About Itoh Peonies
Half Woody, Half Herbaceous-The Best of Both
Get to Know This Wonderful New Group
The Itoh Group cultivars (cultivated varieties, cvs.) make up the most recently hybridized peony type to reach the ornamentals market place in quantity. These innovations are produced by crossing the Lutea Hybrid tree peonies (woody stemmed) with the long grown common herbaceous peonies, the Lactiflora cvs. Historically, attempts to succeed with this cross were for long met by failure. The first known success was for specialist peony grower, Toichi Itoh, in Japan, but afterwards widely repeated in the West. Thus the choice of cultivar group name made official by the American Peony Society in its capacity as International Registration Authority for peonies.
Characteristically, the Itoh Hybrid seedlings which have been named and reached the market place are among the best adapted of any peonies for use in a viewed landscape. They demand minimal care. Both are attractive and easy to grow. The flowers are unique, the form similar to those of the Lutea Hybrid parent but in a wider range of color expression. The plants are as easy to grow as their common peony parent, while the foliage can be expected to remain attractive throughout the growing season.
As a group, plant habit holds up especially well against the weather. The stems are only weakly hardy, but notably stiff, consistently giving season long support of bush shape. Most of them when mature will equal or exceed thirty inches height when in flower. Outer stems of the bush can be expected to spread more widely than is typical of either parent, but do not easily fall. The whole of it gives a medium height bush that may spread wider than tall.
The range of flower form typically is more like those of the Lutea Hybrid parent than those of the Lactiflora parent. Also the leaflets are much notched and pointed like those of the tree peonies. The flower forms vary from the classic Singles to rather full Semidoubles, some of them giving near Full Doubles at well grown maturity. Some give one flower to a stem, others will have up to two side buds, often opening in rotation, leading to an extended flower opening season ranging to three weeks (or longer where spring warm-up remains cool). Flowers open during the same seasons as the Lactiflora parent, the plant and flower adding extra weeks to a tree peony theme flower show when the three types are grown together.
Growing Itoh Peonies
Hybrid Vigor and Disease Resistance Add Up to a Winner
Itoh peonies are hybrids between P. lactiflora and Lutea hybrid woody peonies, which is evident in their growth habits. Their hybrid vigor draws upon their parents strongest traits and provides no nonsense culture.
Like all peonies, Itoh Group kinds give the greatest rewards in a well-drained, fertile soil sites. If the desired planting site does not meet that standard, most gardeners will find it is well worth the effort to make it so. See elsewhere at this web site for discussion of planting site development. These cultivars have among the best hybrid vigor of any peonies, consistent with the wide differences between the inherent genetics of the two parent types. The foliage is less prone to leaf fungi than generally true of the Lactflora Group parents. Do follow the same annual late summer/early autumn cleanup against fungi as recommended for all peonies.
Raised beds and raised rows work well for Itoh cultivars, as it does for other peony types. It serves the valuable purpose of keeping the underground crowns of your peony plants safer from wet season extended water logging of soils. On flat sites do follow the general rule of placing your planter piece so the base of most stem buds will be about one to three inches underground. In raised beds or raised rows this can be deeper, sometimes of advantage (see below).
While specific information on winter hardiness of most individual kinds has yet to be established, cold tolerance is generally similar to that of the Lactiflora parent cultivars. Some of Itoh peonies are performing successfully at locations in the Canadian Prairie Provinces and Alaska.
Unlike the commonly grown herbaceous peonies, overwintering stem buds on some kinds will form at the soil surface as well as a couple inches below. Occasionally one will discover a plant has formed one or more buds up stem, more like the woody peonies. Unfortunately, however, the stems which support those stray buds, as in the herbaceous types, having formed in the above ground light they will be weakly hardy and easily killed over winter.
Propagating Itoh Peonies
Division Much Like a Herbaceous Peony-Though a Saw May Be Needed
Crown division, the traditional method of propagating all, but the woody peony types, works well with the Itoh Group sorts. During a propagation cycle (3 to 4 years), the underground stem (crown) extends somewhat with tuberous growth and swells with food storage similar in habit to the Lactiflora parent type, facilitating the process of division. Tuberous food storage roots will similarly extend outward and downward, but will have a hard core, like the tree peonies. After a three or four year cycle, well grown plants will yield a comparable increase. The tuberous roots are of smaller diameter and longer than the common peony parent and somewhat less so than the woody peony parent. Adjust the length of tuberous root on individual divisions to retain an approximately equal amount of food storage for support of first year growth.
When grown in raised rows, reset them so that the stem buds are deeper, to four or five inches below top of the raised rows, but not lower than the adjacent soil surface. Moisture support during the first year is better when planted more deeply and the buds are protected from excessively wet conditions. So placed, when the stems grow in future seasons, they will form stem buds at multiple levels: the original crown level, very near or at the soil surface and one, two or three internodes in between on fully perennial portion of underground stems. This affords the gardener a maximum flexibility of propagation choices. The buds on perennial stems can be used for grafting scions, or, if left on the replant pieces, the extended stem can be positioned horizontally where all buds will put up stems, contributing to more rapid expansion of the bush in the following seasons. Alternatively, if taken up for dividing after three or four seasons, it may be found the growth at each of the original stem buds will have grown into a quality division which can be taken with a minimal dividing damage.
Additionally, some Itoh Group cultivars, although not all, have proven successful in micro propagation (in glass, under sterile laboratory conditions). When a cultivar succeeds, a large number of its plantlets can be produced in a comparatively short cycle. When grown large enough on artificial media to establish upon transfer to soil, those which survive the transfer can then be grown on to a size that can be cataloged for sale. This system has been going on long enough for production management challenges to have been resolved. A number of these micro propagated Itoh group peonies are now beginning to be offered for sale (inexpensively) in four inch pots. Concern involving the root growth pattern of micro propagated peonies is valid, as these plants’ roots grow in a tight whorl, which is not an easily broken pattern. Mutations of flower and plant structures have also been more common with this type of propagation, but better laboratory techniques have been instituted to resolve this issue.