You may even wish to cut your cuttings down to 3" to 4" and double your plants, but they will be more prone to rot or dry up faster if you let the soil dry too long. The cuttings that are 6" to 8" seem to do much better, and if cuttings are even longer, the water has a longer length to travel up and down, and the cutting may end up more dehyrated with the upper part dying off. So 6" to 8" is a happy medium.
NOTE: During my move, I had cut several rose branches and placed them in a grocery paper bag in my garage--only to have forgotten to bring them home for a week. The branches had been in a broiling hot enclosed garage without water, and needless to say, they looked pretty dried out to a crisp. But I didn't want to just toss them out yet (these were the climbing Charisma roses), so I got an empty plastic detergent tub and completely immersed the stems for 2 weeks (no changing water). Then I stuck them into soil and hoped for the best. Well, I got about a 50% survival rate.
Protect the roses over the winter. Roses that are left tall may be damaged by heavy winds and frosts during the winter. Trim the canes down to 2 feet (0.6 m). Tie them together with twine, to help protect them from inclement weather. Heap a mound of compost around the base of the bush, then top it with a layer of straw. When the weather warms to above 51 degrees, remove the compost mound.
America's most popular flower is also one of the very oldest flowers in cultivation. There are over 2,000 different rose varieties to lure us with their history and fragrance. This is because the rose, like the orchid, cross-breeds readily—a trait exploited first by nature, and then by horticulturalists. Today, we can choose from old-fashioned favorites, as well as modern varieties that are the result of intensive breeding programs throughout the world. The rose is a flower with a rich past, and an exciting future.
Fertilize the roses. After they are established, roses should be fertilized a few times per growing season. Use fertilizer (either liquid or granule) in early spring, when you see the first few leaves sprout. Use it again after the first bloom, and again if there's another bloom. Stop fertilizing the roses at the end of the summer, just before Labor Day.
Español: cultivar rosas usando semillas, Italiano: Coltivare le Rose Usando i Semi, Português: Cultivar Rosas a Partir da Semente, Русский: вырастить розы из семян, 中文: 用种子种玫瑰, Deutsch: Aus Samenkörnern Rosen ziehen, Français: faire pousser des roses à partir de graines, Nederlands: Rozen kweken uit zaad, Bahasa Indonesia: Menanam Bunga Mawar dari Biji, العربية: زراعة الورود من البذرة, Tiếng Việt: Trồng hoa hồng từ hạt, 日本語: バラを種から育てる, 한국어: 씨앗으로 장미 기르는 방법