Agave utahensis in habitat and in cultivation: guest post by Dan Zarrella

As you know, I’m a big agave fan. Out of the 270+ agave species, Agave utahensis, especially varieties nevadensis and eborispina, are among my favorites – and highly sought after by collectors. In 2022, I had the opportunity to see both in habitat in the mountains outside of Las Vegas (nevadensis post here; eborispina post here), but I’m not an expert. Guest contributor Dan Zarrella is. His enthusiasm for this species is bar none.

Dan lives in the Las Vegas area and has spent years exploring the Mojave Desert. His YouTube channel contains 75+ videos on Agave utahensis. In addition, he shares his field observations and his experience growing Agave utahensis on his website Mojave.lv. He also sells choice seed-grown Agave utahensis through Mojave.lv (nevadensis for now, eborispina coming soon) to support his Project Eborispina, a multi-year effort to survey and document eborispina populations in southern Nevada.

This is a long post, but it’s an important one because it highlights spectacular plants that are under threat in their native habitats in Nevada and California.

Agave utahensis var. eborispina. Photo by Dan Zarrella.

Agave utahensis in habitat and in cultivation

by Dan Zarrella, Mojave.lv

↬ Introduction

Botanist George Engelmann was the first European researcher to describe Agave utahensis in the late 1800s, but he was certainly not the first person familiar with it. For more than 7,000 years, humans have collected and cultivated this agave species not only for its nutritional value but also for its fibers that were used for making rope, baskets, and other tools. Ancient agave roasting pits, remnants of indigenous groups, can still be found throughout its range.

Agave utahensis is well known for its remarkable adaptability to colder climates. As the most cold-hardy agave, it has captured the attention of gardeners in regions with harsh winters. Its ability to survive and thrive in such conditions has made it a favorite among enthusiasts and horticulturists. US Department of Energy research reports utahensis as hardy down to -9°F as long as it’s kept reasonably dry in the winter.

Two unique forms with fantastic spines that grow exclusively in California and Nevada—varieties eborispina and nevadensis—have gained internet fame. They’re sought after by collectors around the world, and especially in Asia where they appear in luxury boutiques. Notable specimens command high prices.

My fascination with Agave utahensis goes beyond its resilience and aesthetic appeal. It’s the plant’s rich history, cultural significance, and extraordinary lifecycle that make it truly captivating. The more I learn about utahensis, the more my appreciation for this remarkable species grows. This video explains just a little bit about why I’ve become a total utahensis nerd.

Agave utahensis var. eborispina at night. Photo by Dan Zarrella.

↬ Subspecies and varieties of Agave utahensis

There are four taxa of Agave utahensis: subspecies utahensis (which I lovingly call “regular degular” utahensis), subspecies kaibabensis, variety eborispina, and variety nevadensis. Of those four, two—nevadensis, and especially eborispina—are particularly beloved by collectors and cactus and succulent nerds on Instagram.

(Left to right) Agave utahensis var. nevadensis, subsp. utahensis, var. eborispina. Photos by Dan Zarrella.

Agave utahensis subsp. kaibabensis

Kaibabensis, named after the Kaibab Plateau north of the Grand Canyon, is the largest of the four Agave utahensis taxa, and probably the oldest. The other three taxa display variable inflorescences (they can grow any one of three kinds of flower stalks: spicate, racemose, or paniculate). Many experts consider this an indication that those taxa are the result of a relatively recent field hybridization. Kaibabensis, on the other hand, is believed to only grow paniculate inflorescences, suggesting that it is not the result of a recent field hybridization, and thus, potentially the oldest taxon.

Kaibabensis was formally described by Susan Delano McKelvey (FDR’s cousin) in 1949 in the Journal of the Arnold Arboretum. She noted that she was able to find a handful of photographs of kaibabensis, but that she and others initially considered it merely a “colossal form” of utahensis.

