Perhaps we are just old softies but we don't want to stop our little white pine from growing. We just want to keep it nicely shaped. Any suggestions about timing or procedure? - B.A. -
Dwarf white pines are beautiful plants but the most common (Pinus strobus 'Nana') can be a bit irregular in growth and has the potential to be much larger than its name implies -- over 6 feet tall and wide.
If you did want to keep it small, you could clip it once a year. Treat it just like a mugo pine.
To help it maintain a particular shape -- such as the basic
gumdrop this Pinus strobus 'Blue Shag' has in its
genes -- keep an eye out for any branches that outgrow
the others. They can deform the plant.
Six years (top of the page) ago this pine was four feet tall and wide, and pleasantly mounded. Since then it expanded by about 24 inches to fill all the bare space in the bed and also developed a hump or shoulder. (Right, and below.) As is usually the case, the deformity happened so gradually that one day the gardener walked by and saw it as if for the first time. Thus it seemed to have appeared overnight.
Then, identify and truss up all the branches involved in the hump so you can step back, take a look and decide, "If it's gone, will what's left still be pleasing?" By "truss up" we mean tie a string around them or stretch an elastic tarp strap around them so they are temporarily separated from the rest and you can look on the plant and know what parts will remain.
In this case since Janet's got help, she simply takes all the wayward branches in her hands, presses them together and the others take a critical look.
It turns out there's a single branch to blame -- all parts of the hump stem from there. We look inside the plant for a place where that one branch can be cut back to a side branch that's growing in a more acceptable way. Once we identify that point we see there will be a hole after the cut but also plenty of interior, needled side branches (arrows, right) that will grow to fill it.
So one cut with a small saw removes the offending branch. A hump-ectomy.
You're looking right in at the stub from that cut. Janet's using the blade of her folding saw to point to it. (Below.)
Then we make some lesser but similar cuts -- clipping back to side branches to take the shrub back from overhanging the bed edge.
The patient looks good!
You can do this kind of pruning any time. What you see here happened one evening in late summer.
A case for late winter/early spring cuts: The resulting gap won't begin to fill until the spring. So if the pruning will leave holes that bother you more than the deformity, make the cuts right before growth is about to begin in spring.