We talked on the phone a few minutes ago regarding paling/brown color that’s appearing on my cactus. Based on the attached pictures do you have any advice?
Thanks so much!
It’s hard for me tell for sure, but it looks like a little bit of discoloration at the very bottom of the cactus. What I can see looks like it might be a bit of rot. Looking at the pointed-top shape of the cactus, I’m guessing it is not getting enough light, and even though you are only watering every 3 weeks, with that amount of light it would want less water. But mostly it wants more sun.
First, regarding the discoloration – push gently against it to see if it is soft. If it is then it is the start of some rot. I recommend spraying with Hydrogen Peroxide, and a few days later following up with an organic fungicide like Neem (although not Rose Defense).
Make sure the soil is completely dry before watering. And bring the plant out into more sun – although not all at once. Every day bring it into about 1/2 hour more direct sunshine until it is getting at least 4 hours direct sun.