May is usually a lovely month. We see the last of the frosts, and can get those tender vegetable and flower plants out in the open. It’s also when plants start to pop up in places where you probably didn’t put them the year before! Plants like Geranium phaeum (the Mourning Widow), aquilegia and foxglove are masters of self-seeding and are likely to appear overnight, fully fledged and flowering! Well, perhaps that’s an exaggeration, but they certainly fill out fast so it’s a good idea to move them quickly before they get too comfortable.
Indeed, any perennials that have formed unwieldy clumps can be lifted, divided and re-planted now, unless its very wet. A plant that is too big for it’s location can be sliced into 2 or 3 smaller pieces as long as each retains some good root growth. Enrich the soil if you’re going to replant one piece in the same location, and either put the other pieces in pots for now, or replant around your garden to give a sense of rhythm to your beds and borders.