Following a weekend of memorable stormy weather, I donned my English gardening boots and slicker on a damp, dreary morning and ventured forth into my flooded landscape to assess the damage from the ongoing nor’easter.
Only a few days ago, I spent hours gathering heaps of twigs and branches from my lawn and gardens. As I waded through the expansive puddles in nearly every part of my yard, it became evident that this cleanup will begin anew; drenching rains and fierce winds have delivered a substantial collection of additional branches as Mother Nature continues to perform her annual pruning.
There is an old adage that suggests that one should prune whenever the pruning shears is sharp. Although light pruning in any season is unlikely to cause permanent harm to an established tree or shrub, the timing and magnitude of the pruning process will greatly influence the growth and flowering of most plants.
Our plants store food reserves in their roots and stems during the fall season to help them survive the winter months and initiate growth in spring. Reducing the number of branches and buds in late winter leaves more energy for the remaining shoots. Depending on the plant, pruning may stimulate increased branching, larger leaves, bigger flowers or more prolific blooms. For fruiting trees, shrubs or vines, if the number of stems and flower buds is decreased, the plants may produce fewer fruits, but those remaining fruits are usually larger and sweeter, and fruit production will likely be more consistent from year to year rather than bountiful in one year and sparse the next.
Trees and shrubs that bloom in spring generally bloom on the previous year’s growth, known as “old wood.” Substantial pruning, just before new growth begins, will significantly reduce their flowering, but I am often willing to sacrifice those fleeting blossoms to rejuvenate overgrown trees or shrubs since it is considerably easier to view their architecture when the plants are dormant. March pruning enables easy access to the woody plants that grow in and around my gardens, reducing the potential for damaging emerging plants and allowing for a quicker cleanup.
I adore the glorious blooms of crabapple trees, but their vigorous growth requires annual pruning to thin out interior branches and sucker growth. Since they bloom so prolifically, I generally prune them while they are dormant. Shadbush (Amelanchier), flowering plums and cherries, dogwoods, magnolias, forsythia, quince, lilacs, ninebark, azaleas and rhododendrons also bloom on the previous season’s growth.
If you do not wish to sacrifice the lovely blossoms, prune these spring bloomers immediately after they finish flowering. Large, established magnolias tend to resent major pruning and are best pruned in midsummer only if necessary.
Trees and shrubs that flower in late June or after tend to bloom on “new wood.” Pruning during late-April or May will stimulate vigorous new growth and greater flower production for butterfly bush, sweet pepperbush (Clethra), Rose of Sharon and blue-mist shrub (Caryopteris). Butterfly bushes, in particular, become leggy and unattractive when allowed to grow unrestrained. Cut back these vigorous shrubs to 12 to 18 inches tall in May after all danger of hard frosts. This ruthless pruning will promote glorious quantities of fragrant blooms later in the summer.
Many suckering, overgrown shrubs will benefit from a process known as renewal pruning. Forsythia, lilac, quince, Spiraea, Potentilla, Viburnum, Ninebark (Physocarpus) and Weigela are just a few of the shrubs that tend to become dense and overcrowded. These shrubs will look their best given an annual pruning, including lopping the oldest stems to within 1 foot of the ground. Prune during late winter or immediately after flowering.
Some ornamental shrubs, especially those grown for their variegated or tinted foliage or their colorful twigs, will produce better color and larger leaves on new growth. Red and yellow twigged dogwoods, purple or gold smokebushes, ninebarks and weigelas should be drastically pruned as their leaf buds swell and may even be cut down to the ground to promote vigorous new brightly colored stems or leaves. While spring flowers may be sacrificed, the substantially larger leaves will offer spectacular color throughout the growing season.
The family of Spireas includes many popular varieties, some of which bloom on old wood, including the early-blooming, gold-leafed "Ogon" and the bridal wreath types; prune these vigorous shrubs after blooming for best flowering. Summer-blooming cultivars such as "Gold Mound" and "Gold Flame" can be drastically pruned in spring to produce bountiful blooms and compact growth.
The hydrangea family generates the greatest number of inquiries at local nurseries regarding flowering and pruning. Drastic spring pruning of the lovely snowball hydrangea, "Annabelle," will produce spectacular, massive, white spherical trusses beginning in July.
The Pee Gee (paniculata) hydrangeas, including the delightful "Limelight" also respond to spring pruning which promotes greater flower production in mid- to late summer.
Oak-leaf hydrangeas and the popular blue and pink mophead hydrangeas are exceptions to general pruning practices. Although these deciduous shrubs produce their spectacular blossoms later in the season, their flower buds are formed on old wood at or near the end of the branches. Substantial fall or spring pruning of the stems will eliminate a majority of the flowers. Thin out stems of older shrubs to allow light and air to reach the interior of the plant and remove dead tips or branches as these plants begins to develop their new leaves and flower buds.
The American Horticultural Society’s Pruning and Training manual, is a worthy addition to any homeowner’s library as it offers recommendations for how and when to prune specific varieties of trees and shrubs.
Suzanne Mahler is an avid gardener, photographer and lecturer who has been developing the 1.5-acre property surrounding her home in Hanover, Mass., for more than 30 years. She is a member of two local garden clubs, past President of the New England Daylily Society, an overseer for the Massachusetts Horticultural Society and is employed at two garden centers.
