University of Vermont Extension 
Department of Plant and Soil Science

Summer (early) News Article

Dr. Leonard Perry, Extension Professor
University of Vermont
Peonies are a favorite herbaceous perennial, being long-lived, easy to grow, an heirloom plant, and coming in many colors of red, pink and white in early summer.   Here are a few questions I've received on peonies, and answers that should help you have great plants.
"My peonies get tall and flop over.  What can I do to prevent this?"  Many older cultivars (cultivated varieties) are prone to this, while many new cultivars have been selected to have stronger stems and to be more stocky.  So it could be just your particular selections.  Too little light also may cause them to grow taller (and with less blooms).  If the plants are quite old (maybe 15 to 30 years or more), they may need dividing. 
Some try to stake floppy plants, but this can be tricky.  If you put a cage or "peony ring" around plants before they get too tall, plants may then flop onto the top wire and then break there.  The trick is to get tall enough cages or rings to hold plants upright near the tops.
"When is the best time to divide peonies, and how often should they be divided?" Peonies can live a lifetime given sun and well-drained soil, and may never need dividing.  If they get too floppy, large, or have few blooms, dividing may help. It is best to divide plants in the fall after leaves begin to die back, perhaps October.  Make sure to have at least three plump buds or "eyes" at the base on each division in order for plants to establish well the following year.
"I need to move peonies in summer, before fall, due to construction.  Is this possible?"  Yes it often is,  just make sure if moving peonies in summer to minimize damage to tops and stems, get as much roots as possible, keep well-watered when replanting, and put some light cloth or fabric over to shade from intense sun.  If you can wait until fall though to move plants it is much easier with greater chance of success.
"I have ants on my flowers.  Is this bad?"  No, the ants are merely after the sweet sap secreted by the flower bud scales, or if on leaves perhaps the secretions of aphids.  So there is no need to control them.  They myth that ants are needed to open flower buds is just that.
"My peonies have stopped flowering.  What is wrong?"  Did they get too much mulch?  Peonies should be planted at the surface, with buds no more than two inches deep.  Otherwise they may not bloom.  If mulching heavily around plants, keep the mulch away from the base.
If the buds turn brown and shrivel, they may have gray mold or botrytis disease.  This often appears in cool and damp weather, and also may cause stems to turn black.  Keep plants weeded, with good air circulation, and water early so plants dry before night.  Sprays are available for this disease.  Cool weather also may result in plants blooming later.  Another possible cause for small, unopened buds is the tiny thrips insect.
"My peonies have holes in leaves, notched edges on others.  What is eating them?"  More than likely slugs are the culprit.  These prefer moist conditions to retreat to during day, such as mulch.  Keeping plants free of mulch, with good air circulation, may help.  There are many slug control products, just make sure if using poison baits these don't poison non-target animals such as pets.  Some use saucers of beer, which attracts slugs.  Others just use boards under plants, or rolls of newspaper.  Slugs crawl under or in these, then can be removed.
"When should I cut back peonies?"  Wait until late fall, or even early spring, to cut brown or dead stems back.  You can cut them back once foliage has mostly turned brown in fall.  Cut back close to the ground, as new growth will come from the base next spring.        
"Will peonies produce seeds? "  Yes, but this is not an easy way to start them as they may arise from cross pollination, so not produce the same type of plants; their seeds need special germination requirements;  and they are slow to germinate and grow, taking several years to produce a blooming plant.
"Can peonies be grown in containers?"  Container gardening is quite popular, even including perennials.  Just make sure if growing peonies in containers that that are large enough to hold the large root systems as plants grow over the years, and one that wont fall over with such large plants resembling mini-shrubs.  Keep in mind peonies are quite hardy in the ground, yet containers that are above ground and exposed during winter get very cold.  To prevent peonies, and other perennials in containers, from such cold roots in winter, bring containers into a cool, unheated space such as a garage from late fall through later winter.
"What is the best way to control weeds in peonies?"  Good ground preparation prior to planting, and keeping up with weeds, is the best control.  If grass weeds get established in peonies, there may be herbicides selective for the grass that wont hurt the peonies.  Check your local garden store, and be sure to read the labels. 
Otherwise, if peonies become too weedy, you may need to dig up roots in fall.  Weed the area before replanting, or replant elsewhere into clean soil.  Be aware if using non-selective herbicides around peonies, such as those with glyphosate or even the organic acetic acid (vinegar) based ones, that these can injure or kill peonies just as they do weeds. 

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