It is a common belief that pruning shrubs involves shearing. While this is applicable to certain types of shrubs and situations, a majority of shrubs do not respond well to shearing. Shearing can also harm the plant's natural form and become more susceptible to snow and ice damage. In most cases, renewal pruning should be used.Renewal Pruning
Most deciduous shrubs benefit from regular renewal pruning. Upon examination, you will notice that most shrubs consist of many stems or canes arising from the ground. Renewal pruning involves the selection and removal of the largest, heaviest canes at the ground line. A pruning saw or scissor-type lopper is the best tool for renewal pruning.
Renewal Pruning Benefits
Over the life of the shrubs, you should only have to remove a few canes per year. The benefits of renewal pruning can be easily observed on a Redtwig Dogwood. The younger wood is more colorful, while the older, heavier canes are more woody and less colorful. Simply remove the largest diameter canes with the least color at the ground line, leaving behind the younger, more colorful stems. The following season more bright red stems will appear, giving the plant a more visual impact.
Renewal pruning is very useful on most leafy (deciduous) shrubs. Lilac, Honeysuckles and shrubby Dogwoods respond very quickly to renewal pruning. However, it does not work well for all shrubs. Burning Bush should never be renewal pruned, while other large-scale, specimen shrubs, such as Corneliancherry Dogwood and Common Witchhazel may never require it. Please consult our Pruning and Maintenance Guide for a detailed list of plants that benefit from renewal pruning.
For the bold and unafraid, many of the same benefits from Renewal Pruning can be found with Rejuvenative Pruning. While Renewal Pruning is a gradual process of thinning older wood from shrubs over a period of time, Rejuvenative Pruning is a one shot approach by removing every stem and twig just above the ground all at once.
Rejuvenative pruning is best done just prior to bud break in March or early April, when the plant has stored the most energy. This method works extremely well on Honeysuckle, Lilacs, and a few others. The Pruning and Maintenance Guide should be consulted as this pruning technique can kill a plant if done to the wrong plant at the wrong time.
Among the plants that benefit from annual Rejuvenative Pruning are Annabelle, Snowhill, and White Dome Hydrangea. They bloom only on new wood and, unless annually pruned back, they become floppy from the large flowers. It is important to remember that Pee Gee Hydrangea is not pruned this way and can be seriously damaged if done so. Please consult the Pruning and Maintenance Guide on pruning your Hydrangeas.
Heading and Thinning Cuts are two less dramatic types of pruning. They are useful for detail shaping or adding density to plants. Both produce slightly different results.
Heading Cuts are made just above a bud. They result in a shoot developing from the bud and often from the lower buds also. When you are making a heading cut, leave just enough of a stub to keep the bud or buds below from drying out. A slightly slanted cut is desirable where just one bud is present. However, rot may be encouraged if to large a stub is left. It may be important to prune an outward facing bud to encourage a spreading, non-congested form. The main results of Heading Cuts are an increase in density, although it can be useful in shaping.
Thinning Cuts are made just above a side branch. Make the cut just above a side branch and roughly parallel to it. Thinning cuts allow more air circulation through the plant and make branching patterns more visible. Once again, it may be more important to prune to an outward facing branch.
The "Haircut" Method is a modification on the Renewal and Rejuvenative Pruning. This method is useful on both Potentilla and smaller Spireas, such as Anthony Waterer and Goldflame. In late March, spireas should be cut back to 1/3 their height, while more woody potentillas should be trimmed back to 1/2 or 2/3 their size. Next, selectively remove the oldest, heaviest twigs completely to the ground, similar to Renewal Pruning.
This normally involves removing 2-4 twigs per shrub. Later, these cuts will stimulate the development of new shoots and keep the plant compact, healthy, and finer textured. The "Haircut" Method should be done every 2 - 3 years to maintain plant vigor. If done every year for a number of years, the plant's stored energy reserves dramatically decrease, plus density and both flower size and quantity will decline.
Hedges will always be a part of our landscape in some way, shape, or form. Generally, plants must be sheared after the new growth has flushed, but before it hardens off. Normally, this is in late May or June, although some plants may flush growth again, requiring a second, or third shearing. Remember to use sharp pruning shears so they do not tear the stems. When shearing hedges, remember three basic rules:
These rules help maximize sunlight to the sides so the hedge remains dense to the ground. In addition, this shape helps distribute snowload more evenly, avoiding damage.