How to divide plants
One of the magical – and occasionally frustrating – things about gardening is that nothing in the garden stays as it is. Plants grow, and before you know it, that tiny seedling chosen so carefully for a special location has outgrown its space and is jostling its neighbours. In gardening, we’re constantly looking ahead, to see what a plant might soon become, and also editing what’s in the ground already, making any changes needed to keep the plants happy.
Dividing plants is one of those jobs that can really help to keep plants very happy in their spots. At its simplest, dividing plants just means lifting up a clump of something that has grown too big for where it is, breaking it apart at its roots, and replanting one section, while also getting a lot more plants completely for free! But different plants require different methods of division, so read on for a few general tips…
Why divide plants?
There tends to be two main reasons for dividing plants.
The first one is to reduce a plant’s size if it has grown too big for the spot it is in.
As plants grow, many of them can start to spread out, also often reproducing underground, by spreading stems or bulbs, for example. After a few years, in place of one small plant, you suddenly have a clump of quite big plants.
This can impact on the health of the plant itself, as it might struggle to get enough sunlight or nutrients in the spot it’s in, and it can also impact on the health of its neighbours, smothering any smaller, slower growing plants. By dividing the plant, you encourage it to continue to grow vigorously, maintain good health and generally look better.
So, if you have had a plant in one spot for a while and see that its leaves are getting smaller or it is producing less flowers each year, it could be a sign that it is in need of division.
The second reason is to propagate a plant, and get another one (or more) of the same plant, completely for free…
If you have some bare patches in your garden you want to fill, or you want to share a favourite plant with a friend, dividing it and growing on each section as a new plant is a great way to increase the numbers.
Many clumping herbaceous plants benefit from division to keep them growing at their best, such as the salvia and erigeron in this border
When to divide
Plant division is usually done in the Spring or Autumn, depending on the type of plant. As a general rule, it is best to divide plants when they are not actively growing, so that they are not putting energy into creating new leaves, stems, flowers or fruits, but can concentrate instead on establishing a good root system for each of the new plants.
For Summer flowering plants, this usually means either Spring time, before growth and flowering, or Autumn time, just after flowering. Remember that plants that are divided in the Spring will tend to need more care, as you will have to water them consistently through the drier months ahead in Summer. Plants divided in the Autumn are more likely to benefit from the rain at this time of year, but might need a bit of extra protection for the colder months in the Winter.
Spring flowering plants, which are often plants that grow from bulbs, are best divided after flowering in the Summer months.
It is possible to keep dividing plants through the dormant season, eg Winter, as long as the weather conditions aren’t too drastic, or the plants can be kept in a protected space, like a greenhouse or cold frame.
It’s always best to divide plants on a cool and cloudy day, so they don’t suffer from the stress of heat and water loss while you’re exposing their roots. Early in the morning, when the plant has plenty of water is also best.
Generally, plants that benefit from division should be lifted and divided about every three to four years.
Which plants?
Not all plants can be divided. Trees and woody shrubs are rarely divided. But most herbaceous perennials (plants that grow back year after year, but do not form woody stems) can be multiplied in this way, especially clump forming perennials and those growing from bulbs.
Plants that really benefit from being divided regularly include:
This is far from an exhaustive list though, so if you’re not sure, a quick Google should help to find the needs of your specific plant.
And check out our plant guides for individual information on how best to propagate each plant.
How to divide plants
First, you need to dig out the entire plant and lift it from the soil. It’s best to dig around 15cm away from the edge of the plant, going round the entire outside area and then gently lifting the plant up from underneath, teasing it away from the ground, being careful to keep the clump of roots attached and intact.
Once the plant is removed from the ground, it needs to be divided into sections. Make a decision based on the size of the plant, along with how many new plants you’d like. If you’re just dividing in order to keep the plant in check, you might want to split it into two healthy sized sections. If you’re trying to propagate a number of new plants, then you could divide it into many more smaller sized sections. The crucial thing is that each new part has a good amount of roots attached.
The actual method of division will depend on the type of roots the plant has.
Plants that have formed a clump and have a large fibrous root system are usually best divided by hand. If you can, simply separate the roots apart with your hands, carefully creating new sections of plant. This works well for hostas, heucheras or epimediums.
If the roots are too solid for this, you can use the “two fork” method. Two forks, back to back, are speared through the middle of the plant, and gently pressed against each other to lever the plant into two sections. This can then be repeated if you want to break the clumps up further… This is a method that works for a huge range of plants, from anemones and agapanthus, to larger grasses, ferns and day lilies (Hemerocallis).
Really tough rooted plants or those with woody crowns might need to be cut with a sharp knife or even a hand saw. This would be the best way of dividing hellebores, delphiniums, bear’s breeches (Acanthus) or astilbes.
Finally, plants that have already spread using rhizomes, or modified stems, and grown new “baby” plants next to the parent plant can just be separated by hand, and each baby plant will grow to form an adult.
Once you’ve separated the plants, you should have a number of baby plants, or “divisions”.
Keep these divisions out of sunlight, to avoid any stress on the exposed roots. You can replant one of each division back in the original spot if you were dividing a plant to reduce its size.
Place the plant back into the hole and hold it in position with one hand. Make sure that the new division is at the same height above the ground as the original plant. (You can usually tell this from where the soil marks the stem, or where the stem changes from green to a lighter colour…) Hold in position with one hand, with your other hand back fill around the plant with the soil that was removed. Firm into place and water well.
Other divisions can either be replanted elsewhere in the garden – just dig a hole first and then follow the same method above. Or, if you’re planning to give the plants away to friends, you can pot them up by putting them in pots with some compost. Again, just take care that the plant is at the same position above the compost as it was in the ground. Water well.
