This is one of a new series of posts based on real questions I have been asked. Feel free to add to the answers or include your ideas and experiences
As I mentioned a few days back, it is always best to prune a shrub from an early age, for various reasons. Formative pruning can help encourage low-down bushiness and although that means the plant is slower to gain height, and may delay flowering, the advantage makes it worthwhile.
A few plants need pruning from early on in their life. These tend to be quick-growing, short-lived shrubs and include artemisia, cistus, cytisus, ceanothus, genista, lavender, santolina and sage. They tend to be shrubs that like well-drained soil, full sun and could loosely be called ‘Mediterranean’ though not all are strictly Mediterranean. These all grow quickly and, without pruning, can become loose in habit and bare at the base. Some can be pruned hard if they get overgrown and you can rejuvenate most artemisias and santolina with a hard prune in spring, but lavenders, famously, will not sprout if cut back into bare wood.
The same is true of cytisus, which was the subject of a question that asked ‘Can I cut an overgrown broom bush back hard after flowering and will it sprout from the old wood?’
The answer includes yes and no. The right time to prune a broom (cytisus) is immediately after flowering, before the seed pods form. They usually set lots of seed and this reduces the summer growth and then the flowers the following year. So they need a shear immediately the flowers fade. Every year – from year one. Unfortunately, if you leave them several years, so they get straggly and bare at the base, they cannot be cut back into the old stems because they rarely sprout from these bare stems. If there is no alternative you may have to risk it but it is best to start the pruning early.