Recently, I received a question about the best time to prune lilacs. The short answer is anytime that is convenient for you! But seriously, the best time is just after blooming. These beautiful blooming shrubs produce flowers on new shoots which begin forming during the second flush of growth later in the growing season. The next year, in the later winter and early spring, these shoots and flower buds finish forming and maturing for the blooms in May. Pruning in the earlyspring when many of us think about it, results often in removing the majority of potential flowers. This is the time to head back all the growth that bloomed and thin some of the upright growth that fills up the vase form of lilacs. Maintaining good air circulation and light penetration into the plant will help to produce more and larger blooms. While you are at it, it is a good idea to feed your flowering shrub with a balanced fertilizer to maintain the vigor of the plant and help the shrub build a good food supply as it continues to grow and prepare for the winter dormancy.
I often refer to the use of a balance fertilizer for gardeners wanting to boost plantings in the landscape. It does not matter if your plants are vegetables or flowering shrubs and trees, plant need a nutritious food supply just like we do. Plants utilize a dozen different mineral element regularly, but Nitrogen, Phosphorus and Potassium are the macro elements required in the greatest amounts. The three numbers listed on any fertilizer bag represents the percentage by volume of those 3 in the formulation. A balanced fertilizer is one that has all 3 of the main macros. Nitrogen is the first number and used by the plant in the greatest amounts. It is the catalyst for all above ground growth and important for absorption of nutrients and water. Phosphorus is associated with root development, flower and fruit development. Potassium (the 3rd number) is important for stabilizing nitrogen and phosphorus and maintaining a robust immune system for your plants. There are usually other nutrient elements listed, including calcium, iron, sulfur and others which will often be specific to the crop you are putting it on, but the 3 numbers on the bag or box tell you what that fertilizer will do whether it is organic or manufactured. An unbalanced fertilizer is one that is missing one or more of the big 3.
