It’s good practice to divide most perennial plants every two to five years. If you spot them looking untidy or they are flowering less than usual, it may be a sign that they need your help. Dividing will give them more vigour and helps to alleviate a host of problems caused when plants become congested. Division has the added benefit of giving you lots of new plants for free. Finding other spaces for them is a great way to give your garden an established look, as a group of three or five of the same variety planted together is extremely impactful visually. Plant divisions as soon as you can and water them well until they are established. Each new plant must be placed in a spot at its original depth, so ensure the shoots are above the surface of the soil.
Alternatively you can pot up your extra plants ready to give them to friends and family. Ensure potted divisions well watered and ideally keep them in a frost-free place while they grow on.
The best time to divide most plants is in early spring, while they are still relatively manageable but the ground is not too hard. Plants will be less stressed by division if they are not in active growth, but if you do need to divide plants in summer ensure you water them regularly. Some spring-flowering perennials put down new roots after they have finished blooming, so summer is actually a good time to divide them.
Smaller plants can be dug up with a hand trowel and gently shaken to remove excess soil. Then you can tease them apart by hand. With larger plants it’s easier to dig the plants up with a fork or spade then push two forks into the rootball, back to back, in the centre of the plant. As you lever the forks apart, the plants will be split in two. Larger plants such as hostas may need to be divided again into smaller parts, but ensure each section has five or six shoots. If you ensure any dead leaves and stems are removed, it will be easier to spot the new buds. With plants such as iris that have thick fleshy tubers, you may find it more practical to divide them with a sharp knife or spade. Each piece will need a good growing stem or bud and a sound root system.