Reasons to Prune Shrubs

The most common reasons to prune shrubs are to maintain or improve health, vigor, and appearance. Each pruning cut should have a purpose. Here is a checklist of reasons to prune and suggestions to achieve improved health, vigor and appearance.

• Remove dead, dying, broken, damaged, diseased, rubbing or crossing limbs

• Remove or reduce limbs to achieve clearance from sidewalks, buildings or other structures

• To control shrub size or height (formal shrubs and landscapes only)

• To improve form or shape when dealing with formal hedges or ornamental evergreens

• To increase flowering or fruit production

• Remove older stems periodically to continually renew the shrub or remove all stems for complete renewal (rejuvenation)

The BIG Oak sums up proper shrub pruning =

Proper shrub pruning develops and maintains a shrub’s natural growth habit within the confines of a landscape.  Working with a shrub’s natural form will lead to lower-maintenance healthy landscapes.  Pruning practices, such a shearing, work against a shrub’s natural form and will lead to higher maintenance, unhealthy landscapes.  

Proper Timing of Shrub Pruning

Timing of shrub pruning is critical for maintaining health and maximizing flowering.  The timing of pruning is based on biology and varies for each shrub species.  Shrub maintenance plans should be designed with seasonal visits that take into account proper timing for each shrub species.  The generalizations below assume that maximum flowering is the main purpose of the shrub.  If health of the shrub is the main concern, the dormant season is usually the best time. Understanding flowering versus health is a main consideration in deciding when to prune.

Shrubs that bloom on “new growth”: This includes hydrangea (some), summer flowering spirea, and roses.  Prune in early spring before growth begins. Pruning in late fall is acceptable but can on occasion lead to winter dieback.

Shrubs that bloom EARLY on “old growth”:  This includes lilac, serviceberry, viburnum, spring flowering spirea and forsythia.  Prune these shrubs after they flower which will generally occur around early June. *Forsythia flowers very early and may need to be pruned earlier than the others.

Shrubs that bloom LATER on “old growth”: This includes weigela, potentilla, and mockorange. Prune them after flowering which will be early summer.

Shrubs not necessarily grown for their flowers: This includes shrubs grown for reasons other than flowering, which may include growth form, foliage, attractive stems, privacy, or other reasons.  Shrubs include snowberry, dogwood, euonymus, currant, barberry, and honeysuckle.  Since flowering is not the main concern it is best to prune when dormant in either late fall or very early spring before leaf out.  

Evergreens: When maintaining an evergreen’s overall growth form, late spring through early summer is the optimum timing.  Pruning for formal evergreens should not take place too early in spring, too late in fall or during periods of extreme heat or dry conditions.  Generally, any time is acceptable for pruning deadwood or winter damage.    When trying to increase density of a shrub, prune during the candle stage (generally May for pine and spruce).

3 Shrub Pruning Styles

Natural vs. Formal vs. Indiscriminate

Natural shrub pruning develops and maintains a shrub’s natural growth habit within the confines of a landscape.  Working with a shrub’s natural form will lead to lower-maintenance, healthy landscapes. 

Formal shrub pruning refers to shrubs that are sheared or manipulated into formal geometric shapes.  This style of pruning requires some training for shape and regular pruning to maintain the desired form and size.  Pruning must be done at least once a year and is not in the best interest of the shrub’s health.   Formal pruning of shrubs is acceptable for formal hedges and some ornamental evergreens. 

Unfortunately, it is commonplace to see all shrubs in a landscape sheared into balls, boxes or hockey pucks all at the same time. This is NOT formal pruning. The BIG Oak terms this “indiscriminate shearing”, which is a widespread practice because it is fast and requires no knowledge of shrubs biology.  

Here are the most common reasons why indiscriminate shearing is not an acceptable pruning practice:

• Works against the natural form of the shrub leading to unhealthy shrubs.

•  Unhealthy shrubs have a tougher time fending off insects and disease.

•  Lessens flowering, fruiting, and fall color.

• Cuts are not made at appropriate places on the stem tissue causing decay and decline of stems.

•  Causes an “eggshell” appearance of the foliage which shades out the base and inner portions of the shrub.

•  Since most of the foliage is removed, the shrub must regrow new leaves which is a huge energy expense.

•  Leads to high maintenance landscapes.

• Is generally done during the hottest time of the year which is very stressful.

Both pictures show spirea aggressively pruned in July. This pruning does not look appealing and removed a large percentage of foliage in the hot summer (which will impact health).

The picture above shows an over-pruned juniper late in fall resulting in immediate browning and dieback of the shrub.

The picture shows the result of “trying” to control the height of a large shrub resulting in wild re-growth of new shoots. Pruning is a growth stimulant and typically will not control size (genetics will).

Hedgetrimmers are notorious for destroying shrub limbs leaving ripped and torn tissue, especially for limbs that are larger than 1/2 inch.