Alison Marsden, Gardening by Design
Why do we prune shrubs at all?
Bushes growing in fields and hedgerows continue to flower and produce fruit year after year without intervention from a gardener. So why do we need to bother understanding the how and when of pruning?
Left to their own devices shrubs grow taller and wider each year and often the flowers appear on the ends of the branches. In general we prune flowering shrubs to keep them to the size that we want whilst producing a good crop of flowers each year. I recommend that you consult a comprehensive book on the subject if you have major work to do on any shrub, especially if it is rare or expensive but there are some simple guidelines that apply to most flowering shrubs that you are likely to have or to plant as you start out as gardeners.
When?
Ô Shrubs that flower in spring or early summer generally flower on stems that have grown the previous year. This is because stems that grow in the current year have not had enough time to grow and mature in order to produce flowers in April, May or June. Shrubs that flower in mid summer or later generally flower on stems that have grown the same year because they do have time enough to mature.
Ô The best time to prune all flowering shrubs is just when the primary flush of flowers has faded. This means that for early flowering shrubs, such as Forsythia, you should prune by June and this allows enough time for the stems to regrow that will flower next year. If you prune these shrubs in the autumn or winter when they have finished growing you will cut off all the flower buds that are waiting for next spring. This is only a temporary loss though as the cycle will recover the following year.
Ô Shrubs that flower mid to late summer, such as Buddleia, can be pruned any time from the end of flowering until they start to grow again the following spring as you are not losing any flowering wood in this period.
How
Ô Check how much growth you get each year to decide how much you need to prune off to keep the shrub at the size you want. The current year’s growth is more flexible than the old wood and usually a brighter colour.
Ô Check to see if the shrub regenerates from old wood before doing really drastic pruning. Often you will see small shoots sprouting from stems at the base of the shrub: if so then you know that you can cut it hard back and encourage totally new growth – this may sacrifice a year’s flowers but is worth it to regenerate a shrub that otherwise you would consider removing.
Ô If you do not see new growth at the base, then prune hard 1/3 of the old wood and see what happens next spring. If it sprouts back then go ahead with the rest; if not then the shrub has not been irreparably damaged and you can decide whether you want to keep it or not.
Ô Remove all dead and diseased wood when the plant is dormant in the winter, regardless of when it flowers.
Ô Try to prune to create a balanced shape with an open centre. This allows light and air to the whole plant and gives a pleasing shape. It is often described as a ‘goblet’ shape.
This is necessarily a quick sprint through the basic principles but as with many things in gardening a clear view of what you are trying to achieve coupled with an understanding of how the plant grows will get you a long way.