interest, their leaf color, substance and sculptural qualities, the margins of its broad, thick leaves, with their rhythmic rounded ripples, each tipped with a prominent ‘teat’ and spine. This is not a large plant, typically growing 23″- 47″ in diameter and my plan was always to keep it in a pot as it is from coastal areas of the Mexican state of Sonora, found sporadically in a narrow ‘band’ south into Sinaloa. Agave colorata is very rare and uncommon in nature and growing on steep slopes of the volcanic mountains in the coastal region in Sinaloan thornscrub. It often emerges from apparently solid rock cliffs sometimes clinging high above the water below.
Growing in Sonora and at Home
It is poorly adapted to our wet winter conditions though it is reputedly hardy into USDA zn 8, or as low as 10ºF. Its natural northern limit is thought not due to cold, but by excessive aridity in the northern parts of Sonora. I didn’t test it, leaving it outside under the porch roof, bringing it in when forecasts called for below 20ºF, as any plant is more susceptible to cold with its root zone subject to freezing. With perfect drainage and overhead protection, you might be able to get away with this in the ground, but the combination of significant wet with our cold is likely too much…still if someone wanted to try….At best I suspect this one would still suffer from fungal leaf diseases, disfiguring the foliage.
This is usually solitary, but it can be found occasionally in small clumps/colonies up to nearly 10′ across, pushing up against each other on their slowly growing and short ‘trunks’ to 4′ high. My plant produced just a few pups over the first third of its life.
Sonora has three distinct geographic areas all running along a ‘line’ from the northwest toward the southeast, the Gulf of California and its associated coastal landscape paralleling the Sierra Madre Occidental, sandwiching plains and rolling hills in the middle. The coast and plains/rolling hills are arid to semi-arid, desert and grasslands, while only the higher elevation of the easterly mountains receive enough rain to support more diverse and woody plant communities, scrub and Pine-Oak forests.
This region also varies north to south, the climate drying as you go north into the Sonoran Desert. Moving south on down into Sinaloa, and further, is the some what wetter ‘dry deciduous forest’ biome with an array of woody leugumes, including several Acacia. Agave colorata resides in the transition zone in between, in the portion of ‘thornscrub’ near the Sonoran/Sinaloan border. North and south the Thornscrub itself changes in composition. The Sinaloan Thornscrub serves as a transition zone between the desert and the slightly wetter, taller growing, Tropical Deciduous Forest that continues the south. All along this band running north on into Arizona’s Sonoran Desert are various columnar cactus a food source for Mexico’s migrating nectarivorous bat species. It is a unique flora community, containing species from bordering floral regions and other species unique or endemic to this transition zone itself. The area continues to be under threat, primarily by cattle ranching that moved into the region in the ’70’s and ’90’s bringing with it clearing and the introduction of non-native and invasive Bufflegrass, Pennisetum ciliare, also known under its syn. Cenchrus ciliaris, for pasture. Bufflegrass is also a serious problem north into Arizona. In Sonora many of the cleared woody species have since begun moving back in, while the smaller, more sensitive species have not. Climate change promises to further squeeze it. (The World Wildlife Fund maintains a website with good descriptions of many eco-regions I sometimes find it very helpful when trying to understand the conditions of a plant I’m less familiar with.)
When growing plants like this, one should keep in mind the concept of heat zones. The American Horticultural Society has created a map of the US delineating its ‘heat zones’. It is based on the average number of days an area experiences temperatures over 86ºF. At that temperature most plants begin to shut down their metabolic processes…they slow their growth. Check out the AHS map (AHS US Heat Zones pdf.) and keep in mind that we are warming up! The AHS map has us, Portland, OR, in zone 4, meaning we experience 14-30 days with highs over 86ºF each year. Last summer, ’18, we actually had a record 31 days over 90ºF! Now consider that the coastal/plains region of Sonora likely experiences between 180-210 such days! Agave colorata may not need this, but it is certainly adapted to such a level of heat stress. Something to think about, especially when you consider that we receive the bulk of our rain over the winter when our daily highs and lows average for Nov. 40º-53º, Dec. 35º-46º, Jan. 36º-47º, Feb. 36º-51º and Mar. 40º-57º…keeping in mind that we could freeze on most any of those dates. The Sonoran Desert receives its minimal rainfall in a summer/monsoonal pattern….This is why bringing such ‘low desert’ plants to the Pacific Northwest can add another degree or two of difficulty to your success!
