Pruning is essential to keep control of shrubs

Spiraea billardii needs to be pruned after flowering.
Spiraea billardii needs to be pruned after flowering.

While herbaceous perennials are cut down to encourage regeneration or make way for new colour, don’t neglect the pruning of hardy shrubs that flowered recently.

Think about next year’s forsythia display, for example. This shrub is normally pruned immediately after flowering in April, the stems that have just carried bloom being removed, making way for new shoots that mature over summer. If the pruning opportunity was missed earlier and this shrub is growing too tall, reduce it now, while time remains for growth recovery.

Spiraea billardii is still covered in rose-coloured flower spikes, but as soon as they fade I’ll step in with secateurs with a similar pruning strategy. This plant is notorious for suckering, but the positive aspect of that is that you can lift and pot up, then offer to friends a rather attractive shrub.

The bridal wreath (spiraea arguta) is looking drab now, a far cry from the gorgeous white flower sprays some weeks ago, but we must not let it get too congested with growth. Thin out the centre and shorten some of the longer branches if it’s encroaching on nearby plants.

When a favourite shrub becomes overgrown and ages, as the veronica (hebe) of an acquaintance has, pruning is not always the answer. It is reasonable to follow each stem down from the tip, looking for signs of active buds or young shoots, and reduce it to that point. But pruning any deeper into old wood rarely elicits a response.

We have a large broom (cytisus) that has grown up to about 2.5m, with a thick woody main stem. After 15 years it would not respond with new growth if pruned back to old wood. The options are to trim it as far back as possible, or replace it. A young plant growing alongside was put there with the latter in mind so we’ll remove the giant, encourage the dwarf and restore control.

Whenever a popular shrub is introduced there has to be a realisation that regular annual pruning at the correct time is essential to keep it within bounds, encourage flowers and extend its life expectancy.

The likes of mallow (lavatera) and butterfly bush (buddleja) soon become woody and develop brittle stems without attention, whereas given regular pruning, you can expect at least a decade of healthy performance. Both are easily raised from stem cuttings, soft and hard wood respectively, that there should be no need to buy replacements.

We often expect too much of shrubs in terms of longevity. Less vigour, disappointing performance and greater susceptibility to disease emerge with time. This said, there are exceptions.

We have two escallonias and three Osmanthus burkwoodii (all standards with thick main stems) that still offer vigorous displays after two decades. This is a clear example of ‘if it ain’t broke, don’t fix it’.