Why did these agaves die after the July heat dome?
Winter damage is almost unavoidable. No surprise there. Last winter, we had multiple consecutive days of rain with almost no break. Some aloes developed rot from water sitting in the crown and/or in the flowers, but most grew out of it.
I expect stuff like that in the winter. What I don’t expect is agaves rotting in the middle of the summer. But that’s exactly what’s been happening this year. Here are a few good, but sad, examples:
 |
| Agave chazaroi |
The first victim was the large Agave chazaroi you see above. I noticed rot developing in the center in early July. It progressed so rapidly, there was no stopping it. All I could do was dig it up and toss it in the yard waste bin. Now there’s a large hole where the agave had been.
The second example is a large Mangave ‘Mission to Mars’. I originally bought it in September 2017 in a 4" pot and it has been in the same spot in the sidewalk bed since 2020. It always looks great during the cooler months, but in the summer, the outer leaves fold inward to protect the core. It illustrate, here’s a photo from September 2022:
 |
| Mangave ‘Mission to Mars’, September 2022 |
I don’t like this messy tangle of leaves, but I’ve come to expect it. That’s why I wasn’t surprised by the way Mangave ‘Mission to Mars’ looked last week:
 |
| Mangave ‘Mission to Mars’, August 2024 |
Rot, right in the center. And a lot of it. There’s nothing that can be done at this point to stop the rot. With a heavy heart, I’m proclaiming it a loss. After I dig out the carcass, there’ll be another large hole to fill.
But the loss that hurts the most was this Jeremy Spath hybrid, Agave ovatifolia × Agave parryi var. truncata:
 |
| Agave ovatifolia × Agave parryi var. truncata |
Again, rot right in the center, with no hope of recovery.
The final example is an aloe hybrid by Nick Deinhart I treasured, Aloe humilis × Aloe peglerae:
 |
| Aloe humilis × Aloe peglerae |
Oddly enough, two other Aloe humilis hybrids within a few feet, growing in the same conditions with the same amount of irrigation, are perfectly fine.
The big question, of course: What is the cause? The short answer: I wish I knew.
At face value, this is very similar to what gardeners in hot places like Phoenix have experienced in recent years. When nights are hot (mid-80s or higher), CAM plants like agaves are unable to open their stomata to “breathe” (collect carbon dioxide) and hence take up water. When the soil is wet, be it through irrigation or rainfall, the plant can quickly succumb to rot.
Is this what happened to my plants?
I just don’t know. It’s totally possible that the plants that died had gotten wet from the drip irrigation running. But then, I’ve been watering my plants the same way for years, and I never had any agaves or aloes rotting in the summer before.
Most likely it’s a combination of unfortunate circumstances and no real lesson can be drawn from it. But I’m hoping that some of you might have a better idea. If so, please leave a comment.
UPDATE 8/15/2024: While I still think my plants died of a combination of high heat and moisture, it's possible that the agave snout weevil is the real culprit. I just discovered agave snout weevils in the garden of a friend a few blocks away. Read this post for more details. Warning: It's not for the faint of heart.
© Gerhard Bock, 2024. All rights reserved. To receive all new posts by email, please subscribe here.
I have Agaves in the ground, but not a lot like you. My 4 foot Agave 'Gentry Jaws' is the only one that did the same as yours this summer. It is not on irrigation and we sure have not had any rain. Howeve,r it is within 2 feet of an Oleander hedge in my neighbor's yard. I think it got too much water from that and so the center rotted. Believe me, I feel your pain. I am not strong enough to be able to get it out and will have to find a landscaper willing to do it. That is not an easy task either!
ReplyDeleteI remember you mentioning your Agave gentryi 'Jaws'. I lost one to rot a couple of years ago. And yours sounds like it was even larger!
DeleteDang, that hurts. My losses are just about identical to yours, I wish I had answers. Last winter I would take the leaf blower and blow the water out of the aloes, agaves, etc after a rain. No idea if I was doing anything worthwhile and certainly that's not needed in the summer.
ReplyDeleteIt's aggravating that we don't know exactly what happened so we can avoid this in the future. AAARGH.
