What to do when cactus is rotting???

The before picture. 
when my mammillaria was still healthy in the big pot

Thailand is in the rain season now and some cacti in my garden were also rotten.  At this time, it happened with my favorite mammillaria which became rotten and I just noted it recently.  So I think it’s important to fight with rotting seriously although before that, I led the plant rot without do anything. Here is the way to do that and hope it’ll be helpful when you have same trouble like me.

• How do we know or notice that the cactus is rotting?

The brown base of can mean that the plant is aging (become woody) or rotting. To tell the difference, touch the base and see if it is hard or flabby/soft. Hard means everything is OK. But, it’s soft, it means that plant is rotting and it must be treated with care.  

Here is after picture.  It was so soft and I had to cut some rotten part out and dried the rest for 3-4 days together with the rotting aloe

• Can I still save the rotting cactus? 

The second way to save a rotting cactus is to simply cut of its top.  Using a sharp knife cut off the top of the plant.  After that, let’s it dry for a 2-7 days. Once dry, set about 1/2 the plant into potting mix/perlite or cactus mix/perlite.

Do not water too much. Just enough to make the soil to become a little humid. Over watering at this point could cause rot again. With luck and the right conditions it will start to root. Once it develops its own roots, the watering can be increased.  Establishing the new roots may take several days or weeks depending on the condition of plant and care.

I put them on top of pot with 100% perlite

After several days with humid from rain, the new root came out finally! 

Another option is to take a cutting or two for grafting which need skill & experience to do that.

• What if my cactus is rotting from the top? What shall I do?

If a cactus is rotting from the top you need to act immediately before more of the cactus rots. Just like as if it is rotting from the base, carefully cut off the top of the cactus that is rotting. Dispose of the cactus top.

As for the bottom, clean it with a spray to make sure it does not catch the top's disease. Change the soil unless it looks as if the cactus can't take a repot. The remaining cactus should now be healthy. After a few weeks of extra care, start caring for it as for a normal cactus. It will not grow a new top or increase in height but it will grow branches which will grow.

Source: http://www.botanicalgarden.ubc.ca,  http://www.alexandgregory.com/