Chris Fields-Johnson, technical advisor for the Davey Institute, gives us the science behind when trees will leaf out in the spring and when you should take a closer look if they haven't yet.
In this episode we cover:
To find your local Davey office, check out our find a local office page to search by zip code.
To learn more about when to expect your trees to leaf out, read our blog, When Do Tree Leaves Come Back in Spring?
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Chris Fields-Johnson, technical advisor for the Davey Institute, gives us the science behind when trees will leaf out in the spring and when you should take a closer look if they haven't yet.
In this episode we cover:
To find your local Davey office, check out our find a local office page to search by zip code.
To learn more about when to expect your trees to leaf out, read our blog, When Do Tree Leaves Come Back in Spring?
Connect with Davey Tree on social media:
Twitter: @DaveyTree
Facebook: @DaveyTree
Instagram: @daveytree
YouTube: The Davey Tree Expert Company
LinkedIn: The Davey Tree Expert Company
Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!
Doug Oster: Welcome to the Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much more. Tune in every Thursday to learn more because here at the Talking Trees podcast, we know trees are the answer.
I'm joined, this week, by Chris Fields-Johnson. He's a technical advisor for the Davey Institute down in Charlottesville, Virginia. Chris, welcome to the show. How do these trees know it's time to leaf out? Because I'm ready.
Chris Fields-Johnson: Yes, Doug, I think we're all ready. Trees go through a very specific process throughout the preceding dormant season, to get ready to leaf out. Really, it starts in the fall with how they know to go dormant. As the days get shorter, trees are sensitive to the photoperiod. As the photoperiod, the amount of time that the sun is shining, declines, some molecular processes are kicked off where the trees start to stop producing chlorophyll and decreasing the amount of chlorophyll in their leaves.
The leaves begin to change color. Then eventually, they'll cut the leaves off at the abscission line where they attach to the stems, and the leaves begin to fall down. That's the first indicator that gets things going into dormancy is that decline in photoperiod. Over the winter, the trees do something a little bit different. They're actually counting the amount of time that it's below freezing. It's like freezing-degree days or cold-degree days.
They require a certain amount of time below freezing in order to set off another chain of molecular events that tells them it's going to be okay to break dormancy when things start to warm up. Then finally, as temperatures get above freezing, and in a lot of cases, above 50 degrees Fahrenheit, that sets off the growing degree day clock. You start to accumulate a certain number of growing degree days above 50 degrees.
The trees will then begin to break bud and put out new leaves and flowers when they hit a certain number of growing degree days. That's it. That's the process. They begin by counting down the days getting shorter. That tells them to go dormant. Over the course of the winter, they accumulate a certain number of days or hours below freezing. That tells them winter has passed, so it's going to be safe to come out when things warm up. Then finally, as temperatures rise above about 50 degrees Fahrenheit for long enough, then they say, "Okay, it's safe to put out new leaves and flowers."
Now, sometimes they get burned, right? Sometimes they jump the gun and you get a late frost or a late winter storm and it can give cold damage to those leaves and flowers, and they have to start over.
Doug: That's where I wanted to ask you because I was going to say, why does my magnolia, those buds swell up real nice and I guess one out of three or four years, there's a late freeze and no magnolia flowers for the old-fashioned magnolias. The newer ones are bred to bloom a little later. That's just the way it goes, huh?
Chris: Yes, it's just the way it goes. Trees have been evolving for millions of years. They play the table, right? They gamble, they play the statistics. They're going to try to maximize their growing season. They don't want their leaves to get nuked by a late frost and they don't want something to come up and get them in the fall before they've gone dormant, like an early frost in the fall.
They'll pick indicators that give them the longest average growing season without wasting their leaves and throwing them out there as cannon fodder. They're definitely playing the statistics and they're going to push it a little bit to try to grab a longer growing season. I guess, evolutionarily, it's just come to their advantage to gamble a little bit, maybe come out a little early. Every year out of 10 years, 1 out of 10 years, 1 out of 5 years, something like that, maybe they get burned, they lose some of the leaves that have come out a little bit early.
