Question
Dear Greg

I live in London UK. About three months ago, and knowing nothing about cacti, I moved what I think is an apple cactus (about 5 feet tall) from an indoor location with a lot of north-facing light  to a south facing balcony outside.  After a month or so, we had a couple of weeks of very heavy rain. Shortly afterwards, the south facing surface had become mottled and beige colored. A month or so later, it had started sprouting pups (is that right word?) today we discovered that if we scrape the beige area away there is good green skin underneath.

What caused this, how can we fix it, and how can we prevent it happening in future?

Hope you can help, Greg, and looking forward to hearing from you.

John

Answer
John,

More than likely it was sunburn that caused the plant to turn that color. Typically, a southern exposure has much more intense sunlight, and if there was any direct sun involved, then sunburn is a distinct possibility.

Cacti that are not grown in full sun, will sunburn. Even a cactus that is grown in full sun will sunburn if the north/south orientation of the plant is changed. It doesn't sound like a fungus to me, however if you want to send me a picture to [email protected] I may be able to give you a better answer.

Sincerely,

Greg