Black Willow (Salix nigra)

Black Willow

Whether they grow as shrubs or trees, black willow (Salix nigra) are typical willows, with elongated green leaves and slender trunks. If you are growing black willows, you know that the distinguishing feature of this tree is its dark, furrowed bark. For more black willow information, including tips about how to grow black willow trees, read on.

I. Appearance and Characteristics 

Salix nigra, the black willow, is a species of willow native to eastern North America, from New Brunswick and southern Ontario west to Minnesota, and south to northern Florida and Texas.

Salix nigra is a medium-sized deciduous tree, the largest North American species of willow, growing to 10–30 m (35–100 ft) tall, exceptionally up to 45 m (148 ft), with a trunk 50–80 centimeters (20–30 in) diameter. The bark is dark brown to blackish, becoming fissured in older trees, and frequently forking near the base. The shoots are slender and variable in color from green to brown, yellow or purplish; they are (like the related European Salix fragilis) brittle at the base, snapping evenly at the branch junction if bent sharply.

The foliage buds are 2–4 millimeters (1⁄16–3⁄16 in) long, with a single, pointed reddish-brown bud scale. The leaves are alternate, long, thin, 5–15 centimeters (2–6 in) long and 0.5–2 centimeters (1⁄4–3⁄4 in) broad, usually somewhat falcate, dark, shiny green on both sides or with a lighter green underside, with a finely serrated margin, a short petiole and a pair of small stipules. It is dioecious, with small, greenish yellow to yellow flowers borne on catkins 2.5–7.5 centimeters (1–3 in) long in early spring at the same time as the new leaves appear. The fruit is a 5 millimeters (3⁄16 in) capsule which splits open when mature to release the numerous minute, down-covered seeds. The leaves turn a lemon yellow in the fall.

Salix nigra is dioecious, which means it has separate male and female trees. Flowering may be climate dependent. It flowers during February in the southern part of its range, and flowers until June in the northern parts. These trees are capable of producing seeds when they are around the age of 10 years. The black willow continuously has good seed crops year after year, with only a few failures. The seeds require very specific conditions to germinate. They prefer soil that is very wet or flooded. After they germinate, they can experience excellent growth if they are exposed to high sunlight and copious moisture during the growing season.

II. How to Grow and Care

Sunlight

The black willow likes light; full sun is conducive to the photosynthesis of its leaves. The best foliage color appears when there is plenty of light, so plant it in an open spot in the garden that ensures at least 6 hours of sunlight per day. However, it will also grow well in partial shade.

Temperature

The black willow grows better in a temperate environment, but can tolerate both high and low temperatures. It prefers damp areas, but does have both flooding and drought tolerance. It grows best in a temperate range of 15 to 25 ℃, but can withstand low temperature conditions of about -46 ℃.

The black willow mostly grows in wetlands beside the banks of rivers. Short-term flooding will not lead to its death. The black willow is also often planted in water tanks or vases indoors, but it needs to be regularly provided with appropriate amounts of nutrient solution to meet the necessary nutrient requirements for growth. At the same time, any impurities should be limited as much as possible, and the pH of the water should be alkalescent to avoid the plant blackening and spoiling.

Watering

The black willow likes water. Once short of water, it will develop yellow leaves and withered branches. In the summer months in particular, seedlings and new plants should be watered on a daily basis. However, mature plants will naturally have a certain amount of drought resistance. According to the drought of the soil, plants are usually watered at about 5 pm every day. If there are many rainy days in its growing season, the soil will already be rich in water, meaning that watering will not be required. If the weather is dry, watering daily can be beneficial. The roots of mature plants have strong tolerance to water-logging, so it is generally not necessary to drain away excess water.

Soil

The black willow is a highly adaptable plant with low soil requirements. Although it prefers moisture-retentive soils, it will grow well in a variety of soil types, and isn’t fussy about pH. Good drainage is important in clay soil, otherwise the roots may rot, so pay attention to this during the plant’s growth period.

Fertilizing

Generally speaking, in the early stage of black willow growth, a light fertilizer can be applied 4 or 5 times. A nitrogen fertilizer, such as ammonium sulfate and carbamide, is mainly applied in the growth period. Generally speaking, mature plants do not need too much fertilizer, but some potassic fertilizer, such as calcium phosphate and plant ash, can also be applied appropriately. If a mature black willow is planted in fertile soil, its leaves will be a healthy green. Fertilization is also not needed if nearby lawns are being regularly fertilized.

