I’ve often found it hard to know what shrubs needed pruning when, and with all the new shrubs I have planted or plan to put in this year, this task will get even harder. To help me this year, I’ve made up a pruning schedule by major time of season. If you are reading this schedule it may benefit you to know that my garden is in Southern Ontario and is in zone 5.
My schedule is based on early spring, spring (after flowering), summer and fall pruning times. To know the best way to prune a shrub it is also helpful to know the natural shape of a shrub. Good pruning should enhance the natural shape rather than work against it. Shrubs can be broadly classified as mounding, caning and tree-like and each should have a different approach to pruning.
Early Spring (March – April) before new growth appears
My Spring pruning schedule includes three major activities
- trimming evergreens for shape (boxwoods, cedars and yews);
- cutting to the ground fast growers (a pruning technique known as coppicing); and
- thinning and shaping some flowering shrubs.
Remove damaged or dead foliage and branches, trim for shape. Make sure lower branches are wider than top. Evergreens to prune before spring growth starts include:
- BUXUS (Boxwood)
- EUONYMUS (Broadleaf varieties)
- TAXUS (Yew)
- THUJA OCCIDENTALIS (Cedars)
- CHAMAECYPARIS PISIFERA
As noted earlier, some shrubs benefit from severe pruning. Heavy pruning stimulates rapid growth which will encourage better foliage colour and larger flowers. It also helps keep plants to a manageable size with a neater habit. The stems can be cut back to within 20cm (8 inches) of the ground. Plants in my garden that I prune to the ground include:
- CARYOPTERIS (Bluebeard or Blue Mist shrub)
- CORNUS CERISEA (both my yellowtwig and redtwig dogwood varieties)
- HYDRANGEA ARBORESCENS ‘Annabelle’ (it gets floppy if I don’t)
- POTENTILLA FRUTICOSA
- PRUNUS CISTENA (some I prune this way, others I use renewal pruning)
Renewal pruning, shaping and thinning
The remainder of my early spring pruning is focused on shaping and thinning. I try to prune about 1/4 to 1/3 of these plants every spring in the hope I can avoid heavier renewal pruning down the road. My process involves three main steps:
- Remove any dead or damaged branches along with any branches that look bad (for example are growing down instead of up – except in the case of weeping plants of course, are crossing other branches etc.).
- Remove up to 1/3 of old branches at the base of the plant or the base of another branch.
- Trim the tallest of the remaining branches about 1/5 of the height to encourage branching and to achieve an overall shape.
AZALEA – remove any damaged or dead branches. Azaleas set bud just after flowering so many azalea web sites recommend pruning for renewal take place before new growth so there is enough time to set buds for next year. After growth starts, trim new shoots to encourage branching. Azaleas are slow growing so little pruning is necessary unless the shrub has become overgrown. In my garden I mostly focus on pruning out damage wood and a little bit of shape pruning immediately after they flower.
ROSES (non-climbing) – after frosts, remove any damaged or dead branches. Shorten remaining branches to 4-5 buds.
CLETHRA ALNIFOLIA – remove any damaged or dead branches and prune for shape where I have not done this in the fall.
CORNUS ALBA ‘ELEGANTISSIMA’ AND ‘IVORY HALO’ and some SERICEA- because of the location of these dogwoods in a garden close to the house, I do not prune these to the ground for aesthetic reasons. I remove about 1/3 of old branches to the ground every year (thinning), trim the remainder about 1 foot for shape and branching. Cornus Alba bloom on old wood however the flowers are insignificant compared to the foliage so I prune before new growth begins.
HIBISCUS SYRIACUS (Rose of Sharon) – similar to Clethra, remove any damaged or dead branches and prune for shape if I have not done so the fall before.
MORUS ALBA ‘PENDULA’ (Weeping Mulberry) – prune severely back to main leaders. This plant will need to be pruned again in summer. See Summer pruning section.
PRUNUS CISTENA (Purpleleaf Sandcherry) – As with my Ivory Halo dogwoods, I do not prune many of my Sandcherries to the ground but I do like to keep the foliage bright and stems on the small side. I also find this helps with the tendency of a Sandcherry to split at crotches. I start by cutting up to 1/3 of the larger branches to the ground, cutting back the remainder about 12 inches for shape and branching. Prunus Cistena flower on old wood so I may lose some flowers this way but find it easier to prune before the plant leafs out. I had to spend 3 years rejuvinating a few old Sancherries by cutting out some very large branches using this method and they have come back very nicely.
SAMBUCUS ‘SUTHERLANDS GOLD’ – grown mostly for foliage although mine was only planted late last year. I will likely just prune the tips to encourage new growth this year then follow up with usual renewal pruning depending upon how vigorous the growth is this year.
SPIRAEA (summer blooming varieties bumalda and japonica) – prune out oldest and most twisted branches to ground to maximum of about 1/3. I have on occasion pruned these to within 20cm (8 inches) of the ground if they were overgrown and they came back by summer.
