ID and pointers?

[Nory]

Could anyone let me know what this is please? The smaller one is starting to turn purple-ish and the bottom of each is a bit shrivelled (I watered it last week) - is this a sign that something is wrong or is it quite common? It's in the sunniest window I can manage! Flowers are from last year

[anders]

Mammillaria polythele, perhaps?

[iann]

Mammillaria polythele, perhaps?

Yes. I don't see anything too terrible, although it doesn't normally go that colour.

I suspect you have two separate plants in the same pot, and separating them might help to keep them both healthy. Or just planting them further apart if you want them in the same pot. They tend to get a bit tall or top-heavy with age, but aren't too hard to grow with standard cactus treatment. Soil in the third photo doesn't look great.

[Nory]

Thanks both! I've had them for a couple of years now and they haven't really grown at all so I'll try planting them a bit further apart and see what happens. Soil in the third photo is a shop-bought cactus mix - I've repotted since then anyway but my other plants seem to be doing fine with it!

[iann]

You say they haven't grown, but I suspect they have. The flowers indicate that there is some new growth, but it is possible that the base of the plant is shrinking at about the same rate. Stick with it, cacti are slow at the best of times. They won't grow incredibly fast on a windowsill and trying to force them will probably end in tears.

[Nory]

Quick update: after a few more searches online, I put it in a tub of water to soak for 30 minutes as a bit of an experiment - within a couple of days the larger one in particular seemed to have really filled out. Two weeks later with some good sunlight it's looking even better!