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October 2017
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What shrubs to cut back and what to leave upright for winter

One of the reasons to leave hydrangeas, such as White Dome, upright is the winter interest. Photo courtesy ProvenWinners.com

The fall hustle has begun… rake leaves, fertilizer the lawn and plant spring bulbs, just to name a few seasonal steps.

People like to prune trees and shrubs now, too, but before you do, make sure you don’t cut off next year’s flowers.

Many spring-blooming trees and shrubs form flower buds on branches or stems that are current year’s growth, or they form on what’s called year-old or previous season’s growth. For instance, the flowers of next spring’s lilacs (Syringa spp.) have already begun developing on the shrub. Big leaf hydrangeas (H. macrophylla), oak leaf hydrangea (H. quercifolia), forsythia, crabapples (Malus spp.), blooming dogwood (Cornus florida) and several types of viburnums are a few examples of other spring-blooming plants that form next year’s flowers on this year’s branches.

If you prune these plants now, you’ll cut off next year’s flowers. If they need to be pruned for shape or size, do so within about a month after they are finished blooming.

Beautyberries, including Pearl Glam, comes into its own in the late-summer, early fall garden. Photo courtesy ProvenWinners.com

Summer and fall blooming trees and shrubs, such as rose of Sharon (Hibiscus syriacus); smooth-leaf hydrangeas (H. arborescens), such as ‘Annabelle’; and panicle hydrangeas (H. paniculata), such as Limelight, can be pruned in early spring before they leaf out. The smooth leaf hydrangeas can be cut back to the ground, but only prune the panicles and hibiscus for shape.

Some shrubs are called die-back plants because although winter kills the top growth, the roots usually survive. Beautyberry (Callicarpus spp.), butterfly bush (Buddleia hybrids) and blue mist spirea (Caryopteris spp.) are popular examples of this type of shrub. Because our area is the northern range for these plants, it’s best to leave these upright through winter. The top growth helps insulate the roots. Cut these plants back to about 6 inches from the ground in late winter or early spring. They will grow and bloom just fine come summer.

If you cut back lilacs now, you’ll cut off next year’s flowers. If necessary, prune lilacs within about a month after blooming. (C) Kevin P/morguefile.com

Shrub roses (Rosa hybrids), such as the Knock Outs, Drifts and Flower Carpets, are best left upright through winter. Cut them back to 6 to 12 inches from the ground in late winter before they leaf out.

Don’t prune evergreens now, such as conifers, boxwoods (Buxus), hollies (Ilex), azaleas and rhododendrons. Pruning may prompt new growth that won’t have a chance to harden off before winter hits.