How do vines stick to the wall?

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For the grown-up

The story shows one kind of vine, Boston ivy. Here is what is going on underneath, what to ask, and what to try outside.

What the vine is doing

Reach. Boston ivy and Virginia creeper grow thin arms called tendrils. Each one splits into five to nine little fingers that grow out until one bumps into something.
Touch. A fingertip only turns into a pad after it touches. Darwin watched the tips swell and turn red about two days after contact.
Squish. The pad flattens and lets out a sticky fluid. The fluid runs into the pits and cracks of the wall, so pad and wall fit together like puzzle pieces.
Stick. The fluid hardens. The tendril then coils into a spring, which pulls the stem toward the wall and lets all the pads share the load when the wind tugs.

How strong is one pad?

One pad is about a millimetre across and weighs about half a milligram. Tests found it can hold around 2.8 million times its own weight. That is roughly a 1.4 kg bag of flour hanging from a dot the size of a pinhead.

Darwin tried it in 1875. He hung a two-pound weight from one finger of a Virginia creeper tendril that had been out in the weather for ten years, and it held.

A vine has thousands of pads. They hold so well that they stay behind as little dots when someone pulls the vine off.

Three ways vines climb

Sticky pads: Boston ivy, Virginia creeper. Look for tiny round dots on thread-like arms.
Clinging roots: English ivy, climbing hydrangea, creeping fig. Short roots grow straight out of the stem. Their root hairs push into cracks, let out glue, then dry and curl, which pulls the root tight against the wall.
Wrapping: Beans, morning glory, grapes, peas. These twist around a pole or a wire. They cannot climb a bare wall, which is why they need a trellis.

Questions to ask

Before you start: “How do you think it holds on?” Let the guess stand, then find out together.
“Why does the vine want to go up?”
“Could it climb a window?” English ivy cannot hold on to glass for long.
“What else holds on with lots of tiny things?” Velcro, a gecko’s toes, your own fingers on the monkey bars.

Try it outside

Vine hunt. Find a vine on a wall or a fence and gently lift a leaf near a growing tip. Dots on threads, or short brown roots?
Handprints. Look for a wall where a vine was pulled off. The pads or root marks are still there.
Feel the wall. Rub a brick, then a window. Look at the brick through a magnifying glass, or a phone camera held close.
One or many. Tape a strip of paper to a table edge with one small piece of tape and tug it. Then use ten pieces.

Where this comes from

Charles Darwin, The Movements and Habits of Climbing Plants (1875), on Virginia creeper.
University of Michigan, Climbers: Boston ivy, for tendril structure and pad strength.
Kim, Adhesive disks of Boston ivy during attachment (2011), for the fluid filling the wall’s pits.
Melzer and others, The attachment strategy of English ivy (2010), for clinging roots and glass.

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