Light
While the black willow demands cool wet conditions it does not tolerate the shade of any sort. This is a tree that only thrives if you give it a full six hours of direct sunlight a day, anything less will decrease its vitality.
Soil
The black willow loves moist, well-drained soil but is very tolerant to different soil conditions, especially soil pH. The only issue that will arise is when your soil gets too dry or does not have good moisture retention. Dry conditions can be supplemented by regular irrigation. Avoid planting the tree in fully saturated areas, particularly if it’s an area where it would be hazardous to have the tree fall over.
Water
Irrigation is the most important component in keeping your black willow happy. The species needs to have constantly moist to wet conditions and can even deal with flooded conditions for an extended length of time without suffering any ill effects. Obviously, the best solution is to plant in a spot that is constantly wet contains a good amount of moisture. Planting in an area that is wet regularly will help you avoid the need to add supplemental watering.
Temperature and Humidity
Salix nigra does not perform well in hot dry temperatures and these conditions should be avoided to ensure the health and success of your tree. Your black willow will be much happier in areas that are cooler and damp, like coastal areas. While some locations in its habitable range do get humid the unifying factor is the moisture. As long as its environment is on the temperate side and damp it will thrive, but going out of its USDA hardiness range of 4-9 is not recommended.
Fertilizer
The black willow is not a tree you will need to fertilize regularly. The tree is already extraordinarily fast-growing, and adding fertilizer to the soil will increase the growth rate, further weakening wood that is already prone to wind breakage.
Types of Black Willow
There are not many cultivars of black willow available in the nursery trade. The lack of cultivars available is mostly because other species are more suitable for use in ornamental horticulture. One exception is the cultivar Salix nigra ‘Webb’, which is strikingly different from the straight species. ‘Webb’ has a vase-like form and is smaller in stature than its parent species.
Pruning
Pruning should be done regularly to establish form, help establish structure, ensure a single leader’s presence, and eliminate dead, damaged, and decaying limbs. These chores should be on your regular maintenance list to avoid larger expenses that can occur from property damage in the future if limb and branch breakage occurs during ice or wind storms. If your tree becomes too large to safely cut from the ground, be sure to bring in the help of a certified arborist.
Common Pests and Plant Diseases
Your black willow is bothered by numerous pests and diseases that are luckily determined to be more of a nuisance than anything. The forest tent caterpillar, cottonwood leaf beetle, willow sawfly, and a few different species of borers are most often seen. The wildlife value of the black willow makes the use of pesticides a concern, especially as it is the host plant to numerous butterfly and moth species such as the mourning cloak, red-spotted purple, viceroy, and tiger swallowtail. It is recommended pesticides be used as only a last resort, and other integrated pest management approaches are explored before they are used.
