The beauty of a healthy tree can’t be understated. They add dappled shade to the garden, provide wildlife habitat and create natural barriers against nosy neighbors. However, the lovely little tree you planted years ago can grow to become a monster, shading out all other life below and creating a moonscape of scraggly, leggy plants and patchy sod. In order to increase the tree’s health and for the well-being of lower story plants, it is useful to thin the canopy occasionally to let in light and air. You don’t need to be an arborist to know how to thin out a tree’s canopy but a few tips can be useful.
Thinning Canopies in Trees
The reasons for thinning tree canopies go beyond increasing light and air. The practice is also useful to keep a tree in a certain growth habit, prevent it from getting too tall or keep limbs from getting invasive. Whatever the motivation, canopy thinning is a selective pruning practice that should be done when the plant is dormant for best results.
The goal with tree thinning is to reduce the number and thickness of the tree branches in the crown. Crown thinning trees allows more light to come into the core of the branches to enhance the growth of leaves and stems. It also allows more air to circulate, which reduces fungal and pest problems.
Additionally, thinning tree canopies reduce the weight to stabilize and strengthen the plant. Heavy thinning should be discouraged, as it can encourage the formation of unwanted growth, such as water spouts, but light thinning will encourage new needle or leaf growth, which provides increased photosynthesis and health.
The light pruning required to open up the canopy and bring in a bit more light is mostly done on the outside of the tree. This is where heavy growth has caused limbs to branch out and shade lower story plants. Only the tips of the outer growth are taken back with proper canopy thinning.
Excessive interior limb removal makes the plant unstable and weak. The only interior material you need to remove are water spouts and dead or broken limbs and stems. Thinning should keep the plant in as natural a form as possible and focus on making a balance of branches for a sturdy scaffold.
The general rule is to remove no more than 15-20% of the foliage on mature trees to prevent spouts and weak growth.
How to Thin Out a Tree’s Canopy
Thinning removes branches that are 2 inches thick. The thicker branches should only be removed if they are diseased or dead, as they form the scaffold of the plant and give it strength. Cuts should be at a slight angle to deflect moisture away from the cut surface and must be just outside the parent wood. Never cut into the main leader or trunk, as this can invite disease and rot.
The best time to prune is before the plant has begun new growth for the season and is dormant. Remove growth around the edges of the canopy for a tighter, more compact shape and then remove any broken and dead stems from the interior. Take care not to remove too much interior material as this produces a “lion’s tale” shape which is undesirable and weakens the tree.