDYWhy, thanks for having me. This is a treat.

  • 13:08:41

    NNAMDIAlso joining me in studio for this treat is Diane Vogel, the managing producer of "The Kojo Nnamdi Show" and an enthusiastic gardener herself.

  • 13:08:50

    MS. DIANE VOGELAmateur.

  • 13:08:52

    NNAMDIDiane, tell us what you have been seeing in your neighborhood. What's blooming? What's seems to be resulting from the warming trend that we've been seeing recently?

  • 13:09:01

    VOGELWell, this is a particularly weird year. I think all of us have realized that you don't have to be a gardener to walk down the street and notice the daffodils usually aren't blooming in February. But I guess for me, I've been wondering -- one of the main things I've been wondering is whether or not our ground ever froze yet, because usually spring blooms don't happen -- bulbs don't come up until the ground has frozen for a while.

  • 13:09:31

    VOGELAnd we've had such a warm spot that it seems to me our whole cycle might be off. Now I might be -- I'm just an amateur and that's why I wanted to sit on in and ask these questions. Did our grounds freeze? Can we expect all the normal bulbs to actually come up or is this going to be a weird weather -- weird gardening season just from the start of it?

  • 13:09:54

    NNAMDIWhat have you been seeing? Call us at 800-433-8850. Just as importantly, what is your own informed or, in my case, uninformed speculation about what you've been seeing? 800-433-8850. Send us a tweet @kojoshow or go to our website, Phil Normandy, can you answer any of Diane's questions?

  • 13:10:13

    NORMANDYYes, I can, Diane. The ground has frozen occasionally but not very deeply, maybe only an inch or so. And that would depend on where you are, perhaps not in the city itself but out in the suburbs, and of course the further out. But then we've had these warm spells of 50 degrees or more and it's thawed again. So, we have actually have had some freeze, but not for any length of time.

  • 13:10:36

    VOGELBecause I may be wrong, but isn't it -- doesn't it take a freeze for the bulbs -- don't bulbs usually have to go through that cold dormancy? I forget the name of it, but I was always under the impression that if you don't get a freeze, you don't get blooms.

  • 13:10:51

    NORMANDYThat's correct. And the term for that is the plant's chilling requirements, how many hours they have to have below a certain temperature, usually 40 degrees or 30 degrees. And that affects the root parts of bulbs, but it affects flower buds. And that's why you're seeing some things beginning to bloom or bud out on trees and shrubs now, especially down in the city here. And others are still holding tight.

  • 13:11:19

    NORMANDYAnd so, it really has to do with how their genetically wired -- how many hours of cold do they actually have to have. We've had some cold weather. If we hadn't had any cold weather, then we'd be, of course, be afraid of a nuclear meltdown. But we wouldn't see anything in bloom now. But the things that we are seeing in bloom, like quinces and things like that, have a very few cold hours that they need.

  • 13:11:42

    VOGELAh, interesting. So that means -- and I'll ask the audience, 1-800-433-8850 -- to tell us what's in your yard. I know in my yard the daffodils have come up. They're not blooming on my yard, but that's because I have a somewhat shady yard. People across the street with southwestern exposure have beautiful daffodils in bloom. Crocuses are in my neighbors' yards. I know that hostas have started poking through in the bottom of my -- I know.

  • 13:12:15

    NORMANDYThat's not good.

  • 13:12:16

    VOGELI know. It worried me, too. So, if there are snow drops and others, I think forsythia I saw when I was walking my dog today.

  • 13:12:25


  • 13:12:26

    VOGELNo forsythia?

  • 13:12:27

    NORMANDYYou didn't see forsythia, you saw its cousin, winter jasmine. It has flowers that look just like forsythia. They're yellow and they don't have a very long chilling requirement. They're related to forsythia but they usually look like a big green haystack.

  • 13:12:41


  • 13:12:42

    NORMANDYAnd they can bloom -- have been blooming, some places, since Christmas.

  • 13:12:46

    NNAMDIIn case you're just joining us, it's your turn. You can call us right now. We've been talking about the chill factor. Are you the one who's been chilling so far? And when do you intend to go into your backyard garden given the warming trends that we've been seeing? 800-433-8850. You can simply call us with your gardening questions, 800-433-8850. It is your turn. You can go to our website,

  • 13:13:11

    NNAMDIPhil Normandy is in studio with us. He's a horticulturist and plant collections manager at Brookside Gardens in Wheaton, MD where he oversees all outdoor and indoor displays. Diane Vogel, the managing producer of "The Kojo Nnamdi Show," also joins us in studio. Here is Eric in Washington, D.C. Eric, you're on the air, go ahead please.

  • 13:13:30

    ERICHi. I just have a question about grass seed and whether this warm weather is going to have any impact on seeding now, kind of late in the season I guess. But I was just curious.

  • 13:13:44

    NNAMDIWhat do you say, Phil?

