Slippery Elm

Size, growth and what to expect

Slippery elm grows fast, about 2.75 feet a year in our growth estimator. Expect 40 to 70 feet with a broad, open crown 30 to 50 feet wide. It may live 200 years. The oldest tree dated by its rings reached 103. Only a tiny share of trees is ever dated this way, so older ones may exist.

It flowers in spring before the leaves, from February to May. The flat, round samaras ripen from April to June and blow away as soon as they are ripe. Large seed crops come every two to four years, beginning after about age 15. Songbirds, game birds and squirrels eat the seeds and buds, and the leaves feed mourning cloak and Columbia silkmoth caterpillars.

It grows wild from southwestern Maine and southern Quebec west to eastern North Dakota, and south to central Texas and northwestern Florida. It is most common in the Midwest and uncommon south of Kentucky. Maine lists it as possibly gone from the state, and NatureServe ranks it critically imperiled in Rhode Island and imperiled in North Dakota.

How to grow Slippery Elm

Slippery elm grows best in full sun or light shade on moist, rich soil, but it stands more shade than most trees. It takes clay, loam and dry limestone ground, and soils from acid to alkaline. It lives through an occasional flood of two or three months but does poorly where floods come often or stay long. Plant it 25 feet from a wall and more than 50 feet from overhead wires, and set trees 30 feet apart.

Saplings ship bare-root or potted. Choose each tree's final spot at planting, since larger trees do not transplant well. Plant them dormant, from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the root flare at the soil line, put the native soil back in, and keep the mulch clear of the trunk. Sow the samaras with their wings as soon as they fall in spring, a quarter inch deep, and keep the bed moist. Most sprout within two weeks. Some seed, most often from the North, lies dormant and needs two to three months damp in the refrigerator before a spring sowing.

Water weekly through the first summer and in long droughts after. Guard young trees with a tube or cage against deer, which strip the bark of saplings, and against rabbits, which browse the twigs. Prune in the dormant season to one strong trunk with well-spaced limbs, since severe ice storms break its crown.

Each slippery elm flower carries both male and female parts, but elms seldom set seed with their own pollen. The wind carries pollen between trees, so plant two or more if you want seed. Dutch elm disease, a fungus carried by elm bark beetles, clogs the wood that carries water, so the leaves wilt and fall and the tree dies. It is less severe on slippery elm than on American elm, but it still kills the tree, and it has no cure. The elms that resist it are named clones of American elm and of hybrid elms, and a seed nursery does not sell them. Elm yellows, spread by a leafhopper, also kills it across much of its range. The larger elm leaf beetle favors it, and cankerworms, scale and aphids also feed on it.