There’s nothing quite like the forgiveness of grass. We cut it, hack it, kill it, scorch it, poison it and in a few weeks, given the chance, it comes back for us. Even if you smother grass under a foot of concrete, it won’t be long before the first green nose pops up. Preparing our veg patch yesterday, I noticed a single shoot of grass poking above the soil. When I tried to dig it out, I discovered that it was just one shoot from about 20 feet of roots. Left to itself, these roots (our predominant grass is called Yorkshire fog) would quickly send up enough shoots to fill the whole patch. Grass also spreads by its glut of seeds. Each Yorkshire fog plant can produce up to 240,000 seeds in its lifetime. But grass is essential. It converts pollutants, like carbon and sulphur dioxi