Alder Trees: The Unsung Heroes of Landscaping and Soil Health
Introduction
Alder trees (Alnus spp.) are often overlooked in residential landscapes, but they are truly valuable plants that offer a range of benefits. From their striking appearance to their ability to improve soil health, alder trees deserve a place in every gardener’s toolkit.
Identification
The easiest way to identify an alder tree is by its distinctive fruit, called a strobile. These 1-inch-long cones appear in fall and remain on the tree until spring, providing a food source for birds and small mammals. The female flowers stand upright at the ends of the twigs, while the male catkins are longer and hang down. Once the leaves fall, the catkins add a touch of subtle beauty to the bare branches.
Alder leaves are another key identifying feature. They are egg-shaped with serrated edges and distinct veins. A central vein runs down the center of the leaf, with side veins branching out towards the edges. The foliage remains green until it drops in fall.
Types of Alder Trees
There are several different types of alder trees, each with its own unique characteristics. Tall tree types, such as red and white alders, can grow up to 80 feet tall. Red alders have tightly rolled leaves, while white alders have flatter leaves. Sitka and thinleaf alders are shorter, reaching heights of no more than 25 feet. They can be grown as large shrubs or small trees. Sitka alders have fine serrations on their leaves, while thinleaf alders have coarse teeth.
Benefits of Alder Trees
Alder trees offer a number of benefits for both gardeners and the environment.
- Nitrogen fixation: Alder trees have the ability to extract and use nitrogen from the air, just like legumes such as beans and peas. This means that they don’t need nitrogen fertilizer, making them ideal for areas that are not regularly maintained.
- Soil stabilization: Alder trees have a dense root system that helps to stabilize soil, making them a good choice for planting on slopes or in areas prone to erosion.
- Wet site tolerance: Alders are well-suited to wet sites, but they can also thrive in areas that experience occasional drought.
- Wildlife habitat: The fruits and seeds of alder trees provide food for a variety of birds and small mammals. The dense foliage also provides shelter for wildlife.
Planting and Care
Alder trees are relatively easy to grow and care for. They prefer moist, well-drained soil but can tolerate a wide range of conditions. They can be planted in full sun or partial shade.
Once established, alder trees require minimal care. They should be watered during dry spells and fertilized once a year with a balanced fertilizer. Pruning is not necessary, but it can be done to control the size and shape of the tree.
Conclusion
Alder trees are a valuable addition to any landscape. Their striking appearance, soil-enriching properties, and wildlife benefits make them a must-have for gardeners of all levels.
