I have a yellow Itoh peony about 8 years old that had 18 blooms this year, none of which were visible! They hung head down inside the bush. The stems were all intertwined with leaf stems and not stiff enough to stand upright. Two years ago I moved peony to a much sunnier location and it became huge (about 3 ft diameter), but the stem problem remained. I am in zone 6a, in city of Toronto; soil is rich and loose (U. Guelph bark-based soil), amended with sand around peony, with a clay base about 6-8 inches down; full sun. What can I do to make stems strong? Thanks.
The Itoh peony (also called an intersectional peony) is a hybrid of a tree peony and an herbaceous peony, with the best qualities of each parent – large, long-lasting blooms as well as strong stems. It should not need staking/supports to prevent drooping.
I initially considered that perhaps all the rain we’ve had in the late spring might have tipped the balance such that the flowers became too heavy for the stems. However, it sounds like you’ve had concerns about the stems not being strong enough to hold the blooms for awhile – you mention that the problem persisted even after you moved the peony a couple of years ago.
There are a few reasons that peony flowers droop, including that the stems cannot support the weight of the (large) flowers, underwatering, soil composition, excessively high temperatures and pests. You’ve identified the source of your concern – weak stems.
A weak stem can be a sign of too much shade (not in your plant’s case!) or nutrient deficiency. Some experts point to phosphorus deficiency in particular, although I found nothing in the literature to support this statement or to suggest that anything but a balanced fertilizer is recommended, to promote overall plant health. I located no information specifically on how to ensure strong stems. The plant needs around 3 light feedings a year – in the spring and summer, use a 10-10-10 fertilizer and in autumn 5-10-10 — the numbers refer to (in order) nitrogen, phosphorus, potassium. It’s now late June and blooming is nearly done – time for that summer feeding! As you amended the soil around the peony with sand, it might be a good idea to top dress with compost, to help prevent nutrients from washing away. Come autumn, prune the plant and remove the leaves. See Peony’s Envy – Intersectional peony design, planting & care. This site provides lots of helpful information, including details on all aspects of care for the Itoh peony.
From your description, the plant is happy in its sunny location and is growing well, with lots of leaves (maybe too many?), although not very many blooms. If planted too deeply when you moved it, the plant’s flowers won’t develop — around 1.2 – 5 cm (½ to 2 inches) of soil should cover the top of the root. Another issue – if you’ve been using a high-nitrogen fertilizer, this would promote leaf growth but discourage blooms.
You may want to contact the Canadian Peony Society for additional information.
All the best with your lovely peony!
June 28 2022