Dead Cactus Questions

Q: Hello
I am trying to find out what is the problem with my 6 foot cactus. Started to turn black on the top 4 days ago and is growing down. I had another cactus in the same pot, but died like 2 years ago and started to die the same way. I live in New York and is beeing very cold the last 2 weeks. I also watered the cactus on april 19 and because I was out of the country I watered an extra half of cup. I usually watered every 2 months with no problem. I hope the pictures can talk by themself.
Please give any advise because I don't want to cut it if is no necesary.
Thank you so much.
Carmiña

A: Carmina,
Sorry to be the one to bring you the bad news, but the tip of the cactus needs to be cut off. It is rotting from the top. Cut well below the infected part, look at the tissue and make sure there's no sign of infection (brown/yellow/orange) and then spray the tip with household peroxide every day for 3-4 days. In a month or 2 after it's healed I recommend repotting in fresh well-draining cactus soil. Do not reuse the pot without sterilizing.

We usually water cacti every 3-4 weeks, drenching the soil and letting it drain completely away, never letting it sit in water. It is OK to let it go up to 2 months without watering on occasion.
Good Luck,
Peter