Digging and Dividing the Herbaceous and the Hybrid

By George Hernandez

Over the years, peony growers have observed that peony divisions perform best when the divisions have at least one well-formed bud (eye) and some amount of healthy root. These observations relate to proven physiological characteristics of herbaceous peonies that should be kept in mind by anyone who attempts to propagate herbaceous peony varieties.

First, note that most herbaceous peonies form all of their buds along the embryo axis of their underground stems. The embryo axis of these underground stems is commonly referred to as the crown. Buds that form spontaneously on portions of underground stems or roots that are not aligned with the embryo axis are known as adventitious buds. The common lactiflora peonies are not able to form adventitious buds. A root that does not already have an existing bud will not form one. Each peony division must have a well developed bud with a portion of the embryo axis. (There are some exceptions, most notably among hybrids.

Second, the energy required for the initial growth of herbaceous peonies is derived from carbohydrates that are stored in the below-ground stems and roots of the peony. The only source of energy available for the characteristic rapid early growth and development of peonies is provided by the roots until the chlorophyll in the new leaves is able to sustain the developing plant. A peony division should have enough stored energy to carry the plant from its dormant state to the state where it can produce its own energy.

The intended use of a peony division will determine the number of eyes (buds) that a division will require. Many growers find that a division with only one eye is sufficient for replanting, while peonies sold commercially generally have from three to five eyes.

The amount of root that a peony division should have is determined by the number of eyes that the division contains. An easy way to determine the amount of root to leave per division is to allow a piece of root, no smaller than the size of your index finger, to remain for each eye of the division.

The divisions that the home gardener gives to his friends do not have to meet the rigid standards of the divisions that the commercial grower sells to his customers. The home gardener can use short cuts and techniques that would be inefficient for the commercial grower; however, the methods used by both must satisfy the physiological requirements of the peony in order to perform adequately.

DIGGING

Peonies, like most plants, have a root system that is proportionate to its foliage. The outer edges of the foliage correspond to the outer edges of the root system. An imaginary line that encircles the plant at the outer edge of its foliage is the point where it is safe to dig without harming the root system of the plant. The texture of the soil, the amount of soil moisture, and the strength of the individual digger have to be taken into consideration when discussing the best method for digging. Two common methods of digging are balling and bare-rooting.

The reason for balling a peony would be to remove the peony from the ground without disturbing the root system or the soil around it. This method requires more labor and is time consuming. The proponents of this method feel that the work is justified since larger plants should yield more divisions. The best tool for forming a soil ball is a nursery spade with a flat blade. When digging the soil away from the plant, the blade of the spade should never face the plant. All digging should be done away from or parallel to the plant. The first strokes of the spade should define the outer edge of the ball; the circumference of the ball should be along the outer edge of the foliage. A trench is then dug that encircles the plant, with care being taken not to disturb the soil of the ball. The depth of the trench will be the height of the ball. The length of a nursery spade is 14 inches, which is an adequate depth for peonies. The ball of soil can be undercut once the trench has reached the desired depth. Gently lift the ball as you cut under it. When the entire ball has been undercut, it should move freely. The peony at this point can be lifted out of the hole and is ready to be washed. The weight of the ball can be reduced by removing the soil that will fall away easily before trying to lift the peony.

The method of digging peonies that I prefer is bare-root digging. The reason for bare-rooting a peony is that you end up with all of the root system and as little soil as possible. This reduces the amount of soil that will have to be removed before propagation can begin. Unlike the position of the spade in the balling method, the blade of the spade should face the plant when you are cutting through the soil. The first series of cuts should be along the outer edges of the foliage at the depth that the spade will penetrate easily. The spade should be kept at a slight angle while cutting underneath the plant. Ideally, the cuts that the spade makes will intersect at a point far enough below the plant, so that a cone of soil is made that contains the entire root system of the plant. I can generally do this by cutting around the plant only once, but it is best to make two or three passes around the circumference to be sure that the plant is loosened. Once you have undercut the peony it can be lifted by prying out the plant with the spade. The soil around the plant, which has been loosened by the digging and prying, will fall away from the roots as the plant is lifted out of the ground. Any soil that remains between the roots can be removed with a blunt object such as the handles of a pair of hand pruners or a stick. The stems which I left on the plant make convenient handles for lifting, and are now cut off three inches above the bud. The peony is now ready to be washed.

