We are sharing this great pruning advice from Trees Forever. The best time to prune is in mid- to late-winter (January-March). When pruned during this time of the year, the tree will begin responding to the wounding early in the spring. A coniferous tree planted in a suitable site, will need minimal pruning throughout its life. Pruning at other times of the year will not hurt a tree (read more below about when to prune oaks); however the process of sealing the wound may be slowed. Do not prune during the spring from bud break through leaf expansion, and during the period of leaf color change in the fall. A tree is going through major changes at these times, and branch removal can reduce the vigor of a tree.
One species where timing of pruning is critical is oak. The pathogen that causes the disease Oak Wilt can be transmitted to open wounds by a small beetle. Avoid wounding (pruning) oak between March and November.