  • 13:13:45

    NORMANDYWell, I think it's too early. For one thing, we don't know what March will bring or the rest of February. And grass seed is really not going to do very much until the soil temperatures warm up considerably. So, I think it's okay to hold off. And then as far as fertilizers, if you put them down too soon, the tendency might be for them to wash off, which isn't good for the streams. And it's kind of a waste of your time. So, I would put your seed and fertilizer down at your usual time in spring.

  • 13:14:14

    ERICOh, okay. I thought it was better to seed in the fall.

  • 13:14:17

    NORMANDYWell, it is better to...

  • 13:14:18

    ERICBut I didn't get around to it.

  • 13:14:19

    NORMANDYYeah. Well, then you better wait until the spring. You're sort of in limbo right now.

  • 13:14:23

    ERICOh, okay. Thank you very much.

  • 13:14:25

    NNAMDIEric, thanks very much for your call. Tell us what you've been seeing in your backyard or in your neighborhood and how it is affecting your gardening plans for the spring, 800-433-8850. Diane?

  • 13:14:36

    VOGELYou know, one of the things I've also noticed as I'm walking my dogs is that there are trees that are starting to bud and to fall out. And certainly, you know, weird things happen on different years. But I guess it made me think of two things. First was, the cherry blossoms. I have heard rumors that they haven't been affected yet, but I'm not sure that's correct. And you can probably tell us that. And then I'll ask you a second question.

  • 13:15:05

    NORMANDYOkay. The cherry blossoms, I'm not the expert, Rob DeFoe is. But the base cherry blossom is the one that we have so many of are probably not affected at this point. If this continues, I'm sure they're going to be early. But you're not going to see them next week.

  • 13:15:21


  • 13:15:22

    NORMANDYAnd I believe the standard forecast is give or take two weeks around the end of March to early April. So, I think we're at least a month away from anything.

  • 13:15:33

    NNAMDILater in broadcast we'll be talking about the new plant zone map that will give you an indication of what you may be now able to plant in your own neighborhood that you may not have been able to 10 or 20 years ago. But right now, we'd like to know what you're seeing in your neighborhood and how you think it's affecting your planting plans. Here is Tracy in Annapolis, MD. Tracy, your turn.

  • 13:15:56

    TRACYHi. I was wondering if you could tell me about copper fungicides. I'd like to use it on my garden growing vegetables and the purpose to be for (unintelligible) ?

  • 13:16:12

    NNAMDIDid you hear the question, Phil?

  • 13:16:13

    NORMANDYI did hear the question. And I have to say, I don't know the actual answer. But the standard answer, which is always the best answer and the legal answer is for the product that you're thinking of applying, read the label first. And if you don't have the product, most of the labels are actually available online and you can read. And it will tell you specifically what you can and cannot apply this material on and the reasons why. And that is not only the healthy answer, but it is illegal to apply pesticide on anything that's not on the label for any problem that's not on the label.

  • 13:16:50

    NNAMDIThank you for your call. On to Cherry in Old Town, Alexandria. Cherry, your turn.

  • 13:16:57

    CHERRYOh, thank you, Kojo. Mr. Normandy, I wanted to find out if it's just my imagination or are the red holly berries this year are much larger and less than numerous. I keep seeing them all along the Potomac.

  • 13:17:11

    NORMANDYI think they are because we got good rain at the right time. If it stayed to be quite dry in the summer, a lot of them would have aborted when they were in the small green stage. So I think we had a particularly good time when pollination was occurring and then ample rains to keep them from falling off.

  • 13:17:31

    NNAMDIAnd is this the first year you've noticed this, Cherry?

  • 13:17:35

    CHERRYYes, it is. I don't remember seeing them last year. And I'm used to going -- I'm around on the Mt. Vernon trail so I'm used to seeing the large, really mature hollies that are all along here.

  • 13:17:47

    NNAMDIOkay. Thank you very much for your call. What have you been seeing in your tours around the neighborhood or on your running or biking trail when you have been outdoors lately? It's your turn. Call us at 800-433-8850. On to Neil in Tysons Corner, VA. Neil, you're on the air. Go ahead, please.

  • 13:18:06

    NEILHi. I just heard a comment a moment ago that piqued my interest. But I have pretty limited experience in gardening, but I learned a hard lesson trying to grow a bonsai tree at one point that was an evergreen style that -- two problems. One, it needs to be very moist and humid. And then, two, it needs to have a pretty extensive chill time during the winter. So, I just solved my problem of finding a different kind of plant. But when I heard the comment of nuclear meltdown and insufficient chill, I'm kind of wondering what's the threshold in our area that we wouldn't have enough time to chill the natural plants in our area and we would start seeing kill-offs (unintelligible).

  • 13:18:48

    NNAMDIAllow me to remind you that we are having the plant zone map coming up in the later part of the broadcast, so you'll find out exactly what kind of chilling is going on in this area. But here is Phil.

  • 13:18:58

    NORMANDYWell, this is -- of course, this year is such an extraordinarily mild winter. I cannot imagine we would have a winter ever milder than this. And we've had...

  • 13:19:07

    NNAMDII can.

  • 13:19:08

    NORMANDYOkay. Okay.

  • 13:19:09

    VOGELWell, Kojo, being from Guyana, he dreams of mild winters.

