I made a fire to burn some wood waste and it got a bit out of control and burned some of my cacti on the side facing the fire.

It happened maybe 2 weeks ago. At first the burned side turned yellow, then it shrivelled, and now brown and black spots have appeared.

The biggest victim of this is my T. peruvianus (the tallest of all my cacti), but a pachanoi and bridgesii also got hurt.

Will this heal on its own, or should I cut the columns all the way to where the burned tissue ends? Alternatively, can I cut off the burned side (as opposed to doing a cross section, i.e. a vertical cut rather than a horizontal one; assuming the spines allow me to access it with the knife) to save the peruvianus column?

Damn thats unfortunate. I'm not sure that there is an easy fix. I dont think that a vertical cut would work very well. That would seriously compromise the integrity and strength of the cactus moving forward. How would it be able to support the weight of new growth? It would probably make more sense to cut horizontally and remove a whole cutting from any of the badly damaged areas. I would just toss those cuttings, but if you want to try to save them then you could make a vertical cut on the cuttings to remove the dead/rotting material. After they callus you could plant them log style with the green part facing up. That might work, but you would have to make sure that the callus is very hard and strong. Also you should keep those damaged cacti bone dry for awhile until they heal up all the way. All the best with them Jagube.

Thanks. I've done the deed, a good 5 ft has come down

If the post-surgery scar on the tallest column heals well, maybe I'll root it vertically and plant it again, the scarred side facing the fence for esthetic reasons.

Its sucks to have to cut them. But that big Peruvianus should grow back real strong from the stump. The roots are well established. New pups to look forward to at least. All the best with them Jagube.

Thanks. Just a quick update...

The original peruvianus has produced multiple pups and they're all growing at an impressive rate. Same for the bridgesii.
The pachanoi died sadly. I didn't cut out the rot all the way and it penetrated the cactus insidiously beyond rescue.

The peruvianus cuttings etiolated and grew wonky after being indoors for too long, but I planted them out in the spring and they've been doing well too.

If and when my plants get sunburn like that I just ignore them and they heal and grow, though the scars remain.

I often throw plants outside in the sun with little introduction and I get burns like this on some but not all plants. Some clones do this more than others.