A good rule of thumb when it comes to knowing when to time your trees is knowing their dormant season. As you know, dormant seasons vary depending on the species of tree you have. Trimming them down during these times helps prevent any damages or harm you might accidentally do that may hamper the tree’s growth.

But certain instances call for immediate trimming. These conditions may pose a threat or a potential risk to other plants or people near the tree’s locations. Such instances are:

• The direction or rate of the tree's growth threatens your property If the branches are extending out towards the wall or windows of your house, then it’s probably time to trim the stems down, even if they are not in the dormant season.
• The tree is becoming large enough to block visibility for passersby in the area, particularly if it’s extending towards the street and sidewalk.
• The branches are extending out towards power lines and other infrastructure in the area. It’s better to call a professional tree trimming service as power lines are hazardous in these instances.

Lastly, how often you trim varies on the current overall health of the tree. This will depend on the species, size, and age of the tree. On average, a mature tree needs to be adequately trimmed once every 2-4 years. A younger tree that is very aggressive in growing will need trimming every 1-3 years.