My white pine, transplanted from cottage country 20 years ago, is now growing into a black spruce. Will that be a problem? Should I prune the leader?
If you would like to retain both trees, one option is to leave them to co-exist naturally together. If in the next few years you can discern branches that are rubbing against each other, you could consider contacting an arborist who could advise you on the kind of careful branch pruning that would be helpful. Another option would be to consider moving your white pine.
It is unlikely that an arborist would advise pruning, or “topping” the leader. There are many reasons for this:
- Possibly the most important reason is that pruning the leader disfigures the tree and destroys its natural shape, which can never be regained;
- This may seem counter-intuitive, but pruning the leader in fact stimulates the growth of weaker sucker shoots, or “water sprouts”, where the cut has been made. These are dense, long, upright shoots that grow at the top of the tree. Aesthetically, this is unattractive, but equally importantly, this vigorous new growth will soon return the tree to its previous height;
- Pruning the leader will leave your tree vulnerable to damage from diseases such as wood rots or infestation by insect pests where the tree has been cut;
- Topping reduces the tree’s capacity to produce an adequate store of food, or energy. The needles of your white pine act just like leaves of broadleaf deciduous trees: they capture sunlight, take in carbon dioxide, and release oxygen, providing the tree with the food it needs, as well as water retention.
For these reasons we recommend consulting a certified arborist if you feel that corrective pruning is needed at some point in the future. An arborist can also advise on whether it may be possible to move this white pine successfully. You can search the Landscape Ontario database for a tree expert in your area: https://landscapeontario.com/