Growing Itoh Peony
Paeonia, Itoh
Latin Name Pronunciation: pay-oh'-nee-ah, ee'-toh
Itoh Peonies are Interspecific hybrids (crosses between species) that combine the best qualities of woody-stemmed Tree Peonies and Herbaceous Peonies. Itohs are as tough and easy to grow as Herbaceous Peonies, with the exquisite, long-lasting blooms so treasured on Tree Peonies.
Growing Itoh Peonies
Planting: Do not pre-soak bareroot Peonies and do not fertilize when planting. Bareroot Peonies can be puzzling and roots are brittle, so handle with care. You will see larger tuberous roots and delicate fibrous roots. Plants may have an obvious crown or not, and tuberous roots may be slim or chunky, and oriented horizontally or vertically. Roots may be tangled with “eyes,” those fat reddish buds, pointed in several directions. Itoh Peonies may also have a short vertical somewhat woody stem, possibly with buds, that will rise above the surface of the soil when planted at the proper depth.
How to tell which end is up?
The “eyes” are going to form next year’s shoots, so orient the plant with as many of them as possible facing up, whether they emerge from a fat rhizomatous root or an obvious crown. This is the part of the plant that needs to be at the proper depth. Roots may extend down into the ground or out sideways and some buds may be sideways, but they will still grow in the right direction.
How deep to plant?
Itoh/Intersectional Peonies should be planted with the crown at the same depth as Herbaceous Peonies, but may have vertical stems, possibly with buds, that rise above the surface. Once you have identified the crown or the roots with the most eyes, cover that part with one to two inches of soil in the North and no more than one inch in the South. If the eyes are set deeper than recommended, plants may not bloom. For this reason, do not mulch over the crowns. Container-grown plants should be planted at the same soil level as in the pot.
Patience, please! Plants may have few or no flowers the first spring and early blooms, especially doubles, may not appear true to variety at first. They generally take a few years to settle in and bloom, but get better and better over time, for decades.
Light: Full sun (6-8 hours direct sun during the growing season); afternoon shade in the South and warmer areas of the West is appreciated and will help flowers last longer.
Watering: Water once when planting to settle the soil and then avoid watering until new growth appears in spring unless experiencing extreme drought. Dormant plants cannot take up much water and will rot if kept too wet. Water deeply every week or two during active growth for the first year if there is little or no rain. Once well established, plants are drought tolerant, rarely needing to be watered, although they appreciate a deep drink occasionally during drought. Avoid overhead sprinklers (water on leaves promotes fungal diseases) and automatic irrigation (frequent shallow watering promotes rot).
Fertilizer: Peonies benefit from an inch of compost or aged manure spread as a top dressing around the root zone (not on top of the crown) annually. No other fertilization is necessary, although in times of stress, foliage feeding with liquid fish/seaweed fertilizer works wonders.
Soil: Peonies are very long-lived (50 years and more) and require little care once established, so properly preparing the soil is well worth the initial effort. Peonies thrive in loose, well-drained fertile soil that is rich in organic matter; they cannot survive wet, saturated soil. Turn in a good amount of compost to a depth of 1' (or a shovel’s depth); be especially generous in sandy or clay soil. Near-neutral soil pH (6.5-7) is ideal, so if your soil is too acidic, add a few handfuls of calcitic lime well before planting.
Pests/Diseases: Few insect pests bother Itoh Peonies, but a fungal disease called botrytis may be a problem, especially in very wet seasons or with excessive overhead irrigation. Stems develop cankers or blacken at the base, falling over or simply wilting. Leaves may show black or brown patches and buds may turn brown and fail to open. Spray newly emerging shoots early with modern Bordeaux mix (an organic copper-sulfur mix) or lime sulfur (look for an OMRI label indicating the formulation is approved for organic use), following label directions. Peonies can be susceptible to powdery mildew in summer, especially with humidity. The white, powdery mildew fungus covers the leaves to varying degrees but doesn’t appear to greatly affect the vigor of the plant. It can be treated early with Neem or Horticultural Oil, but that is not often necessary.
Good culture and sanitation in the garden can help prevent or correct both these problems. Plants need good drainage and air circulation, so do not crowd them. Remove and discard diseased foliage as soon as you notice it and deadhead religiously as flowers go by. Cut off all foliage just below soil level after a killing frost in fall and remove it, along with any nearby plant debris from the area—do not compost. Fungal spores overwinter at the base of the plants, and spring rains splash the spores up onto the new shoots. Covering the soil with sand helps prevent reinfection
Dividing/Transplanting: Generally Peonies do not need dividing and some resent it. However, if you must move an established plant you need to divide it before replanting. Do this in the fall, after all foliage has died back completely. Each division should have three to five eyes, and it will usually take a couple of years for the new plants to flower.
Companions: Peonies flower with Roses and Clematis and are lovely with many other perennials; be sure to leave room around the plants for air circulation. White-flowered Peonies are entrancing against a background of evergreens. Spring-flowering bulbs such as Crocus vernus or Scilla siberica create a pleasing color contrast at the feet of emerging Peony stems, which are often reddish.
Reflowering: Many varieties make several side buds that will open after the terminal bloom flowers, so deadheading is beneficial. After each flower is finished, cut the stem underneath the old bloom, leaving the foliage alone. If exhibition-sized flowers are desired, remove the side buds as they form and leave only the terminal bud.
Hardiness: Peonies must experience a certain number of chilling hours (25-40 degrees F.) to set flower buds. Zone 8 is usually the limit for Herbaceous Peonies, but some Itoh Peonies will bloom in Zone 9. Higher elevations and more shade help push the limits.
Calendar of Care:
Early Spring: Water plantings well if spring rains don't do it for you. Side dress plants with compost or aged manure. Set stakes or other supports in place now.
Mid-Spring: Watch for signs of botrytis blight and treat as needed, removing any diseased tissue immediately. Train through plant supports as plants grow.
Late Spring: Cut Peonies for indoor bouquets and remove flowers that are past bloom.
Summer: Peonies do best with an inch of water a week.
Fall: Foliage should be cut back in the fall and removed from the premises to discourage overwintering of pests. Trim Itoh/Intersectional Peony stems down to 4-5", leaving stem sections, which may develop buds. Dig and divide plants now if necessary. Mulch new plantings with evergreen boughs after the ground freezes.