Dividing herbaceous perennials
March is a good time to divide herbaceous plants, just before their spring growth. Dividing plants regularly helps to keep them growing vigorously, as well as being an opportunity to create new plants for free. It’s much easier than it sounds – no expert gardening knowledge required – so here’s our guide.
Which plants are suitable for dividing now?
A perennial plant is one which grows for at least three years, often much longer. Annual (one year) or biennial (two year) plants don’t establish for long enough to ever need dividing. Most perennials can be divided at any time of year, as long as they are kept well-watered, but spring is a good time to divide plants before flowering or if they are a little tender.
Plants that can happily be divided now include Agapanthus, Anemone, Aster, Bergenia (elephant’s ears), Chrysanthemum, Convallaria (lily-of-the-valley), Delphinium, Epimedium, Eryngium (sea holly), Euphorbia, Gentiana (gentian), Helianthus, Hemerocallis (daylily), Hosta, Iris, Lychnis, Lysichiton, Lysimachia, ornamental grasses, Ranunculus (buttercup), rhubarb, Salvia, Sedum, Verbena and Zantedeschia (arum lily).
How to divide a plant
With a garden fork, gently work around and under the plant to loosen it. Keep working your fork in until you can lift the whole plant easily. Gently shake off any soil so you can clearly see the roots.
Now you have lifted the plant, you can be guided by the plant itself on how best to divide it. For example, some plants produce ‘mini-plants’ around their crown which can gently be teased off and potted up as individual plants. Other plants with small, fibrous roots, can be eased apart with your hands into new ‘clumps’. Other plants again will require more serious man-handling; for example, daylily have very chunky roots so two garden forks, back to back, inserted into the centre and then worked as levers against each other will eventually work the plant into two halves.
Finally, plants which have very dense, woody crowns or tubers, like irises, will require a sharp spade or knife to break them apart. Look at where any new shoots are forming and aim to cut the old plant into up to five clumps, each with two or three new shoots. For tuberous plants, look at cutting on the ‘joints’ between tubers and make divisions that will leave some roots and shoots on each section.
Whichever form of division is going to suit your plant, don’t worry too much if it feels quite brutal. Most plants actually respond well to some ‘damage’ like this, by growing new roots and shoots, so it is likely everything will recover and thrive.
What to do with your new plants
It is really important to replant your newly divided specimens as quickly as you can, in a pot or in the ground, before they start to dry out. As always, water them in well to help prevent air pockets and ensure good root/soil contact.
Most gardeners will replace one clump in the original hole, to give that plant space to regrow and fill out again, perhaps with a little garden compost to give them an extra boost. What you do with the others is up to you, as long as you plant them somewhere quickly. Divisions planted into pots can happily stay in pots for a season or so to grow and establish, just ensure they are watered well and kept in a frost-free place.
Dividing plants is a great way to share what you grow with family and friends for free, or simply to help fill your own garden with plants that you know are happy there. If you are in any doubt, pop into our Centre and have a chat with one of our plant experts for some specific advice.