Grafting And Hybridizing Of Roses
In this section, we will be discussing the two methods of propagating roses – grafting and hybridizing, their techniques and benefits.
Precisely speaking, both grafting and budding complete the same job, but they involve different techniques. In the case of budding, you place a bud below the bark of the plant on which you want to grow the new plant. On the other hand, grafting involves placing a stem part on a rootstock. Generally, grafting is done on rootstocks that are in a dormant state – either in the beginning of spring or during winter. You can adopt a variety of techniques to join the stem section to the rootstock. Usually, gardeners use the splice graft method. In addition, they also widely use the whip-and-tongue graft method.
For successful grafting, two things are very necessary. You need to have a thin-bladed, razor-sharp knife as well as strong fingers. In fact, even during the best of times, it is quite difficult to handle rose thorns and they may really prove to be a nuisance while undertaking grafting. You need deftness while grafting and wearing big or leather gloves may make things difficult. On the other hand, wearing thin plastic gloves may prove to be helpful. Thorns of several rose varieties are rather yielding and can be removed easily by pressing them gently sideways, making your job much easier.
If you are making a whip-and-tongue graft, use a sharp blade to cut the rootstock just higher than the roots at an angle that will help to expose roughly three times more of the surface compared to its diameter. Make a second cut close to halfway below the first cut keeping the blade pointing down towards the slope. While making the second cut, raise the blade a little from the surface of the rootstock with a view to create a thin flap. Ensure that the second cut does not exceed 1/4 of the exposed length of the surface in the first cut. Now, use a part of the stem having anything between one and five buds to make a series of similar cuts at the base of the piece of your preferred rose variety. This piece of the plant is called the scion. Slip the scion down against the rootstock in a manner that the slender flaps at the middle of both the scion and the rootstock locks these two pieces. Set the two pieces gently and bind them tightly. Provided the cuts have been made even and the flaps are really thin, the scion and the rootstock will get in touch with each other excellently on their respective surfaces.
After you have set the graft, it is important at no less than one side where the scion and rootstock joins will have the cambium layers aligned. For the uninitiated, the cambium is basically a slender green layer found just beneath the bark. The all important cell division will occur at this place, thereby, knitting the two sections together. In the absence of a good alignment, it will not be possible for the cells to connect. As a result, the graft will not be successful. Even if you have cut the scion and the rootstock in dissimilar sizes, ensure that in any case one side is aligned.
When you are sure that the scion and rootstock have locked properly, fasten the two pieces firmly using a budding rubber, string or a masking tape. When you are binding the two pieces, be careful not to change the alignment at their union. After tying the scion and rootstock, apply grafting wax using a brush on the place with a view to close the graft. Sealing the graft will help to keep it moist and prevent it from drying even before the area heals. There are many different types of grafting wax in the market. Nevertheless, even if you cannot avail any of these commercial preparations, you can melt paraffin wax and use it effectively for the purpose.
There is a disparity of the grafting process and this method is generally used in greenhouses. However, one can also adapt this technique to a humidity tent or cold frame. The preferred scion and rootstock should be collected either during the end of spring or beginning of summer. When you are propagating roses using the grafting technique, you can only use somewhat hardened new wood, which should be robust as well as considerably thick. After you have collected the rootstock from your desired rose variety, remove all the leaves from the stick. Next, cut the stick into smaller pieces, each measuring about 3 inches to 4 inches (8 cm to 10 cm) in length. While cutting the sections ensure that you remember their top and bottom ends.
Make a vertical cut from the top end of the rootstock section down to its center using a razor-sharp knife. However, make sure that the cut is no more than half-an-inch (1.3 cm) in depth. Subsequently, cut a part of the scion or variety stem and ensure that you leave at least two or three leaves on each section. Cut the bottom of the variety section into a wedge measuring about 3/4 inch (2 cm). Open up the top portion of the rootstock slightly with the knife tip and put in the wedged ending of the variety section into the cut on the rootstock and align the cambiums in a manner that the two sections are in surface-to-surface contact. Press the wedged end deep into the cut, but do not push it so hard that it ends up tearing the rootstock. If the cuttings on the rootstock and the variety section are made properly, they will fit in so perfectly that you will not even require tying them with any bandage or string.
When the graft is completed, immerse its base into a rooting hormone. Subsequently, gently place the cutting into a clean rooting medium with excellent drainage. For instance, a perlite and peat mixture in proportion of 4:1 will serve as an excellent rooting medium. You can also add some clean, coarse sand to the mixture, for enhancing its ability to drain water. Provided you keep the rooting mixture adequately moist and sufficiently warm, the grafted cuttings will develop roots in just two to three weeks. When the grafted cuttings have rooted well, they can be planted and grown in separate pots until they are well adjusted to the conditions outdoors, where they will be eventually planted.
The grafting technique is quite simple and, at the same time, a worthwhile technique for growing new roses successfully. Similar to budding, grafting also helps to produce new plants from the union of two dissimilar varieties. In addition, both processes involve the same problems of suckering as well as rootstock hardiness. Generally speaking, grafting is a slightly reliable vegetative propagation process compared to budding, especially when it is undertaken on rootstocks that are growing in the field.
