On Jan 31, 7:16 pm, Jane wrote:
I've got a lovely, large old cactus that got a little bit damaged when I
recently moved house. One of its many 'arms' (wonder what they are
called? It really does look like it's spreading its arms out to take a
bow) got damaged near the 'trunk' of the plant and I had to cut it off.
I trimmed it down a bit and put it in a little bit of water and I was
wondering if it would continue to grow, if I should put it in cactus
compost or something. Any ideas?

First off take it out of the water! And check for signs of rot. If
necessary trim it again.
Cacti & succulents can stand any amount of drought, but they quickly
die from rot with wet feet.

Leave it somewhere cool and frost free for a few days for the wound to
heal and callous hard over. Then prop it up on a pot of moist gritty
compost with a thin layer of grit on the top. Roots will form after a
few weeks - keep the soil damp and don't subject it to long periods of
strong sunlight until it has rooted down. A few species may root
better if just laid on the surface.

A tennis ball sized plant can last a whole season dry without roots if
needs be (but if rot sets in it will die in days).

Regards,
Martin Brown