layering mint runners
The garden mint had a lot of mould on its leaves - perhaps because it's just below the blighted tomatoes. Solution: get rid of the older mouldy leaves, keeping only the small fresher ones; then bury parts of the stem in the soil so it can take root (i.e., layering it).
I took a cutting in water, just to test it out too.
*edit* The cuttings started growing roots in water, but after I planted it out in soil, it wasn't strong enough to overcome the powdery mildew problem.This mint plant used to be in a standard single pot.