Agave americana is a tough perennial that is naturally endemic to harsh desert climates. It not only survives, but is happy in awful heat and dry air without shade. However, a specimen that lived in my garden for about two years succumbed to sunburn and moderate heat in less than a day.
The problem was that it had been growing in a rather shady spot since it arrived. There was enough ambient sunlight to sustain it, but no direct exposure to sunlight. The typically stout steely blue leaves were consequently elegantly elongated and slightly twisted, but well adapted to their particular environment. This would not have been a problem, except that I dragged the plant out to relocate it.
In only a few hours, the leaves were roasted by exposure to sunlight. They melted and laid limp like steamed asparagus. Only the unfurled leaves in the middle remained turgid. By the next morning, the scorched leaf surfaces were already turning ashy white. Now, the desiccating foliage lays flat with slightly curled blackening edges, around the surviving meristem (terminal bud in the middle), like an angry starfish road kill taking its last gasp.
The good news is that the new foliage that eventually develops from within the presently unfurled middle leaves should adapt to the environment where the plant gets relocated to, even if the first leaves to open are not quite adapted. The bad news is that the damaged foliage cannot be salvaged, and will need to be cut before planting. I will put the plant deeper in the ground than the level it had been growing at so that the leaf stubs will be buried.
Just as people can get sunburned, plants that are sheltered can succumb to sunscald when they suddenly become too exposed. It does not always result from the particular plant getting moved, but sometimes happens when nearby plants or features change. For example, foliage of Japanese maples that have grown as understory plants to larger shade trees is susceptible to foliar sunscald if the larger trees get removed or pruned significantly. Replacing old large picture windows with more reflective windows to keep the interior cooler may reflect enough glare to the exterior to temporarily scald sensitive ferns. Aggressively pruning English walnut, avocado or silver maple trees in summer may expose sensitive bark of main limbs enough to cause bark scald.
Damage to foliage may linger as long as the foliage does, but is typically as temporary as the foliage is. Deciduous plants will drop the damaged foliage in autumn, and replace it with more adapted foliage in spring. Bark scald though can be a serious problem, since the bark is not so easily replaced in a year. One of my great grandfather’s old English walnut trees got sunscald on some main limbs when the tree was pruned for clearance from a room addition in about 1950, and remained damaged when the tree was removed about half a century later. The scalded bark decayed decades ago, exposing inner wood to decay.
Tony Tomeo 
Wow, and I thought I gave my plants tough love! Even I have never done anything as tough as that.
Sunburn on plants is something I do talk about all the time when I am lecturing though, whether I am talking about seedlings or transitioning houseplants outside. People tend to remember things if you put it in terms they can remember. So I simply tell them that just as they would never go outside, naked, for 8 hours or more, without sunscreen and work in the garden that first beautiful day, they can’t ask their plants to do that by just plunking them down in the sun and thinking they’ll be fine.
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This is an old recycled article. I would probably explain it differently now.
While in Arizona, I noticed the importance of installing cacti in the same orientation that they grew in. That is not so important here, and I would plant them in whatever orientation they looked best in.
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I would think that’s definitely true with what I am hearing about the kind of heat and weather Arizona is getting. It almost makes me appreciate the frozen north–almost.
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Gardening must be very challenging in much of Arizona. While driving through Phoenix, I noticed several mature specimens of saguaro cactus that were hunched over because of scald that resulted from reorientation in the process of relocation. In other words, their southern exposures no longer faced toward the south. The sides that faced south were not able to accommodate their new exposure. Those relocated saguaro trees are very expensive!
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I imagine that the same thing is probably true–in different sorts of ways–in places like Las Vegas and parts of New Mexico and other places facing weather they are not used to.
I wonder about the Pacific northwest as well. It has had only a couple of summers of extreme heat (which I am sure has been a misery) but considering that they are usually so temperate, I wonder if their plants succumbed quickly?
Such a shame to think about those saguaro. Hard to believe that all that effort was put into obtaining them and then they were planted incorrectly!
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Sunscald is natural, like frost damage. Vegetation does not like it, but its resiliency has its limits. It is more common here because so much exotic vegetation from climates that are not so arid live here now. The same applies to urban regions within desert climates. Sunscald is not as much of a problem in the Pacific Northwest because most exotic vegetation is more tolerant of exposure than it needs to be there for that particular climate. In the big picture, extreme heat is not all that extreme. Weather has been documented for less than two centuries, which is not a long time at all. Ecosystems are adapted to long term climate conditions, so have experienced what, by limited perceptions, seems to be extreme heat.
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Some ecosystems are adapted to long term climate conditions. Others, like the forest systems in the rockies, are struggling with beetles. You can say that the beetles are just a way of clearing the forest, I suppose, but all they do is make it more susceptible to fire, which then clears the forest.
A similar thing is now happening in Maine–different forest and beetle, similar result. And I believe that was why there were Canadian wildfires in the east last summer as well.
So certain types of ecosystems are definitely struggling, particularly across what are cooler regions. They’re still in the frozen north–but at least in the summer, sometimes, not so much.
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They are struggling, but also trying very hard to recover from former violation and disruptions of their ecosystems. Years ago, Monterey pine was dying out so severely, both from insect infestation and disease, within its natural range that some expected it to go extinct. The pathogens were natural though, rather than introduced. The problem was that, because so many now live within their ecosystem, their ecosystem no longer burns as it did naturally prior to urbanization. Not only were there too many deteriorating old trees to sustain the pathogens, but they were interfering with the proliferation of younger trees to replace them. Now that most of the old trees are gone, the ecosystem seems to be a bit healthier, almost but not quite as if it had burned. The problem in my neighborhood is that it had been clear cut harvested more than a century ago, but then not managed afterward. There are now more hardwoods mixed with the redwoods than there should be naturally, and, because several redwood trunks grew from each stump of a harvested tree, the redwoods are more crowded than they should be naturally. Their forest is so horridly combustible that when it eventually burns, and incinerates the homes of those of us who live here, it can also get hot enough to kill some of the redwood trunks, which should naturally survive more natural fires. This could start the process over. If the forest can avoid burning long enough, the hardwoods eventually get crowded out to a less combustible degree, so that when the forest burns, it only burns the hardwoods and foliage from the redwoods, leaving the redwood trunks to regenerate afterward. While this happens, selective harvesting of crowded redwood trunks so that fewer trunks can dominate would actually benefit the natural ecosystem. It is an unnatural process, but helps to compensate for an unnatural disruption.
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