Why pinch out dahlias?
Also known as stopping, pinching out is a technique used by gardeners to remove the tip (apical bud) of a plant to promote the growth of lateral (side) branches, resulting in a fuller plant and more flowers. The apical or terminal bud is the bud located at the tip of the plant where elongation and new growth occur. It was initially believed that auxins, a class of plant hormones produced in the apical bud, exerted an inhibitory effect on axillary (side) bud growth. However, recent evidence indicates that apical dominance strongly correlates with the availability of sugar. Essentially, the shoot tip’s demand for sugar is so high that axillary buds do not receive adequate sugar for growth.
The evolutionary drive of the plant is to grow up as quickly as possible in order to receive more light and undergo photosynthesis. By pinching out the apical bud, the dominance of auxins is removed and the dahlia diverts its energy into producing side shoots, which results in more flowers. Pinching out also produces a more balanced plant that is less likely to topple over.
Pinching will delay the onset of flowering, by a few weeks, but you will be rewarded with more blooms.
When and how to pinch out dahlias
Pinch out dahlia plants when they have four true leaves on the centre stalk and the plant is 25 cm (10 inches). Avoid pinching on a wet day to reduce the risk of infection and always use clean and sterile tools.
- Locate the apical bud, at the tip of the plant.
- Using a sharp pair of scissors or secateurs to ensure a clean cut, snip the very top bud as close to the node/pair of leaves below the bud.
Deadheading for more flowers
Another way to increase the number of flowers your dahlias produce is to regularly deadhead. Faded and dead flowers are removed before they go to seed. Seed production takes up energy, removing the flowers diverts the plant’s resources into producing more blooms.
Should all flowering plants be pinched?
No, flowers with a single stalk or flower spike such as delphinium, foxglove or sunflower should not be pinched.