PLANT a hedge of swift-growing, bland (some would say ugly) Leylandii conifers, and the neighbours will soon have a petition up to force their immediate demise. They are loathed by many, and stories are legion of long-term neighbourly goodwill being instantly eroded as a new rank of Leylandii reach for the sky. Not all conifers should be tarred with the same brush, however. s and their close relative the thujopsis have an immaculate pedigree. Some varieties grow up to a height of 30ft, but the cutest ones are the little round ones that look like fat green hedgehogs. (The Royal Horticultural Society's indispensable A-Z Encyclopedia of Garden Plants, in a rare flight of fancy, rather charmingly describes one variation, "Caespitosa", as "cushion- or bun-shaped".) They are all well-behaved and slow-growing, unlike the rapacious Leylandii.