Sweet Gum: The Beautiful Yet Controversial Tree

Lou Meyer from Davey's Mid-Atlantic region talks all about the sweet gum tree, including its biology, unique features and pros and cons. 

In this episode we cover: 

• Sweet gum's spiky seeds (1:35)
• Why are they called "sweet gum?" (4:12)
• How large do they get? (6:00)
• Sweet gums aren't planted much (7:03)
• What to do about your sweet gum's surface roots (9:07)
• Where do they grow? (10:52)
• Are the black gum and sweet gum related? (11:39)
• Sweet gum identifying features (12:42)
• Crafts with sweet gum seeds (14:54)
• Fruit regulators (16:00)
• Do sweet gums belong in the forest? (18:15)

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To learn more about tree species, read Davey's Tree Identification blogs, such as Tree Identification: Do I Have a Sweetgum Tree and more. 

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Connect with Doug Oster at www.dougoster.com. 

Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!

Transcript

[music]

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, much more. Tune in every Thursday to learn more because here at the Talking Trees Podcast, we know trees are the answer. I'm excited to welcome back Lou Meyer. He is an arborist for the Davey Tree Expert Company in Baltimore. We do an occasional series on different species of trees. Lou, I can't believe the species you picked to talk about this week.

Lou Meyer: It's one of my favorites, Doug, but I completely understand if no one else loves this tree, the sweet gum.

Doug Oster: I get a lot of people when I'm doing this podcast that diss the sweet gum, so you're going to have to do some defending here. [laughs]

Lou Meyer: We're going to talk about both sides, but I will preface it with the tree has spectacular fall color, is a powerhouse for our native fauna, really important seeds, and is darn hard to kill. [chuckles] With that, we'll dive in.

Doug Oster: [laughs] We have one growing in the city by this place called Phipps Conservatory and Botanic Gardens, and it overhangs the sidewalk. Not the best spot for it. Let's get the elephant out of the room. Let's talk about those seeds or seed pods. What do you call them?

Lou Meyer: The sweet gum, the best way to identify that tree is by the little spiky balls. They're little spiky balls. They are known colloquially as spiky balls, sticker balls, gum balls, burr balls, space bugs, and monkey balls. Although monkey balls is also something that we talk about with Osage orange, which is another species we got to do soon. That's one of my favorites. These things, they're the little spiky balls that are just everywhere. Late July through the winter, pretty much, these things produce prolific fruit. The fruit is uncomfortable to step on, and it just hangs around.

Doug Oster: Like you said, it's a good thing if you're not walking on it, right?

Lou Meyer: Yes, absolutely. There's benefits to everything. We're diving right into the fruit here. Each ball contains about 40 to 60 capsules. When you pick one up in the fall, and you shake it sounds like a little baby's rattle. It contains 40 to 60 capsules. Each capsule has two small seeds in it and two terminal spikes, each their spikes. Per little gum ball that falls out of the tree, you got about 80 to 120 seeds and 80 to 120 spikes per ball. This fruit is really important for wildlife because it persists through the fall. It's hard to crack into. Squirrels, chipmunks, and birds, especially finches, love feeding on these seed balls. They've got this food source throughout the fall.

Doug Oster: How do the finches get to it? After some freezes, does it open up, or do they have to crack it open?

Lou Meyer: No, they got to crack it open. Over time, it becomes easier. When they're green, they're really tough to crack open. When they fall off the tree, they're a little better.

Doug Oster: Do they self-sow? With all those seeds in there, will they sprout underneath?

Lou Meyer: Yes, they will. They spread themselves. They're not a species that is in decline right now. They will cast themselves out and will reproduce quickly.

Doug Oster: How big do they get?

Lou Meyer: They get pretty big. Let's go back to the beginning. Sweet gum, let's start with the name here. Liquidambar styraciflua for our tree geeks like me who love the Latin. Liquidambar comes from liquid amber. It's a liquid amber. This tree has a resin or a gum, hence the name sweet gum, that flows through it. Liquidambar is the first word. Styraciflua means flowing with gum. Is what that means. The gum, you could call it styrax or storax, which is a fragrant balsam obtained from the bark of the Liquidambar tree.

