Why is Agave Utahensis v Nevadensis blue and Eborispina green?

I’m a sucker for blue plants. Particularly blue agave utahensis.

Blue-ness in leaves is caused by a waxy or powdery covering called pruina. Blue-ish plants are called glaucous. Studies show that glaucous leaves reflect a much higher percentage (80%) of UV radiation than green leaves (10%), protecting them from harsh sun light. This blue effect is a trait desired by collectors, and generally described as a feature of nevadensis, when compared to the other taxa of a utahensis.

Glaucous agave utahensis v nevadensis leaves

Studies have also shown that higher amounts of UV radiation are found at higher elevations. This altitude effect is somewhere between 2% and 4% per 1,000 feet. I think it’s reasonable to assume that the exposure to the entire solar irradiance spectrum (including infrared) increases with altitude. Experiments confirmed the relationship between glaucous wax, showing that dosing plants with increased UV-B levels increased wax production by 25% in all plant species investigated.

Green agave utahensis v eborispina

Nevadensis is known to generally be more glaucous than the greener eborispina (and the rest of the species). One possible explanation for this is altitude. In my experience, Nevadensis is mostly found growing 1,000 to 2,000, or more feet higher than eborispina. I have recently heard reports of green plants above 7,000ft deep in eborispina’s range but have yet to personally confirm this.

My own experiments show this is both a genetic and an environmental trait—nature versus nuture. Kaibabensis seedlings grown under the same conditions as nevadensis show much greener leaves. This is exactly what you’d expect given the documented descriptions of utahensis.

An agave utahensis var nevadensis seedling grown outdoors under shade cloth

But within the nevadensis variety, some seed batches show much more glaucous coloring than most, appearing almost white. And nevadensis grown close under high powered full spectrum LED panels are much more blue than seedlings from the same batch grown under shade cloth, with much less UV exposure.

One of my indoor, LED-powered, seed grown, blue agave utahensis var nevadensis

With some cactus and succulents, touching or watering a plant directly on the powdery glaucous coating can remove it, aesthetically voiding months or years of growing time. To counteract this, and increase the production of blue coloration, use fans to provide proper air circulation around your a utahensis.

Another green agave utahensis v eborispina