Soil requirements from USDA Extension, gardening books and even peony experts differ.
John M Valleau, head horticulturist at Heritage Perennials recommends rich, well-drained loamy soil in his Perennial Gardening Guide.
Jane Fearnley-Whittingstall writes in her well-research book, Peonies. The Imperial Flower, that
“Peonies are not choosy about soil, doing quite well in poor conditions…“…but the ideal is well-drained, rich and slightly alkaline soil.”
Purdue Extension, backs up Jane’s recommendation, saying that
“Peonies thrive on a wide range of soils; but a clay loam is best. It must be well-drained and yet should hold moisture.”
Clemson Extension backs up Valleau’s soil recommendation for peonies, adding that peonies prefer a pH of 6.5 to 7.0
Looking back at the soil origins might help to sort out the slight contradictions. In Canada, the majority of peonies descend from either the herbaceous peony, Paeonia lactiflora or the tree peony Paeonia suffruticosa or both.
Paeonia lactiflora hail from Siberia, Mongolia to northern China and parts of Tibet. This region is steppe grassland and scrub terrain. In North American terms, P. lactiflora is a prairie perennial! The main soil in this region is termed Mollisols in American soil system or Chernozems in Canadian soil system. Whatever we decide to call the soil…it’s prairie soil found in the Canadian Prairies and American Midwest,
The main characteristics of prairie soil include plenty of organic matter, deep topsoil, alkaline pH and great drainage. Sound familiar?
Paeonia suffruticosa, the tree peony, hails from the arid hills of Yan’an district of Shaanxi province, China. The soils, on the steep hillsides (great drainage) are mostly like Inceptisols (US term) or Brunisols (Canadian term). Here the soft fertile silty yellow loam contains plenty of minerals.
With this information in hand, what is the best soil for peonies?
Well-drained is a must. Peony roots are tuberous. Tuberous root plants, which include the familiar potato, rot when grown in waterlogged soil.
High organic matter is a bonus. Not nitrogen rich soil. High nitrogen has an unfortunate habit of encouraging leafy growth in peonies in expense of flowers.
Slightly alkaline soil. Many perennials prefer growing in soil with a pH between 6.5 to 7.0. Not peonies. They prefer neutral to slightly alkaline soil. So, pH above 7 and below 8.5. Especially herbaceous peonies; they are prairie perennials, after all.
If you don’t have all these conditions, don’t despair. The absolute must is good drainage. If you don’t have this, consider planting peonies in raised beds. You can always add organic matter to the soil and if your soil is very acidic, add lime.
Peonies are very low maintenance tough plants, which are drought tolerant once established. And peonies are very long-lived, in some cases over a hundred years! Provide the right soil conditions for your peonies and you can enjoy them for decades.