Help! It's turning yellow

[fanaticactus]

At first I thought it was getting sunburn, so I moved it into filtered sun. Then, even though I don't water it that often, I thought rot had set in--but the body is still very firm and shows no soft spots. I have not taken it out of the pot yet to look at the roots. All my other Gymnos are doing well and they all share the same substrate. I see no insect pests on it. What's going on?

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[mikethecactusguy]

you should check the roots.

[fanaticactus]

you should check the roots.

I will do that.

[Steve Johnson]

you should check the roots.

I will do that.

Correct -- for good or ill, everything starts out in the roots. By the way, I know that the skin color isn't normal, but it sure looks pretty.

[fanaticactus]

I just unpotted it and eveything looks fine. The soil was loose--not compacted--and is a combo of pumice, gritty/sandy soil with a bit of organics, and crushed rock, so it drains well. The substrate was slightly damp, not wet, as I had watered it just a few days ago. It had a mild acidic odor which, according to all care info I found, it likes--that is, a low pH...slightly acidic. The roots are quite long but do not appear damaged in the least, and the underground base is as firm as the rest of the above-ground body.

When I repot it, should I trim the roots or leave them as is? It is in a fairly deep plastic pot (I gave up on clay), but not overly deep. Should I trim them and let them dry out before trying a new pot? Or should I just spread them out more horizontally in a shallower pot?

Strangely enough, I Googled other sites for care of the G. schickendantzii and found a picture of one in its natural setting and it had the same yellow color as mine. Here is a link: https://www.ruthbancroftgarden.org/plan ... -delaetii/ So is this normal? That would be hard to believe. The other thing to note is that it bloomed once last summer but has not even shown any signs of growth this year.

[Steve-0]

More shade and see if it darkens.

[mikethecactusguy]

Now that you checked the roots. Mine turned yellow 2 years ago and has never changed back. It has slowly kept growing. It goes a bit green after being under shade for a week or two.
As long as it keeps groing, oh well.

[teo]

A bit similar to this (G. mihanovicii hybrid from own seed) but this has always looked like this (variegated, low chlorofyll)

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[fanaticactus]

More shade and see if it darkens.

It's been in a spot that's almost all shade all day, except for a little bit of dappled sunlight in the PM. No hot, direct sun. But we've had a miserably hot, humid summer already with two official heat waves and a possible third coming this weekend.

[fanaticactus]

I appreciate everyone's input. Keep the ideas coming--I'll try almost anything. Meanwhile, I'll repot into a wider, more shallow pot and spread out the roots some more. First, though, I think I'll trim some of the very long ones and let it dry for several days before repotting.

[Steve Johnson]

A bit similar to this (G. mihanovicii hybrid from own seed) but this has always looked like this (variegated, low chlorofyll)

Don't know about you, but I think those skin colors are really attractive.

Fanaticactus -- if your G. schickendantzii's yellowing wasn't caused by sunburn, it might be serious nutrient deficiency. Then again, if that was the problem, you'd be seeing it to one extent or another on the rest of your cacti. Since you're not, this seems to be a head-scratcher.

[anttisepp]

This group of gymnocalyciums often suffers from abundant direct sun and heat.
I'd put it in the slight shade and give more water with fertilizers.

[Steve-0]

More shade and see if it darkens.

It's been in a spot that's almost all shade all day, except for a little bit of dappled sunlight in the PM. No hot, direct sun. But we've had a miserably hot, humid summer already with two official heat waves and a possible third coming this weekend.

I lived in NC from '76 to '06....so I know heatwaves a humidity . Been in Utah the past 14 years with an avg 300 sunny days annually and heat into the 110 range at times. Mostly 90's for summer Temps. My cactus collection focuses on natives for less maintenance and I'm getting a late start at my early 60's to grow a collection. A few cactus for almost ten years ...then added 45 or so this year....and....already in the thinning process now. Hence not many exotics nor seed starts for me. Old and hardy is my mantra.

[7george]

Heat waves + greenhouse location make me think that the Gymno could be overheated if anything else looks OK. Even my fake plastic GH adds 10 - 20 degrees C over the ambient in sunny days so without some ventilation it can be a killer. I'd place that cactus outdoors in shade spot until some recovery is seen. The colour pattern is nice anyway, hope that guy is just sweating.

[fanaticactus]

Thanks, Steve, anttisepp, 7george. This should address all your suggestions...It's true I have not been watering nearly as much this summer because of the highly unusual amount of humidity we've had. I've read in several sources that desert cacti should not be watered when it is humid. Of course, the Epis are an entirely different thing & they're doing very well; no more flowers though. So with less watering, they are getting a reduced amount of nutrients. But I will start correcting that after Monday, when the current heat & humidity are supposed to break. All my collection has been outdoors in the fresh air (split between sun & shade) for two reasons: the greenhouse is far too hot even with an large exhaust fan at the peak and an oscillating fan on the benches, and the vents do not open far enough to allow a lot of air to pass through; second, fresh air works wonders on them...as it does on us humans! Of course, I have to take most of them back inside if heavy rain is expected--and we have not had a lot of that this year. I usually leave out the Gymnos, Echinocereus, Parodias & Echinopsis because they like a lot of water--or at least a moderate amount. I'll see if more fertilizer makes an appreciable difference. I use Schultz's liquid for cacti (2-7-7), which I think is a decent amount of the needed nutrients.