New rose plants grown through the budding technique are often susceptible to winterkill, especially in places where the temperature drops drastically during the winter months and the ground does not have any snow cover. As far as roses are concerned, grafting is one of the oldest propagation techniques used by gardeners and even to this day it is a very reliable method.
Hybridizing can be described as inducing hybrids or crossbreeds by purposely crossing two different species or cultivars. In addition, hybrids may also come into existence due to cross-pollination of two different plants in nature by insects. In earlier days, rose growers usually collected rose hips grown closely with the hope that nature will take its own course and give rise to new hybrids. In contemporary times, hybridizing has developed into a sophisticated process and now breeders are able to develop hybrids of their preference by deliberately cross-pollinating two varieties they have already selected. In order to ensure that hybrids turn out to be as desired, it is best to undertake the deliberate cross-pollination under glass. In the era of greenhouses, growers are able to induce roses to bloom earlier than their expected time, as this helps the complete ripening of the seeds even when the weather conditions are not favourable during summer.
Speaking from the botanical point of view, a rose bloom is considered to be perfect when it has both the male as well as female reproducing organs within the same structure. If you want to prevent self-fertilization of the flowers, you should remove their anthers before they receive pollens from any other flower. This process of removing the anthers is known as “emasculation”, which involves only taking away the anthers without causing any harm to the other parts of the flower, especially the seed pod, which is also known as “receptacle”. Before removing the anthers, you need to remove the petals. The timing for this is extremely vital. This is because you need to select a flower that is completely developed as well as ready for being fertilized, but still is in state when the flower has not undergone self-pollination or cross-pollination by any chance. In the case of a rose bloom, this should be undertaken when the petals remain furled around the male and female reproductive organs of the bloom and immediately prior to the ripening of the pollens.
Hybridizers are fully aware that nothing can be said from before while cross-breeding two hybrids and, therefore, they carefully take into consideration the attributes of the potential progeny by examining the lineage of the roses that they desire to cross breed. They hope that doing this will help them bring about a specific quality in the offspring or prevent the offspring from inheriting serious faults from their parent plants. At the same time, the hybridizers take into account various aspects of the roses they have selected – for instance their growth habit, resilience, foliage, color and aroma of their blooms and, most importantly, their resistance to various diseases.
After you have prepared the seed pod by means of emasculation, pollens from the chosen pollen plant are taken out and, after a couple of days, applied to the stigmas that have become somewhat sticky and receptive. When the stigmas become sticky, they undergo a color change – from creamy-yellow to either orange or golden. You may apply the pollens to the stigmas using a camelhair brush. Alternatively, you may also apply them directly from a completely open flower picked from the selected pollen plant. Subject to the rose variety, the size of the pollen grains can differ – they can be large, in abundance and also very visible or can be very scarce, small as well as not visible to the naked eyes. In fact, nearly all varieties of modern roses are somewhat free as far as pollens are concerned. As a result, pollen obtained from one male has the potential to fertilize numerous seeds, subject to the hybridizing technique you may be applying. Once the pollen has been applied, hybridizers keep a record of the cross on a label and attach it to the stalk under the pod.
The method that is usually adopted to keep record of the crosses is to write the name of the seed parent first on the label. When the cross-pollination is successful the seed pod begins to swell and become ripe. The color of the ripened seed pod changes from orange to red in approximately six to eight weeks from the date of the cross-pollination. The rose hips are harvested and the seeds are taken out during the end of summer. It is best to place seeds from each individual lot in small, separate polythene bags and attach a label to them with a view to handle them easily.
Rose seeds lie dormant during the winter months and it is essential to expose them to the changing temperatures. In recent times, hybridizers used to mix the rose seeds with sand and keep them outdoors with a view to be acclimatized to all weathers – a process called “stratification”. These days, some hybridizers store the seeds in a freezer for some weeks before sowing in order to get the same results. It is possible to improve the germinating abilities of the seeds even before sowing them. This can be successfully achieved by soaking the rose seeds in a diluted gibberellic acid solution.
Ideally, rose seeds should be sown in good compost on a bench roughly 1/2 inch (1.25 cm) deep in February and keep the bench in a greenhouse that is pre-heated. Usually, germination is unpredictable and begins in April when the temperature of the soil is something between 7°C and 10°C (45°F and 50°F). After sprouting, the seedlings have a somewhat rapid growth. In fact, some of the plants produce their first bloom as soon as in six weeks from the day of germination. It is at this stage when you decide which plants you want to retain and which you would discard. The ones you decide to keep can be grown in individual pots or budded outdoors in a nursery and observed further for their traits. When the roses are in their seedling stage, just 10 percent of the plants are significantly different or have enough potential to grow into good varieties and require further examinations. After an outdoor trial for about a year, even fewer than 1 percent of the roses that were selected originally will be deemed sufficiently good for undergoing additional or extended testing.