  • 13:19:13

    NORMANDYThis is my favorite kind of winter, too. But the fact is we've had adequate chill time for most hardy woody plants. So, if they've been left outdoors -- so, I mean, if the temperatures dipped into the 30s and 20s even quite a few times, it probably will again tonight. So, I don't think we need to really worry about that.

  • 13:19:34

    NNAMDIThank you for your call. On to Tom in Warrenton, VA. Tom, you're on the air. Go ahead, please.

  • 13:19:40

    TOMHi. I've got many apples coming up in the backyard. They don't usually come up...

  • 13:19:44


  • 13:19:45

    NORMANDYThat is early.

  • 13:19:47

    NNAMDIYes, indeed.

  • 13:19:48

    TOMI have pictures on there with year, so I have a date time on them.

  • 13:19:51

    VOGELWell, I hope -- I don't know if you're a Twitter or an emailer, but we would love you to tweet those pictures of yours. I actually was going to tweet my daffodil picture. I didn't get a chance to do it this morning, but I'll do my best.

  • 13:20:04

    NNAMDIOr you can simply send to us. You can email it to us at if you can take pictures of your May apples in February.

  • 13:20:14

    TOMOkay. Now, the other question is, I'm using my grandmother's recipe for getting rid of bugs on her garden, which is a mild soap solution. You know, when you wash the dishes, you've got soap left over. She'd go out and throw it on the plants and it kept all the bugs off. I've got a gardenia tree that has a white scale picking -- I'm picking them off now, but a white scale. Will soap take care of those guys?

  • 13:20:40

    NORMANDYYes, it will. You can actually buy a product called insecticidal soap which is very much like dish soap and you mix it up and you mist it onto the plant, make sure it gets, it contacts the insects and it has the effect of suffocating them. If you're using a soap spray like that make sure your plant is not in drought stress, like, if its, it's obviously a house plant. Make sure it has been evenly watered for a day or two before you spray it and it should, it's not residual. It's just going to be a contact killer so you may have a second or third generation coming on. But it is a very friendly way of getting rid of these critters.

  • 13:21:19

    NNAMDIThank you for your call, Tom. We move onto Keith in Vienna, Va. Keith, your turn.

  • 13:21:27

    KEITHHey, Kojo, so Keith Thomason out here at Meadow Lark.

  • 13:21:30

    NNAMDIHey, Keith.

  • 13:21:31

    KEITHWhat a grand show. How are you Phil?

  • 13:21:33

    NORMANDYI'm good. How are you?

  • 13:21:34

    KEITHGreat. Boy, I'm learning so much listening to you. Hey, I just wanted to mention to you guys for anybody who's really, really interesting in the effects of global warming on plants, all that stuff to go to the Botanic Garden Conservation International website. That's

  • 13:21:53

    NNAMDIJust keeping naming the organizations we have the show.

  • 13:21:58

    KEITHWell, it is an organization we're heavily involved with at Meadow Lark and it's remarkable how public gardens, fine gardens like Brookside are becoming bellwethers for plant behavior as the climate warms and it's a remarkable resource so I just wanted to recommend to folks if they get the opportunity.

  • 13:22:22

    NNAMDIGlad you brought that up, Keith, because in our next segment one of the issues we're going to be discussing is whether or not the zone changes that we've been looking at are any evidence of global warming at all and so you may want to stay tuned for that conversation. But Keith, thank you very much for your call. We move onto Susie, in Winchester, Va. Susie, you're on the air, go ahead please.

  • 13:22:46

    SUSIEHey, Kojo, I really love your show. I listen to you every day and thank you for having me.

  • 13:22:51

    NNAMDIYou're welcome.

  • 13:22:52

    SUSIEAnd I just wanted to mention that we do have a wonderful arboretum here called Blandy Farm, which features herbs, trees from all over the world. All sorts of plant life and it's a very wonderful contribution that we are, you know, are very fortunate to have very new to us. And the other thing I wanted to mention is that from year to year, things do change and you will notice different things coming up in your yard.

  • 13:23:28

    SUSIEI've lived in various cities in this area and I've noticed, you know, the crocuses and then the tulips and everything kind of has its -- and I've been given iris that were fancy and, you know, you plant them and you have to -- my thing is that you have to go with the flow. You have to kind of, you know, realize that well this year is different. Yes, we had some pretty bad weather or whatever and just kind of go with whatever you can grow and if not grow herbs in your window.

  • 13:24:13

    NNAMDIThank you very much for that suggestion. Care to comment on that, Diane?

  • 13:24:16

    VOGELWell, certainly. Mother Nature's in charge and part of the fun of being a gardener is the surprise that it gives you all the time. I think as an exuberant, amateur gardener my question is always, is there something I can do to help Mother Nature along or not? So when I see a plant, for instance a tree, that's coming out of dormancy and it's starting to have all of its buds coming and it's February I think to myself, oh my god, am I going to lose out on this beautiful spring Dogwood? Should I put compost around the bottom or should I do something else? Should I throw a blanket over it because it's a young tree? You know, I want to just help Mother Nature. I'm ready to ride the wave or go with the flow but I want to know if there's a roll I can play so. Phil?