A Liquidambar over in Asia, but it's part of the same Liquidambar family. Ours is the styraciflua. It's a gummy tree, which is why it's called gum. Other names for this tree, the American storax, a hazel pine, a blisted tree, storax walnut, red gum. In the South, they call it alligator wood because the bark, when they're older, can get really scaly and gray, like an alligator. They're pretty cool. Then, I used to tell the new guys on the team that they're called star maples when I would send them into the nursery to pick up a star maple. [laughs] Of course, the nursery would say, "What are you talking about?" Like, "Oh, it's the tree with the star leaf." They go, "Yes, you mean the sweet gum?"

[laughs] That was always a fun one for us. We call it the star maple. Now, it does bear some resemblances to a maple, the leaf. If you look at a sugar maple and a sweet gum leaf, you wouldn't be wrong for saying, "Oh, they look a lot alike," because they do, but there are differences. Size-wise, it's a medium to large tree. In cultivation, 50 to 70 feet. Out in the natural, it can grow up to 150 feet tall. On the average, 2 to 3 feet in diameter is a mature sweet gum. Pretty symmetrical crown. They're very pretty.

The national champion is up in Burlington, New Jersey. It is a 72-inch-diameter tree. Just to remind the listeners, when we talk about tree sizes, DBH is diameter at breast height or 4 and a half feet off the ground. At 4 and a half feet off the ground, this thing is 72 inches in diameter. That's a big tree. That's, what, a 6-foot-diameter tree. I'm a six-foot tall adult. If I lay down sideways, I'm 72 inches. That's how wide this tree is. I know you can't see me on this podcast, but I'm an average-sized guy, so picture that. That tree is 72 inches. That wide, it's 132 feet tall with a 112-foot crown spread. It's a massive tree.

Doug Oster: Do you plant them when you're going to a client's place? Do you find places that want to, or you're seeing them in the wild?

Lou Meyer: Usually in the wild. It was a very popular landscape plant for a long time. Again, the fall color is great. There's not really any health issues for them. There's a few, but it's not like a lot of other species where we have reservations about planting them for their health. In the right place, this could be a spectacular tree. Over your driveway, over your pool, not good. Another downside of it, not just the fruit that falls, but it tends to have very surfacey roots, which means that these roots don't go down deep.

For buckling sidewalks and driveways, creating trip hazards. Now, that's what the industry says. My personal thought is because we planted a lot of these as street trees, almost all street trees have surface roots. The reason is that ground is so compacted. When we build houses and buildings and roadways, we compact the soil. We have to because we don't want our foundations to shift. We don't want the roads to heave and thaw with too much moisture in the ground. We pound the soil to a pulp, drive it down so it's really tight, and then we plant a tree in it.

The tree's roots can't break through that compacted soil, so it races to the surface. I get more calls about surface roots than almost anything else in the industry. People say, "I got this maple out front, and these roots are everywhere, and they're driving me crazy." Part of that is the species, red maples and sweetgums. I think a big part of it is when we plant these things in our front yard, and red maples and sweetgums are off in our front yards, we have such compacted soil. It doesn't matter what species it is. Those roots have to race to the surface so that they can get to oxygen and water, and nutrients that are locked up in the compacted soil.

Doug Oster: With something like a sweetgum that has those surface roots, what do you tell people when they're calling you? What can you do, or is that just the way it grows, and you shouldn't be messing with those roots?

Lou Meyer: That's just the way it grows. Once your tree's already established, if you have a teenager-aged maple, if you have a maple in your front yard, 15 years old, or a sweetgum, and those roots are all over the surface of the ground at this point, there's really nothing you could do. Now, if you could back the clock up 15 years, when you planted that tree, if you use the air spade or some kind of tool, a tiller even, to till up a large soil area around the tree, three to five times the width of that root ball. If the root ball is 2 feet wide, you're looking at 6 to 15-foot circle around that, where you're tilling up soil 8 to 10 inches down to allow those roots to travel through the soil.

