U can either help them 'water' their plants with bleach or start a garden festival by putting your own potted plants and should they complain, 'gossip' loudly too.
I have really lousy and inconsiderate neighbours as well. One stopped short of adding more plants, as I'm staying along the corridor, up til my main gate coz I gave them enough black face to see so they got the hint. The other is still irking me with noise, albeit only slightly ever so lesser noise after 5 extremely long years, so I honestly do not believe in holding out your tolerance for too long.