What you do for your peony care, after blooming, determines the quality and quantity of next year’s flower show. Something to remember with peonies is that much of what you do this year is to encourage blooms next year. And there is a lot you can be doing.
Without the proper care and attention, your peony can be left directing energy into seeding new plants, when all you really want to do is get it producing more flowers. In that respect, peonies need a little garden training.
When to Cut Back Your Peonies
Nearer the end of the flowering season, it’s likely you’ll be tempted to reach for the pruners and strip your plant bare. That’s encouraged, but only after the last frost. The leaves on a peony turn yellow when it’s time to prune them back.
Herbaceous peonies and intersectional (ITOH) peonies should be pruned back to ground level. Tree peonies are woody shrubs and shouldn’t be taken to soil level but they should have the foliage pruned.
Pruning of tree peonies should be left until early spring, by which stage, you’ll be removing the deadwood. Much of what you’ll be removing from a tree peony is more for shaping purposes and to encourage increased air circulation during the season.
No matter how ugly your peony begins to look, leave the foliage alone! They are serving a purpose and that’s to gather the energy the plant will need for next year’s flowers. Remove the foliage too early, and you’ll starve it of the energy it needs to bloom next year, so it’s definitely worth waiting.
From spring to fall is when the peony is actively using all the foliage to take in the sun’s rays. That’s then converted into food reserves that’s then used for next season’s blooms.
After blooming, it’s normal for a peony not to look as pretty as all of your other flowers.
Deadheading is What Peonies Really Need
Deadheading is different from pruning because it is only removing the spent flowers from the stems of a peony. Not just the flower.
Unlike other perennials, deadheading a peony does not encourage new blooms this season. Each pod only flowers once.
The right time to remove a spent flower is as soon as it begins to fade. The reason you need to be doing this is because spent flowers still take up energy from the plant and use it to produce seeds to grow new plants.
Unless you plan to propagate peonies, you’ll want all of the plant’s energy focused on flowering. Not seeding. You do that by getting rid of spent flowers so that the plant can direct as much energy as possible into new foliage growth.
How to Deadhead Peonies without Damaging the Plant
Ideally, spent flowers should be removed before a new seed pod starts to form. That’s why you should try to get it snipped off as soon as the color begins to fade.
When cutting, make a diagonal cut using a sharp pair of pruners and make the cut on the stem about 6” below the flower, or as close to the topmost leaf closest to where the flower is.
You only want to remove part of the stem and none of the lower leaves under the flower.
The Best Type of Fertilizer for Peonies and When to Apply it
Like most varieties of garden plants, peonies do better with a little feed once in a while. A 5-10-10 fertilizer is better for peonies as the lower nitrogen content prevents the foliage from growing in too dense and provides a sufficient amount of phosphorous and potassium to encourage more vibrant blooms.
The best time to apply it is close to the start of the blooming season, but not right away. Best practice is to wait until at least the first flower bud appears then apply the first application of fertilizer.
The next feed should be roughly 3-months after the peony started blooming and that’s to prepare it for overwintering.
Conditions that Effect Peony Growth and Can Stop Peonies from Blooming
Botrytis blight is one of the most common fungal diseases that attack peonies. Without taking care of peonies after blooming, the fungus can survive colder winter temperatures and effect the new growth coming through in the spring.
At the end of the season, around the end of September, start of October, or after the last frost, peonies are best taken right down to ground level, unless it’s a tree peony, in which case, remove all the foliage instead.
What you do with the parts of the plant you remove matters a lot because most types of funguses can survive cold temperatures and live on to infect the new growth that comes through next season. Take care to discard everything you remove from your plant. Don’t use it for mulch or compost.
The biggest problem with Botrytis blight is that it can linger in fallen leaves, and other plant debris over the winter and then start to attack new growth on plants in the spring. Peonies infected with Botrytis blight will wilt and often is the case that the flower buds they produce, fail to open.
Another sign of Botrytis blight is dark brown spots on the leaves of peonies. It can be avoided by removing and getting rid of all the foliage you remove from your peony at the end of the season.
Powdery mildew is as a fungal infection that causes a coating of white powder to form over peony leaves. As the purpose of the leaves is to store food reserves for next seasons growth, any foliage that’s coated with powdery mildew will reduce the amount of energy the plant gets from the sun’s rays, resulting in eventual stunted growth and reduced blooming.
As with every disease, prevention is the best cure. Powdery mildew tends to become problematic when temperatures are mild and the plant is getting too much shade.
The Top 3 Reasons Peonies Fail to Bloom
1 – Planting too Deep in the Soil
Peony tubers only need about a couple of inches of soil over the roots. Any deeper is likely to hinder growth. If you have planted your peony too deep in the soil, wait until around Autumn time and carefully lift the entire plant from the ground and re-plant it with much less soil around the base.
2 – Too Little Sunlight
Peonies do best when they get at least six hours of full sun daily. In most zones, that’s easily achievable and considered by gardeners at the time they’re planted.
However, as these are perennials, once they’ve been in the garden for several years, they can become overshadowed by other plants and shrubs, reducing the amount of sunlight reaching the plant.
If you’ve had your peonies blooming for several years successfully, then suddenly found they’re no longer putting out the show-stopping flowers you’re used to, consider what’s changed around the plant.
There’s a good chance another shrub, tree, or other garden plant is overshadowing your peony, blocking the sunlight that it’s been used to.
3 – Insufficient Chill Hours
A chilling hour is when temperatures remain between 32oF (0oC) and 40oF (approx. 4oC). Peonies need between 500 and 1,000 of those chilly hours for them to flower. That’s roughly 20 to 40 cold days with temperatures under 40-Farenheit, or 4oC.
Peonies are extremely winter hardy and do not need a mulch to protect them from the chills. If anything, they need those chilly days.