If Your Peonies Had Fungus Last Year, Spray Them With This Natural Remedy Now for Healthy Blooms This Spring

Peonies never go out of style. Their large, showy blooms bring beauty and romance to any garden. They’re large herbaceous perennials with sensitive roots, but they have the ability to grow in one place and flower for decades if you treat them right.

One important part of peony care is understanding, identifying, and managing fungal diseases. Peonies aren’t especially prone to disease, but they can be vulnerable to mold and some infections that can distort or diminish blooms.

Learning how to prevent these peony diseases, especially if you had problems last year, is vital for good blooming this season. You have to catch fungal diseases early and start treating them as soon as peonies begin peeking out of the soil. I’ll teach you how to know the signs, catch them early, and use a homemade solution to prevent fungal problems this year.

Peony Fungal Diseases

Peonies can develop fungal diseases at any time, but they are most common during periods of wet weather. Factors that increase the risk of fungus include growing plants very close together with little air flow, frequent rain, standing water, and water that splashes up from the ground onto stems and leaves.

1. Botrytis

Botrytis, also known as botrytis blight or gray mold, is the most common fungal disease that affects peonies. Start looking for signs as shoots emerge from the ground in spring, especially if conditions are very wet and rainy. Spots on plants will appear water-soaked and rotten.

Other signs of botrytis on peonies include fuzzy gray mold on stems and leaves and buds that turn brown or black and never open. Without treatment, botrytis blight can quickly kill a peony plant. In addition to treatment, remove and dispose of diseased plant material. Don't compost it.

2. Powdery Mildew

Powdery mildew on peonies is unsightly but not as serious as botrytis. You’ll see it as a white or light gray powdery substance on young leaves and stems and sometimes on flowers. It’s unlikely that this fungal infection will kill your peonies, but you should manage it for the healthiest plants and best blooms.

3. Phytophthora Blight

Phytophthora cactorum fungus thrives in moist soils and can infect your peonies during wet seasons. The signs of phytophthora blight look a lot like those of botrytis. The main distinguishing characteristic is that botrytis causes gray mold. Parts of the plant affected by phytophthora look more leathery than soft and rotten.

A copper fungicide spray, like this one from Bonide, is the best option for managing this fungus, especially if it sets in early in spring.

4. Peony Blotch

You’ll see signs of this fungal infection after the plants have leafed out and just before the flowers open. It's also known as peony measles, leaf blotch, or red spot. Look for small, round red or purple spots on the leaves. The small, round areas may grow together and form larger, irregular shapes.

Like powdery mildew, this infection is unlikely to kill your peonies, but it doesn’t look very nice. Repeated years of blight can negatively affect the plants.

Homemade Fungicide Spray Recipe

If you saw signs of fungal infection on your peonies last year or if you are having a particularly wet and rainy spring, a simple and safe homemade remedy can help. It won’t cure a serious infection, but if mold and fungus have been issues with your peonies in the past, this spray can help keep infections at bay.

Use this homemade plant spray early and often to hold off significant disease, starting as soon as stems emerge from the ground in spring. This mix is particularly useful for managing powdery mildew.

Mix these ingredients together for an easy anti-fungal spray that is safe for peonies and other plants:

• 1 tablespoon (14.7 mL) baking soda
• 1 tablespoon (14.7 mL) neem oil or horticultural oil, both available on Amazon
• 2 to 3 drops of liquid Castile soap, which is also available on Amazon
• 1 gallon (3.8 L) water

Transfer the mixture to spray bottles, which you can get on Amazon, to use on your peonies. The oil helps the solution stick to the leaves and stems, but you’ll still need to reapply after heavy rain for the best results.

Focus the spray on all the areas you have seen mold in the past or currently. This includes the stems and undersides of leaves, not just the tops of leaves.

This homemade recipe is best for minor fungal infections on peonies, and is especially useful for managing powdery mildew. If you have a case of blight that is already causing parts of a plant to rot, it’s likely too late to save it with a neem oil solution.

If you have a rotting peony, it is best to simply remove the plant and destroy any affected foliage to prevent the disease from spreading to other parts of your garden. You can also check with your local extension office or garden center for guidance on more specific advice for your particular region and weather as well as a commercial product that could save your plants.

How to Prevent Fungal Infections

The best medicine is always prevention, so take these steps before a fungus takes over your precious peonies:

• Plant your peonies in an area with full sun and in soil that drains well.
• Space peonies adequately. They need about 3 feet (0.9 m) between them for good air circulation. Thin out some of the new growth in spring, if your plants are very dense.
• Water peonies at the base, not overhead, to avoid standing water on stems and leaves.
• Cut back peonies at the end of the growing season, so fungal spores don’t overwinter on plant material.

Peonies have a tendency to host fungus when grown in the wrong conditions. With careful site selection, good care, and a little homemade spray every once in a while, you can avoid or manage this common peony problem.