DeleteUgh, I am sorry. Ugly, and I'm sure stinky, death to deal with. Here I've removed my Nolina hibernica 'La Siberica'. Some had counseled me to leave it and give it a chance to turn around, but I knew I'd made the right decision when (after cutting off the remaining leaves) I was able to push the trunk over. It was rot. Summer water when it was hot perhaps? I never watered it exactly, but watering the surrounding plants had to effect it. Why after all these years, when there had been no change to my watering habits? I wish plants could tell us what's going on.
ReplyDeleteYour nolina was huge. A much bigger loss than any of my plants. Are you going to try again? You had such good luck with it for many years.
DeleteI'm sorry, Gerhard. I wonder if it had something to do with the heavier-than-usual rainy season followed by the brutal heat dome - one blow too many?
ReplyDeleteIt's got to be a unique combination of factors.
DeleteOh gosh, sorry. It sounds like you have some potential reasons from some of the other commenters. Rot sounds like it might be the culprit as you mention? And one blow too many as Kris mentions? We've had a weird growing season here in my neck of the woods, too. Some plants have struggled while others have performed better than I can remember. I think it's because we've had ping-pong weather since February--warm 70s, then frigid cold, then relentless rain, then 90s and humidity, and now perfect weather (not complaining about the last one, of course). I hope most of us will have a more "normal" manageable garden season next year.
ReplyDeleteThe proverbial straw that breaks the camel's back. Just one adverse thing too many!
DeleteSo sorry for your losses!
ReplyDeleteI lost a potted agave cubic I’d had since 2014 to this center rot. Luckily there are two young pups at the edge of the pot. Fingers crossed for them!
I can't believe how many other people have had the same problem!
DeleteHeart breaking when you lose plants that are one of a kind. Wouldn't it be great if plants could somehow communicate when they are doing poorly so you could get in there early enough to save them?
ReplyDeleteI've heard people say that plants "talk." Sadly, *my* plants don't talk to *me*.
DeleteAgave snout weevil?
ReplyDeleteFortunately, there's no evidence of that.
Deletesome good news, anyhow!
DeleteWhile I didn't see any snout weevils in my garden, I just saw a whole bunch of them in a friend's garden a few blocks away. So....
Deleteš±
DeleteI have to say I have had no summer decline here. It would sure be interesting to know what the environmental hazards are that lead to this. It might be worth a conversation with Brian Kemble. Perhaps RBG experienced this at some point.
ReplyDeleteGreat suggestion! He'll give a talk at the Sacramento Cactus & Succulent Society on August 26.
DeleteHi, Clemens here from South Africa. We must remember that there are numerous pathogens and spores around, and that in times of stress, can cause disease in plants. Just like in humans getting colds and flu during times when our immune system might be struggling with changes in temperature etc. Also, lots of artificial gardens in an area will also cause a higher concentration of pathogens...like in crowded places with humans.
ReplyDeleteClemens, your comment is very well put. I completely agree about plants (like humans) being more susceptible to pathogens when they're stressed.
DeleteHi Clemens, haven't heard from you in awhile! Nice you are on Gerhard's blog! I learn so much!
DeleteHi Nancy. In modern Agriculture, large areas of monoculture is the rule, and even though gardens are obviously more diverse, we often have to revert to chemical means to combat pests. You will note that these large aloes and agaves don't just rot out in remote natural locations, as pathogens loads are within normal parameters. However, I have seen large quiver trees, Aloidendron Dichotomum, succumb to rot caused by plant-lice in the crown, in areas close to towns or argiculture. But I agree, seeing a large Aloe Marlothii, grown for years, rot out from the crown, is very disheartening...so yes, it happens in my garden too.
DeleteThanks for the info, Clemens. It is very discouraging. Interesting it happens in South Africa too.
DeleteSad to see this. My only thought is that with the variety of plants affected, and in different locations throughout the garden, it seems more like an environmental stress that pushed them over the edge and gave any potential pathogens the upper hand. As to what that particular combination of stresses was, it's hard to say. Up here, we are seeing a lot of manzanitas starting to die branch by branch. I suspect it was winter damage to the vasculature that is only showing up now that things are drying out, making it harder to get water through the damaged tissues.
ReplyDelete