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Gazette Gardener: Dividing perennials keeps plants healthy, creates ‘new’ life

Tuesday, April 20, 2010
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The cheapest — and perhaps most joyous way — to fill a garden with tried and true plants is to divide perennials and pass some of them along to friends. It’s a delight to walk in the garden and remember people by the plants they have shared with you.

How do you know if it’s time to divide a perennial? By observing the plant and noticing a few telltale signs. First, is the center a dead zone with few, if any, stems? Has the plant had fewer and fewer blooms in the past years? Or maybe you noticed last year that the center of the plant had smaller leaves?

Unlike annuals, perennials come back each spring, die back each fall and as they mature they become larger and larger. Eventually, most perennials need to be divided to remain vigorous, healthy plants.

When planning to divide a perennial, the first thing to ask yourself is: “When does this plant bloom?” Perennials that bloom from mid-summer to the fall are best divided now. Spring and summer bloomers are best divided in the fall.

There are a few exceptions and these include oriental poppies, Siberian and bearded iris and lilies, which are best divided immediately after flowering.

When to divide

Once you’ve selected which plants to divide, the best time to dig it up is when you have the time to finish the job through to replanting the divided pieces. My advice would be to choose a cool overcast day. If the weather forecast predicts rain, so much the better. A hot, sunny day may wilt the plant. After you dig the perennial up, keep the exposed roots from drying out and work quickly. The sooner the plants are back in the ground the happier they will be. If you can’t finish the job in a day, cover the roots lightly with plastic to keep the plant moist and put it in a shaded area.

Steps for dividing

Following are my step-by-step instructions that I use in my own garden.

A day before the move, I saturate the ground to be certain the plants are well-watered. Next, I clean the plant, removing dead leaves and stalks, and — if necessary — cut the stems and foliage back to 4 inches. This helps reduce moisture loss through the foliage and also makes it easier to see what you are doing.

Begin to dig starting at the widest edge of the plant (at its summer growth) to ensure minimal root damage. I work around the plant to loosen the roots and lift it out of the soil with a fork. If the roots system is stubborn, I borrow another spading fork from my neighbor and place them opposite each other around the plant. Then, I can usually coax the clump out of the earth by pushing down on one side and then the other.

Next, I divide the clump into quarters with the edge of shovel, while it sits in the hole. This makes it easier to lift.

Take one section at a time and place in on a potting table or any spot where it is easy to inspect. I wash the soil off the roots with a stream of water gently flowing from the hose and look to see what I have.

Are there insects? Or any soft spots that indicate disease? Do the roots look healthy? Next, look at how the plant grows. Usually the perimeter of the plant has the most vigorous new growth. Start there and, using a sharp knife or loppers, cut the roots into sections with at least 5 “eyes” or buds on each piece.

Sometimes, you can coax new plants apart with your hands. In many cases, the plants will naturally separate at certain places along the roots.

Often I hear from people that they are afraid to divide a favorite plant for fear of killing it. That is extremely unlikely. Plants benefit from being divided. Trust me.

Where to plant?

As you replant the new pieces, consider where the mother plant was growing and try to duplicate the conditions. Was it a sunny or shady location? Was the soil dry or consistently moist?

I usually mix of shovel full of compost to the new hole, dug large enough to spread out the roots of the new plant. Take care to replant the perennial at the same depth it was growing before. And once the plants are in the soil, water and mulch to provide them with a good start.

The easiest perennials to divide and share with friends include astilbe, monarda, sedums, yarrows, aster, campanula, coreopsis, echinacea, hosta, iris, gaillardia and garden phlox.

Happy Gardening.

 
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