Over the past week my beautiful starfish cactus has started turning black in areas and dying. This is such a beautiful cactus and I have enjoyed it for 3 years now and don’t know what the problem is our how to fix it. Please help me.
Certified GKH Gardening Expert
This looks like it could be a case of cactus stem rot or root rot, probably fungal in nature. Sometimes this is caused by over-watering - feel the soil - is it damp/soggy to the touch?
I would recommend that you read the following article and follow the prescribed treatment which involves removing the diseased parts and re-potting the cactus in a clean pot in sterile soil after washing off the roots thoroughly. There is no guarantee your cactus will rejuvenate itself, but it's worth a try.
And, just in case, you may want to consider starting more starfish cacti plants using cuttings from this one.
For more information on growing starfish cacti, please visit the following link: