by Marilyn Homewood, Master Gardener
Despite the lingering snow, the longer days and stronger sun tell us that spring is indeed here! With that we begin to think about all of the chores we wish to accomplish. Division of perennials is a common task. So why do we divide?
Division is a common means of vegetative propagation. It is an easy way to increase the number of plants you have available. Division is also required maintenance for some perennials in order to achieve maximum bloom year after year. Although a fairly simple process, there are a couple of considerations you must make.
Time of Year
Because successful division depends on the growth of new roots, the best times of the year to divide are spring and fall when the soil is warm, water is available and stressors are at a minimum.
Many perennials can also be divided during the summer months but high temperatures mean an increase in water loss. This leads to a stressed plant so extra care must be provided to ensure the plant remain well hydrated. Also, there are some ornamental grasses that only grow new roots in the spring. These plants should not be divided in the fall as they will not grow new roots that can take up water.
Method of Division
This will depend on the type of root and crown system the plant has. No matter the type of plant, keep in mind that each plant division must contain at least one bud or growing point and a few healthy roots. If you are unsure of the what you are dealing with, there is a link to a list from the University of Minnesota at the end of this blog.
Clumpers – These plants often have fibrous root systems sometimes with rhizomes but grow many smaller crowns at the base of the original each having its own root system. This often makes for easy separation with little tissue damage. Examples include ajuga, daylily and hosta.
Runners – These are plants that spread by covering the ground by shallow horizontal stems. They root along their nodes and send up new shoots making them easily dividable by separating the root ball. Examples include bee balm and goldenrod.
Tight, woody crowns – These plants are a little more challenging to divide as the buds are often tightly packed on a hardened crown. For best results the plant must be older when split to ensure that divisions with have growing points. Examples include baptisia and peony.
Thick rhizomes or tubers – Rhizomes are technically stems that grow underground. Divided sections must contain at least one growing eye. Examples in this group would be bearded iris and dahlia. These varieties should only be divided when dormant.
Tap rooted plants –These cannot rarely be divided unless multiple tap roots have developed and are better propagated by using root cuttings. Plants in this group includes oriental poppies.
Basic Steps for Division
- Dig out the plant. If not replanting immediately, protect from desiccation. Removing the plant from the ground can destroy tiny root hairs (responsible for water uptake). Protecting the plant means a faster recovery on the division is replanted. I often place the root ball in a plastic bag and place in a shaded area.
- Separate your plant into pieces using the most appropriate method. Make sure to take generous divisions of sufficient size to ensure growing points and healthy roots.
- Replant, digging hole wide enough. Roots like to grow out and down so give them enough space to spread out. Be sure that the soil has good contact with the root system by firming the soil then water the division in, slowly allowing the soil to further settle against the roots.
Resources
The Science Behind Plant Division
Divide and Conquer: How to Divide and Multiply Perennials
The Peterborough & Area Master Gardeners 