The problem
If a plant looks a bit yellow or drooping, someone might suggest putting a penny in the pot. The idea is that the copper will leach into the soil, liven up the plant and maybe even ward off fungi. It is one of those tips that refuses to die, passed on like family folklore.
The hack
The promise is simple: pop a coin in the compost and let chemistry do the work. Supposedly, the copper acts as a mini-fertiliser and a mild fungicide.
