(Lophophora williamsii) Shrinking and perhaps suburn care

[Rogusi]

Hello everyone,

I turn again to the forum's wisdom for help. I went on vacations for about 3 weeks and didnt have someone that could come look at my cacti. Most are fine but these two Lophophora have problems. One my theory is it became etiolated and then the new area got sunburnt but not sure, and if so wondering if something I can do.

The other lil guy is shrinking and keeps on doing so despite having returned to normal summer watering schedule for about 2 weeks (thats when I got back). So thinking if there could something more to this shrinkage than lack of water. Will had photos.

Any input appreciated.

Thank you and my kindest regards.

[MikeInOz]

The cause of your problems is the size of the pot. This pot should have at least 8 plants of that size in it. If you don't have more seedlings you need a much smaller pot. About 2 x the diameter of the plant but it is always better to have a lot of seedlings together in a larger pot.

[Rogusi]

It's two different cacti, and while the pot could explain undergrowth and other issues on the second one. I doubt it would starting to act like this suddenly due to the pot, not impossible, but has been living there for at least 2 years (the smaller one).

[Steve Johnson]

It's two different cacti, and while the pot could explain undergrowth and other issues on the second one. I doubt it would starting to act like this suddenly due to the pot, not impossible, but has been living there for at least 2 years (the smaller one).

Mike was correct about measuring diameter at 2 x the diameter of the plant, but he didn't mention the pot's depth. If the pot is too deep for the roots, you'll eventually have a root growth problem which will lead to stem growth problems. Measure from the plant's soil line to its longest root, add a margin of about 2 cm, and this calculates the correct depth of the pot. If Lophophoras have shallow root systems, your pots may be too deep. (And I think they're too wide as well.)

[MikeInOz]

due to the pot, not impossible, but has been living there for at least 2 years (the smaller one).

Mike was correct about measuring diameter at 2 x the diameter of the plant, but he didn't mention the pot's depth. If the pot is too deep for the roots, you'll eventually have a root growth problem which will lead to stem growth problems. Measure from the plant's soil line to its longest root, add a margin of about 2 cm, and this calculates the correct depth of the pot. If Lophophoras have shallow root systems, your pots may be too deep. (And I think they're too wide as well.)
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I just potted a bunch of Loph seedlings. They had massively long and thick tap roots so I had to use very deep pots to get them in. The top to root ratio was probably 1 to 2! Normally, you are correct that squat pots are the go.