How to Care for Peonies

The several dozen species of peonies that are grown mostly by enthusiasts, specialists and researchers are often reproduced by seeds. Seeds are occasionally employed to establish the principal horticultural peonies, but of course seeds will rarely reproduce the beautiful flowers of cultivars that have been maintained as clones. Peony seeds may have complex dormancy requirements, and if purchased it should be from a reliable source that provides germination instructions.

Collecting, conditioning and storing peony seeds can be a demanding exercise, for which information is available in the references provided later. Herbaceous peonies usually produce flowers in their third year following seeding. When established from seeds, tree peonies generally require 5 to 7 years to produce flowers.

The horticultural industry and indeed most amateur gardeners usually reproduce herbaceous peony cultivars by division of the underground portion. This is best done when the plants have gone dormant in the autumn. The entire plant may be dug up. Herbaceous peonies should be divided into portions each of which has several “eyes” (i.e. buds or meristems) as well as several storage roots. he same is true for tree peonies, but each division should also have a vigorous stem or two of the current season’s growth. Herbaceous peony divisions are very widely available commercially in Canada as bare­root stock, and as young, potted plants (which can be established at any time of the season).

The horticultural industry reproduces tree and Itoh peonies almost entirely by grafting cuttings onto the portions of underground organs of herbaceous peonies, a process that is slower than reproduction by divisions, and requires skill. Micro­propagation is currently becoming established, and is expected to lower the price of these classes of peonies.

In Canada, almost all tree peonies are supplied as bare­root, imported material, but potted stock is sometimes available. It is possible to import plants from specialty horticultural suppliers. Guaranteed potted plants sold within Canada are the best option, but availability is limited within the country. Tree peonies are a gamble, and represent an investment in dollars and effort that primarily attract peony v

Planting

Herbaceous peonies often do not respond well to transplanting, unless dormant, and in any event the deep, brittle roots are easily damaged, and up to 3 years may be required for an excavated plant to recover from the trauma.

Where to Plant peonies?

Because they can live for many years, planting sites should be carefully chosen and prepared well. They are best planted away (3 m or 10 feet) from competing roots of trees and shrubs. To avoid disease build­up, avoid planting where peonies have recently grown. Some peony specialists recommend preparing a “$100 hole” – one that will nurture the plants for decades (such a hole could be 45 cm or 18 inches deep and 60 cm or 2 feet across). In hot climates, peonies benefit from some shade, but in most of Canada sites should be sunny (at least 6 hours of full sun daily) although some shade is tolerated (however, shade inhibits flowering). Peonies need excellent drainage.

They are intolerant of waterlogging and, if available sites are overly moist, planting in raised beds should be considered. Divisions should be planted shallowly – the highest buds not more than 50 mm (2 inches) below the soil surface (both shallower and deeper planting can retard or prevent production of flowers). Potted plants should be removed from the pot and planted so that the top of the soil from the pot is level with the soil in the planting site. Planting stock of tree peonies is typically grafted onto a base of P. lactiflora. When planted, the graft union should be 10–15 cm (4–6 inches) below soil level, enabling the tree peony stem to develop its own roots. The stem/root graft union usually appears as a root bulge just below the graft union (caused by the root growing much faster than the grafted stem). To form a hedge, tree peonies can be planted 0.9 m (3 feet) apart. Guidebooks often recommend that tree peonies be planted in somewhat shady areas (to prevent bleaching of the flower colours by strong sunlight; to lower the risk of frost damage in early spring because the warmth prematurely stimulates growth; and to prevent excess drying) and in areas protected from wind (to prevent the petals from being blown away). However, in Canada it is usually more important to provide an open area where good exposure to sunlight is available. Itoh hybrid (between herbaceous and tree peonies) planting stock will have erect basal stems with several buds, attached to a crown which will usually have more uds than on the stems. The crown buds should be 5–10 cm (2–4 inches) below soil level and (if possible) the lowest bud on the erect stems should be at soil level.

