When it comes to pruning your trees and shrubs, timing is everything. Pruning is one of the most critical gardening tasks. The way that a plant is pruned and the timing of the pruning determine whether the plant will develop satisfactorily or not. If done correctly, trees will grow in the desired manner - bushes will look lush, green and healthy - and flowering plants will brighten up the garden with color. On the other side of the spectrum, if pruning is performed at the wrong time, serious, long-term damage can be inflicted on trees - shrubs and bushes are liable to develop an open, gangly look - and many herb plants and subshrubs, while green on top, become bare and unattractive below.
One group of plants that should not be pruned in the spring is plants that naturally drop their leaves during the winter; these are called deciduous plants. During the dormant, winter season, nutrients dissolved in sap are stored in the plant's tissues. When spring begins, the nutrient laden sap is carried to all of the plant’s growing parts. Pruning during this time will cause the sap to seep out of the plant, causing it to lose vital energy sources. Deciduous plants should be pruned in the winter.
Spring is the best time of year to prune evergreens and other trees and plants that are sensitive to cold (which should not be touched during the winter). Since spring is the main growing season for most plants, it is best to direct the new growth just as spring is beginning. Pruning a month or two after new growth has sprouted means that the tree or shrub has exhausted vital energy for no purpose.
Care must be taken when it comes to flowering shrubs. For deciduous species, you will need to know whether the flower buds develop on the current year's spring growth, or on that of the previous year. Lilac bushes, for instance, develop flower buds early – though you may not see them- if pruned at the wrong time all of the flower buds will be removed in the process. Lilac bushes and similar plants, which include different shrubs and species of roses, should be lightly pruned right after the flowers have withered.