Sweetgum can be propagated by cuttings or by seed (1). Cuttings should be taken from half-ripe wood and grown in a cold frame or with bottom heat (3). Asexual propagation by layering should be done in the autumn but will take 12 months to root (3). Seeds are recalcitrant and, as such, will have best germination when they are newly ripened (3). Harvest the seed capsules as they ripen, dry in a warm place and extract the seed by shaking the capsule (3). After storage, the seed requires 1 - 3 months stratification and sometimes takes 2 years to germinate and germination rates are poor (3). The seedlings don’t transplant well, so it is best to move plant them into the soil when they are less than 25 cm (10”) tall (3).
Sweetgum is hardy to USDA zone 5b (-10 to -15F or ~ -26C) and tolerates temperatures up to 38C (100F) but grows best when daytime temperatures are between 20 and 34C (68-93F) (1, 3, 4). During winter dormancy, mature trees will not sustain injury unless temperature fall below -11°C, (-12F) while, young stems are much less hardy and will be damaged at -1°C (30F) (3). It prefers to grow in areas where the mean annual rainfall iis between 1,000 and 1,500mm (40-60 inches) but will tolerate as little as 800mm (30 inches) comparable to ash or Arizona cypress water needs (1, 3). As such, additional drip emitters should be added as the tree matures (1). Sweetgum doesn’t like to have “wet feet”, as it has low tolerance to anaerobic soil, preferring instead moist, well-draining, nutrient rich soils with pH between 4.5 and 8.5 (3, 4). It also prefers full sun but tolerates light shade (1, 3). In their native range, they are susceptible to fungal diseases and insect pests such as the fall webworm, cottony cushion scale, tent caterpillars, aphids, spider mites, anthracnose, chlorosis and sooty mold (1, 4).
When transplanting the seedlings, choose a location that can accommodate the mature size of the tree canopy and shallow, aggressive roots (1). Further, it is recommended to be planted in unamended, native soil with a thick layer of organic mulch on the soil surface. If these environmental or edaphic conditions are not met, disease and reduced growth are more likely to occur.
