I have some SP seedlings that are probably a year or 2 old now (bought them as established seedlings about 6 months ago), and they have been doing fairly well. However, about 2 weeks ago half of them started slightly turning color and softening.
It started with pale yellowing all over, not really localized. I had never fed them, so decided to give that a try a dry organic 3-4-4 at about 25% of what they were recommending for established plants. Now that pale yellowing is turning darker, and they are getting bendy. In the middle in the pic, that section bends very easily.
I have been watering them once a week. They are in a cactus soil that I supplemented with more perlite. They were watered on Monday, and the soil just under the surface is moist feeling, but far from wet.
They were typically indoor until around a month ago, but we've been having 70F during the day, 50F overnight, so I left them out this whole time.