Peony Care newsletter from Green Works

Dear peony grower,

Due to the winter weather and the associated cold hours, the hybrid varieties are emerging early this year. Therefore, please take this into account for your weed and fungicide schedules.

Phytophthora

Phytophthora is an infection that takes hold through injuries under humid conditions. The fungus can survive in plant tissue and in the soil for years.

The first infestation can be recognized by black and weak leaves in the crop. When there is an infection in spring, brown to gray-black spots appear on the stem parts. In that case, the branches may appear like black brackets and will not grow further than about 10 centimeters.

After infection, it is almost impossible to remove. Infected areas often feel spongy and soft, with dark brown marrow and wet rot. Kansas and Duchesse are examples of varieties that are sensitive to Phytophthora. The elements manganese and zinc can help improve resistance.

To help prevent this, from the moment the flower rises until mulching, spray once every two weeks with products such as copper, Pergado V, Paraat, Axidor (systemic), or Ranman Top.

To avoid unnecessary use of expensive pesticides, it is wise to test suspicious plants for the presence of Phytophthora.

Preventive Measures

• Use healthy starting material
• Maintain good soil structure
• Avoid overly wet soil and ensure adequate drainage
• Avoid high soil salinity
• While spraying against Botrytis, occasionally add a Phytophthora agent
• Be aware that early pruning increases plant stress and susceptibility
• Consider planting a cover crop in autumn to improve soil structure
• Phytophthora can be introduced via surface water, but not through spring water
• High nitrogen levels can make plants more vulnerable
• Increase plant resistance, for example by co-planting with Trichoderma

Watering

Paeonia is a sensitive crop. Because of its fast growth after sprouting, it is not particularly strong during this stage. The plant may reject its weakest flowers when growth is rapid and the weather is bleak.

Especially during cold nights, frost is often blamed, but a lack of water is more likely the main reason. A sudden spell of warm weather during stretching can also increase the risk. Do not wait until the soil is dry—make conditions as pleasant as possible for the plant.

In the greenhouse or tunnel, watering is especially important for final results. Because the plant grows so quickly, there is a strong chance that vegetative growth overtakes flower bud development. The plant’s “choosing moment” can be delayed by supplying sufficient water, helping prevent the loss of flower buds before they are large enough.

Irrigation must also take climate into account. Avoid big swings in temperature and humidity, open windows in time, and provide an easy, steady growing period. Opening windows only when it is already warm may encourage Botrytis, while growing too dry in an effort to prevent Botrytis may result in dried-up flower buds.

In short, irrigation should be optimized to support proper flower bud development, rather than solving one problem at the expense of another.

Weed Control

Weed control in peonies is more a matter of discipline than choice of product. Organic matter content is one of the most important factors. Heavy clay soil with little to no humus can act like light soil when it comes to weed control.

The effectiveness of a weed-control product is determined by a fine line between control and crop damage. Most products work best in the first period after application. If spraying is delayed, a higher dose is needed—but that also increases the risk of damage to the plant.

AZ 500 is a soil herbicide that can be used before plant emergence. It works well against many unwanted weeds, including composites such as chamomile and groundsel, crucifers such as Capsella bursa-pastoris and Cardamine hirsuta, as well as poppy, purple dead-nettle, and many other broadleaf weeds.

However, AZ 500 is not effective against cleavers, pelargonium, grasses, or perennial weeds that emerge from rhizomes.

It is time to spray with Corzal SE and Goltix when the flower buds are visible. On a moist surface, Goltix performs best. Do not spray in sunny weather; apply late in the afternoon instead. If night frost is expected, Goltix should not be used because of rapid plant degradation. The newer product Oblix appears to be an effective solution against cleavers.

Leaf nematodes can also infect a parcel by traveling on weeds and seeds.

Fertilization

A quality peony needs balanced fertilization. The time has passed when “a little bit of this and a little bit of that” was enough. Peonies that have stood in the same location for multiple years can deplete the soil and certainly need nutrition.

Start of Cultivation

Until some years ago, phosphate was mainly known for better root development. Now we know plants have a preferred uptake order: sulfur, boron, silicon, calcium, nitrogen, magnesium, and phosphorus. The availability of these basic elements—especially boron, silicon, and calcium—is essential for a good start.

If one of these elements is missing, the chain is broken and the growing process may start more slowly or with more problems.

Main Elements

Trace Elements

Trace elements are essentially the vitamins and minerals of the plant. Uptake inhibition can occur when the pH exceeds 6.5. Important trace elements include iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), and molybdenum (Mo).