Pruning

The black willow grows fast under suitable conditions. Timely trimming of residual, dead and side branches can increase air permeability and light transmittance, so as to avoid providing breeding places for diseases and insect pests. For seedlings and newly-born willows, one main branch should be selected and kept during pruning, while any redundant lateral branches and buds should be trimmed, so that the main stem can grow thick in an upward direction.

For head-removed plants, main branches and new buds in 3-4 directions should be reserved consciously according to personal preference in the cross section, so as to maintain a more graceful shape. Trimming incisions should be smooth and coated with tung oil – this will protect the incision and encourage faster healing. Pruning is best carried out in early spring, late fall and winter.

Propagation

Seedlings can be purchased and easily transplanted, or you can grow them yourself by way of cuttage. The best time for transplanting is after the soil has thawed in early spring. care should be taken at the early stage of transplanting to ensure a good survival rate. If the transplanting seedlings were purchased, sufficient water should be provided, and an appropriate base fertilizer should be applied according to the soil conditions. Too much fertilizer is unnecessary for the seedlings, so fertilization in its later growth stage should not be in high frequency. At the same time, watering shouldn’t be too frequent, but this does depend on the dryness or wetness of the soil. Good drainage should also be maintained to avoid rotten roots.

Early spring is the best time for taking cuttings. plants with faster growth, fewer diseases and pests, and a beautiful natural shape should be selected as stock plants, so that the characteristics of the stock plants can be retained to a greater extent, meaning a better survival rate for the seedlings. Take any cuttings before the plant buds in early spring.

Cut a branch around 15 to 17 cm in length, making the cut oblique to increase water absorption capacity and survival rate. Soaking it in water for several hours can also increase the rooting rate. Insert the branch into the soil at a depth of about 1/3 of its length, and provide sufficient water. Keep the soil moist at all times before it buds.

After budding, the leaf buds at the lower parts of the branch should be removed, and only the buds at the top need to be kept for growing. At the same time, attention should also be paid to weeding and loosening the soil during this period, to prevent weeds from competing for limited resources.

Pests and Diseases

Black willows are susceptible to diseases such as Crown gall and Cankers. Crown gall is caused by bacteria living in the soil where the black willow is present. When black willow are infected, the bacteria stimulate a quick burst in growth of plant cells. They cause the tree to form tumor-like growths, or “galls” on different parts of the tree such as their roots or on the lower branches. As these galls get bigger, they become hard, woody, brown in color, and corky. Black willows do not normally die from crown galls. However, these galls can cause a disruption in the flow of nutrients throughout the tree and can have its normal growth stunted or slowed down due to this disease. Crown galls are less problematic in soils that are more acidic, thus soil pH can be an important factor in helping to limit this disease.

Black canker disease is caused by the fungus Glomerella miyabeana. This disease starts as spotting on the leaves of the black willow, where it then spreads to the petiole and eventually the twig or branch holding the leaf. It then forms black patches on the stem of the tree that are capable of expanding. Black Willows that are in nutrient-poor locations or that are experiencing poor temporary climate conditions (such as a temporary lack of rainfall or short, drought-like conditions) are considered stressed and very susceptible to the spread of these cankers. Tissue on the black willow that is affected by these cankers will not grow with the rest of the tree, and cracks will begin to form.

III. Uses and Benefits 

Black willow roots are very bitter, and have been used as a substitute for quinine in the past. Ethnobotanical uses of black willow by various Native American tribes include basketry, and treatment of fever, headache, and coughs. It was recognized that using the bark and leaves of Salix nigra was useful in treating rheumatism.

The black willow is the only United States native willow species to be used as timber for a variety of different items. Black willow lumber is used in furniture and shipping containers. The largest production site for black willow timber was in Louisiana at its peak during the 1970s.

The wood of Salix nigra is very lightweight. The wood was once used for artificial limbs, such as wooden hands. It is also capable of maintaining its shape, does not splinter very easily, and has a moderately high shock resistance, allowing it to sustain continuous moderate impacts.

It may also be used in environmental restoration. Black willow is very resistant to herbivory, flooding, and is an erosion control tool. Salix nigra is used for marshland stabilization or restoration projects as long as the roots don’t penetrate any clay liner that may be in place. Salix nigra demonstrated some success as a photodegradation tool. Photodegradation is theorized to work by drawing the target chemical, such as Bentazon, up the roots and stem into the leaves where it is degraded by higher energy radiation provided by the sun.

Black Willow (Salix nigra) Details

Common name Black Willow
Botanical name Salix nigra
Plant type Native Plant
Hardiness zone 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Fast
Harvest time Spring
Height 70 ft. 0 in. - 80 ft. 0 in.
Width 70 ft. 0 in. - 80 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Gold/Yellow
Leaf color Green