Propagating Roses

Propagating Roses through Root Cuttings

By Randy Hughes and David Zlesa

Have you ever had a particularly nice plant that you wished you could make duplicates of? Quite often with woody ornamentals one can take stem cuttings and induce adventitious root growth to produce a new plant identical to the original. This is often done with roses, other ornamentals, and fruit species. Within any given classification some cultivars may be very easy to propagate this way, while others may stubbornly refuse to root and grow. What then does the average gardener do if he wants to asexually propagate these hard-to-root types? The answer may be to try working from the other end - that is, root cuttings.

With root cuttings the objective is to coax a section of root to produce new top growth and become a new copy of the original. For this to work the plant needs to be on its own roots. If not, the rootstock will be propagated. An advantage to this method is the fact that roots store a large amount of energy reserves in the form of carbohydrates, providing nourishment to sustain the cutting while it works on the job of putting on new growth. Another benefit of this process is that while unrooted stem cuttings must be carefully protected from dehydration due to water loss through transpiration, root cuttings are buried in moist media and already have a good system to draw water from the soil. That's what roots are designed for. Root cuttings often work where stem cuttings consistently fail.

I have successfully cloned apples, plums, raspberries, azaleas, rhododendrons, and of course roses through root cuttings. The success rate in most cases has generally been about the same as stem cuttings. However, in cases where stem cuttings have failed, root cuttings were much more effective.

To make a root cutting you need a section of root that is between four and six inches long and one eighth to one quarter inch thick. I am sure one could have success with larger or smaller sections, but this is the size I have used with most success. Try to take your root section from the proximal, or top part, of the root mass where it is close to stem tissue. This area of the root is often rich in adventitious bud initials that will form the new top growth. These bud initials are not necessarily visible, but are there to help the plant recover if it should be broken off or otherwise damaged.

It is easy to get at the roots without harming the plant if you are working with potted roses. Simply water well, remove the whole plant, select your roots, and place it back into the pot. If you have a plant in the ground, you can dig away the soil on one side of the plant and carefully expose a root section without disturbing the rest. I have found that in winter when the roses have slowed down their metabolism, the whole plant can be dug, the best roots selected, and the plant replanted with no harm whatsoever so long as it gets plenty of rain or water before and after. A word of caution: never take more than 25% of the total root mass from the donor plant. If you are dealing with smaller plants, you should remove an equal amount of top growth to reduce the demand placed on the newly reduced root system.

Once you have your root cuttings, prepare a well draining mix of sand and potting soil or compost. Lay the root section at an angle with the top of the cutting about a half-inch below the surface. The top of the cutting is the end that was closest to the donor plant's top growth. Keep cuttings in a cool location indoors, or put them outside where they are protected from direct sunlight and kept moist. In two to six weeks you should see new growth emerging.

I have best results in my climate with root cuttings taken in the fall and planted in the ground outdoors over winter. In spring new shoot growth starts a little later than that of established roses. Root cuttings started outdoors in early spring work nicely too, but start growing a little later. When using this method indoors I have found that warmer temperatures are not desirable and results are poor. This is true as well with midsummer efforts when the temperatures reach the eighties or nineties. In addition to the high summer temperatures, another possible reason for poorer summer results is that roots have less stored carbohydrates this time of year.

I have recently read of some interesting results from root cuttings in roses. It seems that there is a higher incidence of sports occurring in root cutting propagation. I am no authority on this topic, but it seems to be due to the fact that while vegetative buds consist of three distinctly separate meristem cell layers in the growing point, root cuttings need to reestablish the three layers from cells that trace back to only one of those three original layers. While the cells should contain the same chromosomes and genetic information, the different layers sometimes harbor mutations and can express different characteristics. This seems to be a unique and exciting way to create new cultivars from old.

Variegated sports of spider plants and sansevieria (snake plant or mother-in-law's tongue) are perfect examples to visualize chimeras, plants having differences between the three meristem layers. In the case of these variegated plants, a layer of the meristem is unable to produce adequate chlorophyll. Some variegated spider plants have white leaf edges and a green center, while others have green leaf edges and a white center. The difference between these two spider plants is that Layer II of the meristem is unable to make chlorophyll in the first plant, while for the second plant, Layer I is unable to make chlorophyll. There's a variegated sansevieria that has a golden leaf edge. It is possible to take leaf cuttings of sansevieria. Adventitious shoots and roots develop from the base of these leaf cuttings. If the shoot originates from the golden edge, the shoot will be albino, but if from the green center, the shoot will be completely green. Adventitious shoots reestablish a new three-layered meristem with all the new layers generally genetically the same as the one the cells that produced the adventitious shoot originated from. The only way to propagate these variegated plants and maintain the variegation is to use crowns or runners, which are produced by normal vegetative buds and retain the three distinct layers.

Root cuttings generally make adventitious shoots arising from cells that originate from Layer II or Layer III. If there was a mutation that occurred in the layer that produced the adventitious shoot and was for a trait expressed in tissue derived from normally a different layer, root cuttings may be able to expose it. All three reestablished layers from the root cutting's adventitious shoots come from either Layer II or Layer III. Rosarians are sometimes discouraged from using root cuttings because of the increased chance of "off-types". Often these "off-types" are expressed as color sports. Through propagating roses by stem cuttings or grafting, normal vegetative buds are used that maintain all three meristem layers of the parent plant making "off-types" less likely. Root cuttings can be used to aid in finding sports of popular cultivars.

In conclusion, we would encourage any of you who have had a particular cultivar that was uncooperative with stem cuttings to try root cuttings. It may well produce what you have wanted and could even offer something slightly different or exotic.