So I bought San Pedro cactuses from Home Depot 3 days ago. I transferred them the same day to a pot, and it's been in my house since. This morning I noticed it was a lighter green on top, and it looked like there was some scarring going on. I had planted it with leftover soil that had some water crystals and watered it once, so I figured that was the problem. I replanted it today with special cactus soil. Should that fix the problem? I'm just afraid because it happened so quickly, and I don't want them to get any worse.
Light green growth close to the apex means that it has grown in poor light, and is typical for plants from dealers who don't specialize in cacti. Do you keep them indoors or outdoors? I think your plants have not yet adapted to their new environment, the spots look like sunburn. Light green areas that have not adapted to stronger light yet are extra sensitive. Too much water and nutrients can have a similar effect, but it usually takes more than 3 days, at least where I live and for my more slow-growing cacti (I have never grown San Pedro). N.B. Soil labeled as "cactus soil" is rarely suitable for cacti (too much peat and holds too much water), but if memory serves me right San Pedro is a quite tolerant species.
The cactus is in my basement bedroom, but it still gets indirect sunlight through a couple of small windows. Since I planted them in the cactus soil, it has gotten a bit better. The soil contains a lot of rocks instead of peat, and I think the drainage is helping. The tops of both cactuses are starting to darken up, and the spots are starting to fade a little.
