Piney: what sort of cactus is it? And did you take a close look at those white spots? Reason I ask is that some cacti and succulents can be attacked by sap-sucking insects, which can cause leaves or pads to collapse. We sometimes get tiny leafhoppers or a thing that looks like a mealybug, or even something like a lerp (we had those on the Mesembryanthemum in the Community Garden this year, and a lot of the leaves were sucked dry and just collapsed in on themselves and withered. If the spots look furry, or like a little patch of foam or bubbles, or waxy and like a very micro turtle shell, take a small probe, say the tip of a pencil or a nailfile, and scrape or lift the surface layer. If there is a tiny bug on the surface, squish it.
The other likely cause is a fungus, from overwatering. This will usually show as a soggy or furry-looking patch, and there is not really a cure other than cutting off and disposing of the infected leaf or pad, and letting the plant recover in a warm, dry, sunny place.
Noodly: I've never tried coffee grounds! Sounds interesting. In this part of the world the usual mix for growing terrestrial fungi (like your ordinary supermarket mushrooms) is a box of aged cowdung or horse manure mixed with compost, sphagnum moss and straw, to which you add the mushroom spawn, then water well and leave in a warm, dim place for a few weeks, keeping the soil warm and molst. I'm trying to grow pine mushrooms on a mix of forest soil and rotting pine needles, to which I have added over-mature pine mushrooms from last years' foraging trips. Might take a few years to do anything. But foraging season starts again in the next few weeks, and I'm looking forward to getting out in the forest with students again!
Asterales: Auricularia auricula-judae, A. polytricha and several other Auricularia species are grown on wood, like oyster mushrooms. You can grow them in a box or bag, on a mix of damp straw and hardwood sawdust, or on a piece of wood. A young friend down in the city grows them by inserting plugs of wood containing spawn into holes drilled in suitable branches (but he has a very live garden where just about anything will grow; this is the guy who had a swarm of bees colonise his outdoor dunny, left them there, and now he and his wife just work around them).
If you want to see what cloud fungus or woodears (Auricularia species) look like, check out most of the scenes in SSSS where there are dead or dying trees or wet indoor wooden beams - they are those ear-shaped or semicircular, hard jelly textured fungi which are growing everywhere on wood. They are a popular food and medicine in the Orient, somewhat known in Europe, not that popular in America, possibly because of the rubbery texture. You can also find pictures in any of Christopher Hobbs's books on edible and medicinal fungi.
I learned to prepare them by cutting them at the base, thoroughly cleaning them, then slicing finely and drying. They can be stored dry and reconstituted in hot water.
