I may have discovered the Elixer of Life for Bonsai trees.

 So, about a month ago I got really lazy while changing the water in the snakes' tanks, and instead of carrying the bowls all the way to the sink in the other room, I emptied them into the bowl I was using to water one of my bonsai trees.  I water my trees by standing their pots in a large bowl of water and letting them soak for a while, which is a fairly well accepted practice in bonsai keeping, as it saturates the soil without the erosion of pouring the water in from above.  I occasionally feed them with a highly diluted plant food, but it's dicey business because if I get the amount wrong they get leaf burn and look manky as all hell.

Anyway, a week after bathing in snake-water, and my fussy little bush cherry bonsai  is looking better than ever.  
I repeated this little cheat for my privet bonsai, and it too is now flourishing (despite dropping a couple of leaves so it can pretend that it's doing normal tree stuff for autumn.)

I can only assume that the minor amount of contamination caused by the snakes slithering through their water (which they do fairly often- hence the frequent changing) provides the homoeopathic quantities of nutrients that these fussy little bastards need to stay green and healthy.  Which is good, because snake-slithered water is something I have plenty of, and I do enjoy nice green, healthy-looking bonsai trees.