Don’t Make These 7 Common Peony-Growing Mistakes This Year

Peonies live for ages where they’re happiest, needing infrequent tending and gracing the garden with fully-petaled cups in spring and early summer. With regular moisture and sunlight, they’re relatively easy-going once established.

There are a few peony-growing nuances, though, to ensure bountiful blooms and vigorous growth. In optimal conditions, they’ll colonize to show even more color. In addition to their gorgeous flowers is their handsome dissected foliage, with many varieties remaining fresh and attractive from spring through fall. Peonies make a pretty stand-in for small shrubs and a leafy backdrop in the perennial border. Their sweet fragrance also adds pure delight.

With the right peony in the right place, they’ll live for years with reliable performance. By avoiding common peony growing mistakes at planting and in care, we set the foundation for healthy, abundant blooms.

Peony Growing Notes

Peonies bud and bloom according to variety with early, mid, and late season timing. They begin blooming in April and go through June. Choosing varieties with different bloom times prolongs the display with a succession of peonies in flower. 

Look to tree peonies (Paeonia suffruticosa) for full, vertical interest and huge blooms early. Woodland species (P. obovata subsp. japonica) offer a naturalistic highlight in shadier spaces, and common garden peony hybrids (P. lactiflora) offer vigor and performance with compact growth and versatility. Itoh or intersectional types combine the best of tree and common garden species, with big flowers on vigorous, leafy forms.

Peonies perennialize in USDA zones 3-8. Climate influences bloom time, with buds emerging and opening according to spring’s warming temperatures. Tall varieties benefit from staking at planting to avoid stems flopping under the weight of hefty blooms. Shorter, sturdier varieties don’t need additional support.

Not Enough Sunlight

Most peonies are sun-loving and need ample light to produce their huge blooms. They also do well with dappled light or afternoon shade protection in climates with intense heat or sun. All species need sunlight to flower, and for many,  six to eight hours is ideal. Some species, like tree and woodland peonies, are better suited to partial shade. If you’re not seeing blooms, insufficient light is often the main peony-growing mistake.

Morning or early sun is optimal for the bulk of the sun, but intermittent periods serve them well, too. If your peonies receive four to six hours of sunlight, you should see full color. This amount provides energy to the flower while striking a balance of cooling protection. As a bonus for those growing in a bit of shade, blooms last longer out of the day’s sun.

Situated beneath deciduous trees or along an open woodland border are ideal placements for peonies that tolerate some shade. Deciduous trees provide spring sunlight while buds emerge, and once leaves emerge, they grant shade in summer.

Planting Too Deep

Peonies sprout root and shoots from tubers (enlarged roots). Planting tubers too deeply, even a little, impacts flowering and may result in a failure to bloom. Position tubers one to two inches beneath the soil surface. 

If you’re planting a nursery-potted specimen, plant the crown level with the soil surface as it is in the pot. The buds on the tubers should stay at one to two inches deep.

Peonies grow beautifully in containers large enough to support their mature size. Situate the tuber in a high quality potting mix. Ensure pots and potting media are well-draining and follow the tuber placement for in-ground specimens (one to two inches beneath the soil surface).

Transplanting at the Wrong Time

September and October are the best times for transplanting, and other events of the year can disrupt the hard-working tubers. Plant peony tubers in the fall for best success. This timing gives them a necessary chill blast, allowing growth before summer’s heat. Nursery specimens are further along, usually around two years old, and do well with both fall or early spring plantings.

During the growing season, peonies store energy to continue root development for future growth post-dormancy.

Tips on Dividing

While the perennials infrequently need dividing (every five years or so), do so to expand the colony or if crowding becomes an issue. They’ll show reduced flowering when it’s time to divide. 

It’s important to note that the move may delay blooming for a year or two as they adjust. Peonies are slow to develop and have extensive roots. Once planted, they don’t respond well to disturbance.

To move peonies in the fall, cut stems to the ground. Capture and lift the roots by digging a berth of six inches around the crown. Transplant immediately to the new garden location and water in well. Don’t expect blooms the following spring for the new transplants.

