In Milan, April is the month of sedum and it has to be my choice for this month's gardener's Bloom Day. Stand in any residential area of town, look up and you'll see balconies lined with yellow - sometimes there'll be container after container across whole apartments. It looks great - from below it's just a mass of colour.

But I've always been intrigued about what happens to it afterwards. The flowering period is only two to three weeks. Do the people who fill their balconies with the stuff really only want flowers for a couple of weeks a year? Are they content just to look at the rather boring grey green plant for the rest of the year? Because if your balcony is full of sedum, there's no room for anything else.