Growing this in a pot made perfect sense to me, but every decision carries consequences, not all of which I anticipated. Most Agave don’t form a ‘trunk’ growing its leaves, in a tight spiral, crowded along a very abbreviated stem, which adds little to its length to separate each consecutive leaf., but Agave colorata adds a little ‘extra’ slightly separating its leaves, resulting in a weak and kind of puny stem. If you’ve ever shuffled pots containing Agave more than a few years old, you understand that their crown, their substantial top growth, is relatively heavy, A. colorata is no exception, in fact their leaves each seem more substantial than leaves on many other similarly sized Agave. This results in a plant that as it grows begins to lean over, eventually, laying flat across the ground. As a Monocot the stems of Agave don’t caliper up over the years as does wood. These have no cambial meristem which would add secondary growth, and diameter, to the stem and as I said, with its relatively massive and heavy crown, it leans. This is the same characteristic that gives their small colonies their height.
On a trip to Arizona we visited Boyce-Thompson Arboretum, BTA, to the east of Phoenix, on land that has lifted up on the edge of the Valley of the Sun as it rises up into the mountains. It’s just beyond the north eastern boundary of the Sonoran Desert, but it is still very amenable to this Agave and many members of the Sonoran community. It has some of the largest Boojum Trees, Fouquieria columnaris, I’ve ever seen, plants whose native range is limited to the Baja peninsula, many amazing Agave, Cacti and other desert plants you would expect including an international collection of the woody legumes. Boyce-Thompson himself was very interested in the possibilities of agriculture in the region and understood and valued these nitrogen fixing plants and what they brought to relatively poor desert soils. Boyce-Thompson was no ‘farmer’ though, he became very successful and wealthy in the early copper industry. Copper mining is still active and very much in evidence today. It’s scale is breath taking. As you drive area highways it is impossible to miss its mining operations as entire mountains are leveled. The massive vehicles used to haul the unprocessed rock and the covering ‘overburden’ away, appear in the distance as tiny ants while nearby to the mills you drive by massive piles of waste, the spoils, for miles. I had many photos of BTA, its collection, the river that winds through it below the carved and broken cliffs along its southern edge where, it cut down into the base of hills and backing mountain, a very beautiful site operated by the State Parks and a large and very active group of volunteers, but, somehow, I lost them. One of those times I wished I had had an old film camera rather than a digital. I highly recommend checking out Danger Garden’s BTA posts, here’s a link to the first of four that she made. Very nice pics.
I bring BTA up because living in the Pacific Northwest and not having ventured very often into the Southwest, this is the first place I saw Agave colorata growing in the ground to any size. The differences from my plant was notable. While mine’s overall form and the shape of its beautiful leaves were very much the same these were larger, their leaves, particularly their lower leaves and their ‘lean’ was different. I’ll address each of these.
Because of the lengthening stem, the crown, the top-growth of leaves, grew toward the edge of one side of the pot I had planted it in. As I potted it up every few years it would continue this pattern the crown growing slowly, ever larger. The problem soon became apparent. It was becoming increasingly unstable and subject to toppling over sideways. As the stem grew longer and the crown heavier the balance shifted the center of gravity to an edge. To counter act this, when up-potting, I replanted it off center shifting the base of the plant to the opposite side allowing the crown to be supported by the edge of the pot opposite, rather than hanging over so extremely. Eventually, as it continued to grow in this manner, lengthening its prostrate stem, which began rooting itself as it was in contact with the potting soil, this soon became insufficient the pot unstable. I changed up my potting mix adding more sand to give the pot itself more weight…and this worked for awhile. I shifted to lower squatter pots, again to try to address the off centered and top heavy growth of the crown. My signal for up-potting was when an inadvertent and slight ‘bump’ would cause the Agave to fall over leaving the pot tilted and the crown resting against the concrete deck of the front porch.
When I finally planted it into its 19″ dia. pot that it eventually flowered in, we had set it on top of a wheeled dolly where it stayed so it could be moved when needed. The dolly at least made it possible to roll it through our front door for those few days down to 20º or below that we might experience in an occasional colder winter. As you can imagine the pot itself, with its sand heavy mix and its crown hanging over one side, made for an extremely awkward and dangerous situation if it needed to be lifted and moved…the whole thing having a tendency to roll and flip, an ugly and bloody prospect. At this point I had decided not to acquire yet another larger pot for it. I was at my limit for dealing with it. So, this pot restriction, the sandy mix with its reduced capacity for water and nutrient retention, combined with the often very hot summer temps on the south facing concrete surface, was something it would have to endure. (The summer of ’18 was our hottest ever summer experiencing a record number of days, 31, with highs over 90º. I’ve no doubt that this treatment both stunted my plant and reduced its storehouse of carbohydrates, nutrients and water as well, a very significant loss when it came to flowering.
