Valley Oak, or Mush Oak, is the largest of the oak trees grown in North America. Found only in California, Valley Oaks can grow more than 100 feet tall and to diameters of 6 to 7 feet. To survive, Valley Oaks must be planted in rich soil and receive plenty of water at their roots. Fully matured Valley Oaks can produce a ton of acorns in one year. Pruning a Valley Oak can be done when it is young and small.
Prune to dictate the tree’s shape as it grows. Trim branches and offshoots with shears to help the tree grow in the shape you choose. Pruning a small tree will create a much smaller wound in the bark, which leaves less chance for contamination and infections.
Cut as near as possible to where the branch meets the tree so as not to leave a stub behind. Cut with a downward and outward angle.
Remove all of the deadwood from the Valley Oak. Any area that is no longer producing leaves or blooms is dead or dying. Use pruning shears when the tree is young and a pruning saw when the branches get too large to trim with shears.
Don’t remove more than 30 percent of live wood. Removing too much live wood can cause the tree to decay and eventually die.
Be careful around the roots. Valley Oak roots occasionally grow above ground, but that doesn’t mean they can be removed. Those roots that are under the canopy of the tree are considered the “critical root zone.” If more than 30 percent of the roots in this zone are disturbed, the tree will likely die.
Prune Valley Oak during winter months. Do not prune between April and July 1st of any calendar year. Pruning during this time makes Valley Oak prone to oak wilt. This is caused by a fungus, Ceratocystis fagacearum, which is spread by beetles during this period.