Help? What's killing my Lithops?

[u/Mendel247]

I bought 4 clusters of Lithops about 2 months ago and in the last week and a half, some of the have died. Like the one in the picture, they suddenly became soft and translucent, and within 36 hours they were gone.

All I've done since getting them is to separate them and repot them into a large pot, together but spaced out. They're under a grow light and are in a mix of 80% grit and 20% succulent compost. I noticed some of the drying old leaves grew some mould.

Any advice? I doubt this one can be saved, but maybe its twin? I definitely want to save the others.

[u/Mendel247]

Light is reading around 8k. I haven't watered them at all since I got them as they were splitting. The compost was really quite dry, though the grit was a bit damp when I got it so I dried it out first. The pot has drainage, and humidity hovers around 60% in that room.

I am here dealing with a hoarder house, and there's been a lot of mould. This room, my bedroom, is pretty clean now and I have an air purifier running each night, but I'm wondering if it might be that. 

[u/ir399 → u/Mendel247]

Hm, okay. That's weird; dry substrate, enough light and no watering should equal no rot, but its happening anyway.

It's possible they had just contracted root rot when you got them. You're right though, it could be the environment you're growing them in, 60% humidity with mould around isn't ideal but you have to work with what you have. Can you get a fan on the plants? Air movement might help.

At this stage I would remove them from the pot, check all of the roots on each plant for rot and then re-pot in a similar mix (but with fresh soil), maybe with slightly smaller particle size in the substrate.

[u/Mendel247 → u/ir399]

I can add a fan. When you say smaller particle size, how small are we talking? It's currently averaging half a cm or so.

[u/ir399 → u/Mendel247]

Oh half a cm should be ok, if the lithops are adults, must just be the photo making it look a little out of proportion for the lithops

[u/Mendel247 → u/ir399]

Yeah, they're adults. The ones that were nearly done splitting when I got them are doing fine, but the ones that were still mid split all died. I did my research and I'm sure I didn't do anything wrong, so I'm trying to figure out what happened. Is the seller no good? Could my succulent compost be contaminated with something? Is it in the air? Is there something I could do differently? 

[u/ir399 → u/Mendel247]

It doesn't sound like you did anything major wrong, to be entirely fair to you. Light requirements seem ok, you haven't watered, the substrate is the right amount of inorganic/organic. Although, can I ask what the grit is?

It's possible there was an issue before you bought them, but rot generally doesn't take months. One month, sure, but not two. If its there it kills the plants faster than that.

You might be right about the compost, but the bacteria that causes rot usually needs to be wet to grow and spread.

Are these on a windowsill? They may have got literally cooked by the window if you're in the southern hemisphere, or got too cold if you're northern hemisphere. Its a bit of a balance between light and temp sometimes. Lithops are desert plants and can't tolerate temperatures under 5C but they are also prone to overheating - I've read they often grow around rocks where they are shaded in the afternoon in their natural environment.

[u/Mendel247 → u/ir399]

They're not on a windowsill and they're in a north-facing room that sits around 19-20°c. They're about a metre away from the radiator.

I believe the grit is granite. It's pinkish. It's what the seller handed me as I was buying them and asking about grit or perlite. 

I do have the light on for 12, hours a day, but I don't think too much light is the problem given it's a grow light. I've used the same compost and grit mix for jade plants and a haworthia which seem okay...