VIBURNUM TRILOBUM – Remove oldest canes and crossing branches before new growth emerges. Thin oldest canes to the base.
WEIGELA FLORIDA – remove any dead or damaged branches. Thin out up to 1/3 of oldest / biggest branches as well as any ugly branches. Like Prunus cistena, I find it easier to prune before the new growth starts. Weigela are said to flower on old growth but in fact will flower on new stems that branch off from old growth so by stimulating vigorous growth I actually extend the bloom time.
Late Spring – Early Summer Pruning
Plants that bloom early on last years growth
Please note that in the early spring pruning section I have already pruned some of these and sacrificed some flowers. For prunus cistena my main show is foliage not flowers so for me, this is not critical. For Weigela I find I do not sacrifice significant flowers as the amount of pruning is small and the vigorous growth actually extends the bloom time.
BERBERIS – Remove dead, oldest or poorly shaped branches. Prune for shape after flowering.
CORYLUS AVELLANA (Corkscrew Hazel) – Remove dead, oldest and straight shoots. Prune for shape.
CORYLUS MAXIMA PURPUREA (Purple Filbert) – Remove dead and broken branches. Prune for shape.
DEUTZIA – after flowering, remove about 1/3 of old branches and cut back remainder by about one quarter. Deutzia can be unruly unless heavily pruned.
FORSYTHIA – after flowering, remove any old branches. Thin by pruning out up to 1/3 of oldest branches or canes to the ground. Can be cut to the ground immediately after blooming to rejuvenate old plants.
HAMAMELIS (Witchhazel) – Little pruning is necessary except to remove damaged wood and to maintain shape.
ITEA VIRGINICA – Sweetspire blooms around June – July on old wood. The only spring activity should be the remove of dead and broker branches. In addition you may need to remove any lingering foliage to encourage new growth. Prune for shape immediately after it is finished blooming.
MAHONIA – in zone 5 we seldom see flowers since the foliage often suffers from winter burn. Prune any severely damaged growth. Also prune to encourage branching as Mahonia can get leggy in zone 5. Remove any suckers.
MOUNTAIN LAUREL – carefully remove spent flowering by pinching them being careful not to disturb buds just underneath. Remove old growth to ground to encourage regrowth.
PIERIS JAPONICA – Pinch off dead flowering being careful not to disturb buds below. Remove any dead or damaged branches before growth begins. Pieris are slow growers so little pruning is necessary but should be done before new growth starts. As mine are still very young, very little pruning other than to remove damaged branches is likely necessary.
PINE / SPRUCE – I haven’t yet pruned any of my needle evergreens with the exception of my MUGHO PINES. To control the growth and shape of these shrubs I selectively remove or cut in half some of the candles each year.
PRUNUS CISTENA (Purpleleaf Sandcherry) – If not pruned earlier remove up to 1/3 of the larger branches to the ground, cutting back the remainder about 12 inches for shape and branching.
PYRACANTHA – prune for shape after flowering. Heavy pruning will eliminate fall berry production.
ROSES (Climbing) – cut back stems that produced heaviest flowers and encourage branching for second flush of flowers and buds for next year.
RHODODENDRON – carefully remove spent flowering by pinching them being careful not to disturb buds just underneath. Remove old growth to ground to encourage regrowth. Prune for shape before growth starts to allow enough time to set buds for next year. Mine are small so little pruning will be done in early years.
SPIRAEA (spring blooming varieties betulifolia ‘Thor’, cinerea ‘Grefsheim’, vanhouttei) – prune out oldest branches to ground to maximum of about 1/3 and reduce remainder of plants by up to 2 feet.
SYRINGA (Lilacs) – prune immediately after blooming to allow enough time for buds to set for next year. Remove young suckers, older canes and dead wood.
VIBURNUM PLICATUM VAR. TOMENTOSUM (Doublefile Viburnum) – prune immediately after flowering.
WEIGELA – prune out oldest branches and reduce height if not done earlier.
Summer Pruning – plants that bloom in summer and rebloomers
EVERGREENS – trim for shape if needed again. Do not prune any later than early September.
HYDRANGEA MACROPHYLLA ‘Endless Summer’ – remove spent blooms to encourage new growth and new blooms
ROSES (Shrub) – remove spent blooms until about mid-August. Leave remainder of blooms to allow for development of rose hips (except in new plants as rose hips use up significant plant energy).
SPIRAEA (rebloomers such as Neon Flash) – deadhead initial bloom for both aesthetics and to encourage a second rebloomer later in the season.
Fall Pruning – cleanup for winter
ROSES – lightly prune and remove any extra long stems to avoid winter wind damage.
HIBISCUS SYRIACUS (Rose of Sharon) – removing seed heads will significantly reduce the amount of babies in the garden in spring. Severe pruning now however can hurt winter hardiness.