No one really does that. In an ideal world, that would be what would have happened 15 years ago. Now that you've got those surface roots, the best thing you could do, don't bury them in soil and put seed over it. That will jeopardize the health of the tree so fast. Typically, that soil is just going to wash off in a rain event anyways, because it's not going to be able to hold onto anything. The best thing is to mulch it. Put 1 to 2 inches of mulch so that you're not tripping over those roots, your lawnmower's not going over the roots, and that helps out. As far as the sidewalks go, that's a different story for a different podcast.

Doug Oster: [laughs] Yes, pushing up those sidewalks all over the country. Yes, where do they grow? What is the range of the tree?

Lou Meyer: Yes, sweetgums are pretty much in the eastern United States. If you think of Connecticut down to central Florida, they range west to Illinois, Missouri, eastern Texas. Interestingly, it also from northern Mexico down through Central America. The sweetgum goes down pretty far south. There are four Liquidambars in the world. Sarasaflua, which is our sweetgum. You also have Liquidambar orientalis, Liquidambar formosana, and Liquidambar acalycina. I don't know how to pronounce it, but another one too. Pretty tight species there.

Doug Oster: Now, is the black gum and the sweetgum, is there any relation there, or it's just a common name that they share?

Lou Meyer: It's a common name based on the resiny sap that they produce. Both of them, in historical times, were used for gum, actually. For Liquidambar, for our sweetgum, they would actually, a few different things. Native Americans first used it. The Cherokees and other tribes would use the resin. They put it in tea. They would let it harden and be used as gum. In Appalachian culture, they would mix the resin with whiskey to chew it to clean teeth, to heal your gums and mouth lesions, and to relieve toothaches. Like when you'd rub a little bit of whiskey on your finger to give a teething child, you can mix it with gum, and you have the same effect. Something there.

Doug Oster: You're quite a dad.

Lou Meyer: That's right. That's right. A very happy child. Very happy child.

Doug Oster: [laughs] How about the flowers?

Lou Meyer: Yes. Some other identifying features about this. The flowers, they're not very showy. They're green flowers. They look like little green bulbs that actually turn into the sweetgums eventually. You don't see them very often. The bark is light brown with red and gray streaks. It's quirky and fissured. One of the things I love about Liquidambar is that the branches are winged, which means that the smaller branches they lose this. Branches that are about, I don't know, your pinky in diameter or smaller have this quirky ridge that grows on four sides of it.

If you took an arrow, like an arrow that you shoot with a bow, and you look at the back of it and it has those four wings sticking out to stabilize it, I guess, I don't know what you call those. It looks almost like that. It's got these little ridges that run along it, and it's quirky. Really cool physical feature. One of the downsides, though, and I never think about this until I see it happen, these things really cause failure in snow and ice easily because they just hold a tremendous amount more snow and ice because they got these wings on these small branches.

After a snowstorm or an ice storm, you go under a sweetgum, and you'll see a lot of these little branches that have popped off because of that. They got these wing branches. The leaves, dark green in the summer. They're alternate. That's another way to tell it apart from maples. Maples are opposite, which means that the leaves and branches they originate opposite of each other on the parent branches. If you have a parent branch that's sticking out, two branches will come out at the same place in opposite directions.

Alternate means they're not opposite of each other, they are staggered. These are alternate. Sweetgums are alternate. Maples are opposite. The dark green leaves, like I said earlier, they turn into, I think, one of the most spectacular fall colors out there. Just these bright reds and yellows that give the sugar maples of the Northeast a run for their money as far as the vibrancy goes.

Doug Oster: Do people do anything with those seeds, like make crafts out of them or something like that? I don't know. There's a lot of them.

Lou Meyer: Yes, you can make crafts out of them. One of our family favorite decorations is a little craft snowman that my son made at a holiday craft show years ago. It's hideous-looking. It's scary as can be. We love it because it's his, and he made it, and we put it up every Christmas. It's got one eye glued to the top of its head, the other eye glued to the second one. You can use them for all sorts of crafts. We like making fairy houses. Fairy houses are when you use natural materials to build little tiny houses out in nature that the fairies come to visit.

