Ten Tips for Dividing Perennials
Sunday, April 1, 2012
The Hort Admin
  1. Start as early as possible—early April is good. Even if shoots are up only an inch or two, you can dig or divide it. (This presupposes you remember which plants are which in your garden.) It is better to pot up smaller, younger plants as, with less top growth, there is less set-back to the plant. Roots, once out of the ground, warm up faster. The main benefit of early digging is that the plant has time to overcome transplant shock and become established, resulting in a happier, better-looking plant in time for the sale.
  2. You can dig up the whole plant and divide it or chop pieces from the edges of a clump using a spade. If you decide to dig up the whole plant there are various ways of dividing it. You may be able to tease the root apart by hand (e.g. day lilies). A large woody or dense fibrous root will need to be chopped or cut apart using a spade, sharp knife, secateurs or small tree saw.
  3. Larger divisions are preferable to very small ones, however this is relative. Try to avoid potting up very large ones (or large whole plants); these can be difficult for people to carry home. Besides, if you can create two or more divisions from one plant, we will have more plants to sell. (Share the wealth.)
  4. You may need to trim the root ball to fit the pot. I use my secateurs for this but sharp scissors may also work. Ideally, there should be a minimum ½ inch space around the root ball, to be filled with potting soil.
  5. Please try to avoid having roots showing or hanging over the top of the pot. This causes the plant to dry out, and just looks bad. If the plant ends up sitting a little high in the pot, remove it and trim some of the root off the bottom! Or use a larger pot.
  6. Each new division should have some foliage (or shoots) and lots of roots. If the plant appears too top heavy trim some of the growth off! (Don’t be afraid, it will grow back.)
  7. When dividing iris or other rhizomatous plants, use a sharp, clean knife to cut the rhizomes into pieces, each containing two or three bud eyes. Allow them to air dry for about an hour to heal wounds before potting them up. If dividing peonies, a larger piece of root with more eyes is better, as they take longer to recover. Ideally, peonies should be divided in the fall. If you plan to donate a peony, consider potting it up whole, unless it is very large.
  8. Please, just donate your plants and not your garden soil. By using a light weight potting soil, compost or a mixture of these, you will end up with a lighter pot, while retaining your own good garden soil. Fill the space around the root ball with soil mix and tamp down with your fingers to eliminate air pockets and to firmly settle the division into the pot. 
  9. Once potted up, water your divisions thoroughly and place in a sheltered spot, out of sun and wind which can quickly dry out newly dug plants. Water as required, especially if the weather turns hot. After a couple of weeks, you can move the pots into sun for part of the day (early morning sun is best) to harden them off.
  10. It is not necessary to fertilize your new divisions; in fact it is probably better if you don’t. It’s best to fertilize after they have been planted in their new home.

There you have it—in 10 easy steps! Think of the benefits: you will have finally got out into the garden to enjoy a lovely spring day; you will have thinned out your plants; and your Hort will benefit from receiving your divisions. I call this a win-win situation. Happy digging.

Article originally appeared on The Horticultural Societies of Parkdale & Toronto (http://www.parkdaletorontohort.com/).
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