I am concerned about my cacti, there is a yellow mold growing in my cactus soil. What can I do about it?
You can scrape an inch or two of the top soil out and replace with new cactus soil and keep the medium dryer between waterings.Make sure the pot is fast draining and not too large (keeping the soil wet). I never tried this but, have read many times that "Tinactin" for feet fungus, has been used on potted plant soil with fungus and killed it quick with a light spray or two....
Cactus soil should be graveley not humusy and should never get moldy. You should replace the soil with the appropriate mix for succulent plants. http://www.cactus-mall.com/clubs/faq.html
