After a few years of cultivation, dividing plants can be beneficial for many perennials. It allows you to rejuvenate the plant, stimulate its growth and flowering, and multiply your favourite plants. However, it should be avoided too frequently, as this can delay the plant's maturity and impact its flowering. As a general rule, divide your perennials every 3 to 5 years, or when you see signs of fatigue, such as less abundant flowering or a bare centre.
Why divide perennials?
- Rejuvenate plants: Over time, many perennials lose their vigour and their flowering becomes less abundant. Division stimulates the growth of new shoots and revitalizes plants.
- Control size: Some perennial species can become invasive. Division helps limit their spread and maintain a well-structured garden.
- Multiply your plants: Division is a simple and economical method of vegetative propagation, allowing you to obtain new plants to enlarge the garden or share them.
- Improve plant health: Division provides an opportunity to remove dead or diseased parts of the plant, thus promoting its overall health.
When to divide perennials?
The right time to divide perennials depends on their flowering period:
- Spring or early summer flowering perennials: Division is done in the fall, preferably in September. This allows the plants to take root before winter and ensure optimal flowering the following spring. Examples: Hemerocallis, Paeonia, Iris.
- Summer or fall flowering perennials: Divide them in the spring, after the last frost. The plants thus have time to establish themselves before their flowering period. Examples: Aster, Phlox, Chrysanthemum.
Exceptions: Some perennials have specific requirements. Bearded irises are divided in July, while peonies and poppies are divided at the end of August.
Division steps
- Choose a cool, cloudy day to minimize water stress.
- Water the plant thoroughly the day before dividing to facilitate root ball extraction and reduce stress on the roots.
- Carefully remove the root ball of the plant using a spade or digging fork, avoiding damaging the roots. In the fall, do not hesitate to cut the foliage to 10 cm from the ground to clearly see the root ball.
- Dig at a distance of about 15-20 cm from the base.
- Gently lift the root ball with the spade, taking care to keep as many roots as possible.
- Divide the root ball into several sections using a sharp tool (knife, shovel) or manually. Each section must have healthy roots and at least one vegetative bud.
- For plants with fibrous roots (such as daylilies), divide the root ball using a digging fork or two forks back to back which you drive into the centre of the root ball and spread apart to separate it.
- For plants with rhizomes or bulbs (such as irises), use a sharp knife or spade to separate the rhizomes or bulbs into sections each with healthy roots and shoots.
- Loosen the roots with your hands if necessary and remove any dead, diseased or damaged parts, as well as weeds.
- Replant the divisions as soon as possible in well-prepared soil, amended with compost. Do not bury the collar, the transition zone between the roots and the stems, too deeply to prevent rot.
- Space the new plants according to their adult size.
- Water generously after planting and keep the soil moist for the first few weeks to encourage rooting.
- Mulch to protect the root system from the winter cold.
Additional tips
- Divide perennials every 3 to 5 years, or more frequently if they become too dense or show reduced flowering.
- Use clean, sharp tools to avoid damaging plants.
- If you cannot replant the divisions immediately, keep them in a cool, humid place, out of the sun, wrapping the roots in damp newspaper or peat moss.
- Feel free to consult resources specific to the variety of perennial you wish to divide, as some plants may require special care.
By following these tips, you can successfully divide your perennials and enjoy healthy, vigorous plants in your garden for many years to come!
