No Flowers - Improper Culture
There are many possible reasons why peonies fail to bloom. Some of the most common cultural reasons are:
1) Plants are too young. They need 3 or more years to mature.
2) Roots are planted too deeply. Be sure eyes are no more than 1 to 2 inches below soil or mulch.
3) The weather is too hot. In hot climate areas choose early blooming varieties.
4) The plant needs dividing. If the clump has been undisturbed for a decade or more, divide it.
5) Competition from shrub and tree roots. Move the plant to a location without dense tree roots.
6) A late spring frost has killed flower buds. Cover the plants with agricultural fleece to protect them when late frost is expected.
7) Waterlogging from too much rain. Move to a higher, better-drained location if this is a chronic problem.
8) Plants are undernourished. Sprinkle a handful of granular fertilizer around the plants.
9) Ground is too dry. Give plants 1 inch of water per week.
10) Too much shade. Move to a sunny or lightly shaded location.
11) Gophers, voles, or moles have harmed the roots. Control the animals.
Weak Flower Stems - Inferior Plants; Deficient Soil; Excess Shade
Weak stems that do not stand up well when the blossoms are out indicate either a weak stemmed variety, a phosphorus deficiency, or the plant is in too much shade. Fertilize with a balanced, high-phosphorus fertilizer. If the plant is in shade, move it to a sunny location. If the problem persists, you may have to either stake the flower stems or try another variety.
Ants - Ants on Stems
Ants feed on the sticky syrup covering the buds, but they do not cause any direct harm.
Flower Petals Eaten - Rose Chafer
Adult rose chafers are tan beetles with a reddish head, and about 1/2 inch long with spiny legs. They feed on peony flowers, sometimes ruining them completely. Hand pick them off the plants. Spray heavy infestations with pyrethrum. For long term control, scratch milky spore powder (Bacillus popilliae) into the soil to kill grubs.
Leaves And Flowers Discolored - Thrips
Flower thrips are slender, lemon yellow to brown, with 4 narrow, fringed wings. They move about very actively, like a bunch of animated exclamation points. The nymphs are wingless. They rasp at plant tissues with their tongues and lap up the sap. Brown spots on light colored flowers and red spots on darker flowers indicate thrips damage. Set out yellow sticky traps as early warning devices. As soon as thrips appear on the traps, check plants and spray with insecticidal soap every 3 days for 2 weeks. For more information see file on Dealing with Thrips.
Small Bumps On Leaves - Scale
Scale insects lurk beneath their rounded waxy shells, which are colored white, yellow, or brown to black, and are about 1/10-2/5 inch in diameter. The first sign of a scale attack is often discoloration of the upper leaf surface, followed by leaf drop, reduced growth, and stunted plants and obvious bumps along stems and branches. Heavy infestations kill plants. Some species excrete honeydew, which coats foliage and encourages ants and sooty mold growth. Scraped minor infestations off plant surfaces with a finger nail or a cotton swab dipped in rubbing alcohol. Spray heavily infested plants with a mixture of alcohol and insecticidal soap every 3 days for 2 weeks. For more information see file on Dealing with Scale.
Shoots Wilt and Collapse; Leaves Spotted - Botrytis Blight
The most common disease of garden peonies is caused by a gray mold called botrytis. In spring when shoots are about 1 foot long, they may wilt suddenly and fall over. When pulled out or cut off below the ground, a brown or blackish rot appears at the base of the leaves and stem. Stalks just above ground level are covered with gray mold. Buds and opening flowers are also attacked. Remove and destroy infected plant parts. Put them into a plastic bag before discarding. Pull mulch away from crowns and don't wet their foliage when watering peonies. For more information see file on Dealing with Fungal Diseases.