• Alison Murray

Things to do in the garden during lockdown day 79: discover how some plants avoid getting wet

The leaves of some plants are expert at repelling water. Being hydrophobic is their superpower. So how do they do it? And why?

water on nasturtium leaf
water on Alchemilla mollis
Alchemilla mollis

Alchemilla mollis is known for being a master at repelling water. The raindrops sit like beads on its leaves. Apparently nasturtiums are even better at this than the alchemilla, and it's all down to surface chemistry and each plant has its own way of keeping the water out.

Alchemilla and lupin leaves have tiny vertical hairs densely pack together, which stops the water from sinking into the leaf so it sits on trapped air on the surface, a bit like a ping pong ball on a hairbrush. The most famous example of superhydrophobic plants is the lotus leaf, Nelumbo nucifera. Nastrurtiums, (Tropaeolum majus) like the lotus, do things differently and have waxy nano-bumps on the leaf surface, the spacing of these nano particles is crucial to keeping the water away. Nasturtiums take first prize for being the most hydrophobic plants on the planet.

Not only does it stop the water sinking in and bringing fungal and bacterial infections with it, but the droplets pick up tiny particles of dirt and dust as they roll off onto the ground. A super-self-cleaning waterproof surface. Nature at its coolest.

Red rose petals (I'm not too sure how the colour plays a part) work slightly differently. The water sticks on slightly larger micro-bumps or papillae, but these in turn have nano folds stop the droplets from sinking in, so they don't role off, but the petals don't get wet either. I've just dashed out into the garden to check this out, and sure enough the water is sitting on my rose in a different way to those on the nasturtium and alchemilla leaves.

Even groovier, some aquatic plants trap the air in between the nano-structures on their leaves whilst they are underwater, so they can obtain oxygen whilst submerged.

There is a fab article from materialstoday here and another on alchemilla leaves here if you want to discover more.

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