We all know that July is the time for pruning roses. But when do you prune all the other shrubs in the garden? And why prune them at all? There are three distinct groups of deciduous shrubs – each of which should be pruned at a different time. The hydrangea is the local anomaly.
There are three reasons why you prune. Firstly, pruning promotes the healthy growth of young and productive wood by cutting out of spent growth, weak shoots and dead wood. It will also improve growth by admitting light and air into the plants.
Pruning is also a great way to retain the natural form of the shrub by shortening branches. And, finally, pruning usually increases the size and quality of blooms. By not pruning, some shrubs soon become nothing but a mass of weak and tangled shoots totally incapable of bearing any but the smallest and weakest of flowers.
Three groups
With evergreen shrubs there is no hard and fast rule as to when to prune. With deciduous flowering shrubs, it is essential to prune according to their time of flowering. If the shrub is pruned at the wrong time of the year, you will remove all the flowering wood and it will then be impossible for the shrub to carry any blossom at its proper flowering time.
There are three distinct groups of deciduous shrubs – each of which should be pruned at a different time of the year.
* Prune in late July: This group flowers in summer on growth developed in the current season. Cut these shrubs back fairly hard in winter to promote ample new growth in early summer for flowering. Examples: Buddleja davidii, Chinese plumbago (Ceratostigma willmottianum), Calycanthus floridus, Caryopteris, St John’s wort (Hypericum spp.), Potentilla fruticosa, ribbon bush (Hypoestes aristata), Spiraea japonica “Goldflame”.
* Prune in late October: Shrubs flowering in late winter and early spring on growth made the previous summer. Shrubs in this group should be pruned directly after flowering so that ample new growth can be made during the following summer. Examples: Prunus glandulosa, flowering quince (Chaenomeles spp.), Kerria japonica.
* Prune by thinning-out: Shrubs flowering in summer on stems that developed during the previous growing season. These are best pruned by the removal of old stems at the base of the shrub. Examples: Abelia, Buddleja alternifolia, Deutzia scabra, mock orange (Philadelphus spp.), banksia rose (Rosa banksias), Cape May (Spiraea cantoniensis), Weigela spp.
Pruning anomaly
Experienced horticulturists such as Randburg’s Andrew Balfour, have always regarded hydrangeas as the anomaly of deciduous shrubs.
As the flowers of the common garden hydrangea (Hydrangea macrophylla) are borne in summer on the old wood, pruning should theoretically be carried out directly after flowering in late January – by removing the old canes and by dead-heading the previous year’s stems which only bore a single flower. “In practice however, the pruning of hydrangeas in South Africa is most successfully carried out in winter when the leaves have dropped from the dormant plants”, advises Balfour.
Hydrangea pruning
When you look at hydrangeas in July, you will find that there are different types of wood, according to age. How you prune a hydrangea stem depends on its age. Here is a step-by-step guide:
* Young stems. There are young slender growths of the previous summer reaching up from the base of the plant. At the end of this stem there is a large bud. This bud, in the next growing season, will produce a short shoot and then a flower.
* Mature stems. There are also mature (slightly older) shoots two seasons old. At the end of these stems there is a dead flower (if not removed by dead heading), while a short distance down the stem will be found a cluster of large buds usually four to six in number. These, if left, will each produce a flower the following summer.
* Old stems. All you need to do is prune the old stems back to just above the cluster of buds. Very older, heavier stems of two or more seasons will also be found, carrying several dead flower heads, and these should be pruned back hard to the base of the plant.
A word of caution: never get too enthusiastic when pruning hydrangeas. If the entire shrub is pruned back hard to the base, or if the stems are pruned to half their length, then it is possible that the flowering buds could be removed. And if the buds go, you won’t have flowers in midsummer. - Saturday Star