Those are really cool. We do a couple of those per year. I've got a 10-year-old son and a 6-year-old daughter, and we still love making fairy houses. They're great for that. You can use them for all sorts of neat crafts, yes. Yes, and landscape use. There are cultivars that have lower fruit levels. We do have cultivars that don't put off as much fruit. Also, ones that have more vibrant colors than others and sizes. There are fruit regulators out there. This is a good species to talk a little bit about this.

There are products that we can apply to trees that minimize their fruit output. If you have an oak tree that's over your driveway, and it just beats the heck out of your car every fall when it's dropping acorns, or if you've got a walnut tree that does the same thing, or a sweetgum that you say, "Look, this fruit is driving me crazy." There are products that you can apply that will minimize the fruiting. None of them will stop it. They might say they stop it, but they don't. They'll minimize it. Now, these have to be applied at the exact right time, in the exact right way.

I'll be upfront, they're not cheap. This is something that, I'll say as a last resort, but you really got to weigh the benefits versus the cost of this one. If you miss it by a week, the application, the results will vary a lot. It's all based on degree growing days. Also, it's not like, "Oh, I need to apply this March 1st." Everyone applies it then. You really got to figure out the timing just right. Generally, you don't know it. There is some guesswork. There are products that you can use to help with that. There are cultivars that fruit far less, and that's what you want to plant.

Doug Oster: I don't like getting hit in the head by an acorn, but I want my trees to keep making acorns and other seeds for the wildlife.

Lou Meyer: Right. No, I wouldn't recommend this for most folks, but there are a sliver of opportunities where this is an option that they'd want to go after.

Doug Oster: Yes, certainly, if you moved into a place and there was a sweet gum over your deck, over your driveway, whatever it might be, that might be a case where you'd want to do it. This is, I think, a great example, too, of right tree, right place. I'm thinking, Lou, you tell me what you think of this. In this declining oak forest, and when we're recording this, the Davey team's coming tomorrow to take out about six big oaks that have failed. In the forest like that, is that a spot for a sweet gum, you think, or not?

Lou Meyer: It's a great spot for that. We want more of these out there. In the forest is where, let's say, they belong, [laughs] but that's where they love it, and that's where we love them. Forests, park settings are good, too. One of the reasons why these were used in the city so much is that they are somewhat tolerant of pollution and poor soils. Put them in a forest, they're going to be happy, healthy, you're going to be benefiting your wildlife, you're going to be benefiting the environment, and replacing those oaks with, yes, a species that has a better shot right now.

Doug Oster: Yes, I'm trying to get diversity into my forest and natives, but lots of other trees, too. I think that might be one I'm going to put on my list to replace some of these trees that I'm losing. Well, Lou, I'm glad there's someone out there defending the sweet gum and telling us what a great tree it actually is, because it is for sure a beauty. Appreciate your time as always. What's our next species? When we get together again, what do you think it's going to be?

Lou Meyer: Let's see. I think Kentucky Coffeetree is a pretty good one.

Doug Oster: Well, I can't wait to talk about that one, because I know a little bit about that one. All right, we will see you next time. Thanks, Lou.

Lou Meyer: Thanks, Doug.

Doug Oster: Always great to talk to our friend, Lou. I'm looking forward to learning about the Kentucky Coffeetree. Now, don't forget to tune in every Thursday to this Talking Trees Podcast from the Davey Tree Expert Company. I'm your host, Doug Oster, and do me a favor, subscribe so you'll never miss a show. I want to know what we should be covering on this podcast. You can either send us an email to Podcasts@Davey.com, that's P-O-D-C-A-S-T-S, @, D-A-V-E-Y.com, or you can click the link at the end of our show notes to text us a fan mail message. Your ideas can be on a future show. Love to hear from you. As always, we like to remind you on the Talking Trees Podcast, trees are the answer.

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