  • 13:25:11

    NORMANDYI actually liked what she said. First of all, she's right, Blandy's a wonderful place. It's got the most amazing woody plant collection. I wish I was closer to it.

  • 13:25:19

    VOGELWhere exactly is it? So for our audience, because I don't know it.

  • 13:25:22

    NORMANDYIt's in the Winchester area, in Boyce, Va.

  • 13:25:25

    VOGELBoyce, Va.

  • 13:25:27

    NORMANDYI would have to agree. I've a lot of people come up to me and say, oh, this weather is so scary. I mean, what's going to happen? And my answer is, just enjoy it. I mean, really just enjoy it. the only time you can do anything or worry is if things are so far along, whether it's early or right on schedule and then there's a major, major change. Like a major freeze coming in the middle spring, then on small scale things you can and should go out there and try to protect them. But right now, there's not a great deal I don't think you can do.

  • 13:25:57

    NNAMDIContinuing to talk with people about some of the things you have been seeing that seem to be different. Here is Carol, in Rockville, Md. Carol, your turn.

  • 13:26:07

    CAROLHi, Phil and Kojo, thanks for having me on. I've noticed the last two years, not just this year that my Christmas Rose, the Hellebore, has actually bloomed slightly after the Lenten Rose or the orientalis, even though they've been in place for about eight years in the same spot. And the same -- the spring blooming Camilla, it used to bloom in April and the last two years it has decided to start opening some of its blooms in January. This year it was actually in December and I was just wondering -- it was my comment and wondered if this is happening at Brookside as well?

  • 13:26:46

    NORMANDYAbsolutely, it is. I've never seen the Lenten Rose bloom so early and it is blooming concurrently with the Christmas Rose and in some cases earlier, depending on the seedling. I have a Camilla at home that did the same thing. I think the secret to this is we had some cool weather, some colder weather between, you know, in November and in December, maybe not normal. And that meant that some of these buds got their cool fix and then it got warm and so they popped out. But not all of them, that was the weird thing. I have some Camilla flowers that bloomed and fortunately not all of them, even on the same bush. So I think again it's a matter of the chilling cycle.

  • 13:27:26

    NNAMDIWendy, in Alexandria, Va. And thank you for your call. Wendy, your turn.

  • 13:27:31

    WENDYThanks for taking my call. Just weighing in on what we have blooming much earlier than usual and that is a witch hazel, which has its scraggly yellow flowers all the while it's still holding its old dead leaves from last fall. Also have a Lenten Rose, the Helleborus and hyacinths poking their heads up. So that's far earlier than usual.

  • 13:27:54

    NORMANDYWell, I should say that depending on which witch hazel you have. We have quite a collection at Brookside and I've been watching them for several decades and I don't make that up. We've had them bloom as early as the first week of January, which was this year and as late as the first week of March depending on the weather and the cultivar.

  • 13:28:15

    WENDYOkay. Mine is a highly fragrant yellow. I don't remember cultivar it is but it never blooms this early. I can just say that.

  • 13:28:23

    NORMANDYYes, and that's the important thing, what you notice in your own situation is the most important part.

  • 13:28:31

    NNAMDIThank you, Wendy, for your call. And now Barbara in Rockville, Md. Barbara, your turn.

  • 13:28:39

    BARBARAHi, I was wondering if there would be any harm to planting bulbs now, spring bulbs now. Would it cause any harm?

  • 13:28:51

    NORMANDYWell, have they been in your 70 degree house?

  • 13:28:55

    BARBARANo, they've been in the garage. They just didn't get planted in the fall so I'm just wondering do I need to wait until fall or can I plant them?

  • 13:29:03

    NORMANDYNo, you're one of those notorious bulb slackers aren't you?

  • 13:29:07

    VOGELShe just asked the question that was my last question I was sure I was going to ask before I left because as Kojo knows, last minute, waiting until the last minutes is a key for me. So I also have leftover bulbs.

  • 13:29:17

    NORMANDYWell, this is great and the answer is do it now, in fact, do it now while the ground is still thawed. What's going to happen is that they're going to be really retarded this year. You're going to have them come up and bloom, you know, a month after they were supposed. They're going to look really small and crappy but they'll make up for it next year. The problem with waiting until this fall is, you risk them drying out totally and becoming, you know, basically dead. Bulbs don't live forever out of the ground. They live a long time but not forever. So plant them now, pick a nice warm day with the sun on your back and get them in there.

  • 13:29:52

    NNAMDIBarbara, thank you very much for your call you...

  • 13:29:54

    BARBARAThat sounds great.

  • 13:29:55 bulb slacker you.

  • 13:29:58

    VOGELThat's a good name.

  • 13:29:58

    NNAMDIBack to work. Thank you very much for your call. We're going to take a short break. When we come back we will begin our conversation on the new plant zone map, allowing you to understand how changes have occurred in your area and what you might be able to plant now. I'm Kojo Nnamdi.

