Picked up a mini topiary ball today, one of those plastic foliage jobs, at BM Home bargains, reduced from £5 to £1.99.
Stripped all the bits of foliage off it - surprised at just how much there was (more than I expected) but I'm also left with two spiky "igloo" shaped plastic frames, about the size of a grapefruit, that might make an interesting basis for a SF/fantasy building.