The better the growing conditions the healthier the plant and the better the flowering performance.
When to Plant
Peony growers dig their peonies in the fall and this is definitely the best time of year to plant them in your garden!
A peony planted in the early fall will have the opportunity to put out a good number of feeder roots before the following spring. I’ve noticed in my garden that fall planted divisions that have had several weeks of growing time before the ground freezes, do better the following year than those that have had less time to develop new roots. This is particularly important if the spring is hot and dry.
Peonies can however be planted right up until the ground freezes if necessary.
A word on spring planting….peonies purchased in the spring more than likely have been held over winter in cold chambers. Planting them in the spring without letting them have the benefit of fall feeder root growth puts the plants under severe stress. Peonies being the tough plants they are will usually recover, however they have suffered a set back and will likely not establish as quickly as those planted in the fall.
A few garden centres will pot up peonies in the fall for sale the following spring. Though containers are not ideal growing environments for the bulky roots of peonies, at least they have had the opportunity to put out some feeder roots in the fall. This is not the case for those peonies potted up in late winter or early spring.
If you are buying peonies from a garden centre, ask a) what size of plant is in the container i.e. a 2-3 eye or a 3-5 eye division for herbaceous and Itoh peonies and 1, 2, 3 or 4 year old plant in the case of a tree peony and b) when was it planted i.e. last fall or recently. Plant containerized plants as soon as you can get them into the ground.
Cooperate with nature and plant peonies in the fall!
Where to Plant
Herbaceous and Itoh peonies generally prefer cooler climates and are easily grown from USDA Hardiness zone 3 through 8. Gardeners in zone 2 and 9 however have reported success with some peonies.
In general, herbaceous and intersectional peonies require a sunny, well drained location. They will however accept, and perhaps benefit, from some light shade in areas that have very hot dry summers. In my area, Southern Québec, the rule of thumb is that 6 hours of direct sunlight a day will ensure maximum flower production.
Tree peonies have a slightly different growing range. They can be grown in USDA Hardiness Zones 4 through 8 or 9 but require winter protection in Zones 4 and 5 to bloom reliably. Tree peonies will also support more shade. Deep shade however will reduce flower production. The best shade is that provided by a high, light foliage canopy.
At our farm most of the peonies are grown in full sun with no shade whatsoever. We do however have peonies growing on the eastern side of the house. These peonies are in full sun only until the early afternoon and they perform as well as those in the field.
Standing water is the number one enemy of a peony!
If water is allowed to stand on the crown or around the roots, rot quickly sets in and the plant declines and can actually die. Peonies, like roses, are heavy feeders and enjoy a heavy fertile soil. They do well in heavy soils however the trick is to ensure that drainage is impeccable.
How to Plant
Peonies are heavy feeders and do not appreciate being moved so it is important to ensure they are planted in good, fertile soil. If the soil needs to be amended it is best to use compost or very well rotted manure. Fresh manure is reputed to burn the plant and spread pathogens.
If you are opening up a new area for planting consider having soil tested for pH and nutrient levels before planting. I believe peonies prefer a pH of between neutral and slightly acidic (pH 6.0 to 7.0) but they seem to tolerate a wide variation. The soil testing facility will usually make recommendations as to fertilizer requirements to correct any imbalances. Though soil testing is not a necessity, it can be useful to know your exact growing conditions, not just for peonies, but for all your plants.
Herbaceous and Itoh Peonies
The bare root division should be planted in a hole sufficiently deep that the highest crown bud is about 5 cm (two inches) below the surface.
Planting too deeply will frequently prevent the plant from flowering. A too shallow planting puts the buds at risk of mechanical or winter damage.
Once planted the addition of organic mulch will help retain moisture in the soil as well as keeping down the weeds. It is important however not to put the mulch directly on the crown. Wet mulch on the crown can cause crown rot.
Contrary to herbaceous peonies, tree peonies need to be deeply planted. All tree peonies from my nursery are marked as to the appropriate planting depth.
Peonies require little maintenance.
Depending upon the fertility of the soil, it is occasionally beneficial to scratch in some granular fertilizer around the plant in the spring, just as you would for any other perennial This is more important on sandy soils than heavier soils. A general fertilizer labeled for use on perennials is appropriate.
If the plant is thriving and the soil is basically fertile peonies do not need regular applications of fertilizers.
Though peony flowers are often irresistible as cut flowers, restrain yourself! Restraint is particularly important for young plants. When cutting flowers it is practically impossible to not also cut the leaves. These leaves are essential to the peony if it is to make its food reserves. So take but a few flowers from each plant and leave as much foliage as possible.
A rule of thumb is to not cut flowers from plants less than three years old and that a mature plant of five years should be left with about 50% of its flowers. When cutting the flowers take care to ensure that at least some leaf is left on the remaining cut stem.
Peonies are very drought tolerant, especially once established.
Mulching around the plants helps maintain a constant moisture level in the soil. Moisture is particularly important in early spring when the flower buds are expanding. The type of soil, along with the weather will determine if you need to water or not. Heavy soils retain water better than sandy soils which often drain excessively. In dry weather sandy soils may well need additional moisture when clay soils do not.
At the end of each growing season the foliage should be removed from the peony growing area. Tree peonies will shed their leaves at the end of the season but the stems of herbaceous and Itoh peonies should be cut down to within an inch or so of the soil level. The foliage of peonies can harbor fungal diseases and the best method to control these diseases is good fall clean up.