By Larry Hodgson
I probably receive more questions about when to prune flowering shrubs than any other. Gardeners seem very concerned about the subject, as if trimming them at the wrong time of the year would kill them. In fact, though, if you prune a shrub at the “wrong” season, in most cases it simply won’t bloom that year and it will be back in flower the following season, so no great harm is done.
But of course, most of us prefer see our shrubs bloom every year, so it is worth learning the best season for each type. And actually that is pretty straightforward: prune spring-blooming shrubs after they bloom and summer- or fall-blooming shrubs either in the fall or, better yet, first thing in spring. Couldn’t be simpler!
To make it clearer, here are some examples and further explanations:
Shrubs that bloom in spring produce their flowers on “old wood”, that is to say from branches produced the previous summer. The only way they could possibly be in bloom so early would be if they had carried flower buds, dormant but alive, over the winter. The ideal time to prune them is therefore within two weeks after their flowers fade. This gives them time to produce lots of new bud-bearing branches for the following season.
Among the shrubs to prune after they bloom in the spring are:
- Azalea (Rhododendron spp.)
- Barberry (Berberis spp.)
- Beautybush (Kolkwitzia amabilis)
- Buffaloberry (Shepherdia spp.)
- Buttonbush (Cephalanthus occidentalis)
- Chokeberry (Aronia spp.)
- Cotoneaster (Cotoneaster spp.)
- Daphne (Daphne spp.)
- Deutzia (Deutzia spp.)
- Dogwood (Cornus spp.)
- Elderberry (Sambucus spp.)
- Flowering almond (Prunus spp.)
- Flowering currant (Ribes sanguineum)
- Flowering quince (Chaenomeles spp.)
- Forsythia (Forsythia spp.)
- Honeysuckle (Lonicera spp.)
- Kerria (Kerria japonica)
- Lilac (Syringa spp.)
- Magnolia (Magnolia spp.)
- Mockorange (Philadelphus spp.)
- Ninebark (Physocarpus spp.)
- Old roses (Rosa spp.)
- Ornamental cherry and plum (Prunus spp.)
- Pearlbush (Exochorda spp.)
- Privet (Ligustrum spp.)
- Pussywillow (Salix spp.)
- Serviceberry (Amelanchier spp.)
- Siberian peashrub (Caragana spp.)
- Snowberry (Symphoricarpos spp.)
- Spring-flowering spirea (Spiraea × vanhouttei and others)
- Spring-flowering witch hazel (Hamamelis vernalis, etc.)
- St John’s wort (Hypericum spp.)
- Viburnum (Viburnum spp.)
- Weigela (Weigela spp.)
- White forsythia (Abeliophyllum distichum)
- Willow (Salix spp.)
Even if you didn’t find your shrub on the above list, if you live in the Northern Hemisphere and your shrub blooms before mid-June, it is best to prune it after it blooms.
Summer and Fall-flowering Shrubs
Shrubs that bloom in summer or fall, on the other hand, produce their flower buds on new growth put on during the late spring. It therefore makes sense to cut them back (if they need pruning, that is) in early spring, as they come out of winter and before their new leaves are fully formed.
Or … prune them in late fall, before winter.
Usually these shrubs bloom after mid-June.
Among the shrubs to prune in early spring, you’ll find:
- Abelia (Abelia spp.)
- Beautybush (Callicarpa spp.)
- Bush honeysuckle (Diervilla spp.)
- Butterflybush (Buddleia davidii)
- Common Witch Hazel (Hamamelis virginiana)
- Dyer’s broom (Genista tinctoria)
- Fothergilla (Fothergilla spp.)
- Holly (Ilex spp.)
- Hydrangea (Hydrangea spp.)
- Japanese spirea (Spiraea japonica)
- Rose (most reblooming types) (Rosa spp.)
- Rose of Sharon (Hibiscus syriacus)
- Sea Buckthorn (Hippophae rhamnoides)
- Seven sons flower (Heptacodium miconioides)
- Shrubby Cinquefoil (Potentilla fruticosa)
- Silverberry (Eleagnus spp.)
- Smoketree (Cotinus coggyria)
- Sorbaria (Sorbaria spp.)
- Stephandra (Stephandra spp.)
- Summersweet (Clethra alnifolia)
- Sweetshrub (Calycanthus spp.)
- Tamarisk (Tamarix ramoisissima)
Shrubs Not Grown for Their Flowers
There are also many broadleaf shrubs that aren’t grown for their flowers, either because their flowers are fairly insignificant—the case of boxwood (Buxus spp.) and euonymus (Euonymus spp.), for example—or because they’re used for something other than bloom. Shrubs used as hedges or in topiary, for example, are generally pruned so as to maintain tight, dense growth and perfect symmetry, even if this suppresses most of their flowers. Examples of shrubs whose otherwise attractive blooms are pretty much ignored when they are grown as hedges include privet (Ligustrum spp.), Siberian peashrub (Caragana spp.), honeysuckle (Lonicera spp.) and ninebark (Physocarpus spp.).
You can prune hedges and topiary at pretty much any season, but most gardeners prefer to shape them in the spring (even if they’re full of flower buds), then to give them a bit of a trim in the heat of mid-summer.
Prune in Any Season
Do note that there is no specific season for removing dead or damaged branches. You can cut them off whenever you see them no matter which species you’re dealing with.
The same goes for suckers and any other growth you want to eliminate. Any time that suits you is acceptable. Just cut them right back!
Some shrubs “age badly” (spireas, lilacs, shrubby cinquefoil, etc.) and after 8 to 12 years start to look pretty ratty, with more dead branches than live ones, excessive height, a definite drop in symmetry and reduced flowering. If so, simply cut the shrub back to 4 to 6 inches (10-15 cm) high, a technique called rejuvenation pruning. You will be surprised how quickly it will grow back. Rejuvenation pruning can be carried out on almost any shrub.
The most logical time to do a rejuvenation pruning is early spring, no matter what the shrub.
There! That wasn’t difficult, was it?
Article adapted from one originally published in this blog on May 3, 2016.