I read that you should never plant the sweetgum tree (Liquidambar styraciflua) between the sidewalk and the street because of the spreading roots, but is this true for all varieties, such as ‘Moraine,’ ‘Burgundy,’ and ‘Rotundiloba?’ Which variety is more cold hardy in Michigan? I read that ‘Rotundiloba’ has no spiky gumball fruit, but is it hardy to zone 5? Finally, which variety can be counted on for reliable fall color?
Sweetgum (Liquidambar styraciflua) grows in a narrow pyramid to a height of 75 feet and may spread to 50 feet. The beautifully glossy, star-shaped leaves turn bright red, purple, yellow or orange in the fall. On some trees, particularly in the northern part of its range, branches are covered with characteristic corky projections. The trunk is normally straight and does not divide into double or multiple leaders. Side branches are small in diameter on young trees, creating a pyramidal form. The bark becomes deeply ridged at about 25 years old. Sweetgum makes a nice conical shade tree for large properties when it is young, developing a more oval or rounded canopy as it grows older as several branches become dominant and grow in diameter.
Be careful when locating sweetgum as a street tree since its large, aggressive roots may lift curbs and sidewalks. Plant trees 8 to 10 feet or more from curbs. (Much of the root system is shallow.) The 1-inch round fruit may be a litter nuisance in the fall; people could slip and fall on the fruit on hard surfaces, such as roads, patios, and sidewalks.
The tree should be planted in soil with a pH of 7 or less. Chlorosis is often seen in alkaline soils. The seeds provide food for wildlife and will often readily germinate in shrub and groundcover beds, requiring their removal to maintain a neat landscape appearance. Although it grows at a moderate pace, sweetgum is rarely attacked by pests, and tolerates wet soils. Trees grow well in deep soil, and poorly in shallow, droughty soil. It is native to bottomlands and moist soils and tolerates only some (if any) drought. Existing trees often die back near the top of the crown, apparently due to extreme sensitivity to construction injury to the root system, or drought injury. The tree leafs out early in the spring and is sometimes damaged by frost.
The cultivar ‘Rotundiloba’ is fruitless. The leaves have rounded tips on this variety, and turn deep purple in the fall. It is hardy to zone 5b. The leaves of ‘Burgundy’ turn bright red-purple in the fall, and this variety is hardy to zone 6. In the fall, leaves are held on the tree longer than the species. The cultivar ‘Moraine’ is the most cold hardy cultivar known today. The star-shaped leaves turn bright red, purple, yellow or orange in the fall, and it is hardy to zone 5. It is the “smallest” of the cultivars with a mature height of 60 feet and a spread to 40 feet.