Autumn is the best time to plant peonies, whether they are newly purchased or simply being moved. You can start whenever the weather cools but should stop at least six weeks before the expected date of frozen ground. (Newly planted peonies won’t mind early fall’s icy mornings because the soil below the surface is still warm, but they must have plenty of time to make new roots before growth sops for the winter.)
Start by choosing a location where they can grow undisturbed for the foreseeable future. Peonies are long-haul plants, not at their best until they have been in place for some years.
Test the soil in the planting spot to be sure it has a pH of at least 6, although 6.5 to 7 is better; amend it with dolomitic limestone if necessary. If you’re moving the plant, cut off the discard the spent foliage. Dig up and handle the roots carefully as they are quite brittle.
Dig planting holes roughly twice as deep and wide as the peony roots. Prepare the soil by working in a few shovelsful of compost. Set the roots in the prepared holes, making sure the budlike eyes are no more than 2 inches below the ground. Backfill gently; don’t tamp down around the plants. Water them in, then top off with additional soil if necessary.
After the ground is frozen 3 or 4 inches down, add a protective blanket of straw, shredded leaves, or bark mulch. Do not fertilize until spring, when a generous application of compost will be welcome.
Note: there is an old wive’s tale that says you shouldn’t cut more than a third of your peony blooms or you’ll have fewer flowers the next year. Wrong, wrong, wrong! Plants get nourishment through roots and leaves and use it to make flowers and fruit. The flowers are takers, not givers, as far as the plants resources are concerned, and you could cut every one without hurting the plant at all. In fact, when flowers are removed, perennials can use the strength that would have gone into making seeds to do things like fight disease, put out replacement foliage, and build up their underground resources.
The one-third business probably got started because peonies have short stems. When you cut them for the vase, you usually take a lot of the foliage, too, and a plant does need its leaves to stay healthy. So, leave the leaves, take the flowers, and don’t forget the “get rid of it” rule: even healthy-looking peonies usually harbor fungus spores that should not stay nearby or be composted. Send all peony flowers to the landfill, bury them a foot deep, or burn them.
And one more thing: don’t attempt to eliminate the ants that crawl all over your peonies!! Peonies have tiny nectaries, specialized tissues that secrete nectar, at the edge of their bud scales (delicate leaf-like structures covering the bud). The nectar is a highly nutritious blend of sugars, proteins, and amino acids and it attracts the ants to the flower buds. In exchange for the nectar, the ants provide protection for the buds. Any bud-eating pest is attacked by the ant who make formidable foes since some of them can bite from one end and sting or spray from the other end. Don’t spray the ants with poisons or water — the peonies know what they need better than you do!