How to Prune Evergreens
With few exceptions, evergreens (conifers) require little pruning. Different types of evergreens should be pruned according to their varied growth habits.
• Prune evergreens just about any time of year, except in late summer and fall. Late-season pruning encourages a flush of tender, fresh growth that will more easily be zapped by winter cold.
• Many evergreens are damaged by winter cold and winds. This is called winter die-back. They are also damaged by deer. When die-back or deer damage occurs, trim off just the dead part. Then do a light shaping to balance the form of the tree. However, except for boxwood, holly, and yews, most evergreens can't take a hard cutting back. They won't regenerate from that interior wood. They'll just be misshapen.
So if a plant is very damaged from winter die-back or deer damage and it's not a boxwood, a holly, or a yew, sorry, you can't do a major cutting back to restore its shape. It's best to dig it up and pitch it.
But do give it a chance until about June. By that time, whatever is going to grow back has grown back, and you'll be able to see more clearly what you're dealing with.
• Spruces, firs and douglas firs don’t grow continuously, but can be pruned any time because they have lateral (side) buds that will sprout if the terminal (tip) buds are removed. It’s probably best to prune them in late winter before growth begins. Some spring pruning, however, is not harmful.
• Pines have a single flush of tip growth each spring and then stop growing. Prune before these “candles” of new needles become mature. Pines do not have lateral buds, so removing terminal buds will take away new growing points for that branch. Eventually, this will leave dead stubs.
• Pines seldom need pruning, but if you want to promote more dense growth, remove up to two-thirds of the length of newly expanded candles. Don’t prune further back than the current year’s growth.
• Arborvitae, junipers, yews, and hemlocks grow continuously throughout the growing season. They can be pruned any time through the middle of summer. Even though these plants will tolerate heavy shearing, their natural form is usually most desirable, so prune only to correct growth defects.