Peonies are extremely adaptable plants; they are easy to grow, tolerate well cold winters and thrive in almost kinds of soil, even though the ideal soil is well-drained and slightly alkaline.
Peonies are still relatively uncommon in Italian gardens and just recently became more appreciated for their ornamental value as bordering, hedging or as specimens.
Flowering occurs between mid of April and end of June, depending on the variety, and it is one of the greatest gratifications for both beginner and expert gardeners.
Basically, peonies come in two types: herbaceous peonies and tree peonies. The main characteristic of herbaceous peonies is that their leaves die during the winter and new shoots emerge from the roots every spring.
Their thick roots act as a reservoir for nutrients and they allow the plant to survive the winter without damages. Herbaceous peonies shoot an herbaceous stem that supports the leaves and the buds on its top.
A bunch of herbaceous peonies, like all perennial herbaceous plants, grows horizontally but not vertically over the years.
Tree peonies, instead, are woody shrubs and have a different kind of growth: they produce woody branches on which, in the spring, appear the shoots of leaves and flowers. As all shrubs, tree peonies grow both vertically and horizontally reaching, in some cases, heights and diameters of 2 meters (6 feet).
This difference in growth conditions affects peonies’ ornamental use. Herbaceous peonies (varieties of Paeonia lactiflora, Paeonia officianlis and herbaceous hybrids) are generally used in beds or as bordering plants and they are more suitable for cutting flowers because of their longer stem. On the other hand, tree peonies (varieties of Paeonia suffruticosa and Paeonia lutea hybrids) look better when grouped alone or used as hedges since their light foliage and exotic look make them beautiful even when they are not flowering.
When To Plant
The best time to plant peonies, either in the ground or in pot, is between September and the end of November; planting during the fall allows the peony to develop its roots before the beginning of blooming. It is also possible to plant peonies during the winter, as long as the ground is not frozen during the day.
After March, peonies in pots can be transplanted.
The best soil for peonies is moderately clayey, rich in humus, deep, permeable and well drained. Optimal pH is sub-acid or neutral: 6.5 – 7. It is important to plow the ground before planting and to mix the soil; the soil could also be mixed with sand and peat and enriched with organic fertilizer (well rotted manure, vegetable compost, bonemeal or dry blood). The roots must not be indirect contact with the fertilizer.
It is very important to avoid water-logged soil; for this purpose, if the ground is poorly drained, a 5 cm (2 inches) layer of gravel can be laid on the bottom of the hole where the peony is going to be planted.
Where To Plant
Peonies are best placed in full sun or light shade, depending on the area. They need room and they should not be too close to the roots of other plants. Both herbaceous and tree peonies are often grown as specimens; herbaceous peonies can be planted with other species of perennial herbaceous, as long as they have enough room for their growth (80 cm / 30 inches all around them). If they are used in beds or hedges, it is necessary to leave about 80cm (30 inches) between the plants for herbaceous peonies and about 150 cm (50 inches) for tree peonies.
How To Plant
Dig a hole of about 15 inches (40 cm) in length and depth; mix well the extracted soil with the manure, completely cover the plant (the depth of soil above buds should be about 3cm / 1 inch).
Dig a hole of about 15 inches (40 cm) in length and depth; mix well the extracted soil with the manure and put the plant in the whole so that the depth of soil above the point of graft is about 8 cm (3 inches). Cover with the mix of soil and manure, being careful not to break the secondary roots.
It is advisable to protect the plant with three sticks forming a pyramid to avoid trampling on it.
Propagation of tree peonies can be done by grafting on a root of Peonia lactiflora using woody shoots produced by the plant during the year; the best period for grafting is between the end of August to the end of September. Peonies can also be propagated by division; large plants can be divided in three or four parts in a way such that every part has a sufficient number of roots and stems. The best time to propagate by division is, again, September.
Propagation from seed is another suitable method of propagation, for both tree and herbaceous peonies. However, the new plant will almost surely have different characteristics from the parent plant.
Propagation from seeds takes a long time – the merely germination of the seed takes two years – but it is the only method that allows to obtain new varieties. In general, it takes seven or eight years to get a flower on a young plant.
It is always useful to cut off the fading flowers. If flowers are cut for the house, a couple of leaves should always be left at the bottom of every stem in order not to put the vegetative cycle at risk.
During the fall, it is necessary to cut off the foliage at the ground level and eliminate the remains to avoid possible sources of diseases.
One of the most frequent diseases that plagues peonies is Botrytis, a fungus causing stems and buds to turn brown and wither; it also produces a gray mould at the base of the buds and stems. Another common cause of disease if Cladosporium that attacks leaves and stems late in the season producing small rounded reddish spots. These two pests are promoted from excess of humidity and damp ground; to alleviate the damages, watering and nitrogenous fertilizers should be limited. During particularly wet seasons, antibiotic treatments are often necessary (Ronilan, Rovral, Sumiscelex).
The worst pest for peonies is, without doubts, nematodes. These microscopic worms attack the thinnest roots producing pea-sized swellings; this pest causes a fast deterioration and death of the plant and there is no cure for it.
If a plant is attacked by nematodes, it has to be pulled out from the ground to avoid propagation and no peonies can be planted in the same spot for many years.
If you want to divide a very big plant, it is necessary to dig up the roots during the fall and cut them with a sharp knife so to leave three or four eyes and about 15-20 cm (5-7 inches) of roots on every new plant.
In the year following the transplant, there is usually no flowering and it is recommendable to wait three or four years before growing peonies on a spot where they lived for a long period.
Tree peonies are also plagued by Botrytis, Cladosporium and nematodes; the treatments are the same as those suggested for herbaceous peonies.
Again, it is a good practice to cut fading flowers to prevent the plant from wasting energy in the production of seeds.
Tree peonies do not require any special kind of pruning; if the plant has an exceeding vertical growth, it could be necessary to cut the biggest branches so that the buds at the base of the stems can develop properly. It is also advisable to cut the dead branches.
Under normal conditions, tree peonies do not need much water; their vegetation ends early in the summer and it may be the case that by mid of September they are already partially withered.
As for herbaceous peonies, excessive lasting humidity makes them prone to attacks of Botrytis.
Some Facts To Remember
Among tree peonies, vegetation comes out later in hybrids of Paeonia lutea than in varieties of Paeonia suffruticosa.
Among herbaceous peonies, instead, hybrids are more precocious than varieties of Paeonia lactiflora.
Generally, a normal development of the plants requires 2 or 3 years; meanwhile, they grow under the ground, so they show very little or no flowering.
Having a very early flowering, peonies also stop vegetating early and they may wither in early September.
To make the cut flowers last longer, they should be cut when the buds start to soften and barely show the color of the flower. If stems are cut when flowers are already completely open, they will last for much less