Kaibabensis generally does not grow the elaborate terminal spines and lateral teeth that eborispina and nevadensis are known for, and so it’s not the Instagram star of the species. It’s probably the least common of the four taxa to be seen in cultivation.

Agave utahensis subsp. kaibabensis in its native habitat at the Grand Canyon. Photo by Gerhard Bock.

Agave utahensis subsp. utahensis (“regular degular” utahensis)

When most folks think of Agave utahensis, this is the subspecies they’re thinking of. It’s likely the most common of the four, and it’s the parent taxon of nevadensis and eborispina. I call it “regular degular” utahensis, because compared to those two varieties, it’s a little boring. It’s generally not very blue, and it usually doesn’t have particularly interesting spine or teeth. But unlike nevadensis and eborispina, it can be found in all four states where utahensis naturally grows: Arizona, Utah, California, and Nevada.

Agave utahensis subsp. utahensis. Photo by Dan Zarrella.

Agave utahensis subsp. utahensis var. nevadensis

Nevadensis is my favorite taxon of utahensis. I’m a sucker for blue plants, and nevadensis has the bluest leaves. Because it’s found growing at the highest elevations (often 5,000 feet and above) where it receives the most UV stress, its blue leaves are likely a protective mechanism against UV (particularly UV-B) damage.

Nevadensis is often found growing in pinyon-juniper woodland areas in a loose substrate of mollisol (decaying organic material from the roots and leaves of other plants) mixed with limestone gravel. In that environment, it can produce large clumps and clonal rings that are potentially hundreds of years old.

In his seminal work Agaves of Continental North America published in 1982, legendary agave botanist Howard Scott Gentry described nevadensis as having a “terminal spine 3-8 cm [1.2 to 3.1 inches] long, slender,  brown to whitish; teeth relatively small.”

Agave utahensis var. nevadensis. Photo by Dan Zarrella.

Agave utahensis var. nevadensis. Photo by Dan Zarrella.

Agave utahensis subsp. utahensis var. eborispina

Eborispina is the internet celebrity of the utahensis species. Whenever anyone is in Las Vegas (where I live) and asks me to take them to see utahensis in habitat, they almost always want to see eborispina. And it’s the utahensis taxon that sells the fastest, and for the most money.

Eborispina was first described in 1943 in the Cactus and Succulent Journal (now the Journal of the Cactus and Succulent Society of America) by J. Pinckney Hester, who noted: “Terminal spine elongated, slender, pungent, straight or sinuate, brown in youth, ivory in age, usually curved inward, 10-20 cm [4 to 8 inches] long…”

In Agaves of Continental North America, Gentry described eborispina‘s terminal spines like this: “Terminal spine 10-20 cm [4 to 8 inches] long, large, thick, ivory white; teeth larger, coarse, crooked.”

And in 2010, in the Czech journal Kaktusy (downloadable for free from ResearchGate), Zlatko Janeba wrote this about eborispina: “terminal spine 10–15 cm [4 to 6 inches] long, ivory white, straight or sometimes curly.”

Can you spot the commonality in these descriptions across a nearly 70-year time span? Eborispina has terminal spines at least 10 centimeters (4 inches) long. There are some other differences between nevadensis and eborispina, including its range—eborispina tends to live to the north and west of nevadensis, and at a lower altitude—as well as its coloration—eborispina tends to be greener than nevadensis. But these aren’t set in stone. There are blue eborispina growing above 7,000 feet.

However, at least according to Hester, Gentry, and Janeba, there aren’t mature eborispina with terminal spines less than 10 centimeters in length. This is important to remember the next time you’re looking at a plant labeled “eborispina” that is listed for sale online. There are quite a few sellers who, either intentionally or unintentionally, incorrectly identify nevadensis and “regular degular” utahensis as eborispina, because eborispina sells for more money. Watch this video to find out if you’re being lied to by a seller.

