Homegrown: When pruning, it’s all about timing

Careful pruning yields best blooms

Spring-blooming shrubs are dominant features in early-season gardens, but they quickly lose their dazzling floral sprays and morph into leafy masses. Summer greenery may not be appreciated as much as earlier blossoms, but dense, branching foliage adds substance to our landscapes.

Shrubs such as spiraea, deutzia, weigela, forsythia, lilac (Syringa), beauty bush (Kolkwitzia), mock orange (Philadelphus), and some viburnums become a filler of sorts between trees and perennials, spreading arching branches 3 to 6 feet high and wide.

It’s easy to take these lavish bloomers for granted as they repeatedly delight us every spring, but ignoring them for too many years takes a toll on their off-season appearance. Branches become gangly, lower stems congested, forms unshapely.

Eventually they need attention.

In general, most pruning amounts to removing only the oldest or largest stems in an effort to promote new, vigorous growth.

But when shrubs have lost their shapely character and become a jumbled, gnarly tangle, it’s time to rejuvenate them completely by cutting all stems to the ground.

Rejuvenation

Some spring-blooming shrubs may never need drastic pruning, but nearly all benefit at some point from encouraging dormant buds to sprout and develop into an entirely new-looking plant.

Gardeners routinely treat roses and potted fuchsias similarly, though canes are rarely if ever cut completely to the ground except on large-species shrubs.

Because of our concerns with limiting outdoor watering during the current prolonged drought, heavy pruning of spring-blooming shrubs has a double advantage this year. In addition to improving their summer-fall-winter appearance, pruning them back allows us to cut back on watering.

When shrubs are pruned low, their lack of foliage prevents them from absorbing as much water as usual, which allows us to reduce irrigation. Soil in the root zone should still contain some moisture, but the surface and upper levels - 2 to 3 inches deep - can dry out before re-watering.

Keep in mind that excessive watering may cause roots to rot.

Timely pruning

Nearly all spring-blooming shrubs develop new flower buds throughout summer months. Because of this natural cycle, any pruning should take place as soon as blooms fade, certainly by mid-to-late June. This allows plenty of time for branches to elongate and flower buds to form.

Pruning later in summer, fall, or winter results in cutting away buds that would normally lead to flowering the following spring. The expression “blooming on old wood” refers to this habit of summer growth and bud formation for spring bloom.

Some gardeners prefer to leave 6 to 12 inches of stem at the base when pruning low, but if you choose merely to shorten stems partially rather than cut any to the ground, be aware that new growth will begin where the cut is made.

Shortening stems halfway generally results in awkward and unattractive top growth. Cutting stems at ground level or just above, in contrast, generates balanced new growth.

If complete rejuvenation seems too radical a step, attack the issue in stages. Complete the process over two or three years by removing a third to one half of the stems, targeting the oldest or largest ones first.

The right tools

Small hand pruners are the usual preferred tool in most home gardens, but pruning large shrubs calls for heftier equipment.

When cutting out a few older stems, long-handled pruners let you reach inside the base of the plant and use ample force. But even these may not be adequate on more mature shrubs.

For trunks larger than 2 inches, you’ll need a sharp pruning saw. Overgrown shrubs that haven’t been maintained for many years may call for a chain saw.

Late bloomers

When embarking now on a pruning expedition in your garden, take care to bypass summer- and fall-blooming shrubs. Those are in process of developing flower buds, many on new wood - on branchlets that have grown this spring. Pruning now will eliminate this year’s flowers.

Summer-blooming spiraeas, butterfly bush (Buddleja), Annabelle hydrangeas (H. arborescens), bluebeard (Caryopteris), and many others summer bloomers should be pruned in the late dormant season.

Pruning popular mophead hydrangeas (H. macrophylla and hybrids) calls for special attention. Cut back stems that have flowered part way, leaving a few pairs of side buds.

On older plants with many branches, remove damaged growth along with a few of the oldest stems. This will encourage fresh new growth that will flower the following year.

Rosemary McCreary, a Sonoma County gardener, gardening teacher, and author of Tabletop Gardens, writes the monthly Homegrown column for The Press Democrat. Contact her at rosemarymccreary@gmail.com or write to her at 427 Mendocino Ave., Santa Rosa 95401.