Fat plants

Cactus with spots

Question: cactus with spots

I keep my cactus on my window sill. there is no direct sun all day but until now it has survived well even in winter a couple of days ago I noticed that it had brown spots, other white ones (like mold) and since it was 3 weeks that I didn't water it I gave him water.
It is not improved !! and I do not know what to do. the tip is still fine but the trunk is full of spots and touching it is a bit soft

Answer: cactus with spots

Dear Giulia,
a large part of cacti is used to living in areas of the globe characterized in winter by a harsh climate, with even intense frosts, and temperatures that can fall below -12 ° C; many, but not all, for this reason it is good, at the time of purchase, to ascertain the species and variety of the plant you are bringing home, in order to be able to control its rusticity. In addition to this, cacti that live in nature are usually used to sunny positions, with at least 5-6 hours of direct sunlight per day; and in areas where most cacti are widespread in nature, when it is cold it does not rain.
The correct growing conditions for a cactacea in winter are:
- full sun for many hours a day, at least 4-5.
- completely dry soil; in general we stop watering the cacti that will live outdoors or in a cold greenhouse already in September, so that when the frost arrives the ground is completely dry.
- away from bad weather; because if we do not water the plant, but the plant receives the rain, the soil becomes damp the same.
Your plant was therefore without sun, and exposed to the elements, besides not knowing any septic and variety we cannot know if it is a cactacea resistant to frost or not.
The least that could have happened to her was what happened to her: she was struck by a fungal disease, which is causing her rottenness.
The only thing you can do is try to save the part of the plant that is still healthy; then arm yourself with a well sharpened and clean knife, and cut the tip of the cactacea, taking care to keep only the still healthy part; also check inside the trunk, if there are small spots or dark zoning, remove them with the knife, after having disinfected it. Allow the stump to dry for at least a couple of days, dust it with fungicide and rooting hormone, and place it on new and slightly damp fatty soil; place the vase in a bright area, with little direct sunlight per day; and hopes the plant will root.
When we buy a plant that we do not know, we always ask the nurseryman the botanical name of the essence; in this way we can then inform ourselves about the place of origin, to try to cultivate the plant in conditions similar to those present in the areas where this plant develops in the wild. Consider that cacti in nature develop in Central and South America; perhaps your cactacea comes (or at least its ancestors) from the highlands of Mexico, check on the internet what the climate of the arid zones of Mexico or Guatemala is.