Agaves, Hybrids and Our Role as Gardeners & Stewards

 

Sharkskin bracketed by its parents, A. scabra left and A. victorian-reginae on the right

Hybridizing is always a bit of a crap shoot!  Cross two species and the progeny will range all across the morphological map!  Hybridizers grow on their seedlings and select those that share the characteristics that they’re looking for or individuals with startling and unusual features.  They toss the rest.  They in effect are giving their selections an advantage, an advantage they would never receive in nature on their own.  In nature hybrids can only occur when the natural ranges of the two parent species overlap and their proclivities align with the possibilities.  Plant breeders are not limited by this.  Pollen can be collected and stored from anywhere and used to pollinate selected plants.  In nature, survival is a numbers game.  Seedlings must be competitive in an existing plant community with limited available niches.  They have to possess a certain robustness.  Those that survive, grow on and perpetuate themselves, possessing survival characteristics that allow them to do so and have been blessed with the conditions that favor them.  Hybrid creations of nursery people and breeding programs may be lacking in these survival features.  They are pampered, lined out in nursery rows and flats. The result of their intentions may actually put their selections at a competitive disadvantage if they were to be left on their own in nature.

Watching the flowering process of ‘Sharkey’, my Agave x ‘Sharkskin’ has gotten me thinking about this.  When Ruth Bancroft, I believe it was her, made this cross and selected this one plant out of many, she was looking at its blend of physical characteristics that is its basic rosette form and appearance.  She did not wait an additional 15 years or so to take into account its flowering characteristics.  This was a plant selected for the garden.  As a monocarpic plant, its flowering, though spectacular in the plant world, is momentary, something the gardener or designer, would not necessarily consider in their selection process.

This Agave is a first generation hybrid, an F1, in the hybridizing world.  F1’s have such a mixed bag of chromosomes that to grow the seed on from one of these is a roll of many dice.  Their progeny will range widely, another reason that these are propagated asexually.  This is common practice among growers of hybrids.  (The seed for F1 vegetables are grown every year from the original cross…each time!) Some plant breeders will grow several generations on over the years selecting those with the features they are looking for and in the process gradually eliminating the chance for variability and stabilizing it.  Sometimes seedlings of these are offered as a named series, the progeny of which, will vary across a defined range sharing many identifiable characteristics.

My worry here is that because the inflorescences of the two parents are so different, the resultant plant, Agave ‘Sharkskin’, may possess an inflorescence, that its rosette and roots, cannot support.  In nature such a hybrid would be ‘tested’ and if it toppled prematurely, and so failed to flower, set seed and maybe even produce offsets in its uprooted state, it would die without its particular set of genes being passed on.  The ‘experiment’ would have failed.  Is Sharkey’s mass big enough to produce and physically support such a tall structure?  If not, is its root system substantial enough to make up for this?  Of course growing such a plant in my Latourelle Loam of the northern Willamette Valley is another issue as the anchoring material for the whole plant structure.  The soil is the medium that roots anchor themselves within.  Our relatively wet winters translate into wetter soils than those Agaves evolved with and I wouldn’t be at all surprised to find that their roots are more shallow than those of their desert cousins.  This shallowness would translate into a structure that would be more liable toppling and uprooting itself.

Typically, parent, Agave victoriae-reginae has an inflorescence 11’-13’, while Agave scabra, the other parent, is around 13’-19’.  Sharkey has apparently topped out at 20’ 5”, taller than either parent.  In a world with no wind the inflorescence would grow absolutely plumb and place no rocking stress on the rosette and its roots.  All of its weight would be carried vertically, directly on top, requiring only that the stem and its base be strong enough to withstand the compression forces of its mass.  But wind there is and the flowering stem has been shifted SW of plumb.  This ‘weight’ now constantly exerts a levering force at the base of the plant.  Remember the fulcrum.  I’ll be generous and say that the roots go down into the soil one foot to anchor the plant.  They can only spread the 3 1/2’ between curb and sidewalk.  This gives the flowering stem the leverage force of 20:1, given its just over 20’ height.  A pound of pressure at the top exerts 20lbs of force at the base.  10lbs exerts 200lbs!  The big question is whether, this hybrid, genetically untested until now, has the ability to withstand these forces.

To its advantage is the fibrous nature of the structure of this genus.  The long fibers lend strength to the structure allowing a degree of flexibility that can absorb some of the force as this long lever, effectively a sail, moving back and forth in the breeze and wind, much like bamboo and trees.  A weak point is potentially where the stem ‘attaches’ to the fixed rosette base, as this part of the structure is basically immovable, much of the force will be focused on this point.  A failure here and it snaps, suddenly and ‘catastrophically. If it remains strong here there is the possibility of a failure of the roots, snapping, as the whole plant rocks back and forth causing it to topple over out of the soil, roots and all; or, the third possibility of the separation and twisting of the longitudinal fibers in the stem causing it to fold/twist down to the ground as tree branches are often prone to do.

Tuesday morning I wrapped a flexible strip of tree lock or chain to the stem, 10’ up along the listing inflorescence and tied it to two points on the steel railing on my front porch with monofilament line.  No one in particular would care if an Agave toppled over in the desert, but I feel responsible for this one.  And, like any gardener, I have invested myself in this plant.  Its existence here is not a natural occurrence and I want to see it through.  It was created and contains the ‘flaws’ of its origination.  I planted it here.  Its life here would never have occurred without my own intervention and less directly, that of others.  We are responsible for these changed landscapes.  We gain nothing from neglecting them other than in a short sighted way.  When we care for them, nurture their life, they in return, nurture and support us.  We are doubly responsible for the landscapes we have broken, removed from the flow of history and life that created them, and provide for the richness of the life that once occupied these now highly urbanized places….So I intervene.  I take care and am careful to not disturb what is already working.  We as a society have not been very good at this.  Our plants and landscapes are more than just a monetary investment in the world, they are a changing of, a re-creation of the life that once lived here.  If we are sloppy and uncaring, if we fail to recognize and support the complex and intricately interwoven web of life, if we fail to take on our role as its stewards, then one day we will find that the life supporting systems that once functioned so beautifully without our intervention are gone and the earth poorer for it in ways that we will find diminishes us and the life that we are ultimately dependent upon for our very survival.  It is a reciprocal arrangement that we’re in, each requiring the benefits conferred by the other.  In their absence each will suffer, decline and eventually fail.  It has always been important to recognize our relationships and the responsibilities that they place on us.  It isn’t a burden, it’s an acknowledgement of the connection that has always been there.  Gardening can teach us this.  It is not just about ‘pretty’.  It is about learning about how critical this relationship is to not only our well being, but our own lives.  Our gardens  and landscapes are ‘kind’, but they, like anything, can absorb only so many mistakes, tolerate only so much indifference.  So I choose to support ‘Sharkey’ to see him through, knowing, that in ‘his’ own way, ‘he’ is doing the same for me.

Plants are amazing fetes of natural ‘engineering’.  They exist in a dynamic world within a range of changing forces, forces that they have evolved with, that their structures, as successful plants have adapted to.  Failures still occur, but in the main, they do very well.  When we alter the conditions and/or the plants themselves, we in a very real sense must take on the responsibility of their future health and welfare.  If we can’t or won’t do this, then maybe we shouldn’t be ‘meddling’ with life.  If we choose to alter the living plants and organisms of the Earth, or the conditions and forces that effect the life around them, we need to be engaged in their care.  Nature has a great deal of inherent wisdom.  By comparison we know relatively little, but if we engage and pay attention then we and the rest of life will do alright.

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