These elements are needed for water regulation, cell division, and metabolism, and are primarily absorbed through the roots. For that reason, strong root growth is essential. Many commercial fertilizers contain little to no trace elements, so supplementation may be necessary.

Signs of Trace Element Deficiencies

• Iron (Fe): young leaves turn light green, yellow, or white between the veins
• Manganese (Mn): older leaves yellow between the veins
• Boron (B): reduced flower count, malformed growth points, and distorted foliage
• Zinc (Zn): growth problems and chlorosis spots on young leaves
• Copper (Cu): dying flower buds, curled young leaves, yellow or grey foliage
• Molybdenum (Mo): yellow discoloration, malformed foliage, and problems with nitrogen conversion

Added Value of Proper Fertilization

Peony cultivation is characterized by three key factors:

• It is a perennial crop harvested from the same plant for several years
• Its annual growth cycle has two phases: before cutting and after cutting
• Customized fertilization pays for itself in plant vitality and yields per square meter

Period Before Harvest

This period begins around February, when the rhizome becomes active and starts sprouting as soil temperature rises. The first fertilization usually occurs at this time. The goal is to support sufficient length growth and a deep green leaf color, which requires all essential elements to be available in the right amounts.

Nitrogen is especially important for length growth, but the form of nitrogen matters as well. Since this period lasts several weeks, the plant needs a steady supply—not just a quick mineral burst. Magnesium and trace elements are also important for rich foliage color.

Green Works notes that DCM offers fertilizers tailored for this stage, generally organic-mineral blends. The mineral fraction gives a quick start, while the organic raw materials provide long-lasting support. Commonly used fertilizers include:

• DCM MIX-5 (NPK 10-4-8 + 3 MgO)
• DCM START (NPK 18-3-3 + 2 MgO)

For trace elements, DCM MICRO-MIX is commonly used as an organically bound trace-element fertilizer that releases nutrients gradually over time.

Period After Harvest

The period after harvest is just as important. During this time, the peony rebuilds energy reserves for the next year’s crop. Assimilation is the central process.

Since the plant has lost several stems and undergone stress, the emphasis shifts to crop recovery and sugar production. Important elements during this stage include potassium, magnesium, calcium, and trace elements.

Fertilizers after harvest usually contain high potassium and lower nitrogen, since nitrogen is no longer needed for length growth but still helps maintain color and vitality. Commonly used fertilizers include:

• DCM MIX-2 (NPK 7-6-12 + 4 MgO)
• DCM MIX-6 (NPK 6-3-18 + 3 MgO)
• DCM VIVIKALI (NPK 2-0-20)

Why It Matters

Proper fertilization improves plant growth and development. In perennial crops, sugar levels in the rhizome during winter reflect the plant’s energy reserves for the following year. Trials and demonstrations have shown that mineral-organic fertilization can raise sugar levels.

Practical measurements among peony growers have also shown that optimized fertilization strategies can increase production, often resulting in several more harvestable stems per square meter.

Leatherjackets (Crane Fly Larvae)

Adult crane flies feed on only a small amount of nectar, but their larvae—known as leatherjackets—are much more destructive. They are relatively large, soft, and thick, and they feed on a variety of plants, including peony stems just below the soil surface.

Life Cycle

Crane flies pass through six developmental stages: an egg stage, four larval stages, and an adult stage. Adults live only a few days. Some species have one generation per year, while others have multiple generations, allowing larvae to be present year-round and continuously cause damage.

Damage Symptoms

During the day, leatherjackets stay in the soil. At night, they come to the surface and feed on the stem base and lower green parts of the plant, sometimes pulling the plant slightly into the ground. Stems with damaged bases will wilt.

Control Measures

Biological control is possible using parasitic nematodes such as Nemasys H, C, or F.

Botrytis

The first treatment against Botrytis takes place during emergence. Because the fungus overwinters through spores at the soil–air interface, the new shoots become infected as they emerge.

Watering with Collis can reduce the number of toppled plants by more than 90% in sensitive varieties such as Flame. This highlights the importance of timely, preventive treatment.

Loosening the topsoil in tunnels and greenhouses can also significantly reduce damage from toppled plants.

Because peonies grow rapidly, they are not very resilient to sudden climate fluctuations. Around damaged tissue, Botrytis often develops readily. Especially when peonies are not protected during growth, the fungus can cause major problems.

Additional sprays are therefore needed during this critical period. Effective and recommended products include Teldor, Kenbyo, Flint, Luna, and Switch.

After a night frost, do not spray for 2 days due to weakened plants.

Fungicide List