Over the weekend I spent time weeding the Lawn Beds. There were spots that had few weeds because the plants had developed into such large clumps that the weed seeds had no place to land. Some clumps were so big that it was clear it was time to do some dividing.
As a general guideline perennials need to be divided every 2 -4 years. A clump will outgrow its spot and start crowding the plants around it. Sometimes it will begin to die in the center, or start producing smaller leaves and flowers.
Autumn is a perfect time to divide plants because temperatures are cooler and there may (if we are lucky) be rain. New plantings need to be kept watered whether in spring or fall.
When I divide plants in the fall I cut the foliage back first. That will make it easier for me to see where I can make my cuts. Then I dig up the whole plant, starting from the drip line. I want to make sure I dig up as much of the root as possible. I put the clump on a tarp or piece of plastic so I don’t lose any soil while I am working with the plant.
With the plant out of the ground, the first thing I do is see what weeding I can do. If this means disturbing the soil and loosening the roots that is all to the good. Sometimes during this process little divisions will fall off the mother plant all by themselves.
With the plant weeded, I look to see where I can get my spade in to make my divisions. Volunteers at the Bridge of Flowers often use a serrated hori hori knife to make divisions. Spade or knife, it is up to you. You want to make as neat a cut as possible. One good clump can probably make four or five good divisions, each of which will make rapid growth in the spring.
Some people water plants they are going to divide the day before. This is a good idea as long as you are careful not to make the soil so wet you are digging in mud. Whether you water before dividing or not, you will want to make sure your new divisions are well watered afterwards. If you are not going to plant the divisions immediately, keep them in the shade and keep the roots covered and damp.
Dividing your plants is an opportunity to enrich the soil of your garden beds. Add compost to the hole where the plant came from, and put a good helping of compost underneath the new division in its new location.
Many plants can be divided in the fall including plants that are often used as ground covers like lamium, foamflower (tiarella), coral bells and heucharella, lamb’s ears, pulmonaria, lady’s mantle, and ajuga. These are all easy to pull apart by hand after they have been dug.
Popular perennials that will need a sharp spade or knife, include bee balm, asters, garden phlox, daylilies, Echinacea (coneflower) and achillea.
Some perennials have a woody crown that may best be cut with a saw. These include peonies, astilbe, Joe Pye weed, and gayfeather.
A special word about peonies that are such long lived plants. Unlike many perennials, these rarely need to be divided and will live happily in the same place, growing bigger and more beautiful every year. A top dressing of compost is all they will need. However, if you want to divide your peonies to have more plants, or to make a gift to a friend or because it is necessary to move them, it is best to do this job in the fall. I know they now sell container grown peonies in the spring, but if you are going to divide a peony fall is the time to do it.
Cut back the foliage to a couple of inches. Old peony plants have large brittle root systems. Make sure you are digging up a large root ball and be as careful as you can because the brittle roots break easily. Some root loss is probably inevitable, but you want to limit it as much as possible. Each peony division should have at least three eyes.
When re planting your peony, as with any new planting, make sure you enrich the planting hole with good compost. For the peony you can add a handful of lime because peonies prefer a pH between 6.5 and 7 which is nearly neutral. Just remember that herbaceous peonies must be planted so the eyes are only one or two inches below the surface. If they are planted too deep the plant will not be harmed, but it will not produce blooms.
It doesn’t take many years before a perennial garden produces more plants than it can contain. This is part of the reason gardeners are so generous. They have to pass those extra divisions on to friends, and friends of friends who may be starting new gardens. They can also put those divisions in a holding bed where they can be dug up and potted in the spring for fund raising plant sales. The extra plants from our gardens can not only spread the beauty around the community they can raise money for other community beautification projects.
What plants are you dividing this fall?
Between the Rows September 15, 2012