If they have years of time to recover in between, they have no problem putting out a second set of leaves. It's when that happens multiple years in a row and that keeps going on and on that they might get into trouble and start to decline.
Doug: Up here in Pittsburgh, we're still waiting. If I got the question, "Hey, when are my trees going to leaf out?" My answer would be, "Just be patient. They'll leaf out when they leaf out. It's going to happen." Let's say, for instance, we get worried. We get into that 50 degrees and we don't see the tree leafing out. Do we just wait? I guess it depends on the tree, huh?
Chris: Yes, it's going to depend a lot on species. They don't start leafing out immediately when you get days above 50 degrees. When you start getting 100 or more growing degree days, you should start to see the early leaf outs happening. Some of the invasive species, like a multiflora rose and autumn olive, they'll start to put out leaves pretty early. They're a little bit more hardy. Then others will start coming out.
A lot of times, we see flowers coming out before the leaves. That's another thing to look for. It's a little bit of an early warning sign. Around this time of year, you might be seeing forsythia blooming. That's a good indicator. Things like Kwanzan cherries, in some cases, might already be blooming. Then pretty soon, you'll start seeing the Bradford pears and other calorie pears blooming, the big, showy, white flowers.
Then the leaves come out pretty soon after the full bloom of the calorie pears and Bradford pears. You'll start to see their leaves coming out. For other species, they'll put out leaves before the flowers. Another species you probably are seeing blooming now is red maple. Small red flowers on red maple. Then like the silver maples and sugar maples will come shortly after that.
Then you'll see the leaves come out after those have gone through their blooming cycles. Yes, look for those early indicators. The main thing to be worried about is if you see an individual tree of a given species where all the other members of that species that you can observe have leafed out and that individual has not. If it continues to lag for one, two, three weeks, or more, that's an indicator that one tree is pretty stressed out. It might be dead or, if it doesn't leaf out at all, ever, that means it's just dead. If it just leaves out really late, that can be a sign of stress and there might be something wrong with that tree. You might want to have it looked at.
Doug: Up here, it's just when you're driving down the freeway and you see the maples and those buds starting to swell and change color, that's exciting. We're getting close. You brought up something I wanted to talk to you about—autumn olive. I need your opinion on this because I inherited two autumn olive trees on my property. Now, they have the most amazing fragrance. Those little berries are edible, but it's an invasive and that's concerning to me. The other thing that's concerning to me, it's my wife's favorite two trees on the property. [laughs]
Chris: Yes, no, they are invasive. They tend to take over areas that are disturbed. They don't get very tall, but they're a pretty large shrub, and they can form a continuous canopy and really restrict the ability of other species to move in and grow like a native forest there. They can invade fields and pastures if the goal is to have like an open meadow or a pasture or hayfield or something like that.
Yes, they do present a problem. They are edible. I've actually made wine out of autumn olive berries before. It took all day to gather three or four gallons of them to make wine because they're so small. They are an edible. Of course, the birds love them. The birds are really the primary vector for them. They eat the berries. The berry seeds go through their digestive tracts and get scarified and spread all over the place.
It's a plant that's certainly out of the bag. It's ubiquitous. It's everywhere you go. Your particular autumn olive plants in your yard are not a particular problem because this is a plant that's already everywhere. I would just make an individual decision. If those plants are your favorites and they're worthwhile to you, yes, that's okay in that domestic context. Somebody else who finds them out in their pasture or in an area they're trying to reforest with native trees, they might be a big problem for them.
Don't feel like your particular plants are going to create any significant difference in the grand scheme of things. They are an amazing plant though. They fix nitrogen so they can help to restore soils. Originally they were planted for reclamation purposes, for restoring soils that were eroding or that weren't able to support other vegetation originally. They're extremely hardy. They do have perhaps a use, but yes, they start to take over certain areas. We need to manage them appropriately where they become a problem.
Doug: Chris, that's exactly what I wanted to hear because I was afraid you were going to say, "Cut down those autumn olives. They're invasive and you're ruining our environment." That's good news.
