In order to maintain a shrub’s intended shape a thinning method of pruning is required. By no means will I attempt to describe every situation in this limited space.
By merely stating to prune shrubs, we are generalizing. Some of us understand pruning as giving a shrub a haircut. In general this is not the right remedy in all cases.
Exceptions are where the shrub is planted in the wrong place i.e. in front of a window. In this case one must consider the species growth habit.
This practice can result in creating a thick bush that is very difficult to remove older wood from. It can become so dark inside the crown that new growth’s only choice is to shoot skyward, leaving bare legs at the bottom. I am sure we have all seen this sort of display in older gardens in Chilliwack.
On the other end of the scale is the ridiculous pruning of the Memorial Hydrangeas at the Chilliwack Middle School. They are cut back hard each year so they have no chance to ever flower.
This has bugged me for years. Pruning flowering shrubs is not generally understood. For most species this means removing one third of the older shoots to as close to the ground as possible, after the second year of growth and thereafter.
This should be done the minute the flowers fade. If we wait too long we will be cutting out new growth and potential flower buds. In this group fall some common shrubs like Abelia, Deutzia, Flowering red currant (Ribes). Forsythia, Kerria Japonica Pleniflora, except for Kerria Variegata only remove old and dying wood. Beautybush (Kolkwitzia Amabilis). Leucothoe, Philadelphus, Potentilla, Rosemarinus and Lonicera nitida (shrubby evergreen honeysuckle)
Follow this by giving the shrubs a good shot of nitrog
en to stimulate new bud growth for next year’s flowers.
Shrubs requiring little or no pruning include Hibiscus Syriacus, Hamamelis (Witch Hazel), Camelia, Callicarpa, Skimmia, Spiraea, Syringa (Lilac), Viburnum, Pieris Japonica ( I cut ours after the first flowering to get the red foliage for a second time). From the foregoing occasionally remove long shoots or branches. Pyracantha, (firethorn), Winter Jasmine, trim or train as required, Photinia can be cut back moderately hard. Mahonia (Oregon Grape). Remove terminal clusters of foliage after flowering to encourage side growth.
Now the ones that the growth is cut to near ground level in late winter before flowering include:
Hardy Fuchsia, Spiraea Anthony Waterer, Cornus Alba types, i.e. C.a. Flavoramia, Elegantissima and Oxidentalis (other Cornus need no pruning).Salix (ornamental shrub Willow and Buddleja to 4”.
A tricky one is Lavatera Barnsley, cut all shoots produced in spring and summer to within 2” in mid to late spring to encourage strong flowering shoots. This prevents the shrub from dying out. It is important to wait until new growth begins.
This is definitely not the whole story. There are more variables. Consider some questions if you are not clear on this.
Flowering shrubs are one of my favourite subjects. I grow quite a few of them. They add a lot of interest to a garden, whether in mixed plantings or stand alone.