Tried-and-trusted techniques to help plants to grow back more strongly than ever

• Published date: 05 May 2024
• Author: Fionnuala Fallon
• Publication title: Irish Times: Web Edition Articles (Dublin, Ireland)

The simple answer to all of the above, strange as it may sound, is that pinching out, pruning, and cutting back are all tried-and-trusted gardening techniques, which rely on a plant's innate urge to react to physical injury, by growing back more strongly than ever

When you pinch out a cosmos seedling or the young stem of a dahlia, for example, you remove its soft-growing tip. This growing tip is very rich in growth hormones and is responsible for a process known as apical dominance, which directs growth upwards rather than outwards. The seedling or plant's reaction to this physical injury is to quickly throw out multiple side-shoots positioned lower down its stem at intervals along its leaf axils, an ingenious survival mechanism that plants growing in the wild use as a means of surviving damage from grazing animals or harsh weather. So by deliberately inflicting this very targeted injury, you're using this natural defence mechanism to your advantage to produce a much more resilient, bushier, floriferous specimen.

The same goes for thoughtful, selective pruning which can be used to shape and train plants as well as to positively affect their flowering display. In this case, good timing is everything. For example, some (but not all) spring-flowering woody shrubs benefit from being pruned immediately after their seasonal display of blooms has come to an end. Examples include: forsythia; flowering currant (ribes); kerria; chaenomeles; exocharda; philadelphus; and very early-spring flowering varieties of lonicera. Prune them carefully at the end of spring and you encourage the plants to produce an abundance of young, healthy growth with the potential to flower abundantly the following year. Conversely, if you leave it to late summer, you'll be removing a lot of that same precious young healthy growth essential for next year's flowers. Meanwhile, any subsequent new growth produced as a result of your poorly timed pruning won't have enough time to ripen and develop nascent flower buds before the arrival of winter. So the result will instead be a poor display of flowers the following spring.

That's not the case, however, when it comes to cutting back late summer-flowering perennials in late spring, a useful way of delaying their normal flowering period by an average of two to three weeks. Known as the Chelsea chop, because its timing normally coincides with the staging of the annual RHS Chelsea Flower Show in London in late May, this technique allows gardeners to...