How to Trim Old Fashioned Lilac Bushes

Sharpen all the blades before you begin. A sharp tool makes a clean cut without tearing the bark. Tearing opens the plant up to pathogens, which can make the tree diseased. Hold the blade at a 45-degree angle and stroke across the sharpener once or twice.

Use the hand pruners to remove any suckers at the base. Do not prune during rainy weather or when the temperatures are over 75 degrees Fahrenheit. Extreme conditions put strain on the bush, and the additional stress of pruning will shock the plant. Prune off the water spouts, which are new branches that grow upward. Remove any broken or diseased wood.

Saw out a third of the oldest wood. The wood that remains should be spread out from each other and not touching. The cuts should be straight across and 1/2 inch away from the branch collar, which is the swelling at the mother wood. Keep an open vase shape in the bush.

Remove up to a quarter of the small twiggy wood from the center to increase air flow. Prune the top a foot lower than the desired height. This gives the bush room to leaf out. Deadhead old flower heads if you wish. This is a cosmetic procedure and is only necessary if the old flowers appear to diminish the look of the lilac.

Cut the entire plant down to 1.5 feet from the ground if the plant is completely out of control. This aggressive pruning is only done if the lilac has been neglected for years. It means you will get no flowers the following season, but will give the lilac a chance to recover and you can begin to retrain the plant.