In most parts of this country we are blessed with a long growing season. This means that some herbaceous perennials (plants that go underground in winter) can be sheared down to the ground immediately to produce a fresh flush of foliage, and in some cases, flowers. Among these are lady's mantle (Alchemilla mollis), hardy geraniums, chives, mint and lemon balm. A top-dressing of garden compost and the fertiliser of your choice (I favour pelleted chicken manure) will give them a boost.