Reading Agave Leaves

What is it saying?  

If you are not familiar with Agaves, it might seem they don't change all that much, but lighting conditions affect them as much as any other plant.  For example...
Here's a small Agave parryi truncata grown all its life in full sun:

  This is also an Agave parryi truncata of the same size and age as the first.  Note the elongation of the outer (oldest) leaves:

 Why does it look so different?  Because it was covered up by a mass of Cistanthe grandiflora.  It was growing in darkness.  The newest, innermost leaves resemble the previous Agave, because this plant has been back in the light for several months.  In low light levels, the leaves elongate and flatten out so they and the plant's central growing point can maximize what light they receive.  

Here's Agave ellemetiana, which doesn't require nearly the sun that A. parryi does, but it displays the flattened posture of an Agave that would like more light.

Same thing with this A. gypsophila.  The rose that has shaded it was described as "compact".  Hah!

Another example:  Agave pygmeae 'Dragon Toes' was shaded out by an oak tree.  Note that while the newest leaves at the center of the plant are vertical, the oldest leaves are horizontal, in an attempt to gain more light exposure.  Note also that there is no curl at the sides of the leaves--they are quite flat--again, to maximize light exposure. 

From under lit to over lit.  Here's a mild case of sunburn on an Agave guiengola.  If the damage is superficial, the bleached area will gradually green up again.  More severe damage is permanent.

Slightly more sun damage and some dessication on this A. gypsophila 'Ivory Curls'--pinkness and wrinkles.  In addition, the leaves are curling inward to reduce their sun exposure.  Time to water.

Here is an Agave at the Desert Museum in Tucson, Arizona.  Permanent sun damage to those oldest leaves, and a plant grown "hard"--in extreme conditions.  Note also that the leaves are upright, not flattened out:  no additional sun exposure desired. 

This Agave ocahui suffered damage at some point, though it has  recovered, because the central (newest) growth looks healthy and in excellent shape--no brown tips.  Perhaps it was planted in summer heat, or it got insufficient water when working to establish itself.

 Here is a more subtle difference--'Joe Hoak' in full sun is upright.  Compare the way the central growing point is surrounded by leaves with the form of the shaded A. ellemetiana:

 In morning sun and afternoon shade, 'Joe' flattens out slightly:

Here's 'Joe' stressed by moving from a mostly shady nursery bed to its all-day-sunshine permanent home.  The leaves are folding in on themselves, and they are also quite thin in texture--not fully hydrated:

I should probably shade this 'Joe' for a few weeks, until the root system recovers and begins to grow again, to avoid damage.  Two commenters kindly reminded me that all plants moved from shady conditions to fully sunny ones need gradual introduction to the sun to avoid stress.
Stressing:  the "taco fold"

 There, that's better!
Here's another example of a heat/drought/sun stressed Agave, Agave sebastiana.  Note the "taco fold" of the leaves and drying out of the leaf tips. The plant is trying to protect itself and conserve moisture.

 Not a sunlight problem, but Agave americana 'Medio Picta Alba' has a tendency to get brown marks from water sitting on the leaves.  Best to avoid water sitting in the leaves by planting at an angle, so that water drains, or by avoiding overhead watering.  

I have no examples to offer of rot, edema, bacterial/fungal infections, or freeze damage--Agaves like it here--so my leaf-reading is limited, but the effects of light are interesting.   

Keep in mind that many Agaves are native to higher elevations and are found in open pine and oak woodlands.  That means cooler nights, somewhat cooler temperatures, partial shade, and excellent drainage.  There are relatively few Agaves native to the extreme low desert conditions of areas like Phoenix or Palm Springs with summer temperatures over 100F (38 C) for weeks at a time.  A few Agaves, like Agave attenuata or A. ellemeetiana, are nearly tropical in that they can take significant shade, and regular water (given good draining soil). 

So, after seeing what light can do, Test yourself:  what's wrong with this 'Snow Glow'? 

 Nothing.  Absolutely nothing.