Rosebush is an ornamental shrub from rosaceae family. There are about twenty species and a very high number of varieties in particular hybrid varieties. Interspecific hybridization was of big importance in cultivated roses evolution, but it needed almost a century to find associated china rosebush (rosa indica) blossoming characters from one side, and french roses (rosa gallica) strength and hardness characters on the other side.
|Nowaday, the principal
agronomical characters on which are selected roses are:
- Reflowering character the continuous flowering capacity.
The propagation of roses can be performed by different ways :- By plant division and layering (for hardwood species).Remenber: Roses with patent canít be propagating for 17 years after their date of introduction without paying a royalty to the patent holder.
- For other species (sarmentous rosebush and hybrids) by grafting and propagation by cuttings
- By seeding (as for all species giving grains).
- "in vitro" propagation : a very short time , 1 to 2 months instead of 12 to 18 months with upper methods.
Division and cutting means is really popular, itís a good way to propagate quickly and easily roses.
Most of the roses grow as well or better on their own roots than grafted. The old roses varieties are in general well adapted to the growing condition where they are used. So, itís useless grafting them. Moreover cuttings root is general really well.
Roses can be root at any time of the years but the best results occur during the cold months. However the extreme cold can damage the cutting.
The best stem to do cutting are usually these that they had some flowers. A good cutting length is about 7 inches, cut with a 45 degree angle. The leaves of the lowest half part of the cutting should be removed. At this time we should take care, the cutting should not dry, exposed at too the high or too low temperatures.
Before planting the cutting, rooting hormones can be used to improve the success rate and the rooting number. Nevertheless, this propagation works pretty well without hormones.
A good rooting medium is a light soil. So, itís generally use sand added to 1/3 of peat. The plant should receive the bright light but not directly the sunshine. Then, the cutting should be watering regularly especially during the rooting time. The cutting should be rooted by April-may. But, itís only by late fall or winter that the young plant are able to move to their permanent location.
This same period is the best to divide rose and plant the new one. The air or soil layering can be practice too. The roots appear in 28 days with this technique. Itís one of the quickest ways.
New varieties are usually propagated by grafting. The rootstock allows adapting the root system to the soil (climate, diseasesÖ). The budding are commonly employed and give good results. Nevertheless that method requires more time and more skilled labor than others methods. At the end, the plants are more expensive to produce.
But grafting has many advantages:.- Grafted plant are usually more uniform in their growth than rose obtain by seedling.
- Rose grafted begin to flower sooner. The rootstock provides vigor to the propagated rose.
- Budding allows producing rose trees
Itís mainly the T-bud method that is employed. To provide better result, in August (fall or winter are period possible too) the bud is removed from a deflowering stem. In fact, the best time to practice budding occurs when the bark of the rootstock can be removed easily. The cut should be straight and smooth. The rootstocks should be in good condition of watering and fertilization several weeks before.
Then, itís possible to do the budding. The main cases of failure come to a dehydration of the surfaces cut. So, itís better to work in a cool area with good moisture. After the budding should be properly wrap. This wrap can be leave during 3 or 4 weeks but longer is better. It can stay until the next spring.
Since the bark can be removed easily, the t-bud is the best method because it provide good result and easy to do. Other way, chip bud is another good method nearly as easy to do.
The stenting technique is practice by some growers to perform rose multiplication. The cutting and grafting are done in the same time. In fact, we make a cutting of the rootstock and we graft the scion on at the same time.
The genetic improvement = Seedling
This is a long and uncertain way that takes a long time to obtain a rosebush. Nevertheless itís the only technique for finding news varieties and improved the current varieties.
Anther should be collected first and try, and then they can release their pollen. The petal of the female blooms are removed and the anthers too. That avoids a self pollinisation. After we put the pollen on the stigma and three to four months later the hips will be ready to collect and after a drying time the seed can be extract.
In general for a properly roses germination the breeder simulates a winter. In fact he puts the seed 6 to 10 weeks in the refrigerator. Then, the seed can be planted in a sterile peat-based soil media and the germination start immediately and the plant grow for 2 to 3 months. This growth is faster and faster according the leaves apparition. After about 6 weeks the buds appear. The rose is still small but that allows to select early the plant material. It possible to answer at many question: What color are the flowers, how many petal, is it fragrant?
One some the limit of this kind of propagation take place in number of chromosomes (x=7). But Wild rosebushes and cultivated rosebushes havenít the same number of chromosomes. In fact some wild rosebushes are diploids and cultivated varieties are tetraploid. To cross these two kinds of rose, it needed to reduce the number of chromosomes. This technique is called haploidization.