Along with Agave montana, Agave atrovirens has to be the highest elevation plant in the genus. I have seen these massive giants in the north of Oaxaca growing among the pines, straddling the border with Puebla, and while driving past coffee farms and the famed mushroom town of San José del Pacifico, up to 10,000' elevation. These noble giants of the mountain grow up to 10' tall and in excess of 16' across. Somewhat resembling Agave americana, Agave atrovirens has a wider rosette and leaf and remains solitary. For anyone who has grown Agave americana in their garden, this ought to be a desirable feature, as removing the prolific offsets rarely occurs without loss of blood. Besides, as often is the case, an agave standing alone is preferable to look at compared to one covered in offsets of various sizes. Despite their high-altitude origins, Agave atrovirens do well at sea level in California, as well as the inland zones where the high temperatures can be in the 90's or more, and to low temperatures down to at least 25 degrees Fahrenheit without frost damage. Upon bloom time, expect a towering inflorescence resembling a telephone pole covered in orange- red buds opening to yellow flowers.
The species name means 'dark green', and there are dark green strains, but most images from habitat and cultivation show much more blue plants. These blue plants are A. atrovirens var. mirabilis. Howard Gentry gave the blue plants varietal status based on "the leaves consistently light grey, glaucous' color." In my experience, the plants growing under the canopy of the pines are dark green with a more open rosette, whilst those exposed to the sun are bluer with tighter leaves. Individual leaves can weigh over a hundred pounds, and this is reputed to be the agave with the tallest inflorescence - up to 40 feet. Although it lines up visually with A. americana, the leaves are fewer, wider and larger.