  • 13:32:04

    NNAMDIWelcome back. Phil Normandy is still with us. He's a horticulturist and plant collections manager at Brookside Gardens in Wheaton, Md. where he oversees all outdoor and indoor displays. Diane Vogel left the room to go back and manage the show again. But joining us now by phone from Oregon is Chris Daly, founder and director of the PRISM Climate Group at Oregon State University, which specializes in geospatial climatology and created the new USDA Plant Hardiness Zone Map. Chris Daly, thank you so much for joining us.

  • 13:32:37

    MR. CHRISTOPHER DALYYou're welcome. Glad to be here, Kojo.

  • 13:32:38

    NNAMDIPhil, I'll start with you. This map is not the only tool that gardeners use to decide what to plant but it is widely consulted. How do gardeners use it?

  • 13:32:46

    NORMANDYWell, often they will be shopping in plant catalogs or reading in books and they'll say, I wonder if I can grow this? And it'll give a range of hardiness from say, you know, zone 5 to zone 8. We are now solidly in zone 7 here in the Washington D.C. area, all of us and some warmer than others and anything that's zone 5 to zone 8, sure we can grow, you know, if it were say this is a zone 8 to zone 10 plant, we'd know that we couldn't. Now, we'd also say that doesn't give the adventurous or the foolhardy any breaks if they really, really want to do it.

  • 13:33:26

    NNAMDIWell, this map was last updated in 1990. Phil, are you at all surprised by how much the map changed?

  • 13:33:31

    NORMANDYWell, the thing I love to say about this map and I don't know how Chris feels about this, this is validating what gardeners have observed for the last 20 years. We were just waiting for permission from the government to believe it.

  • 13:33:47

    NNAMDIWe have the antidotal evidence, now we have the scientific evidence of what is going on.

  • 13:33:50


  • 13:33:51

    NNAMDIIf you're a gardener wondering what this new map means for you and your yard, give us a call at 800-433-8850. Chris Daly, you say that this is a map of extremes. What exactly does it show us and what does it leave out?

  • 13:34:06

    DALYWell, what this map shows -- we mapped what's called the plant hardiness statistic, which is the average coldest temperature it reaches each year. So if the coldest temperature it reached in the Washington area was 10 degrees Fahrenheit in a given year, you would then look back 30 years, we used the period 1976 for 2005 and then averaged those coldest annual temperatures each year to come up with a plant hardiness statistic. So it's really only telling gardeners what the deep cold is like in the middle of winter. It doesn't tell them how their first and last frost dates have changed or anything or average growing conditions. It's just about surviving the winter if you will.

  • 13:34:52

    NNAMDII understand that the last hardiness map was created by hand rather than being computer generated so it's not a huge surprise that the newer version is more precise. How do you get that degree of precision?

  • 13:35:06

    DALYWell, we're using a computer interpretation routine called PRISM, which I first started to develop back about 20 years ago and had been improving it ever since. And it's very, it's what I call an expert system which mimics the process that an expert climatologist would use in drawing a map manually except we can be much more precise with computer technology. So the map incorporates things such as proximity to oceans and coastlines, elevation, where you are in the topography. If you're in a cold, cold bowl you could have frostier conditions than up on a ridge top nearby, things like that. So we kind of went through the process of seeing what information does a human being access in being able to draw one of these maps and put it into computer ease.

  • 13:35:55

    NNAMDICurious about the technology that goes into making an interactive map like this? Give us a call at 800-433-8850. Chris, you mentioned how more precise this is. You apparently point out that the precision and accuracy are not exactly the same thing.

  • 13:36:12

    DALYThat's correct. Precision is how detailed the map is and each -- this map is essentially a collection of pixels on a grid where each pixel is about a half mile on a side. So the precision is within a half a mile, which is very small. But there's also accuracy and accuracy describes how close we to what reality would be on the ground and there's no way of exactly knowing what that is but in general the map is -- in the central plains area where we're away from coastlines and the terrain is flat, we're probably within about a degree Fahrenheit, plus or minus degree Fahrenheit.

  • 13:36:51

    DALYIn eastern U.S., probably a degree and a half and the most difficult area is in the western U.S., probably two degrees Fahrenheit. So I think users of the map should think of these zones as blurry zones. That is there's slop on either side and so if they're on the edge of one zone that doesn't mean they can't grow something in the adjacent zone.

  • 13:37:10

    NNAMDIWhat does that make you think of, Phil?

  • 13:37:12

    NORMANDYI think he's right and I also would say in your own very small micro-climate, that is your, you know, your front of your house, the side of your house, next to the garage, whatever, you can create or you already have small micro-climates that maybe are warmer or colder than the surrounding area and if you're really trying to push that, make that tender plant grow and live through the winter for you, you would site them accordingly. I'm fascinated to hear what he says about the zone edges being sloppy. I think that's a great description.

  • 13:37:46

    NNAMDIThe zone edges being sloppy?

  • 13:37:48

    NORMANDYYes, the zone edges are sloppy. I like that.

