Fall Pruning

by Carol Barany, Master Gardener

It won’t be long before the buzz of electric hedge trimmers taking this year’s growth off garden shrubs will echo up and down the block.  

According to a well-respected Seattle arborist and pruning specialist, “Just because you can doesn’t mean you should.”  

This advice from PlantAmnesty founder Cass Turnbull is a reminder that sometimes in gardening, ‘what NOT to do’ is more important than ‘what TO do’. 

Turnbull estimated that 80% of pruning done by homeowners and professionals alike is bad or unnecessary, resulting in plants that are “unhealthy, unpretty, unmanageable, and costly to maintain.”   She considered it a myth that gardeners must prune regularly to keep their shrubs in good condition. 

Just think of it. Your garden may really not require as much maintenance as you’ve been grumbling about giving it.  

Look at early spring bloomers like lilac, magnolia, forsythia, or big leaf or oak leaf hydrangea. All the fuzzy nubs you see emerging from the stems are flower buds.  If these shrubs are pruned now, you’ll eliminate flowering next spring.   

That’s because these shrubs bloom next spring on ‘old wood’ which are the stems that grew this year. If you really must, wait until flowering fades next year to prune.  The ‘Do Not Prune in the Fall’ list also includes andromeda (Pieris), beauty bush (Kolwitzia) choke cherry, cotoneaster, daphne, deutzia, fothergilla, kerria, mock orange, pyracantha, quince, some early blooming spireas, sweetshrub (Calycanthus), viburnum, weigela, wisteria, and witch hazel. 

There are summer-flowering shrubs that bloom from buds on wood that grows in the spring of the same year, which means they bloom on ‘new’ wood.’  This list includes abelia, barberry, burning bush, butterfly bush, Caryopteris, Clethra, dogwood, honeysuckle, panicle and ‘Annabelle-type’ hydrangeas, hypericum, Japanese spirea, ninebark, potentilla, Rose-of-Sharon, sandcherry, smokebush, and Vitex.   

They are typically pruned in late winter or early spring while they’re still dormant.

Turnbull’s mission was to teach gardeners to cultivate and manage their ornamentals based on sound horticultural practices and a measure of art.  

These days, gardeners are challenged to go even further.

Wenatchee entomologist Julie Banken was the guest on a recent podcast of Washington State University’s ‘The Evergreen Thumb.’ She encouraged listeners to consider their gardens as more than places to grow healthy and beautiful plants. It’s time to also consider our gardens as places to grow and nurture insects. 

Insects are essential drivers of life on Earth, providing critical ecological services that keep natural environments functioning.

Banken feels that one way to accomplish this is by replacing the term ‘fall cleanup’ with ‘fall rest’ for both insects and gardeners.

Leaving leaves, stems, and other natural debris provides essential winter habitat for an array of insect guests overwintering in your garden in a diapause phase.  This genetically programmed state of suspended development allows them to survive harsh winters and emerge in the spring. 

The traditional idea that a good gardener cuts everything back to the ground in the fall and tosses it into the yard waste bin is shortsighted because the life of the next generation of insects you’ve spent your whole summer trying to attract is in those stems. 

Less work on your part means more life on theirs. 

Taking a messier approach can offer vital winter shelter for cavity-nesting native bees and pupating butterflies and moths. By waiting until after the last frost to remove the material, overwintering insects have time to emerge and complete their life cycles.

30% of native bee species are stem or cavity nesters. Banken makes a compelling example of the female. She spends her entire adult life building a nest and laying eggs inside the pithy or hollow stems she finds in your garden.  If you cut and remove that stem in the fall, there goes her entire life’s work.

In nature, plants die in winter, but they are not cut down and removed. Choosing plants that look good in every season means you won’t be so tempted to cut them down in the fall. Make a visit to the Winter Garden at the Yakima Area Arboretum. You’ll find a garden that’s beautiful in all seasons, and breathtaking in winter. 

If not in the fall, when do you clean up? Wait for consistent 50°F+ daytime temperatures before cutting back hollow stems or heavily raking leaves. This gives beneficial insects time to wake up and safely exit their winter homes. Since roughly 70% of native bee species nest in the ground, avoid heavy mulching or tilling early in the season so they can burrow out safely. 

If you absolutely can’t wait to spring clean, begin in the warmest, sunniest patches of your yard where insects emerge earliest. Avoid the shady corners under shrubs that stay cold longer and house pollinators that are still dormant.

There are parts of every landscape that simply must be cleared in the fall for safety or disease reasons.  Instead of filling bags or yard waste-bins, leaving piles of loosely packed twigs, branches, and hollow stems keeps the habitat intact for late-emerging insects.

It’s challenging to disrupt routines and ingrained habits.  Instead of trying to change everything at once, why not let just one area of your garden rest this fall.  Start with an area in a corner or one that’s less visible.  

Small steps can lead to big changes.