The American sweetgum is a tall, deciduous tree with glossy green leaves in summer, best grown for its fall foliage; often, multiple colors (red, orange, yellow, purplish) will be found on the same plant in autumn. They are easily recognizable for their fruits that look like spikey gumballs, which is why it's called a "gum tree."
The leaves have toothed margins. Some of its other common names refer to its traits: It has star-shaped leaves of 5 to 7 lobes (thus "star-shaped gum"), corrugated bark (thus "alligatorwood"), and some of the branches are "winged," as on winged euonymus, also called "burning bush" (Euonymus alatus), displaying corky flanges.
American sweetgum tree fruits come in clusters, turn dark brown in fall, and become as much as 1.5 inches in diameter. While some people find these fruits ornamental, most dislike them for the mess they cause when they drop. To avoid the mess, look for the non-fruiting cultivar Liquidambar styraciflua 'Rotundiloba.'
|Common Names||Sweetgum, sweet gum, alligatorwood, American sweetgum, American storax, gum tree, redgum, star-leaved gum|
|Botanical Name||Liquidambar styraciflua|
|Mature Size||80 ft. tall, 60 ft. wide|
|Soil Type||Well-drained, loamy|
|Soil pH||Acidi, neutral|
|Hardiness Zones||5 to 9 (USDA)|
|Native Areas||North America|
American Sweetgum Care
American sweetgum trees are best planted in spring. You will have a low-maintenance tree if you grow the 'Rotundiloba' cultivar of American sweetgum. Growing the cultivar eliminates most of the need to rake up gumballs as they fall. 'Rotundiloba' may eventually produce a gumball here or there, but not in a quantity that causes a problem.
With its shallow root system, this tree shouldn't be planted near sidewalks, concrete patios, etc. The best location for the tree is far away from the house and any outdoor areas where people will be walking (people have been known to sprain their ankles from walking on the gumballs). One option for those with large properties may be to plant their sweetgum tree on the south side of a woodland garden so you will not have to bother with the landscape maintenance required to clean up the fallen gumballs.
American sweetgum trees are not tolerant of shade, so be sure to select a spot in full sun for it.
Although American sweetgum tolerates clayey soil, give it a well-drained loam for optimal performance. It will also prosper the most in deep soil. It does not like alkaline soil.
Keep the soil of American sweetgum trees evenly moist until it has been established for a few years.
Temperature and Humidity
As a tree native to areas such as Florida, American sweetgum tolerates heat and humidity well. But it isn't reliably cold-hardy north of zone 5.
Because American sweetgum is not a heavy feeder, you only need to fertilize it once every few years. Fertilize with compost, manure tea, or an all-purpose fertilizer.
Types of Sweetgum Trees
The Liquidambar genus contains a few other species besides styraciflua, as well as cultivars other than 'Rotundiloba,' including:
- Liquidambar formosana: More drought-tolerant than most sweetgums; 40 to 60 feet tall and wide; zones 6 to 9
- Liquidambar acalycina 'Burgundy Flush': Burgundy-purple-bronze leaves; 50 feet tall and 25 feet wide; zones 6 to 8
- Liquidambar styraciflua 'Slender Silhouette': Columnar shape; 50 feet tall and only about 4 feet wide; zones 5 to 8
- Liquidambar styraciflua 'Variegata': Variegated leaves streaked with yellow or off-white markings; 60 feet tall and 25 feet wide; zones 4 to 10
- Liquidambar styraciflua 'Gumball': Dwarf variety in shrub form; 5 feet by 5 feet; zones 5 to 8
If you must prune, only remove dead, diseased, or damaged branches. The best time to do it is right after the blooming period, April or May. Otherwise, this tree doesn't require pruning.
Propagating Sweetgum Trees
American sweetgum is challenging to propagate via cuttings, so propagation via seed is more common. However, if you wish to try to grow a new plant by taking a cutting from a green, non-woody stem, here is how the process works:
- Sterilize scissors with alcohol.
- Make your cut just below a node. The cutting must have two leaves and a node and be 4 to 6 inches long.
- Dip the end in rooting hormone.
- Scoop soilless potting mix into a container and poke a hole in the soilless mix.
- Insert the cutting into this hole, gently firming the soil around it.
- Add water to the mix.
- Simulate a moisture-retaining greenhouse by placing a clear plastic bag over the pot.
- Place the container in bright, indirect light and keep the soil moist. Mist the plant regularly.
- After a few weeks, check the plant by tugging gently on the cutting. If there is resistance, rooting is successful and you can transfer the cutting to a larger container. Allow the cutting to grow to sapling size before planting in the ground.
How to Grow Sweetgum Trees From Seed
While 'Rotundiloba' is a non-fruiting cultivar, the species plant reliably produces gumballs that mature by mid to late autumn. The tricky part of using them for propagation is the timing.
On the one hand, green gumballs aren't ripe. On the other hand, if you wait too long after they've browned, the seed can be lost. This is because, when drying is complete, tiny holes will develop on the surface of the gumball. The seeds are ejected out of these holes.
The ideal time to gather them is after they have turned brown (indicating maturation) but before the fruit has dried. So there's just a tiny window of opportunity for you to work with. You want to bring the fruit indoors to complete the process. A dry place is ideal. Place the fruit in a shallow pan. Drying will be complete typically in 5 to 7 days. The seeds will be ejected at that point, and you can gather them.
Since sweetgum seeds have a chilling requirement, insert them in an envelope, and refrigerate them for 30 to 60 days. Sow the seed outdoors after all danger of frost has passed.
American sweetgum is cold-hardy to zone 5. You don't need to take measures to overwinter it unless you live north of zone 5; you can protect its roots from severe winter cold through mulching.
Common Plant Diseases
The species tolerates pests (such as rabbits) quite well. But it is susceptible to some plant diseases.
The spots of the leaf spot fungal disease come in various colors, shapes, and sizes. The spots appear on top of the leaf. But they're usually dark (or light with a dark border), with a rounded or irregular shape. Leaf spot is rarely fatal but inhibits photosynthesis, weakening the tree and rendering it more susceptible to other plant diseases.
Leaf spot is best controlled by taking preventive steps:
- Avoid late-evening watering: You're not allowing the sunlight to dry the plant's foliage before night falls. The result is that moisture lingers all night, creating optimal conditions for fungal diseases.
- Irrigate at ground level. Moistening the foliage invites fungal infestation. For the same reason, avoid irrigating from above.
- Practice sound garden hygiene. Rake up leaves that have accumulated around plants. Promote airflow by spacing plants correctly. Properly dispose of diseased plants.
If your American sweetgum is growing in too alkaline soil, it may develop a disease known as "chlorosis," which is caused by a deficiency in the soil. Chlorosis is often signaled by leaves or leaf veins turning yellow.
You will have to correct the soil deficiency to address the chlorosis problem. Before doing so, send a soil sample to your county extension office. They will specify the deficiency in your case and suggest a soil amendment as a remedy. For example, fertilizers geared to acid-loving plants are often used to lower the soil pH.
Is American sweetgum deer-tolerant?
Deer tend to leave American sweetgum alone.
Is American sweetgum drought-resistant?
American sweetgum trees are fairly drought-tolerant trees once mature.
Does American sweetgum have good fall foliage?
Its fall foliage is perhaps the plant's best selling point. Another good feature of this plant is that its fall foliage develops later in the autumn, meaning that it gives your landscaping color after the leaves of the maples have fallen.