White Pine Trimming

(Question)

I have about 75 white pine trees on my property which I’ve been trimming every July in order to keep the branches close and the tree a good visual screen. I did not do any trimming of my trees last summer since I would prefer to do the trimming in the winter or early spring, if not harmful to the tree.

My question is: If I trim back some of last year’s new growth in February or March, will the cut ends of the branches develop new growth areas in late spring when the new growth normally occurs? In other words, will the tree respond in a similar way whether I trim it in July or trim it in February or March?

Thanks for your response.

(Answer)

It’s great to know we’ve reached you so far away in St. Joseph’s, Michigan. Generally speaking it is not necessary to prune pines at all unless you wish to remove wayward growth or dead branches. Presumably you are trimming your trees to maintain denser and bushier growth. Pruning should be minimal and occur in later winter or early spring when trees are dormant. You are making the right move by discontinuing pruning in July, thereby lessening the risk of fungal infection attacking your trees.  Also, avoid pruning in late summer and early fall.  Pruning at this time can stimulate new growth that may not harden off before winter.  Most conifers are unable to regenerate new buds from really mature wood and therefore do not withstand drastic pruning. Your trees should do just fine by trimming the ends, which includes last year’s growth, as long as you do not go back further than about 1/3. New growth should develop after trimming in February/March this year.

The following information is taken from a previous posting on the Toronto Master Gardener website.

“There are two opportunities to prune your white pine (Pinus spp.): while the pine is still dormant and again when the ‘candles’ which are the expanding new growth have appeared. Pruning the candles can be used to shape a pine and keep it dense and within bounds.  Completely breaking off the candle will discourage further elongation at that point.  Shortening the candle, decreases the distance at which the next whorl of branches develops and makes the tree denser.  Snapping the end off with your fingers rather than with pruning shears will avoid cutting off any expanding leaves which would then brown at their tips. (Do not remove more that 2/3 of the growth).

White pines can also be pruned to control growth while the tree is still dormant and just before growth begins.  The new growth will hide the cuts.  Cut branches back to side branches within the tree.   Dead and diseased wood can be cut out at this time and if necessary lateral branches removed to reduce overcrowding and avoid branches dying from lack of light.”

Further reading:

https://www.cals.uidaho.edu/edcomm/pdf/bul/bul0644.pdf

Hope this helps.