On 04/08/2010 21:16, Craven wrote:
Hi, I have a very old cactus that I don't water often.

I noticed this week the new growth at the top is going brown (an
unhealthy brown) on one side. The cactus is about 3.5 foot tall - the
last 5" are affected.

A picture would be useful. Rotting from the top is unusual. Noticing
when the rot which started from the roots reached the top is more common.

I suspect it's overwatering as it turns out someone has been watering it
for me (a kind gesture but...).

If it is overwatering then the soft rot starts at the roots and works
upwards. A tall plant tends to fall over if this happens. In summer it
is hard to overwater unless you leave them standing in water for ages.

Obviously I'll stop watering it for a while... a long while!

It is hard to kill a cactus by underwatering. I had one ~4" diameter off
its roots for a year and thought it was dead and shrivelled up. It was
sat unpotted for a season and then came into flower as its last defiant
act. Potted it up again at that stage and it rerooted.

I don't recommend this method of cultivation.

Does anyone know if they generally recover? I've never been in this
situation before.

Hard to tell. If it is just going brown then it could be scarring from
pest damage at the growing point rather than a rot. A picture would help!

Regards,
Martin Brown