Hedge Bindweed put on a great show this year with lots of hedgerows sporting the plant's large, white, trumpet-shaped flowers. While attractive in the wild, it is an unwelcome species in gardens as it can become a troublesome weed.
However, sustained pulling out of the straggly shoots soon weakens the root and the invader can be easily eradicated with persistent effort over a number of years.
Compared to the large flowers, the stems are straggly, skinny and wiry. They are so skinny they cannot support the plant, so they cling to any structure to hand. They twine around the branches and twigs of a garden hedge always growing upwards but doing so spirally in an anticlockwise direction. But how can they always grow in an anticlockwise spiral?
Plants have hormones in the same way that we have. Plant growth hormones are a small family of chemicals called auxins. Auxins are found in cells in tiny quantities. They are more concentrated in the growing tips of plants and it is that increased concentration that causes the tips to grow. More hormone means more growth.
Plant shoots always grow upwards, so it appears that plants 'know' up from down. Auxins respond positively to light and negatively to the pull of gravity. The combined effect of their positive response to light and their negative response to gravity causes auxins to migrate to the tops of cells thereby concentrating maximum growth there resulting in the plant growing upwards towards the light and away from the pull of gravity.
In addition to that, auxins are sensitive to touch, not just any touch but in Hedge Bindweeds touch specifically on the left-hand side. So, if the tip of a shoot growing upwards in a hedgerow touches a twig on its left-hand side, the cells immediately respond by diffusing auxins to the right-hand side of the cells and tissues.
The resulting increased concentration causes the right-hand side to grow faster than the left resulting in the shoot turning to the left. The more the plant touches on the left the more it grows on the right causing the skinny shoot to twine anticlockwise around the twig while growing upwards all the time.
In addition to auxins, other chemicals are involved either by increasing their concentration or by blocking their impacts. Exactly how Hedge Bindweed manages to scramble through hedgerows by always twining around supports in an anti-clockwise direction is still the subject of ongoing investigation.