WASHING

Peony roots are brittle when first dug. Some advocate letting them “cure” for a day enabling the roots to wilt a bit and become more supple. When large quantities of plants are being processed, this takes place in the time that the peonies are waiting to be washed. With proper care the plants can be washed and handled immediately after being dug. Avoid digging and handling the roots when the temperature is below freezing. Any hose nozzle that emits a high pressure stream of water is adequate for washing the roots. All soil should be removed from the roots, with particular care being taken to clean the area around the crown. The peonies are now ready to be divided.

DIVIDING

The two tools that I prefer to use for dividing (or cutting) are a paring knife and a set of hand pruners. Both should be kept as sharp as possible. The blade of the knife that I use is three inches long and flexible enough to bend during a through cut when necessary. It is best to dip the blade of the knife and shears in household bleach after each cut.

Any plant that is over five years old will be extremely difficult to divide because of the density of the matted roots. Three to five-year-old plants seem to yield the greatest number of usable three-to-five eye divisions.

Before starting to cut it is best to count the number of eyes on the plant. Then after looking over the plant and counting the eyes, try to find where all major roots join the crown. Before cutting anything, you should determine how many three-to-five eye divisions can be made. This is done by looking for those portions of the plant that have three-to-five eyes and where three-to-five finger-sized roots or their equivalent are connected to the crown or to each other. As the plant is being assessed to determine where the first cut is to be made, prune off any broken or damaged roots and trim the stems back to the eyes. The stems are tough and should be cut with hand pruners.

When you are ready to make the first cut, place the plant on a stable work surface and keep it secure while you are cutting. Start all cuts by carefully inserting the point of the knife into the root and smoothly complete each cut with a single motion. Do not chop or hack at the root or it will split unevenly. Next, if the portion of the crown you are trying to divide is too thick to cut through completely, then with your knife cut around the crown where you can reach and gently pull apart the cut portions. The three-to-five eye division that you have cut is now ready to be trimmed.

The roots of the division should be trimmed to a length of six or seven inches. Peony divisions perform best when all of the smaller thread-like roots are removed. This forces the plant to produce new large secondary roots, which are formed near the ends of the remaining roots. The removal of these smaller roots not only promotes new root development, but also aids in the prevention of disease. The smaller roots desiccate more readily and in their weakened condition become more susceptible to attack by fungal organisms.

A well-trimmed division will allow ample room for new roots to form and for existing roots to increase in girth without growing into one another. Any diseased portions of the root should be removed and irregular wounds should be cut smooth. Older plants with large roots often have hollow centers. These should be cleaned and examined for rot.

Hybrid peonies often have roots different from the lactifloras and thus sometimes are difficult to divide, but the same basic method is used. Experienced cutters will always look any plant over before making a cut. It may be necessary to trim excess roots away in order to see more clearly. Patience seems to correspond to success in the division of peony roots. The physiological requirements of a peony are the foundation of the viability of their divisions. The dividing of hybrid root requires not only patience and common sense but also practice. Expect smaller divisions when cutting hybrids, because there is less root mass than with other peonies. However, these hybrid divisions must have enough root to support the eyes that remain.

The crown of the hybrid is very distinct. The eyes develop on its upper portions, while the roots radiate from its lower portions. This unique formation is what makes dividing the hybrid difficult. Longitudinal cuts of the crown are often the only cuts that will yield divisions. A steady hand is needed to slice through the crown while avoiding any eyes that may lay in the path that the knife must follow. There are no secrets or short cuts for the successful cutting of hybrid roots. Practice is the best way to master this skill.