How to . . . divide perennials
by Rhiannon James
Pulling your plants to pieces might seem like a rather odd way to help them along but for clump-forming perennials such as asters and sedums which reappear year after year, division really does help them to keep growing strongly and is an easy way to increase your stock of plants too.
Many perennials naturally form clumps which grow outwards from the centre so the new, vigorous growth emerges at the edges while the centre can eventually become weak or even die off. By splitting perennials and re-planting the sections, you can get rid of any old, unproductive bits and give the rest a new lease of life. You can also use division as a quick and reliable way to create new plants instead of buying them or growing them from seed.
It’s often recommended that you divide perennials every two or three years to maintain their vigour but it’s usually quite easy to see if and when this job needs doing (the clump might be congested or bare in the centre or the plant might simply have outgrown its space). If you’re not sure it’s best to check the advice for your specific plant.
Perennials can be divided at almost any time of year as long as the new plants are not allowed to dry out while they reestablish themselves, but in general plants are best divided in autumn (if the soil’s not too wet or frozen) or early spring, when they’re dormant (although some spring-flowering plants such as irises are best divided in summer).
Things you’ll need
You can often tease the parent plant apart by hand but if this proves tricky because your clump is very large or congested, you may need a pair of hand or border forks, a spade or possibly a knife.
Step by step
1. Lift the perennial you want to divide out of the border using a garden fork. Try not to damage its roots or those of the plants around it. If the perennial’s growing in a container, then just empty it out of the pot.
2. Carefully shake or wash off as much loose soil as possible so you can clearly see the roots and shoots of the plant and remove any weeds, dead leaves or other debris.
3. You’re now ready to divide your plant. Many perennials can be gently divided by hand. Take sections from the edge of the crown (the area at the base of the clump from which both roots and shoots emerge) and gently pull them away from the main clump.
4. Clumps can be split into lots of small sections to get the maximum number of new plants or they can be divided just a few times to produce bigger, more mature plants. Just make sure every section has at least a few strong roots and some buds or shoots.
5. If the crown is too big or tough to tease apart by hand, try using a pair of hand or border forks. Push them into the centre of the plant’s crown back-to-back, and then gently move the handles backwards and forwards to separate the plant into two pieces. You can then either go back to dividing the plant by hand or repeat the same process to progressively split the plant into more sections. Alternatively, if the clump has very densely interwoven roots, you can use a knife or a sharp spade to chop the plant into sections. Some perennials, such as delphiniums, which have fleshy roots are generally better cut into sections using a sharp knife or spade.
6. Discard any old, weak sections from the centre of the crown and trim any dead or damaged material from each division.
7. Work some organic matter into the soil and plant the divisions as soon as you can, making sure that each one is planted at the same depth as its parent plant. You can also pot divisions up in containers if you want to. Water the plants in well and don’t let them dry out while they’re settling in.