Chris: Yes, I'm not an anti-invasive plant warrior. I think they do create specific problems in specific contexts. I think we have to acknowledge that a lot of these plants are here to stay. They're naturalized. We have to find ways to integrate them into the ecosystem and manage them. It's like we can't eradicate a lot of these things anymore. Just like we can't eradicate certain diseases and certain insect pests, things like the Emerald ash borer. They're here to stay.
We can protect individual trees where we can, but we're not ever going to get rid of the Emerald ash borer. It's impossible. Same's true for autumn olive—we're never going to get rid of all of them. Where they're specifically a problem, we can manage them and push them back a little bit.
Doug: Well, you just saved my marriage. That's good news. Great. Tell me a little bit about your job. What does that mean, technical advisor for the Davey Institute?
Chris: I work with the Davey Institute in the East Atlantic region. I cover the area roughly from the western New York City metro area down to Atlanta and out to Charleston, West Virginia. I provide technical support for our various operations in the region, mostly for the residential and commercial tree care, and also for Davey Resource Group. A lot of what I do is technical support for plant healthcare, so helping to diagnose plant issues, pest diseases, soil issues. I troubleshoot, come up with management plans.
I do a lot of employee education, so putting on educational programs and also field visits, doing ride-alongs to client properties, and helping to solve problems. Quite a bit of inspecting pesticide safety issues, like how pesticides are stored, how personal protective equipment is used. Helping to educate all of our people about safe practices with pesticides. I do quite a bit of research as well. Whether it's reviewing literature and extension publications to get good information to our field people, or just original research. You always have quite a few little experiments going on, testing different soil amendments and water practices and all kinds of different things.
Doug: What kind of path do you take for that job? How did you find your way to it?
Chris: Well, primarily, I have a doctorate in soil science from Virginia Tech. Getting the graduate degree was really important to be qualified for this job. On the work side, when I was young, I worked in the adventurer and rock climbing field, teaching kids rock climbing and running adult workshops, and working at a climbing gym. I did that through some of my college years.
On the side, I did tree work, taking down trees for people and pruning, that kind of thing. That helped me pay for college and get through. When I was in graduate school, I was employed by the university as a research assistant, so helping with various projects, including my own thesis and dissertation work, but also other graduate student and professors' work projects.
That's a pretty involved job. When I initially got out of graduate school, I worked for another tree company as a plant healthcare technician. I would be out in the field with a rig, providing treatments for any problems that I saw. During the winter when there wasn't as much plant healthcare work, I would work on their tree crew. Initially, just working as a grounds person, dragging brush, chipping it up and sharpening chainsaws, and supporting all the climbers, and then eventually doing more climbing.
Climbing up in trees either with a rope or accessing trees with a bucket truck for doing trimming and removals and that kind of thing. Eventually, there was an opening to be a technical advisor on the East Coast for Davey. I switched companies and took a different job where I was able to combine all the practical experience I had with the educational background. I find myself in a pretty good position now to use a lot of my experience in education.
Doug: Yes, that's a quite a resume. You know all the stuff on the ground, you've been up in the trees, and then you've got, of course, it's great science background too to use. That's pretty cool.
Chris: It's fun to be able to pull all those threads in my life together and have a job that's fairly dynamic and where I can help people every day, both our employees and clients, solving problems. It's really fun because I'm always solving a new issue or problem every day. It's always something new. Visiting some new place I've never been before and solving new problems. It's a lot of fun.
Doug: Down where you're at, in Virginia, has everything started to leaf out?
Chris: Not everything. We're in the 100 to 200 growing degree day phase now. The forsythias blooming, the calorie pears are just starting to bud out. The quans and cherries are blooming and not seeing a whole lot of leaves coming out yet, except on things like the autumn olive and multiflora rose and some of the really-- the early leaf-out stuff.
In the next few weeks, a lot of stuff is going to start to leaf out. As those flowers come into full bloom and kind of fade away, then the leaves really start to come on. That'll continue through about, in Virginia, usually, everything's done leafing out and all the spring blooms and stuff are out around May 10th or so. It's all finished and we get more into a summer state of affairs. We have about two months of a rollout of new leaves coming out almost on a day-to-day basis, between now and early May.
