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 favorite plants. However, you should avoid doing it too often, as this can delay the plant's maturity and impact its bloom. As a general rule, divide your perennials every 3 to 5 years, or when you observe signs of fatigue, such as less abundant flowering or a bare center.
Why divide your perennials?
- Rejuvenate plants: Over time, many perennials lose their vigor, and their flowering becomes less abundant. Division stimulates the growth of new shoots and revitalizes the plants.
- Control size: Some perennial species can become invasive. Division helps limit their expansion and maintain a well-structured garden.
- Multiply your plants: Division is a simple and economical vegetative propagation method, allowing you to obtain new plants to enlarge the garden or share them.
- Improve plant health: Division offers the opportunity to remove dead or diseased parts of the plant, thus promoting its general health.
When to divide your 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 root before winter and ensures optimal flowering the following spring. Examples: Hemerocallis (daylilies), Paeonia (peonies), Iris.
- Summer or fall-flowering perennials: Divide them in the spring, after the last frosts. This gives the plants 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 in late August.
Steps for dividing your perennials
- Choose a cool and cloudy day to minimize water stress.
- Water the plant heavily the day before dividing to facilitate the extraction of the root ball and reduce stress on the roots.
- Carefully loosen the plant's root ball using a spade or a digging fork, being careful not to damage the roots. In the fall, feel free to cut the foliage to 10 cm (4 inches) from the ground to see the root ball clearly.
- Dig at a distance of about 15 to 20 cm (6 to 8 inches) from the base.
- Gently lift the root ball with the spade, taking care to preserve as many roots as possible.
- Divide the root ball into several sections using a sharp tool (knife, shovel) or by hand. Each section must have healthy roots and at least one vegetative bud.
- Plants with fibrous roots (like daylilies): divide the root ball using a digging fork or two forks back-to-back that you push into the center of the clump and pull apart to separate it.
- Plants with rhizomes or bulbs (like irises): use a sharp knife or a 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 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 crown (the transition zone between the roots and the stems) too deeply to prevent rot.
- Space the new plants according to their mature size.
- Water heavily after planting and keep the soil moist for the first few weeks to encourage rooting.
- Mulch to protect the root system from winter cold.
Gardener's tips for division
- Use clean, sharp tools to avoid damaging the plants.
- If you cannot replant the divisions immediately, store them in a cool, damp place, away from the sun, by wrapping the roots in moist newspaper or peat moss.
- Do not hesitate to consult specific resources for the perennial variety you wish to divide, as some plants may require special care (e.g., avoid dividing lavender and lupine, which do not like to be disturbed).
By following these tips, you will be able to successfully divide your perennials and enjoy healthy and vigorous plants in your garden for many years to come!
