When should we prune and how much? These are standards that we may refer to in a general way. When dealing with nature, we can deviate and break some rules if our knowledge is adequate enough to be aware of the end results.
Any shrub that appears to be in a weakened condition should be pruned with caution. Severe pruning performed on a plant in decline could cause more stress and possibly the death of that plant.
Keep your shrubs in the best possible condition by finding your local certified arborist and requesting a consultation today!
When we suggest dormant pruning, it should be understood that late dormant pruning in February and March seems to produce the best results, especially when pruning to ground level. Ground level should be interpreted as leaving the stubs about two inches (2”) above grade. When we suggest pruning after bloom, our goal is to enhance the flower for the next year. Many shrubs produce the flower bud for next year on the current season’s stems. If we prune in the dormant season or after the flower bud has been produced, we may be removing the next year’s blossoms. Most plants don’t care if they bloom. Depending on the shrub species, dormant pruning may result in little or no bloom for one or two years. A healthy shrub can tolerate aggressive pruning.
Formal pruning produces very straight lines or neatly rounded lines. This is a high maintenance activity. The informal or natural shape is usually better for the shrub. If we must prune in a formal manner, we should maintain the top narrower than the bottom. This looks like an upside-down U or A shape. Formal pruning may also encourage disease and insect problems.
Listed in alphabetical order by botanical name, the following are the most commonly-used plants for formal hedges: Berberis species (Barberry), Cotoneaster acutifolia (Peking Cotoneaster), Euonymus alatus (Winged Euonymus), Ligustrum amurense (Amur Privet), Lonicera species (Honeysuckles), Philadelphus species (Mockorange), Physocarpus species (Ninebark), Ribes alpinum (Alpine Currant), Spirea species (Spireas), and Viburnum dentatum (Arrowwood Viburnum).
Rejuvenation pruning is usually our most severe pruning. Generally, this means cutting the entire shrub to near ground level, leaving a stub about two inches above grade. If reasonable, we leave a few stems or suckers growing from the removed canes. This enables the shrub to produce new growth quickly the next season.
Shrubs that Respond to this Type of Pruning:
Hydrangea arborescens f. grandiflora (Hills of Snow Hydrangea), Lonicera species (Honeysuckles), Ribes alpinum (Alpine Currant), Cornus sericea cultivars(Dogwoods), Hypericum species (St. Johnsworts), Ligustrum species (Privets), Syringa chinensis (Persian lilac), Viburnum lantana (Wayfaring Tree Viburnum), Symphoricarpos species (Snowberry, Coralberry), Spirea species (Spireas), Kerria species (Kerria), Cotoneaster acutifolia (Peking Cotoneaster), Viburnum dentatum (Arrowwood Viburnum), Berberis species (Japanese Barberry), Cotinus species (Smokebush), Kolkwitzia species (Beauty Bush), Potentilla species (Bush Cinquefoil), Syringa vulgaris (Common Lilacs), Viburnum opulus (Cranberry Bush), Viburnum trilobum (American Cranberry Bush), and Salix discolor (Pussywillow).
The best time to do rejuvenation pruning is late in the dormant season - February or early March. The listed plants will respond to this pruning if they are in good health and have a substantial root system. A shrub in weakened condition may be injured or possibly killed by severe pruning. There are other shrubs that may respond in an acceptable manner to rejuvenation pruning - ask your arborist when in doubt.
This is the removal of up to 50% of the major canes and/or selective removal of branches to reduce size or change the form of a shrub.
Shrubs that Respond to Moderate Pruning
Listed in alphabetical order by botanical name (All shrubs on the Rejuvenation Pruning list also respond to Moderate Pruning): Aronia arbutifolia (Brilliant Red Chokeberry), Calycanthus floridus (Common Sweetshrub), Caragana arborescens (Siberian Peashrub), Chaenomeles species (Flowering Quince), Cornus alba species (Tartarian Dogwood), Cornus mas (Cornelian Cherry Dogwood), Cornus racemosa (Gray Dogwood), Corylus species (Hazelnut), Cotoneaster apiculata (Cranberry Cotoneaster), Cotoneaster divaricata (Spreading Cotoneaster), Euonymus europaeus (European Spindle Tree), Forsythia species (Forsythia), Hamamalis species (Witchhazel), Hydrangea paniculata (Panicle Hydrangea), Philadelphus species (Mockorange), Physocarpus species (Ninebark), Prunus species (Cherry, Flowering Almond), Rhus aromatica (Fragrant Sumac), Syringa meyerii (Palibin Meyer Lilac), Viburnum burkwooddii (Burkwood Viburnum), Viburnum carlcephalum (Carlcephalum Viburnum), and Weigela species (Weigela).
An accepted practice when maintaining large shrubs over many years is to remove several (3-5) of the largest canes every year or two. This method often maintains the plant size at acceptable levels as well as keeping the shrub thinned out. Frequent pruning is certainly in the plants’ best interest. Infrequent, but severe pruning is not a good long-term maintenance practice for plants in this category.
This is a selective thinning out and/or dropping back to maintain a specified size or form. It may also be to eradicate insect-infested or diseased stems of a shrub.
Shrubs that Respond to Light Pruning:
(All shrubs on the Rejuvenation Pruning and Moderate Pruning lists also respond to Light Pruning): Viburnum carlesii (Koreanspice Viburnum), Viburnum juddi (Judd Viburnum), and Viburnum prunifolium (Blackhaw Viburnum).
The shrubs listed in this basic standard are the most commonly encountered shrubs; however, there are many more species that we may encounter. Do not hesitate to ask for help with identification as well as with recommended shrub pruning procedures for the more exotic species. It is only through such processes that we gain more knowledge and become better acquainted with the many woody plants on job sites.