Tom writes
Hi, someone gave me quite a big cactus arm that broke off the main
plant about a year ago.

They say it's still possible to plant it and grow it.

Should be.

Is this true? I've planted arms that have only just dropped off with
considerable success.

I've planted it in cactus compost, I'm just wondering how often I
should water it. And in what quantity. I haven't watered it yet.

Keep soil just slightly moist, enough to let it know that it's worth
putting out roots, not enough to risk rot.

Any advice appreciated!

I'd be inclined not to 'plant' it but to use a couple of sticks to
secure it on the surface of the soil.

In nature, it would expect to be lying on the soil, and then put roots
out from the end bending down into the soil. But you'd probably like it
to be growing in a vaguely upright position, hence the support.

But you're an old hand at this! Have confidence in your knowledge!

--
Kay