Planting and Growing Peonies
Peonies are one of the longest-lived perennials and will probably be blooming after we are gone . . . all the more reason to plant them so our children and their children can enjoy their unparalleled beauty and fragrance year after year! Herbaceous peonies (ones that die back to the ground in winter) are easy to grow and reward you with spectacular blooms year after year. Tree peonies have woody stems that persist through the winter, unlike herbaceous peonies that die back completely every year. Intersectional peonies are a cross between tree and herbaceous peonies, with the best qualities of both parents. Tree and Intersectional peonies are also the only varieties that come in shades of yellow-there are no yellow herbaceous peonies.
The first rule of peony cultivation is identical to the first rule of real estate—choose the location carefully! They are not fond of being moved about in the garden and in doing so you may delay blooming for a year or more so it is important to pick a permanent spot. Herbaceous Peonies grow 2-3 feet tall and wide. Space them at least 4 feet apart. Tree Peonies can reach 4-6 feet tall and wide, but grow very slowly. Both types prefer not to be crowded by other plants. Peonies prefer neutral to slightly alkaline soil (pH 6.5-7.5). Good drainage and at least 6 hours of sunlight are critical. Standing water will kill peony roots. In our climate, a reprieve from hot afternoon sun will ensure good bloom with less stress on the plant.
In planting container grown peonies, dig your hole at least 2 feet deep and 3 wide and amend the soil well: add well-rotted compost or soil conditioner along with composted cow manure in the bottom of the planting hole. Cover this with a layer of outdoor planting soil to keep the roots of the peony out of direct contact with the manure. Add BulbTone fertilizer to the existing soil that you have removed from the hole and mix together with more soil conditioner. Place a shovelful of this in the planting hole and tamp it down to prevent the peony from settling too far and sinking later on.
Herbaceous and tree/intersectional peonies have very different planting depth requirements. Planting too deep is one of the main reasons herbaceous peonies fail to bloom, as they are very sensitive about the depth of their eyes (the shoots that develop from the crown). Planting too shallow is a problem for tree peonies; if you are worried about the planting depth of your tree peony it is always best to err on the side of planting it a little too deep. Grafted tree peonies should be planted so that the graft is four to six inches below the surface of the soil. In most cases with container grown peonies, the existing soil level should be matched when planting in your garden.
As herbaceous peonies begin to grow in spring, use a peony support early to allow your peony to grow through it naturally for support. The stems and leaves grow through the grid without injury and it protects the heavy flowers as they develop so they won’t droop so badly. It’s a good way to avoid staking later on. Older tree and intersectional peonies generally do not need staking if they are receiving enough sunlight, however, younger woody-stemmed peonies may need some support until their stems mature and thicken.
During the first two growing seasons after planting a new peony, ensure that it gets a good soaking every two to three weeks. This will allow the plant to get enough water while the fibrous root system becomes established. Remember that peonies do not like wet feet and be careful to not over water, the soil needs to dry out fully between watering.
When the flower buds begin to swell, you are sure to see ants crawling on them. Sorry to put those old wives’ tales to rest, but ants are not necessary for the peonies to bloom. The unopened flowers secrete a super sweet substance that the ants like to eat, and they won't do the peonies any harm, so leave them be!
After the bloom, unless you are interested in seeing if your peony will produce seeds, deadhead your peonies to promote root growth over seed formation. Just cut the stem to the first set of true leaves.
Peonies don't need any special fertilizer except a fall side dressing of rotted compost or BulbTone, placed 16 to 18 inches out from the crown to keep them healthy. Peonies do need to be kept well watered before blooming in spring and well weeded in summer to prevent competition for nutrients and for good air circulation to avoid disease. Cut the stems of herbaceous peonies back to the ground in late fall and destroy all plant debris to keep the peonies healthy. Do not add this to the compost heap. The blooms of peonies last 2 weeks, but the glossy foliage lasts all season.
Leaves are covered with a white, powdery substance. While unattractive (and fairly common), powdery mildew won’t kill the plant. Heat and high humidity promote the disease. Keeping the leaves sprayed with neem or horticultural oil can prevent some mildew, as can foliar fungicides containing sulfur or mancozeb. Follow all label directions when using fungicides. One home preventive is 1t backing soda, 1qt. water and a few drops of liquid soap sprayed on leaves weekly. Once started, powdery mildew is difficult to reverse, but it can be slowed.
Buds turn brown or black and fail to open. This is brought on by cool, moist conditions. Prune off dead buds to prevent the disease from spreading further down the stem. If conditions are right for botrytis, use a systemic or foliar fungicide labeled for botrytis on peonies as label directs before the disease takes hold.
WHY HERBACEOUS PEONIES DON’T BLOOM
Some peonies fail to bloom their first year or two in the ground, following the old adage about planting: “First year sleep, second year creep, third year leap.” If it’s been several years and still no bloom, it’s possible your peonies have been planted too deep-they are very sensitive to being planted even slightly too deep. If peonies had bloomed in prior years, be sure that mulch has not built up too deeply over time. Check the depth of your peony by carefully moving a bit of the soil from the top portion of the plant being cautious not to break off the delicate pink eyes. The top of the root should be from 0.5 to 1.5 inches below the surface of the soil. If the peony is too deep, replant and adjust the depth in the fall, not spring or summer.
If all else seems right and still no blooms, check that your peony is receiving at least 6 hours of sunlight a day. If your peony gradually has fewer and fewer flowers over the years, this may be the reason, as surrounding trees and shrubs grow and give more shade.
WHY TREE OR INTERSECTIONAL PEONIES DON’T BLOOM
Lack of bloom on intersectional peonies is usually due to age or establishment. It can often take three years for intersectional peonies to establish in your garden-do not move them during that period or you will set them back another year.
This is also true of tree peonies. Another factor in tree peonies not blooming is that they are not planted deeply enough (the opposite of herbaceous peonies). There should be no roots exposed on your tree peony.