Alina W

Rooting cuttings with potatoes

My guess would be that the potatoes took up any excess water, so keeping the soil airy and allowing better rooting.

Just a guess, though.

Moth Orchid

Trim the flower stem to just above the next node (the swelling on the stem with a tiny triangular leaf lying flat against it). Continue to water as you have been doing and it should flower again in a few months.

Getting aerial ivy roots off brick

A wire brush should shift them.

What you really need is hot sunshine to dry them off, which makes them easier to shift.

Hydrangea Macrophylla.

Yes, you will be able to restrain it - just don't exceed the 1/3, and it should be happy.

Hydrangea Macrophylla.

Yes. Prune out a third of the branches to ground level; do this for three years and you will have a smaller bush but plenty of flowers and a good bushy plant.

What animal is this please?

Frogs can certainly make a sort of "cave" in soft soil when it's hot and dry. It would be about that size, but the ones I've seen have the soil heaped up a little.

mushrooms

Don't worry about them. Compost contains rotted-down material, including wood and old plant material, and that is what the fungi feed on, breaking things down in the process. The chances of them being honey fungus - which generally feeds on old tree stumps - is very, very low indeed.

Begonias and Pelargoniums (geraniums)

If you have a cool windowsill indoors you can overwinter them there instead. The begonias will form tubers in a couple of years providing they are the right type.

mystery bulbs

Could it be over-congested clumps in wet, therefore soft, soil?

Aconitum (aka monkshood / wolfs bane)

Don't cut it to the ground, let it die back on its own and then remove the dead stems.