I'm watching Matt James (Britain's "Urban Gardener") on HGTV and he just finished 'painting' some clay pots with yoghurt. With the plants planted into the pots and set out in the garden, moss and algae will grow wherever the pots were 'painted'.
I never knew that.
(I don't know if it would work with plastic pots, but it certainly wouldn't cost much to try it.)
I never knew that.
(I don't know if it would work with plastic pots, but it certainly wouldn't cost much to try it.)

