Thursday, September 20, 2012

Autumn Perennial Divisions

Most folks know that spring is the optimum time to divide perennials, but some don't realize there are some perennials that benefit from autumn divisions.

Such as: 
On this peony, it's stems and leaves were covered in powdery mildew. Time to be moved to a sunnier, dryer location.

Perennials will give warnings to let you know that they would like to be divided.

Some signs to watch for:
  • flowers get smaller, or reduced flowering
  • sometimes the growth in the center of the plant dies out, leaving a weakened hole in the middle with all the growth around the edges
  • plant loses vigor or leaves become yellow, browning in mid season
  • plant starts to flop or open up needing staking
  • may have outgrown its area

The trick is timing.  Waiting until shorter days and cooler night time temperatures are key. The month of September is ideal in Southern Ontario. These perennials need at least 4-5 weeks  to establish roots - in weather unhampered by heavy frosts.
Dividing Hosta's and...
 and daylilies can be done in a pinch this time of year. Unlike the peony and iris, they can be easily divided and replanted.

Easy to chop portion of iris out with sharp spade

Place rhizome clump on grass; divide further if you like. It's easier to section off on the grass.
Iris and Peonies have fleshy roots. Iris don't want to be planted too deeply.  Once uprooted, divide the sections and cut out any dead or rotting bits that may compromise the plants.

When you transplant after dividing, cut back the foliage to about 8 inches for iris and for peony, to the lowest leaf node. This prevents further die-back (decay) reaching the roots and it evens out the above ground growth with the below the earth growth. It helps establish roots - setting well before winter arrives.

Cut back iris leaves to about 8 inches; remove any brown, damaged leaves and any damaged rhizomes as well.

Peony roots have carrot thick root segments that meander all about. Dig deeply to remove as many roots as possible. Keep intact as many as you can.
Here I divided the peony in two. Leaving only 1 leaf segment at the top.

You may have broken roots that easily snap - not to worry. Look for a root node - the white fleshy shoot to the right of my thumb. Try not to damage them. They are like an eye on a potato; this is what you're after when dividing.

I've had peony come back with smaller roots that have been broken off - smaller than what you see above. However, they take AGES to flower when this happens

. So it's best to make sure you have thick and as many roots unbroken as you can.

Be sure to keep iris shallow when planting. Some rhizomes should be visible from the soil.

Peony are tricky. Make sure they are not planted too deep. Flowering is hampered when the peony are planted too deep. Just make sure the top of the roots are no more than an inch below the soil level.


  1. Leaving only 1 leaf segment at the top? How come? I've never divided before, wondering if it's better to not have a lot of leaves at the top. Thanks, Love your site by the way :)

  2. Glad you like my blog, Blissful.

    Leaving one leaf segment just equals out the root to above ground growth ratio. Because many roots were severed from transplanting, the roots left can't support all that green foliage. Reducing them to a leaf node, helps to lessen the shock of dividing. Plus in autumn, the weather becomes harsher and lots of leafy material above ground gets blown about. Too much foliage and the newly transplanted peony can get dislodged and knocked about.


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