Boxelder

Boxelder (Acer negundo) is native to eastern North America. It grows there in moist to wet soils on the shores of lakes and in riparian forests. It is one of the most commonly planted foreign trees and, as a neophyte, wild-growing populations are found in some regions.

Boxelder usually has a multi-stemmed growth form. It develops a loose, broad, rounded crown, and can grow 50 feet tall and 30 to 40 feet wide with age. The main branches have a very sprawling growth habit. They protrude almost horizontally at the bottom and the branches hang down slightly. Boxelder grows very quickly as a young plant and can get up to three feet taller each year.

The opposite leaves of Boxelder do not have the typical lobed appearance of maple leaves, but—like ash trees—are odd-pinnate compound, and usually have three or five (in rare cases seven) light green leaflets. However, these are sometimes slightly lobed. The leaves of Boxelder turn yellow in fall, sometimes even shining in orange colors.

The flowers of Boxelder open before the leaves sprout in March. The plants are monoecious, meaning that they have both female and male flowers. The male flowers in particular are highly ornamental, the stamens of the grape-like flowers hanging down in clusters on long yellow to reddish stalks. The female flowers are also grouped in clusters and have large yellow to reddish carpels.

The small winged fruit of Boxelder have a reddish color at first, later turning pale yellow to beige, sitting in clusters in the leaf axils of the branches. In the botanical world, they are known as nutlets. The wings form a remarkably acute angle.

Boxelder feels at home both in the sun and in partial shade. It is very frost-hardy and therefore also does well in colder locations. However, it also needs some protection from the wind as the branches of older trees can be damaged by strong winds. Dry urban climates and polluted air are not a problem for boxelder.

As a pioneer species, Boxelder can cope with almost any soil. It grows in moderately dry, poor sandy soils and also in loamy, wet soils with a high water table. It prefers slightly acidic substrates but tolerates lime.

Leave plenty of space for Boxelder as the tree will grow to a considerable size in the garden. The tree is low maintenance so there is no need to prepare the soil. Garden paths in the root area should be bordered with edging stones supported by backing concrete, otherwise the roots close to the surface may damage the paving.

Boxelder does not require any special care. However, freshly planted trees should be watered regularly in dry conditions. Do not use fertilizer, as a good supply of nitrogen can make the wood even more brittle than it already is.

While the Boxelder is tolerant of pruning, it does not need to be pruned regularly. You should particularly avoid heavy pruning of the main branches as the points where new shoots emerge are very fragile throughout the tree’s life. If the crown becomes too big, whenever possible, the branches should be pruned back to the existing stronger side shoots and not simply cut off. Like all species of Maple, if you need to prune boxelder, the best time to do this is late summer as the pruning cuts bleed heavily in spring.

The variegated forms of Boxelder are particularly popular house trees as they have a weaker growth habit and do not grow tall like the wild species. In the USA, Boxelder is also used as a pioneer species for afforestation measures in the open countryside. However, this should be avoided in Germany as the tree is not native to this country. When it comes to underplanting the trees, the only suitable options are shrubs and trees that can tolerate high root pressure, as boxelder roots heavily penetrate the topsoil. However, the light crown of the trees allows plenty of sunlight through, so species that need a little more light can also grow below the tree.

Wild species of Boxelder can be propagated by seed, cultivars are generally propagated by budding. With this grafting method, a bud of the cultivar is grafted onto the bark of the seedling rootstock. With a little bit of luck, it is also possible to propagate the tree from hardwood cuttings: Take hardwood cuttings from the current season's shoots in early winter and put them in a shady spot in the garden in moist humus-rich soil. With this method, the rooting percentage is around 10%, so you need to take plenty of hardwood cuttings to be successful.

Boxelder is somewhat susceptible to fungal diseases. This includes, among others, powdery mildew, which causes a white powdery coating to appear on the leaves. In terms of pests, the Boxelder is occasionally affected by the leafcutter bee. They make small holes in the leaves but do not cause any lasting damage to the tree, so pest control is not necessary.