Cactus questions.

[TheLetterZ]

I have been gifted a large, tall cactus - about 80cm tall. I have only had small cacti before so I have a few questions.

I needs repotting - the pot looks too small plus it is unstable and topples over so a wider heavier base is needed. How big a pot should it go in? Any tips on repotting a very prickly cactus? Does it need cactus specific compost?

Finally, is there anyway to identify what type of cactus it is / how old it is / how big it will get?

Any tips on repotting a very prickly cactus?

Wrap some paper round the prickly bit so you can grip the length of the paper as in the photo.

I repot ours in normal compost but do put a load of fine grit through it so it’s not too rich & has plenty of drainage. We have had our cactus for years & it keeps getting bigger so I must be doing something right! no clue how to identify them though. Maybe if you post a photo someone could identify it.
www.gardenersworld.com/how-to/grow-plants/how-to-repot-cacti/

There's an app called Picture This which scans and identifies plants and will give you the necessary care information

A couple of photos in case that helps.

I’ve been growing cacti for over 40 years, with a large collection in two greenhouses. Although I don’t grow the taller cereiods, I’m pretty sure yours is Pachycereus pringlei.

To repot, you can wrap the stem in towels, or use two slabs of packing polystyrene if you have it, or folded newspaper in a collar wrapped round the stem, or even a couple of scrubbing brushes with the bristles against the spiny stem. It would probably be easiest to lay it gently on its side, and try to ease it out, you might need to run a knife around the edge of the pot to loosen it.

It appears to be in a terracotta pot, so it might be best to use a slightly larger terracotta pot, you can get shallower half-pots in terracotta. But it doesn’t need to be much bigger - cacti should never be over-potted.

The best potting mix is John Innes number 2 or 3, mixed with horticultural grit - about 50/50. Once repotted, do not water for a couple of weeks to allow the roots to heal. Normally, in a greenhouse, cacti are winter- dormant and receive no water between October and March, but if you are keeping it in a centrally heated room, then modest watering every few weeks or so will probably suffice.

Remember, these plants have evolved to survive drought conditions, and overwatering kills!

Thank you @NanTheWiser, that is really useful.

My daughter is keen on learning more - do you have any recommendations?

Glad to help! There is a Facebook group for the British Cactus and Succulent society that can be very helpful - www.facebook.com/groups/434020283466998/

And if she gets really serious about cacti, there is a national society of the British Cactus and Succulent Society that she could join ( I think juniors get a cheaper subscription if she is under 16). There are branches all over the country that normally have monthly meetings, but obviously not happening right now, but we are having weekly Zoom meetings every Tuesday evening, which have been wonderful, with speakers from all over the world.