Around the Garden

The season of showy spring blooms is winding down, and that means it’s time to prune. Spring-blooming shrubs such as viburnum, lilacs, mountain laurel, azaleas and rhododendrons are candidates as soon as their flowers die back, especially if they have suddenly turned into leggy monsters. The worst part of that legginess is that all the blooms are just out of reach when you want to cut some flowers for a bouquet.

Shrubs are highly forgiving plants, and will generally reward pruning with a burst of new growth. In most cases, a shrub is a multi-stemmed woody plant that grows to fifteen feet or less. New growth typically occurs only at the top of the stems, unless you remove an entire stem. When you cut a stem to the base, new growth will be stimulated, and shoots will begin to grow shortly. Do not remove those shoots if you want your shrub to be rejuvenated!

Removing a quarter to a third of the oldest stems down to the ground is the best way to rejuvenate a shrub over three or four years. After repeated annual prunings, you will have a new, vigorous, and much shorter shrub.

If your shrub hasn’t gotten out of control, and you just want to keep it to an attractive size and shape, now is also the time to prune. New flower buds will grow over the summer, so cutting off unwanted branches or branch tips before those buds emerge will conserve the plant’s energy.

The tools for this job are sharp pruners and loppers – never a hedge-trimmer! This isn’t just an esthetic issue, although improper pruning might turn your shrub into a grotesque muffin or meatball. The scientific basis for pruning one stem at a time relates to how a plant grows. Plants, like all organisms, grow in response to hormones. The growth hormone in plants, auxin, is concentrated at the tips of stems. When the tip of the stem is cut back, the bud or buds just below the cut receive a jolt of auxin, and begin to expand and elongate. So, if you want a shrub to be shorter and fatter, you will want to cut each stem just above a live bud or leaf that faces the outside of the plant.

Some shrubs, such as viburnums, will have a pair of buds at each node. To avoid sending new growth into the center of the plant, snip off the inward-facing bud or twig completely.

Another important reason to prune just above a bud or twig is to avoid leaving a length of woody stem to die back. Decapitated twigs not only look unsightly, they are also a conduit for decay to enter the plant.

A bad pruning job is usually not irreparable, but you can do some serious harm nonetheless. Good pruning is done slowly – cutting only when you know what your overall goal is for the plant’s ultimate height and width. Happy pruning!