Containers

Peonies grow very well in large containers, and indeed in Asia potted tree peonies are popular. However, most cultivars develop roots that are too large for standardsized pots. Peonies acquired in pots from stores are meant to be planted soon.

Soil and Ferrtilization

Peonies can grow in infertile soils, but fertile loams are best. Both clay and sandy soils can be used, but supplementary fertilization is desirable in the latter case. Preferred pH varies from slightly acidic to slightly basic, although many peonies have a preference for slightly alkaline soil. Peonies are heavy feeders, benefitting from soil that has been fertilized with well­rotted (never fresh) manure worked well into the ground, and from annual top­dressing with well­rotted manure (avoiding contact with the plant). Some growers recommend adding inorganic fertilizers, but never high­nitrogen fertilizers; the level of nitrogen should never be higher than the levels of potassium or phosphorus (e.g., 10­15­10 would be suitable). The fertilizer should be applied away from the main crown and distributed on the soil around the drip­line of the foliage. Spring application as shoots emerge is desirable, although some gardeners also apply fertilizer in the autumn after the plants have gone dormant.

Hoops

The flowers of most cultivars of the common peony (P. lactiflora) are notorious for flopping over and lying on the ground (tree peonies are quite resistant to this problem). This is because the flowers are poorly supported by their relatively weak stems (peduncles). Wind and rain may cause the flowering stems to bend over, but often large double­flowered blooms, especially of old­fashioned cultivars, droop to the ground simply because of their own weight. Bamboo stakes set around the plant and tied together by garden twine woven around the plants can be employed to support the plants. However, rustresistant wire “hoops” or “rings” are widely employed to support the flowers in an erect position, installed in the spring at least before the plants have reached half their height. Peony hoops (“wire cages”) designed for the purpose are usually employed. Tomato ring supports should not be substituted because their diameter is too small.

Pruning

Some gardeners deadhead peonies after the flowers senesce, but this isn’t necessary, and some cultivars develop attractive seed heads. Peonies (both herbaceous and woody) don’t require pruning, except for damaged stems or branches. Foliage or branches that become senescent during the growing season should be removed to lessen the chances of fungal infection. The most serious disease is botrytis (gray mould), which thrives in cool humid conditions; diseased portions should be cut away (using pruners dipped in a 10% bleach solution), and discarded. All senescent aboveground material can be removed after significant frost damage in late fall. Herbaceous peonies should be cut about 2.5 cm (1 inch) above ground. Itoh hybrid peonies should be cut 5–10 cm (2–4 inches) above ground. To avoid accumulation of disease organisms, the harvested material should be discarded.

Winter Protection

Where winter temperatures fall below ­20°C (­4°F), especially where snow cover is limited, an insulating mulch layer (hay and evergreen boughs are suitable) might be necessary to prevent loss of herbaceous peonies. Mulching is advisable in colder areas of Canada during the first year of establishment, removing the mulch when the shoots emerge. However, P. lactiflora peonies usually survive well with minimal or no winter care in most of the large urban areas of Canada. Some tree peonies can survive in the warmest parts of eastern Canada (Ontario to Newfoundland) and in British Columbia. They are occasionally grown in the Prairie Provinces, with limited success, because tree peonies are not adapted to very cold winter temperatures (Itoh hybrids are preferable). A burlap wrap can be helpful. In areas that are marginal for growth, the shrubs can simply be cut off at ground level (this will lo

Ants

Ants (and indeed other insects) are commonly observed on peony flower buds. Tiny extra­floral nectaries produce a sweet liquid along the outside edges of the bracts covering the developing buds.

Apparently the ants and peonies have established a symbiotic relationship, the peonies furnishing a sweet carbohydrate to the ants which in turn often drive off other insects. There is a common misconception that ants are necessary for peony flowers to open. To get rid of ants on peony buds to be used indoors as cut flowers, simply leave the cut stems in a vase outdoors
for a period for the ants to leave.

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