A last note on the differences, this is the maritime Pacific Northwest and for much of the year it is cool and damp here so when foliage gets wet it tends to stay that way much longer than it would across its Sonoran range. While I would roll this under the over covering roof on its dolly, the leaves could stay damp for quite some time which would encourage various fungal growths. Laying on its side the broad, somewhat cupped leaves were perfect for holding any rain that might blow in on them where it could stay for days…not ideal. These lower leaves lost some of their ‘sparkle’ and may have been lost more quickly than normal due to disease adding even more to the lean. In a larger pot. With better soil conditions, growing where I could have better protected it from winter wet, my plant would have likely looked more like the plants at BTA.
The Flowering Phase
The flowering phase began in early July on the 3rd first exhibiting itself as a kind of crowding of a cluster of leaves, emerging from the center of the rosette, in an uncharacteristic manner. Normally, on all Agave, the leaves emerge tightly clasped together in a ‘spear’ like structure, one leaf expanding and lifting away from the spear at a time permanently ‘imprinting’ itself into the surface of the spear. It also displayed a slight pinkish tone to this new growth. Extension of the peduncle was slower than I expected extending less then 2′ in the following month while being maybe an 1 1/2″ in diameter. It wasn’t until Aug. 28 that the first sign of developing flower buds showed from beneath the lowest bracts clasping the peduncle.
There was a break in my reportage as we left to NYC on Sept. 4 and didn’t arrive back home until late on the 12th…but while the secondary peduncles and buds had expanded over the intervening period, none of the buds had yet opened…in fact none of them had opened even by the 27th when we left for a trip to Enterprise, OR, Boise and McCall Idaho. It was Oct. 12 before the first flowers finally opened, a little more than 3 months since the process began going into the Fall. As slow as the process had been it seemed to have slowed more when our hot summer came to an abrupt end on Sept. 10 with significantly cooler and wetter conditions asserting themselves. Flowering which works up from the lowest branches on the peduncle proceeded very slowly up. Warm days were separated by cool damp days, cool enough to drive area bees into their hives several days at a time (One neighbor keeps 3 hives so I have plenty nearby!) I have a video of the bees working the three lowest branches on Oct. 24. They were back on the 27th as our days continued to shorten and cool. By the 20th our weather pattern had taken a consistent turn toward our typical cool/wet Portland pattern receiving about 2″ of rain over the last week of the month, the warm/dry done until next year. For a quick review of the year’s weather check this link to the Portland NOAA site. It was simply too much for this Sonoran species. While a few more flowers opened in what turned out to be a mild for us November, that was pretty much it. What flowers remained were quickly weather beaten, their pollen dehisced and wasted, many of the buds permanently stalled. Though I kept it in its pot and the winter remained mild, our cold finally making a showing in February and early March, no other flowers opened and no seed was set.
As I noted before, my plant was on the small side, overall in its diameter and in the size of its leaves. This with its limitations imposed by its pot and growing conditions resulted in a stunted peduncle as well, mine growing just over 5′ long, when typically these grow to 10′. My plant seemed to lack the oomph it needed….
By early May, of what was a cooler and drier than normal Spring, I removed it from its pot, cutting up and discarding its inflorescence. The leaves that remained had much of the water and nutrients drawn out of them. Agave are very efficient at this leaving a largely dehydrated and shriveled rosette of leaves, hard and tough filled with the strengthening fibers that remained. This ‘dehydration’ process proceeds very uniformly beginning at the tip of each leaf, a distinct ‘line’ marking the shriveled from the still healthy tissue. The contrast is stark. This process begins as the demands of the inflorescence exceed what the roots could supply. Now it was over and I hung it up out of the way to dry the rest of the way as my wife want the beautifully patterned dry leaves for projects.
It’s now October and near as I can tell the tissues haven’t dried anymore! This shouldn’t surprise me because these plants are extremely conservative of the water within their tissues. Eventually I took a hatchet to it cutting away one leaf at a time, chopping into still very wet tissue that literally spilled water my having cut through the tissues and damaged cell walls. It wasn’t growing, but it had far from yielded either. Additionally, as I cut away leaves, I realized that there was no large heart either from which the flowering had been drawing reserves. As I chopped up the length of the stem it appeared that there never was. I don’t know if this is typical for this species or, and this is what I suspect, my Agave had had a difficult life with inadequate water and nutrients when it was needed over the years, again, not surprising given the conditions it was forced to live under. This would help account for the fact that this was an under sized specimen, maybe 24″ in dia. and the inflorescence about half the height of the type, probably smaller in diameter as well than on a typical flowering Agave colorata. Stress can do these things. It may sound kind of strange, but I do suspect that I drought stressed this resident of the Sonoran Desert.