Box elder (Acer negundo) is a type of maple tree native to North America, but which is now found throughout the world. It is a hardy, medium-to-large tree that grows quickly and has a relatively short lifespan of up to 60 years. Older trees are prone to storm damage. Box elder wood is relatively flimsy because the tree grows so fast.
I. Appearance and Characteristics
Acer negundo, the box elder, boxelder maple, Manitoba maple or ash-leaved maple, is a species of maple native to North America. It is a fast-growing, short-lived tree with opposite, compound leaves. It is sometimes considered a weedy or invasive species, and has been introduced to and naturalized throughout much of the world, including in South America, Australia, New Zealand, South Africa, much of Europe, and parts of Asia.
Acer negundo is a fast-growing and fairly short-lived tree that grows up to 10–25 metres (35–80 feet) tall, with a trunk diameter of 30–50 centimetres (12–20 inches), rarely up to 1 m (3 ft 3 in) diameter. It often has several trunks and can form impenetrable thickets. The typical lifespan of box elder is 60 – 75 years. Under exceptionally favorable conditions, it may live to 100 years.
The shoots are green, often with a whitish to pink or violet waxy coating when young. Branches are smooth, somewhat brittle, and tend to retain a fresh green color rather than forming a bark of dead, protective tissue. The bark on its trunks is pale gray or light brown, deeply cleft into broad ridges, and scaly.
Unlike most other maples (which usually have simple, palmately lobed leaves), Acer negundo has pinnately compound leaves that usually have three to seven leaflets. Simple leaves are also occasionally present; technically, these are single-leaflet compound leaves. Although some other maples (such as Acer griseum, Acer mandshuricum and the closely related A. cissifolium) have trifoliate leaves, only A. negundo regularly displays more than three leaflets. The leaflets are about 5–10 cm (2–4 in) long and 3–7 cm (1+1⁄4–2+3⁄4 in) wide with slightly serrate margins. Leaves have a translucent light green color and turn yellow in the fall.
The yellow-green flowers are small and appear in early spring, with staminate flowers in clusters on slender pedicels and pistillate flowers on drooping racemes 10–20 cm (4–8 in) long.
The fruit is a schizocarp of two single-seeded, winged samaras on drooping racemes. Each seed is slender, 1–2 cm (1⁄2–3⁄4 in) long, with a 2–3 cm (3⁄4–1+1⁄4 in) incurved wing; they drop in autumn or they may persist through winter. Seeds are usually both prolific and fertile.
Unlike most other maples, A. negundo is fully dioecious and both a male and female tree are needed for reproduction to occur.
II. How to Grow and Care
Sunlight
The box elder has a certain requirement for sunlight and prefers a partially shaded area. In cases of exposure to direct sunlight in the summer, the leaves of most varieties will wither, so shading is required. As the plants get older and their root system grows, this condition will be less of a problem. A few varieties will tolerate exposure to direct sunlight, such as ‘Beni Maiko’ and ‘De Shojo’. Some weeping varieties can also tolerate exposure to direct sunlight, such as ‘Ao Shidare’.
Sunlight conditions will directly affect the ornamental appearance of box elder leaves. In the spring, sufficient sunlight will make the maple leaves more vivid, while in cases of insufficient sunlight or partial shading the leaf color may fade. During the fall, sunlight can also affect the leaf color. For potted plants, full exposure to sunlight is recommended during the spring and the fall, with partial shading in the summer.
Temperature
The box elder has good cold resistance and is able to tolerate low temperatures. The box elder is native to the margins of forests in China, Japan, and North Korea, so these trees generally prefer a humid environment. Most box elder plants have shallow root systems, so they should be watered frequently during the summer. For some varieties, a sprayed mist should be provided during the summer to increase the humidity of the air around them.
Watering
The box elder prefers the soil to be kept moist, especially during the summer, because dry weather can cause its leaves to scorch and even fall off in severe cases. During the summer, in addition to watering the roots, foliage can be sprayed during the evening to increase the humidity.
- In the summer, seedlings growing in pots may need watering twice a day, in the morning and the evening.
- In the spring and fall, watering should be carried out depending on the actual conditions. Watering can be reduced slightly as the temperature drops in the fall, which will help the leaves to change color.
- In the winter, it is only necessary to ensure that the soil does not dry out.
Attention should be paid to the watering of seedlings grown in gardens during the early stages. At later stages, water should be supplied according to the weather, that is if there is no rain for more than two weeks in the summer.
