Dividing perennials is a quick and easy task that will keep your plants happy and healthy, with the added benefit of increasing your plant stocks for the garden, or to share with family and friends.
Perennials that can be divided are those that produce new shoots from the crown each year. All you need to do is dig them up and divide them. Examples include alstroemeria, sedum, salvias, dahlias, rudbeckia, ornamental grasses, agapanthus, chyrsanthemums, echinacea, clivias, kangaroo paws, daylilies etc. Woody based perennials should not be divided.
1. Perennials are vigorous plants and the tubers and crown can become congested. This can cause poor air flow around the foliage which can lead to disease and mildew.
2. Without division plants may grow and flower poorly as there is too much competition for nutrients and water so they lose their vigour. By dividing your plants you can rejuvenate them by cutting out the old growth, allowing the young, healthy growth coming through.
3. Some plants such as sedum may grow away from the central crown which can look unsightly, dividing them will improve their appearance.
4. It keeps the size of plants in check.
5. It makes good economic sense as you get extra plants for free!
You will need to dig and divide your perennials every 2-5 years depending on variety and vigour. When you divide them the ‘offspring’ will be genetically identical to the parent plant.
The best time to dig and divide your herbaceous perennials is between autumn and spring after you have pruned them. If your garden bed is largely made up of herbaceous perennials don’t dig and divide them all at once, it is best to spread over a few years so your garden continues to be lush and full. Evergreen perennials can be divided any time as long as they aren’t in flower.
For early flowering plants autumn is the best time to divide. Autumn is ideal as the plants are going into dormancy so won’t be easily disturbed, and the soil is still nice and warm so the roots can put on growth before winter. Plants are more easily moved after they have been cut back.
For late flowering perennials early spring is a good time to divide as the plants are just starting to their active growth which allows you to easily see where to divide them. Dividing in spring will allow you to quickly enjoy the efforts of your labours realised as the plants will take off.
All plants are forgiving and if you get mixed up with what to move when, it is unlikely to damage the plant, it will just set them back a little. However if you divide in mid winter there is no growth and it is cold and wet it may cause the plants to rot.
Try to time dividing your perennials to after you have had some rain, or water them the day before so the soil is moist and easy to dig. However, you shouldn’t dig over wet soil as it will compromise the soil structure, it should be just nice and crumbly.
Never divide when it is very wet or when there is imminent chance of frost.
Start digging 10cm out from the base of the plant. Use A lever action from the spade or garden fork to gently lift the growing crown from the soil. You can leave some soil on the roots to help reduce disturbance, though most of it will fall off.
Check the health of your plant at this stage, there is no point in dividing disease ridden plants, you are best to dig them out and start again. You want to see a nice plump, healthy root system.
First split the foliage so you can see clearly where the plant should be divided. Some plants will easily pull apart in your hands. Others may require shears or a sharp knife or shovel for cutting through, in extreme cases such as Hostas you might need something like a saw to get them apart. Aim for 3-5 divisions depending on the size of the plant.
Keep only the outer sections that show a number of new shoots or growth nodes and a healthy root system, they will look like mini versions of the original plant. The old centre of the plant can be discarded to the compost heap if it is old and dying.
Larger clumps or divisions will have a more instant effect. Smaller divisions can be grown on in pots, or put straight back into the garden with a bit of extra care. With smaller divisions you will get more of plants but they will take a little longer to grow to full size, but perennials grow surprisingly quickly.
Remove any dead or damaged leaves before replanting. Long roots can be trimmed with sharp secateurs. If you are dividing an evergreen perennial, you are best to remove some of the foliage to reduce water loss after planting – the root system has been reduced so it will help reduce the time it takes to re-establish. The amount to remove depends on the plant, around half for a developed plant is the general rule of thumb.
Even if you are planting back into the same spot the plant has just come from it is a good idea to dig over the soil and add some well rotted manure or compost. Water the soil and then replant your divisions.
Ideally replant your divisions immediately. If this is not possible place them somewhere cool and keep the roots moist until you are able to plant them out. Be vigilant, the roots will dry out quickly and this may compromise the plant. You could wrap them in newspaper or hessian and wet it to help keep them healthy.
Replant your growing crowns at the same level they were previously growing then gently pat the soil surrounding them.
This is very important. You will need to treat these divisions as if they were new plants and water them regularly and deeply for at least two to three weeks. Adding a seaweed solution after planting will help to fortify the plant. If you are dividing in autumn, do not fertilise until the plants begin to grow again in spring. If you are dividing in spring, adding fertiliser after replanting is very beneficial.
It is worth noting that some plants, especially those with tap roots such as sea hollies and poppies resent root disturbance so may take a season to regroup before they flower at their best.
By dividing perennials you will encourage good health for your plants which will mean more flowers for you, not to mention you are also able to create more plants for free! Once you have done this once or twice you will realise how easy it is and soon be doing it with ease.