I really wanted to blame this on the company we hired to remove the moss from our roof. Yes, as immature as that sounds, I REALLY wanted to. But, as the story unfolded, it became obvious the only one to blame...was me. And infuriatingly not because I'd ignored a potential problem, but because I'd done what I thought best to avoid it...
We've had a moss problem developing on our roof for years now, changing home insurance companies provided the impetus to finally do something about it, in fact we had 30 days to take care of it or else they were cancelling our policy. I interviewed a couple of companies and went with the one I felt had a plan to provide the least damage to the garden.
Here they are working on the garage roof, which was worse than the house roof (this surface was on the north side). I know it's not of the best quality but it's the only photo I have of the work in progress.
Here are some of the chunks of moss that came off the house roof. They're dried up and dormant.
The company did a great job of cleaning up what they could, but there are hundreds like this scattered around the garden. At least they kind of blend in with the gravel...
Being pro-active I decided it would be smart to cover the Agaves nearest the house. I had been assured they would be very careful in spraying the moss preventative (the final step, after scrapping and removing the existing moss), so it wasn't so much to keep them from getting over-spray, but rather to keep all the bits of moss and shingle grit out of them. After all I've picked out small pieces birds toss from the gutter on numerous occasions, and knew it wasn't a project I wanted to tackle on a larger scale.
I used burlap; old coffee bags and just random pieces I had laying around.
Also a sheet and an old duvet cover...
The guys who did the work were very efficient and done by noon, everything was fine when I took off the covers. Disaster adverted! (I had been dreading getting the work done, fearing the worse).
The next day when I went out to get the mail this is what greeted me. I quite literally felt like I had been punched in the stomach. How was this possible? My prize Agave ovatifolia 'Frosty Blue', ruined! Chemicals! My mind immediately went to the spray they'd used. They must not have been careful after all. Damn them!
The photo above was taken with my phone on August 17th, so I could quickly post it to Facebook (more on that in a minute). Here's what it looks like now. One of the leaves has folded back, so its damage (on the bottom side) is less visible.
The damaged tissue on the other leaves has either completely died (white) or kind of regained a bit of the "frosty blue" that makes this plant so desirable.
After first jumping to blame the workers I calmed down and looked around.
These Canna leaves were not covered — ditto for the Yucca rostrata, Amsonia hubrichtii and Opuntia — and yet none of them showed signs of damage. Perhaps something else, not the chemicals, was to blame.
Agave utahensis, tucked in next to the A. ovatifolia and also covered and damaged.
Quickly after posting photos on Facebook information started rolling in from the experts: Agave edema was the likely culprit.
I'd heard of that before, and even wrote about it. But it never occurred to me that covering my Agaves with burlap for all of 4 hours could cause it. The eventual high that day would reach 87, but the morning hours, when things were covered, were overcast to party cloudy. We had just come off a heat wave though, 94 and 98 under bright blue skies the two days prior.
Here's another piece of this (complex) puzzle. Notice the Agave ovatifolia on the far right above? Not a bit of damage, and it too was covered.
However with the single layer of "fabric store" burlap, which it turns out has quite a loose weave...
Unlike the double thick weight of the old coffee bags, which lets no light through. The flawless Agave also faces slightly north, thus may receive less intense sun?
The damage continues on the other side of the front steps...
Agave americana
Ugly. It too was fine when I uncovered it, the damage showed up later.
New growth is fine...
Minimal damage on this, which I think is Agave neomexicana (it came from an Agave rescue, with mixed up labeling)...
And nothing on it's pup.
Agave gentryi ‘Jaws’
And A. desmettiana variegata...
Agave 'Kissho Kan' is such a sun wimp that it's back further, mostly in the shade...and has no damage at all.
Before I launch into a few more random photos I want to share information from that Facebook thread I mentioned, I think it's interesting and potentially valuable. Feel free to skip on if it's too plant geeky for you! Names included because if you're an Agave lover you'll no doubt recognize a couple of them. (oh and this is just the sciencey stuff, there were also dozens of kind and caring comments on that thread from friends, while extremely important to me I figured you didn't need to read them all!)...
Gerhard Bock: Oh no, I feel so bad for you! I would be devastated. Based on my personal experience, it looks like what is sometimes described as "agage edema." People theorize it's caused by sudden changes in temperature and/or light exposure. Both might be the case here. I have an Agave guadalajarana that had the same kind of damage after being in the trunk of my car overnight.
Greg Starr: I agree with Gerhard about the "agave edema". Although not really edema, this damage tends to show up when plants are subject to unexpected shade in the middle of the day. I never really had this happen to any agaves in the ground, except A. montana, until this year. I've had it happen when taking plants indoor for shows and sales, and when transporting plants for sales. New leaves should be fine, but that damage will stay on the older leaves. Maybe it will get covered up as the new leaves grow out.
Greg Starr: Another thing that I've noticed is that plants that had been recently watered seem to be more prone to this damage than those that have been kept dry. So I try to let my plants dry out some before taking them to sales. Also, when I have spotted plants, i have never had anybody mention that they arrived with any similar damage. Of course I ship without soil.
Daniel Serrano: Money on CAM respiration being the primary culprit -- they just can stand differential cellular pressure.
Greg Starr: Aren't agaves primarily C3? I thought they had the ability to switch between CAM and C3. If CAM were the culprit wouldn't we see similar damage in cacti? I have never had any cacti show similar damage.
Daniel Serrano: True, money on c3 -- whatever their f-Ed up respiration mechanism, they just blast under disparate and seemingly inconsistent conditions.
Jennifer Zynischer: CAM fails when the nights are over 80 degrees. (piping up from Phoenix, where this happens often during our summers) No water at all during those times. Bone dry soil.
George Hull: Greg is of course quite right. The damage is permanent though. We would get this damage shipping agaves light dark light.
Greg Starr: I attribute the damage to the process of respiration being interrupted very suddenly, causing the stomates to shut rapidly and not allowing gas exchange to slow normally, thereby causing the surrounding cells to burst from a "gas overload". I think it has nothing to do with air flow, primarily a light-dark change frequently in conjunction with a change in temperature. I have noticed this happen more when transporting plants from a cooler to hotter location, but that is not consistent.
Interesting, right?
Okay just a few more photos. These little guys were covered with a single-weight, light-colored sheet, and there is no damage.
Ditto for this A. parryi...
And this NOID (but maybe one of the A. parryis?)...
Interestingly I later discovered these pups, and the container they're in, got a little over-spray on them — no damage.
And this! This little guy (Agave 'Silver Surfer') wasn't covered but rather stuck in the (dark) garage overnight and into the next morning. After all it's right by the garage and easy to move.
This showed up the same day I noticed the other damage. Again, there was no cover, just moved into a dark space overnight and into the next day (approximately 18 hours).
Finally, when I mentioned I'd heard of, and wrote about, Agave Edema
this is the blog post I was referring to. I did my best to sound like I understood the condition, and I guess I thought I did, but for it to happen in the summer months just plays with my mind.
More info on Agave Edema can be found on the San Marcos Growers website
here and
here. Robert Muraoka writes about it
here. Still want more? There's a lively discussion on the
Xeric World page about whether or not Agave Edema even exists, page down to the comments from "agavemonger" to read the best feedback. And finally
here's a post my friend Gerhard did about the same thing on one of his plants. At first he thought it sunburn but then Agave Edema was diagnosed.
As with all my "learn from my mistakes" posts I truly hope you do learn from this mistake. I know I have, although the differing reactions from the different types of Agaves, and what they were covered with, tells me there is no hard and fast answer. As I've said before, this gardening thing is not for wimps!
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