Pom pom is a cultivar of the coniferous evergreen pine species know botanically as Pinus sylvestris and more commonly as Scots or Scotch Pine. The tree naturally develops clumps of fine needle foliage on branches that are upright but on limbs that are horizontally spreading. This gives the appearance of floating cloud-like layers of foliage that can be further enhanced to a pronounced puff-ball appearance with pruning. Like most evergreens, Pinus sylvestris is slow growing and does not require heavy pruning for health but will readily tolerate regular, very light pruning to maintain the decorative and well defined pom pom shape.
When To Prune
Unlike many other narrow-leaf evergreen trees, where you want to focus pruning in the later winter or early spring while the tree is still in its dormancy, you want to handle pom pom pines differently. Wait until the later spring or early summer after new tufts of green growth become visible to shape the plant. This timing ensures you are not cutting into old growth that cannot be replaced. It also helps stimulate branching and more dense green growth at the branch tips, which in turn makes the definition of each pom pom more complete.
Removing Damaged and Dead Tissues
As an exception to the regular maintenance pruning, removal of diseased or badly damaged branches, limbs or foliage should be done when the problem is first identified, irrespective of the time of year. At a minimum, make an inspection of the tree in the later winter or early spring each year to ensure there are not any problem tissues that require removal. Though maintenance pruning of Pinus sylvestris is only recommended for new growth, clearly diseased or broken branches pose a risk to the health of the tree and must be removed. Breaks or bad cracks in limbs or branches can invite further damage or disease if they tear the cambium or branch wood. Cut the problem tissues back to a point of healthy stable wood to just above a side shoot or all the way down to the limb or main trunk.
Pruning to Maintain Natural Form
Regular pruning maintenance, save the removal of damaged or diseased wood, is entirely optional and is infrequently warranted. You can trim back errant branch growth that appears out of scale with the tree structure and mars its appearance. Place any and all cuts just above where the needles emerge from the branch in a whorl pattern. This will allow new lateral branches to develop, and they, in turn, will produce needles to fill in and disguise the cut site. Though suckering is not heavy on pine trees, you can snip off any shoots that do emerge from the lower trunk or root zone as these can make the tree look unkempt if allowed to proliferate. Fine shoots can be removed with secateurs or loppers, but any larger than 3/4 inch in diameter should be taken off with a fine-toothed pruning saw to prevent tearing of the cambium.
Exaggerating the Pom Pom Shape
More extensive surface pruning of the pine foliage falls into the category of topiary and is simple to do, but it is very detailed work that can be time-consuming. Pines should not be sheared with electric hedge trimmers or large-blade shears, as this can easily cut into old growth and makes it difficult to effect the rounded pom pom shape. Fine topiary work is best achieved with secateurs or small pruning shears. Each branch tip should be evaluated within the larger appearance of the individual pom pom as well as the balance of the tree and then cut individually. Be conservative with your cutting as you can always remove more. Regrowth is a slow process. Place each cut just beyond a whorl of the fine needles so you will not end up with holes in the pom pom sphere or oval. Work on one pom pom at a time and periodically stand back a few yards from the tree to assess your work and determine how to shape the next pom pom.