Pine trees are winter-hardy evergreens covered in needle-like foliage that, unlike broad leaf evergreens, neither require nor easily tolerate aggressive pruning. Pines are ubiquitous in the Pennsylvania landscape and thrive in the climate covered by USDA Hardiness zones 5a through 6b, where winter temperatures drop well below freezing each year, across the state. As a rule, pine trees require little to no pruning save the removal of disease or damage, and look most lush and attractive when left in their natural form.
Prune your pine tree growing in Pennsylvania in the fall well before temperatures drop below freezing, or in the spring when temperatures go back above freezing, advises Purdue University.
Reduce the size of your pine tree gently by pinching or trimming back the tip of the candle (the longest central tip of foliage that protrudes from the end of a branch tip). Trim only candles that are at least 2 inches long, and never remove more than half of the candle length. Make a clean cut on the bias with your loppers and discard or compost the cutting. Trim back each candle, one by one, as needed; and never shear off the tips uniformly, as this destroys the form of the pine.
Thin an overgrown, diseased or congested pine canopy by removing the problem branches down to healthy wood, but never so far back into wood without the green needles present. Never remove more than one-third of the bulk of the tree tissue or you risk causing extreme stress to the tree or instigating a shock response.
Remove large, diseased, damaged and dead branches down to the main trunk, placing the cut just outside the slightly swollen branch collar. Never cut closer to the main trunk than 1/4 inch to 1/2 inch. Remove any diseased cuttings from the area to prevent the spread of pathogens.