Cut down to size - the art of pruning
Getting over-grown? Time to get out the pruning shears
When shrubs leaf up in spring, it is not unusual to think how much bigger they seem and of course they have just grown a new layer of extended twigs and small branches. Faced with shrubs that are getting too big, most of us think we should cut them back. But if there is space for a shrub to grow, why not allow it to grow to its full size?
But often, there is not enough space available, and size reduction is necessary. Flowering shrubs generally benefit from a little careful pruning. It helps to maintain a good display of flowers and prevents the shrubs getting too big, or growing lop-sided or out of shape. The aim should be to encourage the replacement of old shoots by new ones, removing some of the old ones completely, from where they arise on larger branches or from the ground.
Shrubs are plants of woody growth but do not produce a big trunk and main limbs as trees do. Instead, they make many woody shoots from the base or, at least, from low down. Trees, by contrast, have that single or, at most, two or three large main stems. The result of a shrub having no big stems is that it does not have the structural capacity to grow tall, more than a few metres at most. So shrubs have a more twiggy appearance.
This is made more complicated by the inclusion of species in the lists of shrubs that are actually small trees, such as small Japanese maples, pieris, rhododendrons and camellias, even pittosporum in small forms. These are trees, as are lilac, hoheria and magnolia, often considered to be shrubs, an eye-opener 50 or so years on with trunks and strong branches, and standing at 10m tall in some cases. Crinodendron, or Chinese lantern tree, is sold as a shrub can manage 10m tall and 10m across.
Most small trees, treated as shrubs, are simply not pruned at all, like those mentioned, and they are only pruned when they have grown big, removing low branches to allow access. These plants may need to have an occasional wayward shoot removed.
Shrubs like forsythia, weigela, philadelphus, deutzia, spirea, viburnum and many others produce new shoots sprouting from lower down on, or along, existing branches. The new shoots replace old shoots, flowering and, in turn, some of them might be out-competed by other branches. So pruning very often simply reflects a replacement programme that happens naturally, but somewhat more messily.
Most shrubs flower in spring or early summer on buds formed during the previous summer, such as forsythia, flowering currant and ceanothus. But some kinds flower on current year's growth, such as fuchsia, roses and buddleia, which can be cut hard back in spring. Whereas, if that were done to previous season shrubs, all the flowers would be cut away.
As a general rule of thumb, shrubs flowering before July can be pruned immediately after flowering. Later-flowering kinds can be pruned in winter or early spring. Very many flowering shrubs need no pruning or very light shaping of the bush.
Too much pruning affects flowering and shapes a bush unnaturally. Hedge-clippers shouldn't be used on shrubs as there is a tendency to make them rounded, spoiling their natural outline. The exceptions are small shrubs like lavender, rock rose and heathers.
Sometimes, if growth has been poor, people have a mistaken view that a hard pruning will help. While this can encourage new growth to replace that cut away, which was healthy anyway, it can also weaken the plant further.
If a shrub has grown too big and cannot be thinned out, another method is to cut the plant right down to ground level. The cut stumps will sprout again and the shrub will regenerate itself. This drastic treatment should be carried out in April.
DON'T MISS A TRICK
n If you're heading to the annual Bloom festival in Phoenix Park (May 31-June 4) to browse the 20 show gardens, stalls and workshops, be sure to pop into the OPW marquee where some of its beautiful heritage sites, such as Garinish Island, pictured, are on show. Bonus? Expert gardeners from the walled garden in the Park will be at the OPW marquee to answer your garden queries. Bloominthepark.com
ADD A LITTLE ROCK CHIC
n Rock rose or helianthemum is a delight from the moment it opens its small rose-like flowers in a sheet of colour on a low bush, often planted to trail down a bank or over the edge of a low retaining wall. It flowers in yellow, orange, red, pink and white over green or grey foliage. It is easy to grow and long-lived.
CATCH IT QUICK
n The Burren is unique. A limestone plateau on the Atlantic edge, its dazzlingly complex history gives rise to an endless variety of landscape forms. Colonised by myriad wildflowers including Arctic, Alpine and Mediterranean species, and modified by humans over many millennia - be gob-smacked at the 'Secrets of the Fertile Rock' until Wednesday, May 30. Education & Visitor Centre, National Botanic Gardens, Dublin 9; botanicgardens.ie