The cedar elm (Ulmus crassifolia) is a sprawling deciduous tree native to the American south that grows from 50 to 90 feet high and 40 to 60 wide; it is planted as a shade tree on large lawns and around buffers surrounding roads and parking lots. The proper time to prune a cedar elm is governed largely by the need to prevent the potentially fatal Dutch elm disease that strikes new wounds. Cedar elms may be increased in U.S. Department of Agriculture plant hardiness zones 6 through 9.

Avoiding Dutch Elm Disease

The Dutch elm disease was discovered in Ohio in 1930. Elm bark beetles, believed to have been inadvertently imported from Asia, carry the spores of the respiratory disease and deposit them on tree wounds. The elm bark beetle, attracted to new tree wounds, is active during the growing period between April and August. Cedar elms should not be pruned during this period.

Pruning Drooping Branches

The long, drooping branches of the cedar elm are susceptible to breaking in the crotch in which the branches join the back. To prevent this, branches are pruned to maintain just those that are about two-thirds of this width of the trunk. If cedar elms are pruned to distance the major branches along a central trunk, they are simple to keep. Prune just from late fall through winter.

Other Pruning Chores

When nearby trees have been removed, the abrupt unlimited lighting can cause cedar limbs to grow rapidly. They need to be pruned to keep them from becoming too long, which makes them susceptible to breaking. Cedar elms also will need to be pruned so that trunks and branches do not rub against each other. Pruning secondary branches from main branches lowers the prospect of a main branch splitting from the tree. Cedar elms look best if they are not pruned to restrict their size. Much like pruning limbs to stop them from drooping, these pruning chores should be run from fall through late winter.

Pruning Infected Trees

Some jurisdictions require that cedar elm infected with Dutch elm disease be removed instantly. If regulations do not require the tree be removed, its infested branches are pruned and the wood buried or burned. To prevent tree removal, the Dutch elm symptoms have to be limited to one or a few limbs using at least 10 ft of healthy wood involving the infected area and the point on the primary back at which the pruning cut is made. Diseased logs that have been removed can be sealed tightly under clear plastic left in place for 7 months to leave them unsuitable for beetle breeding.

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