Black cottonwood is the largest of the poplar trees. It grows to a height of more than 100 feet, with a trunk diameter of 2 to 3 feet. It has a large, open crown and a trunk that ranges from white to gray. Black cottonwoods bloom from February to April and are usually found in sandy soils below 6,000 feet in most of California. Prune the trees when they are youngto produce a strong structure. As they mature, pruning will maintain the tree structure, form, health and appearance.
Cut small, thin branches with a hand pruner. Lopping shears or small pruning saws can be used for slightly larger branches with bigger cutting surfaces and greater leverage. If you're dealing with even larger branches, about 6 inches in thickness, use a pruning saw. Chain saws will work on those thicker than 8 inches.
Make cuts at nodes, where one twig or branch meets another.
Thin the crown of black cottonwoods in order to increase the amount of light and air that gets to the tree. Light is essential for development, but a dense canopy may not allow it beyond 12 to 18 inches inside the canopy. Air movement helps prevent disease infestation.
Remove branches with narrow, V-shaped connections because they are weaker and are likely already cracked. Keep all branches that are attached with strong U-shaped joints.
Remove all the branches that are facing downward, at the bottom of the tree to raise the tree's crown. This will make the tree more aesthetically appealing and provide clearance for pedestrians, traffic and lines of site.