Agave utahensis var. eborispina. Photo by Dan Zarrella.

Agave utahensis var. eborispina. Photo by Dan Zarrella.

↬ How to spot wild-collected Agave utahensis

When it comes to buying Agave utahensis, the most important thing we can do (at least if we’re at all concerned with conserving this amazing species) is to ensure we’re buying seed-grown plants, rather than ones that have been dug up from the wild.

To be clear: not all wild-collected utahensis plants are poached. Poaching is a crime where plants are illegally taken from the wild, typically from lands where such collection is banned or restricted. There are absolutely legal operations harvesting Agave utahensis in the wild. This is not to say that these people are operating ethically or sustainably, merely that they are operating legally.

So how can we tell if a plant we’re thinking of buying has been dug up from the wild or grown from seed? It’s actually pretty easy.

Wild-collected Agave utahensis var. nevadensis? Photo by Gerhard Bock.

Roots

The biggest giveaway of a wild-collected plant is its roots. In habitat, Agave utahensis grows a large and fibrous root system that spreads out laterally to gather as much water as possible. When they’re dug up, it’s impossible for their roots to be extracted intact. As a result, wild-collected plants generally have their roots severely pruned.

In contrast, seed-grown plants will have a big ball of those fibrous roots still attached, generally in the shape of the container they were grown in.

Shape

Shape can also be a pretty big indicator of wild-collected versus seed-grown. Agave utahensis plants that have spent decades growing in habitat have been exposed to a lot of UV stress, and not a lot of water. This leads to a very compact rosette structure, with very vertical leaves. These leaves sometimes even curl back towards the center, a trait referred to in the Asian market as “ball type.”

Seed-grown plants will most often have a much more open shape, with horizontally oriented leaves. While a compact structure isn’t a guarantee of a wild collected plant, it’s a pretty big red flag.

Yellow leaves

Agave utahensis habitat is an unforgiving place. Even plants adapted to it, as utahensis is, bear the scars of its brutality. Most mature wild utahensis have a layer or two of dried, yellow leaves ringing the outside of their rosettes. In contrast, it’s fairly uncommon to see this in a seed-grown plant unless it’s been exceptionally “hard grown.”

Age

Agave utahensis is a very slow-growing plant. So if you see an online seller with a bunch of mature-looking utahensis plants for sale, it’s highly likely that these are plants dug up from the wild. In comparison, seed-grown plants are often still in 3-inch pots after a several years of growth.

Agave utahensis var. nevadensis in the snow. Photo by Dan Zarrella.

Agave utahensis var. nevadensis in the snow. Photo by Dan Zarrella.

↬ Growing Agave utahensis in cultivation

As the northernmost agave species, utahensis is also one of the most cold hardy, regularly surviving snow-covered, sub-zero winters in its habitat. This makes it an excellent choice for growers in colder climates who’d like to have an agave hardy enough to survive the winter.

A lot of hay is made about “hard growing” desert plants. Some folks worry that watering and fertilizing their plants will produce undesirable shapes. In my experience, Agave utahensis loves to be treated well. Plenty of water and nutrients produce faster growth in terms of both above-ground rosettes and below-ground root systems. The primary factor separating growing conditions that produce beautiful plants from those that produce boring ones is light. In addition, underwatering won’t produce the shapes we all love.

I grow my plants primarily indoors, so most of my recommendations are based on that experience.

Light

In habitat, Agave utahensis grows in high-altitude, high-light desert environments, sometimes under the shade of nurse plants or rocks, but not exclusively. Indoors, Agave utahensis plants require artificial light to be at their best. This means that plants grown indoors under artificial lights do best when placed as close as possible to the strongest lights possible as long as temperatures are under control. High-lumen LED bulbs, high-wattage LED panels, and fluorescent fixtures all work well.