Soil
The box elder does not have many specific requirements for soil. It is a forest native, so it prefers well-drained soil that is rich in humus and slightly acidic. Its main root will extend deep into the soil, but its tiny fibrous roots will be concentrated near the soil surface, so accumulated water in the soil tends to cause root rot.
Fertilizing
Potted seedlings should be given slow-release fertilizer only. For seedlings grown in gardens, fertilizer should be applied three times a year: once in the early spring, once in early summer for the growth period, and once in the fall.
Planting Instructions
The best time for planting or transplanting a box elder is following defoliation in the fall. At this time, the leaves will have fallen off so there is little transpiration and water loss can be avoided. In addition, the root system will still be growing at this time, preparing for regrowth the following spring. Transplanting should be avoided on the coldest days because cold wind can kill some of the shoots and branches. During the winter, in areas that cannot be sheltered from the wind, it is recommended to cover the branches.
Pruning
Pruning is mainly used to enhance internal ventilation, improve shoot formation, promote growth, and for shaping. The common approach to pruning is to remove any old or weak branches, remove any branches that disrupt the shape of the tree, and remove any branches that cross other branches. Pruning is used to control the plant according to the required height and shape. Generally, this follows the “Y-type” pruning method.
It is possible to prune a box elder throughout the year, but the coldest winter months should be avoided to prevent damage to the plant. Major pruning to shape a maple can be performed following defoliation in the fall, or prior to leaf growth in the spring. It is recommended to prune in the fall because withered and full buds can be easily distinguished.
According to the shaping plan, you can prune any withered buds and keep the full ones, thus making your tree healthier. For pruning in the summer, diseased, weak, or dead branches can be removed, mainly to enhance the tree’s ventilation.
If grown as a potted plant, the roots can easily occupy the entire flowerpot due to the limited space. This can make a box elder prone to aging if an old flowerpot is not changed. It is recommended that old roots are pruned during the dormancy period, that is, cut off any old, coarse, diseased, and weak roots.
Propagation
Common propagation methods include grafting, taking cuttings, and sowing seeds.
Grafting is the most common propagation method. Seedlings of Acer palmatum or Acer oliverianum are usually selected for the rootstock. Grafted seedlings have strong roots and grow rapidly, but poor affinity is occasionally present in some cases. Seedlings with Acer oliverianum as the rootstock are less hardy.
Cuttings take longer to grow and are mostly used in the production of bonsai.
Sowing seeds is a common way to cultivate new varieties. The hybrid offspring of two different maples are sown and valuable individuals are then selected from the seedlings. The traits of the parents may not be maintained in the selected offspring.
Pests and Diseases
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.
III. Uses and Benefits
- Wood
Although its light, close-grained, soft wood is considered undesirable for most commercial uses, this tree has been considered as a source of wood fiber, for use in fiberboard. There is also some commercial use of the tree for various decorative applications, such as turned items (bowls, stem-ware, pens). Such purposes generally use burl or injured wood, as the injured wood develops a red stain.
The wood has been used for a variety of purposes by Native Americans, such as by the Navajo to make tubes for bellows, by the Cheyenne to make bowls, and by the native peoples of Montana who use the large trunk burls or knots to make bowls, dishes, drums, and pipe stems. The Tewa use the twigs as pipe stems and the Keres make the twigs into prayer sticks.
The Dakota people and the Omaha people make the wood into charcoal, which is used in ceremonial painting and tattooing. The Kiowa burn the wood in the altar fire during the peyote ceremony.
Acer negundo was identified as the material used in the oldest extant wood flutes from the Americas. The flutes, excavated by Earl H. Morris in 1931 in Northeastern Arizona, have been dated to 620–670 CE.
- Medicinal use
Acer negundo has been used by Native Americans for several medicinal purposes. The Cheyenne burn the wood as incense for making spiritual medicines, and during Sun Dance ceremonies. The Meskwaki use a decoction of the inner bark as an emetic, and the Ojibwa use an infusion of the inner bark for the same purpose.
- As food
The sap has been used to make syrup by Native Americans, including the Dakota, Omaha, Pawnee, Ponca, Winnebago, Cree, Sioux, and the indigenous people of Montana. The Chiricahua and Mescalero Apache dry scrapings of the inner bark and keep it as winter food, and they also boil the inner bark until sugar crystallizes out of it. The Cheyenne mix the boiled sap with shavings from the inner sides of animal hides and eat them as candy. The Ojibwa mix the sap with that of the sugar maple and drink it as a beverage.
- Garden Use
Box elder is considered a good variety for planting in gardens and yards, and can also be suitable for planting along streets. It has been commonly used as a landscaping tree in suburban neighborhoods for its dense shade, and pairs well with other maples.