Water Issues

Established specimens thrive with average seasonal moisture, though they benefit from supplemental water during dry spells. To avoid a common peony growing mistake of fluctuating water, provide regular moisture for the best overall health. They withstand periods of drought but won’t flower under stress from heat waves or dry spells. Prolonged drought hinders growth and causes them to enter conservation mode, dropping leaves and buds.

Consistent moisture for peonies usually means watering once or twice weekly in the growing season. About an inch of water per week, whether from rain or supplemental irrigation, is sufficient. They don’t tolerate saturated soils, so ensure good drainage.

Water at the base around the perimeter of the leafy canopy to reach all the roots. Water deeply to reach the extensive root system and moisten the surrounding soil. Avoid splashing the leaves when feasible to prevent foliar diseases, and offer plenty of air circulation to minimize damp conditions.

Overfertilizing

As we want to nourish our prolific bloomers, too much fertilizer is a common peony-growing mistake. Peonies relish organically rich, loose loams with good aeration. Amend soils with compost at planting, especially if they’re primarily clay or sand compositions. 

While nutrient-rich soils may be enough to support growth and flowering, peonies use and store a lot of energy in a single growing season. An all-purpose organic fertilizer does the trick as new growth emerges in spring. A slow-release granular 5-10-10 or 5-20-20 organic fertilizer promotes blooming without sending too much nitrogen into leaf and stem production. 

Excessive nitrogen from overfertilizing produces leafy stems but reduces flowering. The plant directs energy into quick stem and leaf growth rather than reproduction (flowering). Opt for a fertilizer higher in phosphorus (the P in the N-P-K fertilizer ratio) to promote flowering. 

If not using a slow release but a straight granular, provide three applications of a low-grade supplement. The first is as new growth springs up, the second as buds form, and the third in late summer to support energy stores in the tuber. Kelp, seaweed, fish emulsion, alfalfa, or a phosphorous-rich formula are beneficial amendments.

Extreme Temperature Exposure

Peonies are native to the northern hemisphere, particularly Europe and Asia, with two species native to Western North America. Most flourish in a Mediterranean climate type, where summers are warm and winters are cool and wet. In hot climates, they’ll struggle to achieve the winter chill they need to thrive and face heat and humidity stress.

The flowering perennials grow best in temperate to cool climates. On average, 55-60°F night-time temperatures and 70-80°F daytime are prime (13-16°C in the day and 21-27°C at night). In hot climates, they may not thrive. Try shade protection from the midday heat and keep them out of drying winds. Offer plenty of moisture to those in more sun in warm growing areas. And, the blooms last longer on the stem in cool conditions.

Mulching helps regulate temperatures in spring and summer by keeping roots cool and retaining moisture. Add more mulch before cold winters, especially in zones 3 and 4, for overwintering protection.

Not Scouting For Fungal Problems

Peonies are sometimes prone to fungal issues. Common fungal diseases and viruses impact overall health and become a problem in bloom production. These relate to cultural practices that harbor spores and promote their spread. Common peony-growing mistakes include crowding plants and promoting damp situations through irrigation. Peonies require good air circulation with proper spacing and pruning. Allow a three to four feet spacing between selections, depending on the variety.

As herbaceous types die back after fall’s heavy frost, remove the dry stems and leaves. For tree peonies (whose woody stems persist through winter), remove fallen leaves. This cutback and debris removal prevents fungal spores from developing or overwintering to affect the next season of blooms. Bulk up the mulch layer for seasonal insulation.

Powdery Mildew

Powdery mildew is a common fungal disease that is a grayish-white powdery substance on leaves, stems, and buds. Leaves may distort and drop due to the pathogen Erysiphe.

Spores travel on the wind, through contact with infected plants or tools, or splash up from the soil via raindrops and irrigation. They begin on the leaves and spread to the stems, depleting energy and nutrition.

Leaves turn yellow, distort, and drop during severe infections. The fungus spreads quickly, and if left untreated, growth declines. Fortunately, powdery mildew doesn’t usually kill peonies and lessens with fall dormancy and cleanup.

Botrytis

Botrytis is a fungal disease especially prevalent in high-humidity conditions with limited air circulation. It shows as brown spots and “fluffy mold” on leaves and stems. Botrytis thrives in the cool, damp conditions of spring and fall.