As a garden designer, I’ve created gravel gardens for clients and while they are good for water retention and can benefit biodiversity, there are some worrying trade-offs. Gravel and sand are extracted from the natural environment, either mined from the land or dredged from river or sea beds. You could use waste products from construction instead, though they come with the carbon cost of crushing and transportation. Laying aggregate can also smother good garden ecosystems, potentially wiping out wild flowers and fungi — and affecting the wildlife dependent on them.