1 out of ten baby cacti I transplanted 2 weeks ago. Funny these cacti are almost year old. Spent all last summer under the mimosas in filtered light, sparse but regular watering. Some were stunted for whatever reason and this one volunteered after a midwinter watering, literally appeared out of nowhere. Others in the group are larger. after i moved them into one clay pot in a cactus mix I had set them out in the garden to start hardening up. We had some heavy rains for two days this morning on my rounds I discovered this one in poor health, maybe dead. One other small one has a small white spot on its side. Too much water? to much sun?

Anyhow I moved them to the porch to get out of the sun and rain which are both intermittent today. The plan is to let the soil dry and move them under shade cloth when they go back out. I am hoping the water isn't the issue but i can control that somewhat but not as easy as shading them. The tallest is about 3" and still looks great.

Image would not attach so I will try again later.

The image

other one developing white spots?
too much water or too quickly into the sun

soil looks like an awful lot of organic matter

Yeah it was an out of the bag cactus mix. Thought it might not have enough sand. taking a long time to dry.
The others look OK and the whit one has one tine bit of green.

50:50 organic material to drainage is a good benchmark for trichocereus. Then you can modify it for your climate depending on moisture level in your area. Perlite is cheap and works fine for drainage, if you don't want to get all fancy with pumice or something heavier.

I may re-pot them in a week or so and mix some perlite in. i have a pretty decent bag of it. I think I am going to make my own mix too. IME bagged mixes usually aren't that good. Stuff I mix always works better. The lil white baby's green spot looked a little bigger today so maybe she isn't lost. I've been talking to them when i check up on them in the mornings.