Not sure what is wrong with my cactus?


This is my first prickly pear cactus, I have it in a bright indirect sunlit windowsill, I have it on a watering schedule so I try not to overwater- making sure the soil is dry in between waterings. My house is fairly warm and I have it in a cactus/succulent soil mix. I just noticed these light coloured spots and I’m not sure what is causing it, my other cacti that are beside it seem to be doing okay.


Hello – It is impossible to accurately diagnose the cause of the light coloured spots on your cactus without a visual inspection or really good photos.  However, I did find an article (link below) that lists five causes of white spots on prickly pear cactus.  Reading through them may give you some insight as to the cause of the problem and potential solutions. The five are:

  •  Pest infestations particularly scale and mealybugs
  • Extreme sunlight resulting in sunscald
  • Fungal diseases such as powdery mildew
  • Nutrients deficiency due to poor soil quality
  • Mineral buildup which can be caused by over-fertilization and poorly draining soil.

If you have access to the internet, you can search in Google to find pictures of cactus exhibiting some of these symptoms.

The article also points out that providing optimum growing conditions for your plant is always the best way to avoid these issues and maintain plant health.  Prickly pear cactus benefits from 4-6 hours per day of direct sunlight.  Your cactus may do fine in your bright, indirect light but will not be as robust as the optimum light conditions would provide.  Overwatering is the cause of many issues with cactus.  Try watering once every 2-4 weeks.  I’m including below a link to an article on the care of prickly pear cactus.  Sounds like you have caught this issue early so your plant will likely respond well.

Are you aware that eastern prickly pear cactus (Opuntia humifusa) is native to southern Ontario (it is considered endangered) and can be grown outdoors in Toronto gardens?  If possible, your cactus will benefit from spending some time outdoors during the summer.

Good luck!