Old-fashioned garden favorites, both hybrid garden or herbaceous peonies and tree peonies produce large, fragrant flowers. Appealing perennial foliage is ideal as a flowerbed backdrop. But peony flowers are the main attraction, and not just for humans. Ants are drawn to nectar and other ant attractants that are produced by some peony flowers, it is thought, to encourage ants to help open dense double flower buds. Once buds are open, ants disappear–neither essential to flowering nor harmful.
Rich, loamy, well-drained soil grows the best peonies. Largely disease and pest free, peonies do require well-drained soils. Good soil drainage will help prevent the various fungal diseases that can pose problems. Amend heavy clay soil with well-rotted manure, compost and finely ground pine bark to increase organic matter and improve drainage. Peonies like full sun, but in hot areas dappled or light afternoon shade will help protect flowers from fading and sun damage. They generally do best in cool climates; most cultivars require 100 to 300 winter chill hours. Spring flowering for any cultivar is usually just one week, but by choosing from among early, mid-season and late blooming types peony lovers can create a six-week peony season.
Given the tall, thin stems that often support very large, heavy peony flowers, extra support is often needed to keep blossoms from falling over. This is true for many herbaceous peonies, but particularly for tall, double-flowered types. You can buy commercial support hoops designed just for this purpose. Another option is making your own support system by driving in three or four stakes then using plant ties or loops to support vulnerable stems. Use stakes shorter than plant vegetation so they aren’t visible.
Flowers of peony plants that have been "disbudded" are particularly vulnerable to falling over due to their own heft. Disbudding is done to produce very large flowers; the terminal flower bud on each stem tip is left while all side buds are removed. Again, staking will prevent these giant flowers from bending or breaking under their own weight. Loosely attach flower stems to the stake with plant tape.
Fungal disease, encouraged by poorly drained soil and spread by overhead watering, can weaken stems and cause blossom stems to bend or break. An overwintering fungus that softens stem tissue and blackens flower buds causes botrytis blight. Control it during the growing season by removing diseased foliage as it appears, then after the first heavy frost cut plants back all the way to the ground and destroy the foliage. Apply copper sulfate fungicide early the next spring, as vegetation emerges, and avoid overhead watering.
Root rots encouraged by poorly drained soils can devastate entire clumps of peonies. Plants may rot right at the ground line or crown. Phytophthora blight is usually fatal but can sometimes be arrested before roots rot by destroying all infected plant parts, applying fungicides and following general vegetation cleanup and disposal practices. Verticillium wilt is fatal. There is no cure for either fungus beyond destroying infected plants and removing diseased soil.