  • 13:37:52

    DALYYes, Phil brings up a really good point, is that there are the micro-climates, we're never going to be able to reproduce the micro-climates in someone's garden and you can really change things quite dramatically if you work at it. So you're absolutely right about the micro-climates. That's something that we'll probably never be able to really fully reproduce in the map.

  • 13:38:11

    NNAMDIMaybe not in your garden but the interactive map on the website will give you very specific information for your zip code including the actual temperature value for the coldest night over the 30 year span that they average. But it'll also show you if, it'll also show you more precisely where you are, if you are on the aforementioned edge of a zone, if you happen to be in 7B, you may be close to 8A and consider plants for the 8A area, if you're in 7B.

  • 13:38:39

    NORMANDYThat's correct.

  • 13:38:39

    DALYYes, the map actually, the interactive map you're referring to, Kojo, actually will give you the temperature or the plant hardiness temperature so that if you show that you're in 7B but you're right down at the very edge of let's say the colder edge of 7B you'll be able to see that. I think 7A is zero to five and 7B is five to 10 Fahrenheit. So if you're sitting, let's say, at the top edge of 7A, let's say 4.5 or almost 5 degrees Fahrenheit, you're essentially right straddling the border between 7A and 7B. It'll give you that precise information for you.

  • 13:39:16

    NNAMDIChris, how did the creation of this new USDA Plant Hardiness Zone Map differ from other projects you've worked on?

  • 13:39:23

    DALYWell, it certainly is the most highest profile project we've worked on. We actually do produce the USDA's official, what are called normals, climate maps which on every decade, the 30 year period moves up one. So right now we're working on the 1981 for 2010 precipitation and temperature normals maps and these are maps that we've done for about the past 15 years or so. So it's similar to that and actually we use those maps as a guide in producing this new extreme plant hardiness map because the variations in extremes follow very closely the variations in average winter temperatures let's say for the month of January, which is typically the coldest month of the year. So we actually use those maps we created previously as a guide to create this map.

  • 13:40:14

    NNAMDIPhil, before the gardeners in our audience start ripping shrubs out of the ground and completely reconsidering what they plan to plant this spring, let's talk about what this means. Are certain kinds of plants more likely to be affected by these changes?

  • 13:40:29

    NORMANDYI guess my take on this is, and I've been working at the same place and in the same location for about 33 years. I've seen dramatic changes from the early '80s to now as to what border -- what used to be called borderline plants are now considered reliable plants. So for example, we would be talking -- we could success with Camellias out in the open now. We can have success with Crepe Myrtles, even Paper Bush is being considered safe, and gardeners, of course, always want what's harder and but maybe they can't have and they like to push the envelope.

  • 13:41:11

    NORMANDYSo I guess that's what I've noticed, that this -- again, what gardeners have seen in the last 20 years is now just being validated in print with really good statistics, and we're delighted.

  • 13:41:23

    NNAMDIIf you're a gardener wondering what this new map means for you in your yard, give us a call, 800-433-8850. What factors do you consider when deciding what to plant in your yard? You can call us, or go to our website,, send us a tweet @kojoshow, or email to We're gonna take a short break. When we come back we will continue our conversation about the new plant hardiness map and what it means for you. I'm Kojo Nnamdi.

  • 13:43:38

    NNAMDIWelcome back to our conversation about the new plant zone map. We're talking with Chris Daly. He's the founder the director of the PRISM Climate Group at Oregon State University which specializes in geospatial climatology, and created the new USDA Plant Hardiness Zone Map. He joins us by phone from Oregon. Joining us in studio is Phil Normandy, horticulturist and plant collections manager at Brookside Gardens in Wheaton, Md., where he oversees all outdoor and indoor displays.

  • 13:44:06

    NNAMDIWe're taking your calls at 800-433-8850. Chris, before the map was made public it was sent to a number of experts across the country for review. What kind of feedback did you get, and did their insights change anything?

  • 13:44:22

    DALYYeah. It's a good question. Even with the long-term USDA normals maps I mentioned just a few minutes ago, we also go through a review process. This is really important because we can't know every corner of the country accurately, and we rely on local experts to help tell us when we've gone wrong. Probably the first thing that came to light was that the northern zones along the border of Canada and U.S. and the great plains looked a bit too warm to some of the experts up there, and we found that we had very little information in Canada to help kind of pin down those colder zones across the border, and so we brought in a lot more Canadian data from Environment Canada and that really helped.

  • 13:45:07

    DALYAnother example was New Jersey state climatologist, David Robinson saw that the coastal areas of New Jersey some weren't -- they were a little bit ragged. You expect to see areas near the ocean be somewhat milder than areas inland along the east coast, and so we worked to improve our coastal proximity algorithms to be able to care a nice kind of a good integrity of the nice warm coastline that New Jersey sees. So those are some of the examples of feedback that really helped improve the map.

  • 13:45:38

    NNAMDIOnto the phones, here is Mike in Takoma Park, Md. Mike, you're on the air. Go ahead, please.