Outdoors, acclimation to the site is a must, as is balancing light and temperature. Young utahensis plants will melt in a matter of hours in full sun; on the other hand, plants grown under dense shade cloth will probably be much smaller and greener than you want them to be. If you’re moving an indoor plant outside, spend a few weeks exposing it to sun for a gradually increasing length of time. For example, start with two hours of morning sun for a week, followed by two hours of mid-day sun for a week, then two hours of hours of afternoon sun for a week. After that, your plant should be ready for full sun.

To learn more, watch this video on how to care for Agave utahensis.

Seed-grown Agave utahensis var. nevadensis. Photo by Dan Zarrella.

Watering

Agave utahensis is not a cactus, so don’t water it like one. It can withstand drought, but it doesn’t have to stay dry all the time. As long as the soil dries out between watering, I suggest giving it as much as water possible.

If you grow Agave utahensis in pots, it can be helpful to measure the specific drying rate of your plants. Simply use a kitchen scale to weigh the pots before and after watering. Record these numbers for a few cycles and you’ll be able to see how long it takes for your plants—in your situation and in your soil mix—to dry out in between waterings.

To learn more, watch this video on how to water Agave utahensis correctly.

Fertilizer

In habitat, utahensis often grows in small pockets of highly fertile soil mixed with limestone. As studies on other agave species have shown, not only does fertilizing with macronutrients (nitrogen, phosphorus, potassium) produce faster growth rates, but plants also respond well to micronutrients like boron and calcium. Look for a fertilizer with a balanced NPK profile and a full range of micronutrients. Half or quarter-strength fertilizer solution can be applied once a week.

Soil mix

Utahensis is famously a calcicole, i.e., it prefers to grow on limestone soils. Chemically, these soils provide a lot of calcium, and they’re basic (alkaline), not acidic. But in my understanding, the big reason that utahensis loves limestone is that most limestone substrates, be they cracks in large boulders or rock faces, or limestone gravel mixed with highly organic mollisol, are very well draining.

This means that when designing a soil mix for utahensis in cultivation, sharp drainage is our primary concern. I live in Las Vegas where it’s very dry, so I can get away with using a roughly 50/50 mix of water-retaining organic material and fast-draining inorganic material. In the desert, a soil mix with this ratio still dries very quickly, but if you’re in a more humid climate, you may need to reduce the amount of organic material to ensure your mix dries faster.

My organic components are store-bought cactus mix and worm castings, and my inorganic material is stuff like lava rocks, perlite, and Turface. I don’t think there’s anything magical about any of these ingredients, so feel free to use whatever is available and affordable where you are.

To learn more, watch this video on the best soil mix for Agave utahensis.

Air flow

Other than light, if there’s a secret to growing really gorgeous utahensis, it’s air flow. This is particularly important indoors and in a greenhouse environment. I grow my plants indoors, and I recommend you use as many fans as you can. The more airflow you can provide across your utahensis plants, the faster they’ll dry and the more frequently you can water them.

Agave utahensis var. eborispina. Photo by Dan Zarrella.

↬ Project Eborispina

Agave utahensis var. eborispina has the lowest number of documented populations compared to nevadensis, regular utahensis or kaibabensis and probably the smallest population size overall. It’s under attack from a number of factors, including climate change, development, and worst of all: wild collection. Illegal poaching and legal, but unethical and unsustainable harvesting, are putting a strain on eborispina population numbers and genetic diversity.

I’ve set myself a goal to survey all existing eborispina populations in southern Nevada. I hope to produce two kinds of output: a visual recording of eborispina populations (both video and photographic) and a statistically defensible numeric estimation of how many plants are actually living in the wild right now. These field surveys will involve pretty intense hikes, and some places will require long stretches of four-wheel off-road driving. In this video, I explain my plan to document and help save these amazing plants.

If you want to support Project Eborispina and my efforts to provide ethically propagated Agave utahensis to the collector community, please consider buying some of my seed-grown plants on my site.

Project Eborispina update, October 3, 2024:

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