Shrub Pruning

by Bryan Fischer, Curator and Horticulturist, Gardens on Spring Creek

Grumbling, mumbling, yanking, ripping. Outside. Late winter. Lots of debris to deal with afterward. An experienced gardener probably knows the scene already: winter pruning. 

So, if the job appears so unpleasant, why would I subject myself to it? 

Winter pruning of shrubs easily becomes one of the most irritating tasks we handle in the garden, especially if carried out on an overgrown shrub where pruning needs have been deferred. Timing your winter pruning thoughtfully, however, and making it an annual chore make the job not only manageable, but pleasant, offering a garden task on a sunny winter day – even if there is snow cover. I winter prune my flowering shrubs and any of my established deciduous, non-flowering shrubs, the exceptions being evergreen shrubs and marginally hardy woody plants (like Chilopsis, desert willow), which I prune more lightly and irregularly. 

Wait for a warm, sunny day in late winter (I like February or even March). Use a serrated pruning saw – Silkie makes some of the best – and prune only well-established shrubs (4+ years old). Most shrubs excel if one-third of their branches are pruned all the way to the ground each winter. Aim to remove the oldest, largest ones with clean cuts near the soil surface. If the branches are over an inch or two in diameter, making a cut higher up to reduce the branches’ weight, followed by a second cut near the soil surface, can be best. This also reduces bark tearing if your initial cut is on the lower side of the branch. 

By pruning about one-third of a shrub’s branches annually in winter, you remove material when plants are dormant, minimizing shock. This style of pruning also results in the full turnover of a shrub’s canopy every three years, ensuring that the majority of wood on a plant is young and vigorous at any given time. Since most flowering shrubs produce flower buds best on two- to three-year-old wood, one can use this method to keep their shrubs flowering exuberantly without requiring the gardener to deal with the bald shrub left behind after a rejuvenate pruning. 

Appropriate for very overgrown or tired, thin shrubs, rejuvenate pruning is as effective as it is terrifying. As simple as cutting every branch on a shrub to the ground, this technique forces plants to use root reserves of stored food to produce a preponderance of vigorous, juvenile growth. Within two or three years, shrubs look full and vigorous, and blooming shrubs flower well. I occasionally use this technique to kick off pruning for long-neglected shrubs – after the first winter’s rejuvenate pruning, a lighter, annual “one-third” pruning (outlined above) keeps the shrub looking at its best. Since rejuvenate pruning results in only first-year wood the following summer, shrubs that bloom on second- and third-year wood are unlikely to flower if pruned using this method. 

Whichever pruning method you might use, avoid heading cuts, which are cuts made partway up a branches length intended simply to shorten the branch. These will result in excessive twiggy growth and lead to structural problems over time; shrubs requiring heading pruning regularly to remain an appropriate size are simply too big for their abodes! Gripes aside, thoughtful pruning – whether conservative or rejuvenate – serves to increase vigor and will benefit most established shrubs. Take advantage of the season and invest some time now to keep your woody plants looking their best for spring!