A bit of agave magic

One of my favorite plants from our recent Santa Barbara trip to San Marcos Growers is Agave horrida. The clone most frequently seen in cultivation, tissue-cultured by Altman Plants, is very nice (here is Kyle’s specimen), but the San Marcos plants are even more beautiful:

Agave horrida from San Marcos Growers

Take a good look at the photo above, especially at the marginal teeth and the spines at the end of the leaf tips. They’re light gray, right?

Imagine my surprise when I watered my plant:

Same plant with wet teeth and spines

Whaaaat? The teeth and spines are almost black now!

Here’s a short video that shows the transformation even better:

What kind of alchemy is that?

I knew it had to be an optical phenomenon, and Google provided the answer: Agave teeth and spines change color when wet primarily because the water temporarily alters the way light reflects through their translucent outer layers. This highlights the underlying pigments and microscopic textures, creating a deeper, darker hue that vanishes as the teeth and spines dries out.

If your eyes are starting to glaze over, stop here. If you’re still mentally engaged, here is a closer look at the mechanisms behind this color shift, as per the all-knowing internet:

• Dry spines often have a microscopic waxy coating that scatters light, making the color appear muted or gray. When moisture is introduced, it fills these microscopic gaps, acting as a clear lens that allows light to penetrate deeper and reflect the natural melanin (dark color) of the spine.
• Some agaves absorb dew or rainwater directly through their spines and specialized cells. As the spine absorbs moisture, turgor pressure (water weight within the cells) increases, which can slightly expand the tissue and alter the color.

Physics was one of my least favorite subjects in high school. I won’t profess to know exactly what makes my Agave horrida change color, so I’m OK with calling it magic.

© Gerhard Bock, 2026. All rights reserved. To receive all new posts by email, please subscribe here.