  • 13:45:46

    MIKEYeah. Hi, thanks, Kojo. My name is Mike Tidwell, and I'm director of a group called the Chesapeake Climate Action Network, and what's really astonished me, and all the news of the USDA's change in hardiness zones for gardeners is the almost complete lack of the question why is this happening? Why is our planet warming, why do we now have this incredibly precise data showing that, you know, things bloom earlier here and you can plant things later there.

  • 13:46:16

    MIKEI mean, our climate is changing, and the reality is every major academies of sciences all over the world have said it's because of human use of fossil fuels, oil, coal, and natural gas, and it's just amazing, it's almost -- the coverage in the press of this changing gardening zones has almost been a, you know celebration, hallelujah, and in reality it's the early stages of a really huge agricultural and civilizational crisis, and I wonder why you guys think there's been so little coverage of what's causing this.

  • 13:46:52

    NNAMDIWell, Phil and Chris, you've heard Mike. There's clearly controversy over the map and the question of whether or not it shows global warming. The USDA was very explicit in saying changes in zones are not reliable evidence of whether there has been global warming. Other says that whether you attribute it to climate change or not, this map reflects a new normal. What do you say, Phil?

  • 13:47:16

    NORMANDYWell, it's a question I've wondered about myself, but I don't know the answer. All I know is that we are going through a warming trend, and whether that trend is a predictor of true global change that is ongoing, or whether it's a cycle that we're going through, I'm not, you know, I'm not smart enough to know that or have any experience with that. I guess that the reason why so little discussion in gardening circles where this is often -- I mean, the announcement in the Washington Post was in a gardening column, as you know, is that rather than focus on the cause of it, we're trying to figure out how this affects, you know, deal with the results of it, and what does that mean for our hobby and in my case, my profession, and it is good news in the sense that it expands the choices of plants that we can grow that may wanted to do so before, and I guess we don't know why it's happening, we just know that it is for mow.

  • 13:48:19

    NNAMDIIt is, in fact, a new normal in a way. Care to comment, Chris Daly?

  • 13:48:23

    DALYYes, absolutely. I think the reason why the USDA was reluctant to tout this an indication of global warming, if you look back at the 1990 map, it was generated from only 13 years of data, 1974 through 1986, a very short period of time, and as it turns out, a very cold period of time.

  • 13:48:45

    NORMANDYYes, it was.

  • 13:48:46

    DALYIn fact, I went back and looked that the National Arboretum temperature statistics, and starting in 1949, and moving to the present, so over 60-some-odd years, four out of the five coldest extreme minimum temperatures occurred during that 1974 through 1986 period, just amazingly cold period. If you go back to the 1960 Plant Hardiness Zone Map, you find that all of the D.C. area was in 7B. The 1990 map put Washington in 7A, and now in the 2012 map, we're on the edge of 7A and 7B.

  • 13:49:22

    DALYSo if you look at a longer context, and you really put the 1990 map in its historical perspective, you're seeing a dip in cold temperatures in the '70s and early '80s that hasn't really occurred before or since. So you need to be careful in trying to think about this in terms of a global warming trend, which is something you really expect to see over the 50 to a hundred year period, not a couple of decades.

  • 13:49:49

    NNAMDIMike, thank you very much...

  • 13:49:50

    MIKEYeah. But this fits a larger body of data. I mean, we have overwhelming evidence that the planet is warming. I mean, the notion that these hardiness zones are now clearly and rapidly I might add, moving northward, and this has nothing to do with the melting Arctic ice, nothing to do with more intense precipitation patterns, all these things that scientists all over the world are telling us.

  • 13:50:18

    MIKEThat's what's amazing to me is how the press has almost gone out of its way to not connect any dots. USDA has also been hesitant to come out with this Hardiness Zone Map in my view for political reasons. Under the Bush administration...

  • 13:50:36

    NNAMDIWell, wait a second, Mike. Mike, we're doing a show here for people who do gardening their backyard gardens.

  • 13:50:42


  • 13:50:43

    NNAMDIWhy is it you think that the central theme of our show for the gardeners who are thinking about what to plant in the spring coming up should be that this is more danger than opportunity?

  • 13:50:56

    MIKEBecause I'm a gardener as well, and while there are some exciting new things that we can plant in this area, the overall trend is that this is trouble for anybody who wants to grow anything, whether they're doing it recreationally, or...

  • 13:51:09

    NNAMDIWell, let us say our gardeners accept that as a troubling trend as you assert. What are we missing here? What are we not seeing here that disturbs you?

  • 13:51:22

    MIKEI believe that the media, as well as those who have been releasing this data have a responsibility to connect a few dots beyond a very strict USDA responsibility to say you can plant a Blue Spruce here and not there. In other words, gardeners are not fully served when we keep the conversation on this detailed data without saying overall, by the way, our energy choices are gonna make it very hard to grow wheat in Kansas in the coming years according to data released for years and years by scientists all over the world.

  • 13:52:02

    NNAMDIWell, Mike, your voice has been heard in this conversation, so you have clearly made the connection as a part of our broadcast, but I get the impression that you feel that this should really be a part of recruiting backyard gardeners into a movement, and that is not our responsibility here. But thank you very much for your call. What is our responsibility, Phil, is to try to make local gardeners aware of what the changes in the map may mean to them.