Doug: You have a different winter than we have up here in Pittsburgh, but do you have the same feeling that someone that lives in a little further north has when we come out of that winter? Because we can't wait, we can't wait. I'm watching those forsythia, we're behind you probably three weeks, and I'm seeing those buds swell. Like you said, that's the first indication those yellow flowers explode. Do you have the same feeling of coming out of winter?
Chris: Yes, winter in Virginia is different. We only had one fairly major snow event this year. It was a pretty nasty snow event, so a lot of Virginia pines and red cedars got crushed. A lot of storm damage and stuff happened from that one event. A couple icy sleety storms after that. It was really just that one-month period in January where we had wintery conditions. Since then, we've had routinely had days above 50 or 60 degrees, and gets below freezing at night.
Other than that, it's fairly mild. The winters in Virginia are fairly mild. We don't really dread them. It happens often enough in Virginia that we do have the plows and the salt trucks and stuff available to actually clean up the roads. We don't have total bedlams breakdown of society when it snows like you might have in the Deep South. Here, we're fairly well prepared for the winter events, but they don't drag on.
Yes, I don't really get a huge sense of relief around this time of year because it really hasn't been that bad, to begin with. I enjoy the snow. Sometimes I wish it snowed more. With climate change and everything, I'm probably going to have to move north if I want to enjoy more snow. We seem to get less and less of it down here over time.
Here in the South, we dread the summer more, just the relentless 100-degree days and the high humidity, that can really drag on. We really get a sense of relief in the fall when things start to cool off and the weather's nice and people want to be outside more. In the middle of summer, it can be really, really difficult to be outside for days on end, working.
Doug: Well, I'll guarantee you anyone that lives up here is not wishing for more snow, okay? Before I let you go, I was wondering if you had a couple trees that you think are pretty cool that might not get planted as much as you think they should, something that you really like. Is there anything come to mind?
Chris: Yes, there's are some species that I feel like do really well that could be utilized more. One would be the Kousa dogwood. It's a small snatcher tree, has a long bloom period, a really interesting bark. It has a lot of winter appeal as well. It doesn't have nearly the same number of problems as the flowering dogwoods do, which get anthracnose and borers and all kinds of issues.
I get very few calls and issues with Kousa dogwood coming up. That's a good one to consider if you want a small-stature, ornamental flowering tree in your yard or on your property. Another one that I find pretty interesting and hardy is the sawtooth oak. It's a prolific acorn producer for wildlife. Has very few of the other oak issues that we're seeing. Whether it's an oak wilt, oak decline, things of that nature.
I think sawtooth oak is an interesting one that has a lot of possibilities. If you want more of a native oak tree that does really well, the swamp white oaks are resistant to a lot of the issues that we're seeing out there. That is one that's native to North America. Sawtooth oak is native to China, and of course, the Kousa dogwood's native to Korea. The other name for that is the Korean Dogwood.
Those are a few that seem to do really well. My favorite trees on the deciduous side, I really like American beech. Of course, that's got several issues now, the beech bark disease and the beech bark scale, and now the beech leaf disease as well. That's a native tree that's very much under threat from all sides. On the conifer side,
I love bald cypress, and I think there's a lot of potential to use those more in urban contexts. Of course, that's a deciduous conifer, so it's very unique. It's like dawn redwood in that respect. Dawn redwood is another one that I really like.
Both of those really do well in urban environments. They can deal with compacted soil. They shed their leaves in the winter, so they allow the sunshine in to give you a little bit of your solar gain for your home or your cars or whatever, but then they provide shade in the summer when you need it. They just seem to be really hardy with compacted soils and poor conditions. I think either one of those is a cool choice.
Doug: That's a great list, and I sure appreciate all that great information. Thanks very much for sharing your stories, and thanks for being on the show.
Chris: Yes, thanks a lot, Doug.
Doug: Boy, that was great information, wasn't it? Next week, we're going to learn all about the best small trees for the landscape and even trees for planting in containers, too. Tune in every Thursday to the Talking Trees podcast from the Davey Tree Expert Company. I'm your host, Doug Oster. I'd love if you would subscribe to the podcast. We are having a bunch of fun, aren't we?
As always, we'd like to remind you on the Talking Trees podcast, trees are the answer.
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