The clamour surrounding wild gardening has become so popular that the Royal Horticultural Society received a surge of calls about it last year, with the trend showing no sign of slowing down.

It’s a wild style that encourages biodiversity by blending large swathes of different flowers and grasses like a wild prairie, but with sections colour-coordinated in different tones.

Greening tree pits is a form of guerrilla gardening. Whether and how the mini-bed on a street tree may be planted depends on ...