It's Chelsea Flower Show, so it's time to go around the garden doing the Chelsea chop. This isn't a new type of dance, sweeping the gardening world, but a method of pruning for herbaceous perennials. The name comes from the timing of the task, which is best done towards the end of May.
The idea is to cut back flower stems by about 50% (for smaller plants, leave at least 6" of foliage), before they flower. This encourages more stems, delays the flowering to later in the summer, and produces tidier clumps of plants. There are two main ways of doing this.
The first is to chop the whole plant down by 50% and the second is to selectively cut a third to half of the stems. The former is easier and probably better for bigger gardens where there are plenty of other flowers during early to mid summer and the latter is better when you want to prolong the flowering period of a single plant. Another benefit is that there's less need for staking as it results in shorter, clumpier plants. You will have more numerous, although possibly smaller, flowers. Note: this method is only suitable for herbaceous plants.
Don't try it with evergreen shrubs! While you're doing it, you may just spot some gaps which require filling with new plants and we have hundreds of interesting plants available, many currently at reduced prices!