May and June are wonderful months in which to experience the first flush of herbaceous planting and no flower symbolises the glories of early summer more than herbaceous and tree peonies. Both of these genera hit their peak at this time of year, producing wonderful ephemeral blooms and both come in a variety of species and forms. Most peonies in the garden come in two forms, either herbaceous P. lactiflora or hybrid cultivars, or the woody stemmed tree peonies.
Paeonia lactiflora was first introduced into Europe towards the end of the eighteenth century and has given rise to thousands of cultivars. It is one of the easiest and most popular peonies to grow, tolerating a wide range of soil conditions. Peonies grow best in fertile, well drained soil but can be grown in sandy or clay soils with the addition of plenty of well-rotted manure. In fact manure is a must for herbaceous peonies. Applied during the dormant season, it is best to avoid the crowns of the plant to prevent scorching of the developing buds.
Paeonia lactiflora cultivars come in all colours although, because of genetics, there is an absence of a good red, the closest being magenta. On the plus side many are deliciously fragrant; ‘Boule de Neige’, ‘Duchesse de Nemours’ and ‘Gainsborough’ are a few of the most fragrant.
Paeonia lactiflora has given rise to a number of hybrid herbaceous peonies when crossed with other species. These hybrids flower over a long period of time from early spring, when the majority of the species flower, to early summer when the lactifloras are in bloom. Amongst these are also good red forms such as ‘America’ and ‘Scarlet O’Hara’.
By contrast, Chinese Tree Peonies are amongst the oldest cultivated plants in the world and make an indelible impression on anyone who sees them. They often appear delicate because of their exotic flowers and delicate foliage but in fact they can withstand very low temperatures as well as summer drought. However, they are slow growing: a mature specimen may be 3m tall but this could take 50 years or more! Many tree peonies will tolerate some shade as well as full sun.
It is an oft quoted fallacy that peonies cannot be moved, or that if they are they will sulk. Herbaceous and tree peonies can be moved when dormant and herbaceous peonies can be propagated by division. As long as care is taken when replanting they should continue to grow well, although flowering may be affected for one or two seasons.
The main disease that affects both herbaceous and tree peonies is Peony Blight which can seriously damage them. Infected tissue turns brown, then black and finally wilts altogether. It is most prevalent in wet springs, so good air circulation is important. It can be controlled by removing and burning infected tissue as soon as it appears. A preventative fungicidal treatment is beneficial.