When to prune Spiraea, including the early flowering varieties and the summer flowering Spiraea

Last updated on April 22nd, 2022

Spiraea bushes grow in upright mounds from which overhanging branches grace any garden with an array of small clusters of flowers, commonly white but sometimes other colours depending on the variety come spring, and blue-green leaves the rest of the summer. These shrubs are a showpiece in themselves for nothing but the floral displays they create, which are made even more appealing thanks to their large size. In fact, mature plants can reach just shy of 2 metres tall. 

These shrubs do best when they are properly trimmed each year. Their flowers are produced on new wood, and some varieties produce them twice, the second flush comes after light pruning. Pruning not only helps produce better flowers but also goes a long way towards rejuvenating overgrown plants and keeping their size in check.

Pruning Spiraea once a year

Early flowering varieties

If you want to prune your Spiraea once a year to keep it within a certain size then we recommend pruning straight after flowering, which, in the UK, is usually around June for most varieties. These are all the early flowering varieties that flower in spring. Cut back the flowering stems hard, by as much as 60cm. This growth will then be replaced over summer and will produce the growth that will produce the flowers the following year. These varieties include the Spiraea ‘Arguta’, Spiraea ‘Snowmound’, Spiraea ‘Goldflame’, Spirea ‘Little Princess’ and the Spiraea japonica ‘Shirobana’.

Late flowering varieties

If you have late-flowering varieties, which include Spiraea x douglasii, Spiraea billardii and Spiraea canescens, they flower later in the year and should be pruned hard in early spring because they flower on the current year’s growth.

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Pruning Spiraea for the dedicated gardener

The question of timing has four parts, one for each season. There are pruning measures to be done in each season, each with its own purpose. 

Spring

Firstly, spring is when you want to prune the tips of your plant after the initial flush of flowers. Think of this as a cross between deadheading and pruning. 

To do this:

1. Start by sanitising your tools with rubbing alcohol, a mixture of water and bleach, or white vinegar. 
2. Sharpen your tools to ensure a quick, clean cut.
3. Trim the stem tips back from their highest leaf bud. 

Try to maintain the natural shape as you do this. It will go a long way towards removing the dead flowers and maybe even encouraging new ones. 

Summer

Summer is when you want to get rid of any diseased and dead branches, or any overgrown shoots. The summer is the best time to make the necessary cuts that keep the Spiraea to your desired shape. The cuts should be within 1-2cm of a bud or leaf, if possible. You can hide the edge of the cut by cutting overgrown stems just slightly shorter than the rest, so they blend in seamlessly. 

Autumn

Thirdly, autumn is when you trim back the overgrown foliage. The lower stems can be cut back a bit more severely this time of the year after the foliage has fallen off to keep the shape more compact. The stems can be cut back within 20-30cm off the ground. 

Winter

Finally, the end of the year brings with it another opportunity to get rid of dead and damaged wood. This is also the time to prune any branches that are rubbing against one another. If left unchecked, this will result in damage to the overall plant. 

It is very important to follow these seasonal recommendations. Spiraeas need regular trimming in accordance with the four seasons. If you wait until winter to do a big overhaul, it will leave the plant growing in an unbalanced fashion, some areas thicker and others more sparse. At a minimum, be sure to trim them twice per year.