When pruning any plant, it is always good to know what your goal is and that will help you determine how to best prune your shrub. Here are the 5 main goals of pruning and the questions that you should be asking yourself before you begin:
GOAL 1 – Control the Size of Plant
The best way to control the size of a plant is by natural pruning. Natural pruning means that you are making selective cuts in order to thin or reduce the overall size of the plant. This cannot be done with shears, but with secateurs or loppers. It means cutting one stem at a time and not just shearing off the tips. When all you do is shear back the tips, the plant loses its natural form because it increases the number of branches and creates a branch structure that resembles a candelabra. Your shrubs will become very wide at the top because of this increased branching, giving your shrub an ice cream cone-like appearance. And because the top is so wide, it stops the sunlight from hitting the base of the plant and you are left with a plant that is bare at the base. Always prune back to a point just above a side shoot or back to just above a bud. When pruning is completed it should look like no cuts have been made. It should still have its natural form.
GOAL 2 – Increase the Amount of Flowers and Fruit
Proper pruning will aid in the production of more flowers and more flowers produce more fruit. Most flowers are produced on the tips of the stems, therefore, the more tips that there are, the more flowers that the plant will produce and the more flowers you have the fruit will be produced. In order to accomplish this goal, you cut back the stem tips, stimulating the side branches and developing more tips for the flowers to form on. Just remember that the more flowers that a plant produces the smaller the flowers will be. Fewer flowers usually mean larger flowers.
GOAL 3 – Maintain a Certain Shape
One of the goals of pruning might be to maintain a certain shape such as a hedge, a globe form, or specimen plants like spirals and pompons. This is best achieved by shearing. With shearing you are just removing new tip growth, creating a full dense look. Even though electric shears makes the job easier, hand shears make a much nicer job of things. Electric shears just tear the plant tissue while hand shears makes a cleaner cut. When the plant tissue is torn there is more die back at the tips giving the sheared shrub a brownish tinge. Always make sure that any pruning tool is sharp and clean before using to prevent this from happening.
GOAL 4 – Encourage Colourful Bark
There are certain plants, such as red or yellow twig Dogwoods and Japanese Kerria, which have colourful bark. In order to keep the colours as intense as possible special pruning is required. It is the youngest stems that will give you the brightest colour. As the stems age, they start to lose their colour. So the best way to encourage colourful bark is by pruning out (right to the ground) one third of the oldest growth every year. You will be able to tell which ones are the oldest stems because they will be thicker and more grayish/brown in colour. This encourages new growth to come up from the base, which will then give you more colourful bark.
GOAL 5 – Rejuvenate an Older Shrub
In most cases, we tend to let shrubs grow and grow and once they become too large, we hack them back hoping that they will survive and become beautiful again. It is much easier to do a bit of pruning every year than to wait until the shrub is out of control. It is sometimes very hard to rejuvenate an old shrub that has been ignored for too long. The best way to rejuvenate an old flowering shrub is to do so over a three-year period. This can be achieved by removing one third of the oldest growth every year right back to the base, which will then stimulate growth to come from lower down. In three years you will have completely rejuvenated the entire shrub. With some flowering shrubs you can drastically cut the stems back to about 4”-6” above the ground. It may look funny for that season, but it will fill back in eventually.