Dividing Perennials

May 20th, 2022

Dividing Your Perennials: Sharing, Caring and Rejuvenating Your Garden Spaces!

By Carol and Lois with Peterborough Master Gardeners

In the Spring and Fall we often look at our garden spaces, picturing them in the peak of their growing season and taking a mental picture (or for some, like me, copious notes) about the things we are going to change for the next season. As we envision the changes, it is likely that dividing (splitting) our plants is one of our fundamental “go to” garden strategies….and if it isn’t, it is certainly worth considering. Not only does dividing established perennials help to reinvigorate the plants themselves and your garden, but it enables us to share with our friends and community, save money and in the process continue to expand our own network of like-minded people.

When developing your garden plan (usually during the cold, snowy winter when we are dreaming about Spring and the fresh smell of earth), determine which plants would benefit from splitting. In general, plants should be considered when:

  • the centre of the plant has died back or the stalks, leaves and flowers are weaker,
  • the plant has run out of room in its’ space in your garden (and is overtaking or crowded), and/or
  • you really love the plant and just can’t wait to have more of it or share it!!!

Once you have decided on which plants you will be splitting, then you should do a little homework. Keep in mind that not all plants lend themselves to splitting. Dividing involves splitting the crown and root ball so should be limited to those plants that have a “clumping” growth habit and central crown. Plants that have tap roots or runners (spread underground) should be propagated by “cuttings” or seeds instead.

However, be careful… because many of these plants can be terribly invasive as well. Even though your intentions are good to “share the wealth”, we don’t want to transfer an invasive plant problem to a friends’ garden (unless you plan to spend lots of time with them pulling it all out 😊).

Proceed with caution if you are thinking of “sharing” purple loosestrife, Bloody Cranesbill, Common Daylilly, English Ivy, Goutweed, Periwinkle, Micanthus, etc… For a complete list of plants to avoid in this regard, check out this link: https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/

Examples of plants that lend themselves well to dividing include:

  • hostas
  • Ornamental grasses
  • Daylillies (beware of the common “ditch lilly” as it can take over
  • Yarrow
  • Daisies
  • Phlox
  • Irises
  • Coneflowers

Timing is also important. Some plants do not like having their roots disturbed at all and should be split (or transplanted) when dormant. Others can be split in early Spring, others in fall after they have bloomed, and others can be split anytime (very hardy). Spring dividing should be done early when there is only a few inches of growth, or for Spring Bloomers, wait until they have finished blooming. Try to choose a day that is overcast and cool and the ground is moist.

Organize the tools you need (and clean them thoroughly) as follows:

  • garden gloves
  • sharp garden spade
  • shovel
  • large garden fork (2 preferred for some jobs)
  • garden knife (optional)
  • watering can
  • plastic bags/transport pots (if sharing)
  • small amount of compost (for mulch)

Once you have done your homework, selected the right tools and have picked the right day for dividing, the rest is quite easy:

Step 1: Find a healthy plant suitable for dividing

Step 2: Water the plant well

Step 3: Dig up the entire plant as one (dig all around the plant about 8cm from new shoots; dig deep enough to get all of the roots and pry the plant gently from the ground)

Step 4: Split the Roots (knock off the soil so that you can visualize the crown and root system; use your hands, spade or knife to break the main clump into smaller pieces).

Step 5: Replant in the same new locations or share with others.

A few special things to keep in mind:

  1. If the centre of your plant was woody and has died off, use the new growth/vibrant sections around the outside, if possible, for your new plantings
  2. When replanting, do not use compost in the new hole. Use the native soil if possible and spread a handful of compost on the surface instead.
  3. When transplanting (or planting for that matter), keep in mind that plants need sufficient pore spaces in the surrounding soil (to collect gasses and provide space for water). So don’t “stamp down” and compress the soil completely. Don’t worry, the new plant with seek spaces to solidly root.
  4. Although most plants can be divided with a sharp spade or garden knife as discussed above, a very well established/dense root system may require the “big guns”. For example, a large established hosta can often be separated without too much pain using two garden forks inserted “back to back” with the root system being pulled apart using a downward and outward force.
  5. When sharing plants…a few things to consider: a) The new plants can be placed in plastic bags and put in the shade if they are being replanted in the next day or so…just keep them cool and protected from the weather, and b) Ontario is facing a new issue with the presence of jumping worms. These worms can be destructive to the soil structure needed for healthy plant growth (https://www.mgoi.ca/resources/resources.html. To prevent spread, it is advisable that you thoroughly wash the root system of a “gifted” plant before planting in your own garden.

With all of this said, I am hoping that you and your friends will enjoy splitting and sharing your plants this season. It is through sharing both knowledge and goods that we can truly build a stronger community and enjoy the true natural environment that we are so blessed with in Ontario.

Ciao!!!

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