I always find this very weird

[ElieEstephane]

This is one of the weirdest thing i have seen on my cacti. First it started with my echinocactus grusonii on the roof when temps hit 34 in spring (it still hasn't reached 34 in mid summer!) And the cacti were only watered 2 days ago at the time.

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Then last week this happened to these echinopsis in part sun. They had been watered maybe one week ago at the time and tenperatures were around 32 and humid.

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Now i don't consider this a problem at all and it's easily solved by watering and they perk up the second day. But why is it that cacti, that are advanced water storage tanks, can dehydrate so easily overnight? The conditions are considered very mild compared to habitat. What's also weird is that it happens to all individual of the same species at the same time. The first time, my 2 big golden barrels, the one pictured, and 2 of its rooted pups all in different locations did it at the same time.
It was suggested that my soil is too gritty but what does the soil have to do with a plump cactus losing a lot of water.
Anyone had this experience?

[Aiko]

Looks like a local dehydration, not a total dehydration of the plant as a whole. So I would think these were on the brim of getting sunburn.

[ElieEstephane]

I thought of an impeding sunburn too aiko but in case of the echinocactus, the wrinkling occured on all sides on 6 plants in different locations/exposure . They are all in full sun since winter so they are used to the intense sun.
Maybe it was a combination of strong sun that almost burned them and a wave of dry air?

[DaveW]

"But why is it that cacti, that are advanced water storage tanks, can dehydrate so easily overnight? "

Cacti are CAM plants and only open their stomata at night, therefore that's when they could loose water if the atmosphere is cooler but dry. Usually if too hot at night they do not open their stomata and go into summer hibernation (estivation) and stop growing to avoid water loss until night temperatures cool again.

Also it could depend on if the roots are taking up the water.

See:-

https://askabiologist.asu.edu/cam-plants

[ElieEstephane]

Summer dormancy is a concern right now as i have some crassulaceae in dormancy but cacti are still growing. The echinocactus incident happened several times in spring.
Im not living close to my cacti right now but the weather channel gives temperatures at an almost steady 32-33/24-25 degrees celsius. I don't think 25 degrees at night is too high. Is it?

[DaveW]

Only thing I can find is this Elie. Obviously in humid night conditions a plant would loose less water than in dry ones, just like us sweating.

http://forum.bcss.org.uk/viewtopic.php?t=165875

[keith]

Make sure you don't have root mealy bug . Temps are not too high. Somthings going on with the roots I think ?

[greenknight]

In the case of the Echinopsis, those are not desert plants, they need a little more water than desert species - and those are pretty crowded in that pot. The E. grusonii is also tightly potted, and in a very gravelly mix. Not that surprising that they were unable to keep up with water loss in hot, dry conditions.

The topography there is similar to here - we have mountains and desert to the east. Humidity can drop to extremely low levels when we get east winds, some of my cacti benefit from daily watering then. I have had some wrinkling develop on a Ferocactus pilosus, which is a Mexican species adapted to a much hotter climate than I have - I think it's ready for a bigger pot!

[toadstar]

My young E. grusonii do the same when they're on the verge on being sunburned it seems. I have to make sure they get some shade in the afternoons.

[ElieEstephane]

No root mealies, thankfully! Echinopsis are less than part sun, anything more they stop growing altogether. The echinocactus pot is pretty big and deep. Only the main stem has roots so only the offsets are crowding the pot. In fact all my golden barrels are very overpotted because it's a scary repotting job!
I think you are all correct and it's a combination of intense sun, a sudden humidity drop at night, the gritty mix and overcrowding that caused the pots to dry out too fast and hence the cacti.
Yes i should use a less gritty mix (i use 66% grit) but it performs very well under abundant spring rain: 10 days consectuve rain, not a single plant rotted. And yes i should probably water more but it's because i barely have the time i moved to cacti. It's always interesring to see how they behave year after year.

[kuni1234567]

I have seen problems with some of my cactus and very hot weather can sunburn cactus as well as other succulents. I know that sunburn damage is permanent and this is why commercial growers use shade cloth to protect their plants.