Dividing Perennials

What is a perennial?

Remember, a perennial is identified as a plant that comes back year after year bringing growth to the landscape for many seasons. Trees and shrubs are examples of "perennial" plants. However, there are many plants, such as daylilies, hostas, peonies, and tulips that are also perennials and yet are not what we consider a tree or shrub. These "non-woody" plants are known to the gardener as "herbaceous perennials". These plants do not grow on existing growth from last season. Instead, they sprout new growth from their established root systems.  

These plants can be split, propagated, or divided. Most woody plants cannot. At least not in the same way or to the same degree that this plant group can.  

Why divide perennials?

If your perennial plants show any of the following, it may be time to rejuvenate them through division.

• The flower quantity or flower size is poor.

• The stems and branches have become tangled.

• The center of the plant dies leaving a ring of new growth around the perimeter.

• The plant loses strength, flopping over or requiring staking when it never did before, or the leaves are pale or yellow.

• The plant has outgrown the space you have given it. This is especially likely if it grows in a particularly hospitable site.

• The plant is in the wrong place in your garden.

• You want to share this plant from your garden with friends and neighbors.

If plants in your space are exhibiting any of these characteristics, it could be a good idea to consider dividing them.

When should I divide perennials?

This question is perhaps a little more difficult to answer well. Perennials can be divided in early spring (generally early April) or in the Fall (late August through September).

The general rules are: 

• Summer and fall-blooming plants in spring

• Spring blooming plants in the fall.

How to go about dividing perennials?

Tips for successful division of fleshy, fibrous, tuber, and rhizome perennials are as follows:

• The day before, water the plant thoroughly.

• Choose a day that will be overcast and not too hot. Work either in the cool of the morning when the plant is fully hydrated or late afternoon when the night will allow for better recovery. 

• Remember that exposed roots dry out quickly.

• Dig the hole the divisions are going into, or have pots ready for them.

• Some plants benefit by having their top foliage cut back. This allows you to see where the natural divisions occur.  This can be helpful when making your cuts.

• If the plant is large, use a spading fork to dig all the way around it, well away from the base to minimize the loss of roots. Generally, a fork does less damage to the roots than a shovel. Lift the entire clump out of the ground.  You may have to remove some of the dirt to see the roots.

• If the whole plant doesn't require division and you only want a few new plants, you can dig or cut out clumps around the edges. The parent plant will recover quickly and appear unchanged.

• Remove any weeds or grass before you replant. 

Inspect the plant for unhealthy parts, usually an old woody center or rotten roots.  Eliminate them.

• For fibrous-rooted plants, use a spade (or two), an old bread knife, or your fingers to separate the clump into plants the size you want. Very old and well-established perennials, like daylilies or Astilbe, may require more aggressive handling.

• Keep the divisions moist and shaded. Save the youngest pieces for replanting, usually the ones at the edge of the plant. Each piece should have roots and a minimum of 2 buds/piece of the crown. Discard the rest. The larger the pieces, the sooner the plant will bloom again.

• Plant each division in a hole twice its size. Fill in with good quality soil mixed with organic matter, keeping the plant at its original depth. Don't feed with nitrogen until the following year - nitrogen encourages top growth and the divisions need to focus on their roots.

• Water well.  If the weather is especially hot and sunny, you may need to shade the plant for a few days.

The need to divide perennial plants usually means you've been successful in growing them.  Enjoy the time spent in your garden and the fruits of your success.

Good luck and happy growing!