How to Grow and Care for American Sweetgum Trees

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. The leaves have toothed margins. Some of its 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 fruits that look like spikey gumballs (thus "gum tree"). Some of the branches are "winged," as on winged euonymus, also called "burning bush" (Euonymus alatus), displaying corky flanges. The 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. If you'd like to avoid the mess, look for the non-fruiting cultivar discussed in this article.

'Rotundiloba' American Sweetgum Care

American sweetgum is best planted in spring. If you grow the 'Rotundiloba' cultivar of American sweetgum, you will have a low-maintenance tree. Growing the cultivar eliminates most of the need to rake up gumballs as they fall. Even 'Rotundiloba' may eventually produce a gumball here or there, but not in a quantity that causes a problem. Craft enthusiasts actually value the gumballs, however, for use in Christmas kissing balls, wreaths, potpourri, and dried floral arrangements. With its shallow root system, this tree shouldn't be planted near sidewalks, concrete patios, etc.

In fact, if you wish to grow the species plant because you enjoy crafts and can make use of the gumballs, 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). For those with large properties, one option may be to plant their sweetgum tree on the south side of a woodland garden. Thus located, you will not have to bother with the landscape maintenance required to clean up the fallen gumballs.

Light

One thing American sweetgum is not tolerant of is shade, so be sure to select a spot in full sun for it.

Soil

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.

Water

Keep the soil of American sweetgum evenly moist, at least 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.

Fertilizer

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
  

Pruning

If you must prune, as is true when dead, diseased, or damaged branches are present, the best time to do it is right after the blooming period, which is April or May. But this specimen usually doesn't require pruning otherwise.

Propagating

American sweetgum is difficult to propagate via cuttings, which is why 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:

1. Sterilize scissors with alcohol.
2. Make your cut just below a node. The cutting must have two leaves and a node and be 4 to 6 inches in length.
   
3. Dip the end in rooting hormone.
4. Scoop soilless potting mix into a container and poke a hole in the soilless mix.
5. Insert the cutting into this hole, gently firming the soil around it.
   
6. Add water to the mix.
7. Create a moisture-retaining tent over the pot using a clear plastic bag.

How to Grow Sweetgum Trees From Seed

While 'Rotundiloba' is a non-fruiting cultivar, the species plant does reliably produce gumballs, which mature by mid-to-late autumn. The tricky part of using them for propagation is in 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 totally dried. So there's just a small window of opportunity for you to work with. You want to bring the fruit indoors to complete the drying process. A cool, dry place is ideal. Place the fruit in a shallow pan. Drying will be complete typically in 5 to 7 days. At that point, the seeds will be ejected and you can gather them.

Since sweetgum seeds have a chilling requirement, insert the seeds in an envelope, and refrigerate them for 30 to 60 days. Sow the seed outdoors after all danger of frost has passed. 

Overwintering

American sweetgum is cold-hardy to zone 5. You don't need to take any measures to overwinter it unless you live north of zone 5, in which case 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.

Leaf Spot

The spots of the leaf spot fungal disease come in a variety of colors, shapes, and sizes. But they're usually dark (or light with a dark border), with a rounded or irregular shape. The spots appear on top of the leaf. Leaf spot is rarely fatal, but it 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 giving the sunlight a chance to dry the plant's foliage before night falls. The result is that moisture lingers all night, creating optimal conditions for fungal diseases. 
• For the same reason, avoid irrigating from above. Moistening the foliage invites fungal infestation. Irrigate at ground level.
• Practice sound garden hygiene. Properly dispose of diseased plants. Rake up leaves that have accumulated around plants. Promote airflow by spacing plants properly.

Chlorosis

If your American sweetgum is growing in soil that is too alkaline, 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 problem of chlorosis. Before doing so, send a sample of the soil in 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.