The joy of most perennials is their relatively undemanding nature: give them a well drained soil and more than half a day of sun, and they will thrive with only a bit of tidying, some feeding and watering in the growing season, and hopefully not much weeding because they cover the soil so well.
Our RocketGro Compost Soil Improver is the stuff for any tired garden border, while perennials in pots often prefer the slightly richer Container & Basket Compost.
Dividing
As perennials mature past a few years, they tend to form clumps that bulge or spread. In many cases, you can dig these up, split them, and replant the pieces - remember to water them as if they are new plants in their first summer.
September-October is a great time to divide early flowering perennials, so they can put down some roots before winter, and Spring is also fine for late flowering plants, right as the new foliage shows signs of emerging. Remember that if your soil is sticky clay, early Spring is always the best time for moving any perennials.
If you water them well, you should often get away with splitting them during the growing season if you have no choice.
What does not divide well? Hellebores and Dieramas don't like it at all.
Plants with a deep taproot, like lupins, hollyhocks, acanthus, most verbascums, poppies and eryngiums can't be divided easily, but they either spread by seed, or you can propagate them via root cuttings in late Autumn or early Spring.
It's a myth that splitting plants every year is beneficial for most plants. Helenium and Phlox are the most "demanding" - every two years tends to suit them best, and older heucheras and primulas might creep into that range as well to keep them fresh looking.
You can see for yourself when clumps are ripe to divide every few years, and if there is a bald patch in the middle, it's overdue a breakup! Roll Moody Blues.
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