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When to take root cuttings
When propagating plants from root cuttings it is vital to understand how seasonality affects the capacity of root cuttings to produce stem buds.
The subject of "on" and "off" seasons appears to have been virtually unconsidered until the mid-twentieth century. However, recent research has established that fluctuations in the ability of roots to produce stem buds do exist and that it is pointless to propagate while the plant's response is inhibited by adverse seasonal influences.
It is this fluctuation in the capacity to propagate that has probably produced the uncertainty which has led to the propagation of plants from root cuttings being virtually ignored by nearly all gardeners.
It is therefore necessary to determine whether the plant from which root cuttings are required does have different seasonal responses, and, if so, what is the best time to take cuttings.
Without prior guidance, the natural inclination for the gardener would be to take such cuttings in the growing season, but
Preparing the plant experience has shown that this has met with little success; although results sometimes improved if cuttings were taken very early or very late in the season.
A few plants can produce new plants equally well at any time of the year, but these are relatively uncommon. Perhaps the best example is the horseradish, which can make itself into a pernicious weed by virtue of this characteristic: when the roots are broken, it is capable of establishing itself as a new plant from each root piece.
Virtually all other plants demonstrate a seasonal response. Early observations suggested that plants propagated most successfully during the winter, but experience has shown that, although this is typically true for woody plants, the real feature is not the winter but the dormant season. Many herbaceous plants and more especially alpine plants are not necessarily dormant during the winter. Some alpines, for example the Pasqueflower (Pulsatilla vulgaris), start growing in the new year and if root cuttings are made after this period they do not respond; success is only achieved during their dormant
1 Lift a healthy plant from the ground during the dormant season.
2 Cut back any top growth. Shake any excess earth off the roots.
3 Wash the roots in a bucket of water or hose them clean.
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Although propagation from root cuttings is likely to succeed throughout a plant's dormant season, it is best to keep to the mid-part of that season, as a maximum response may not exist while the dormancy is still developing or once it is phasing out.
Before propagating from root cuttings, it is preferable to prepare the parent plant itself so that it will develop roots that will have a high capacity to regenerate stem buds and so produce new plants.
This ability to produce adventitious stem buds on a severed root is already present in most plants, but it can be enhanced. Lift a healthy plant prior to the growing season and shorten any top growth. Reduce its root system by cutting off the roots close to the crown of the plant, using a knife. Then return the plant to the ground. The pruning upsets the natural root/shoot balance of the plant, and it will grow quickly during the following season to bring the plant back to its normal equilibrium between root and shoot. As a result of this treatment the vigorous, quickly grown roots will exhibit a very high level of ability to develop stem buds.
The roots will have developed fastest at the beginning of the season, and the rate will gradually have declined as the season progressed until, as the dormant season approached, growth will have ceased altogether. At the point where any root started its growth in the spring, and where it grew fastest, will also be where it has the greatest capacity to produce buds; in other words, there is a direct correlation between the rate at which a root grows and its ability to produce stem buds. If, therefore, plenty of root material is available, it is best to take a root cutting only from the top of the root where it began its development in the early spring.
In order to obtain cutting material, lift the parent plant and shorten any top growth. Wash it free of soil either in a bucket of water, or by hosing it down. It is then possible to distinguish the young roots which are suitable for propagation. Cut these close to the crown
4 Cut off the roots close to the crown, using a sharp knife.
5 Return the plant to its position in the garden.
6 Leave the plant to reestablish during the growing season.
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