  • 13:52:33

    NORMANDYWell, it depends on whether you're an adventurous gardener, or you're a reticent gardener, and an expression I like to use is for the reticent groups, now they have permission. They may go out and try things that they really just wouldn't do because the rules said that they couldn't. For the more adventurous people, there are several wonderful plant experts who like to say I never consider something fully not hardy until I've frozen it three times or something like that.

  • 13:53:02

    NORMANDYNow, we have the ability to grow a lot of different things, and that's strictly from the standpoint of the hobbyist or even the professional and, you know, and not maybe the greater climatological issues that have come up. I guess what we're saying is we know that for now this is what's going on. The map verifies it, which is also something that Mike saw, and then what do we do about it, and what we do about it is we get to go out and try new things, and there are a number of nurseries, mail-order nurseries, and others, that are specialized in unusual plants, and their mantra for years has been zone denial. I love that expression.

  • 13:53:45

    NNAMDIMe, too.

  • 13:53:46

    NORMANDYZone denial. I'm gonna grow this, even though the book says I can't. Well, now the plants can read the book and say, oh, I guess it's all right not to freeze, and so we're able to grow things. I've had this experience, what Chris was mentioning about that cold period, he's absolutely right. The '70s and early '80s in the Washington area, even if you take out the really extreme winters of '76, '77, there were a number of things we just could not grow.

  • 13:54:15

    NORMANDYWe could not grow Crepe Myrtles, and today's generation of gardeners is looking at that going, what do you mean? It's hot as hell here in the summer, of course we can grow Crepe Myrtles. We couldn't in the early '80s. We couldn't grow Aucubas. We couldn't grow a lot of things, and now, even this very warm extraordinarily strange winter notwithstanding, we can grow those things with impunity.

  • 13:54:39

    NNAMDIOnto Joe in Hamilton, Va. Joe, you're on the air. Go ahead, please.

  • 13:54:45

    JOEOkay. Kojo. Boy, wonderful show. I love listening to you. I'm a pet sitter, and I drive around the Louden County roads lots of times just listening to all you guys down there. One quick question. Is there an application that these (word?) have put into place somewhere where the regular average organic gardener like myself can enter data if I was really had enough time to take my own rain measurements and temperature measurements and on a daily basis, weekly basis (unintelligible) enter this stuff into some sort of a computer application that would give me my own hardiness zone for my backyard?

  • 13:55:29

    NNAMDIIf it doesn't exist, Joe, you just suggested the idea to somebody else. Does such an app exist, Chris Daly?

  • 13:55:37

    DALYWell, first of all, you have to have 30 years of data that's been heavily quality controlled, and at least 85 percent of the data has to be there, so it would take him quite a long time to do that. I think that, you know, the zones certainly have temperatures ascribed to them as I mentioned before, but I think that these are long-term values. If you wanted to see where his zone would be in any given year, he can collect that temperature data and look at the coldest temperature of that year and see what zone that would have put him in for a one-year zone out of 30.

  • 13:56:12

    DALYAs far as taking weather measurements, as a citizen scientist, there actually is a really good and extremely popular network for precipitation observations, and it's called Cocorahs, which is C-O-C-O-R-A-H-S dot org, and Cocorahs now is the largest precipitation measurement network in the country exceeding even the National Weather Service cooperative network and it's expanding dramatically each year. So I would encourage you to take a look at and sign up as a citizen observer. It's quite a fun and very useful way of learning about science as a citizen.

  • 13:56:54

    NNAMDIJoe, thank you very much for your call. And finally, we go to Robert in Braddock Heights, Md. Robert, you're on the air. Go ahead, please.

  • 13:57:02

    ROBERTThank you, Kojo. I just want to make a comment that came out in some of your preliminary advertisements for the show. Of course, you can grow bananas in Maryland, I've been doing it for well over a decade. I have only now the Japanese Hardy Banana because I'm too lazy to bring the things in for the winter to store as I did when we lived down (unintelligible) quite a few years ago. But now I grow just the hardy banana. It has come back every year.

  • 13:57:33


  • 13:57:33

    ROBERTSome years more lushly than...

  • 13:57:35

    NNAMDIPhil Normandy tells us we know you can grow at least one kind of banana in Montgomery County, but that's not just the result of warmer temperatures. You only have about 30 seconds.

  • 13:57:44

    NORMANDYOkay. Yes. And that was a point I really wanted to make in this broadcast. Because people always want to grow something that's not usually possibly, one of the avenues that was taken was finding hardier germplasm of what would seem to be tropical plants. This banana is a new species that is just naturally hardier. It's not a fruiting banana, unfortunately, but it does give us that tropical look.

  • 13:58:07

    NNAMDIPhil Normandy is a horticulturist and plant collections manager at Brookside Gardens in Wheaton, Md. Chris Daly is the founder the director of the PRISM Climate Group at Oregon State University which specializes in geospatial climatology, and created the new USDA Plant Hardiness Zone Map. Thank you both for joining us, and thank you all for listening. I'm Kojo Nnamdi.

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