With every perennial garden, you will eventually have to divide your plants.
Unlike trees and shrubs that grow taller each year, perennials grow by expanding the diameter of the clump.
For example, a single hosta that you purchase in a 6" pot will multiple to form a clump that can measure a foot or two across.
As perennials grow, they may eventually outgrow their space in the garden.
This is one indication that it's time to divide and replant.
Another sign that a perennial is ready for division is when the centre of the clump dies away leaving a ring of healthy foliage.
In this case, dig up the entire clump and divide the healthy outer ring into pieces.
The centre section can be discarded.
Timing is key when dividing perennials, you should divide opposite bloom time.
Spring and early summer flowering plants should be divided in the fall.
Late summer and fall bloomers are divided in the spring.
Those plants that bloom in summer or are grown for their foliage only, can be divided spring or fall.
If dividing in the spring, time the work so that the new growth is barely emerging.
You will be able to see where to divide, but won't be stressing tender new growth too much.
In fall, you can begin dividing as soon as plants start to look 'fallish', as foliage loses its healthy summer appearance.
It is often easier to see where to divide in fall as stems emerging from the ground are still evident.
If you don't have a choice about moving or dividing a perennial except when in bloom, be sure to remove all flowers and buds from the plant you're disturbing.
You want to ensure that all the plant's energy is directed towards root development.
Flowering expends an incredible amount of energy!
Once you have determined that your plants need to be divided and the timing is right:
- choose a cool overcast day as opposed to a sunny, warm time
- water the garden the night before if soil is dry; digging will be much easier
- plan to work on as many plants as you can manage in the time you have available since plants should be out of the ground the shortest amount of time possible
- have soil amendments ready: compost, composted manure, peat moss, coir fibre or sand depending on your soil requirements
- be sure to have Bonemeal or other transplanting food to help plants develop healthy roots
- collect the tools you will need: a sharp, straight-edged spade or root knife depending on the size of the plant; shears to cut down excesses foliage; a digging fork for turning in soil amendments; some damp burlap or newsprint to cover exposed roots to keep them from drying out; a watering can or hose for watering plants in once replanted
- cut down excess foliage to 3 or 4" from the ground to make the job easier
- dig up the plant and take the time to remove any weeds or grass around or through the crown
- if very weedy, soak the rootball in a bucket of water to loosen the soil and make the task easier
- divide plants between stems
- discard poor roots or damaged portions of the crown
- replant the piece of perennial, using transplanting fertilizer, at the same level it was growing previously
- firm soil around roots and water well
If you have extra pieces of plants and don't have a spot for them immediately, set them in the shade with roots covered.
You can also temporarily heel them into an empty garden or pop them into a container with soil around the roots.
Dividing perennials can be a very social event.
You can set up a 'plant garage sale' to make a bit of cash, and you could share plants with family or friends.
Extra plants can also be donated to the local Horticultural Society for their fundraiser plant sales!