Ignore Shrub Pruning Guidelines: Timing Really Explained
Most guidelines note that shrubs should be pruned after they are done flowering, which is commonly in late spring through summer. In general, pruning shrubs during June, July and August will be the most stressful time of year. Most shrubs expend large amounts of energy for new leaves and flowering leading into spring and summer. Pruning (and removing) live tissue at this time of year will most certainly impact shrub health. Factoring in high summer temperatures and I would argue this could be the worst time of year to prune shrubs.
Timing guidelines are generally based on one premise, which is flowering. While flowering is important, there are many other factors that SHOULD come into play when factoring shrub timing. We also need to factor shrub size, health, age, location and privacy. As mentioned, I can easily argue that pruning during the summer heat is the worst time to prune, even factoring shrub flowering. Without getting too complex, “prune after shrubs flowering” only makes sense IF the type of pruning severely impacts flowering. If you need to prune a large percentage of a lilac shrub which impacts flowering, then yes, prune in June to get flowers for next year. However, the only pruning needed is removing a few dead limbs, pruning back for sidewalk clearance or removing a few older canes to renew the shrub, then I suggest waiting until fall (or the following spring). None of these pruning moves will hugely impact shrub flowering, so do it when it is best for health (not during the super hot, dry summer).
Hand pruning a yew shrub to reduce a limb.
Here is a further deep dive into the confusion:
#1 In theory, when determining WHEN and HOW to prune shrubs the following items are factored:
Type, age, health and size of shrub
Amount of growing space
Type of landscape (natural or formal)
Importance of flowering
Importance of other shrub benefits (fall color, growth form, stem color, fruits, privacy, etc….)
Type of pruning needed
#2 To simplify the process, The BIG Oak says that the proper timing of shrubs should be dictated by 2 main considerations: shrub flowering AND health, but really mostly health as discussed.
General rules for “prune after flowering” are based on the assumption that flowering is the most important reason for having the shrub.
If flowering is the most important element, then go ahead and prune after flowering (even if it is hot). If not, prune later in fall or early spring when it will not impact health so much. Good pruning really should not impact flowering greatly anyway, so pruning for health makes more sense.
#3 Exact specifications of pruning will also dictate the timing of pruning.
Reduction of height (must be done after flowering ONLY IF flowering is the most important element)
Reduction of overall size (must be done after flowering ONLY IF flowering is the most important element)
Deadwood removal (can be done anytime, has no impact on flowering)
Rejuvenation (early spring, must be done prior to leaf out)
Minor clearance / thinning (fall is best, but anytime is OK because minimal impact on flowering)
Hand prune reduction cut on a chokeberry shrub in fall.
The Lilac Example; Here are 4 examples in which specifications dictate the timing of pruning:
i. Reduction of height on large lilacs (prune after flowering)
ii. Removing 1/3 of older canes (prune in fall or early spring)
iii. Deadwood removal (prune any time, minimal impact on flowering)
iv. House or sidewalk clearance (prune any time, minimal impact on flowering)
#4 If HEALTH is most important, then late fall or early spring (dormant) is the best time.
#5 If you chose to prune shrubs with a hedge trimmer, then factoring health and flowering really no longer matters (so no guidelines make sense).
Important Distinction from The BIG Oak = If shrubs are being sheared to manage shrub size, then you are basically just “shaping” shrubs and are really not really properly pruning shrubs. All decisions regarding health and flowering become less important, and the plan just becomes keeping the shrubs not out of control. This is NOT pruning so guidelines are irrelevant.
General flowering timings for common shrub types:
a. Early spring flowering = Magnolia, forsythia
b. Late spring flowering = Lilac, Bridal Wreath spirea, Snowmound spirea, weigela, mockorange some hydrangea
c. Early summer flowering = Potentilla, summer flowering spirea, some hydrangea
d. Not necessarily grown for flowering = Dogwood (stem color), burning bush (fall color), ninebark (purple foliage), cotoneaster (hedge), alpine currant (hedge), viburnum (flowering, fall color, berries)
e. Evergreens are not grown for flowers = Juniper, arborvitae, yew, boxwood
A Sample Yearly Plan for Shrub Pruning
Most landscapes can be managed by 2-3 yearly visits. Here is a sample property requiring 5 yearly visits (which would be a very high maintenance property);
Visit 1 = Late March / early April visit for cutting back hydrangea & roses or rejuvenation (cutting to ground) for specific shrubs
Visit 2 = May visit for pruning for forsythia & magnolia (early flowering plants)
Visit 3 = Mid-June visit for pruning for all evergreens and spring-flowering shrubs grown for flowers (visit set after lilac flowering)
Visit 4 = Mid-July visit for pruning for later flowering shrubs (visit set after summer spirea are done flowering)
Visit 5 = Late October visit for pruning for all shrubs not grown for flowers or touch up work
Winterberry shrubs showing their magnificent red fruits.
