Mysest56 
November 14, 2020
Box elder (Acer negundo), sturdy in U.S. Department of Agriculture plant hardiness zones 2 through 10, isn’t a bush or tree, but also a maple tree which bears a slight resemblance to an elder (Sambucus spp.) . The deciduous maple species grows between 30 and 50 feet tall, with an equal spread. Box elder thrives in damp, sunny places. It is vigorous and will usually survive being cut down almost to the ground. Pruning the ensuing shrub-like growth could be somewhat different than fortifying a box elder that was left to grow in its natural tree form.
Severe Pruning
Reducing box elder to ground or near-ground degree will eliminate the pioneer or central trunk of the tree. Resprouting from the stump, paired with the species’ tendency to produce ample root suckers, could then bring about a multi-stemmed plant with a fast growth habit. After the initial acute pruning, the box elder can be maintained subsequently at whatever size and shape fits the landscape scenario. However, pruning repeatedly to ground level might weaken or kill the plant and would restrict size. Box elder can grow up to 25 inches in 1 year.
Pruning Tree Forms
If the box elder is growing in it natural tree form, it may be kept lower than the maximum height. To do so, determine the desired height and then eliminate large branches above there. Use sharp loppers or a pruning saw, disinfecting with a cloth dipped in household cleansers between cuts. It is critical to prune in a way that doesn’t weaken the tree. Cut every large branch in the point where it meets a lower, lateral — flat — branch. Don’t leave a stub of the large branch. Continue this process until all the big branches have been pruned.
Pruning Time
The best time for pruning box elders, whether they grow in tree form, is late winter, before active growth has started for the year. This also allows for elimination of weak or dead branches. Box elder tends to “bleed” sap when pruned at this time. Though sometimes unsightly, this isn’t dangerous. The alternative is to wait until the plant is fully leafed-out in spring and prune at the time. When pruning the tree form, it is wise not to remove over 1 quarter of the total plant.
Shrub Considerations
Instead of pruning box elder so severely that it grows in tree form, it may be be better to substitute American elder (Sambucus canadensis), hardy in USDA zones 4 or 3 through 9, depending on variety. American elder is an actual multi-stemmed shrub, with compound leaves similar to box elder. It also shares box elder’s accelerated growth rate, but tops out in a smaller 5 to 12 feet tall with a rounded habit. American elder can also be appropriate for comparable states — always moist, sunny sites. It may be cut back to ground or near-ground degree.