Cover the cutting loosely, pot and all, with a plastic bag or plastic wrap and keep the soil moist. Putting a tall stake into the pot will hold the plastic away from the leaves. If the plastic touches the leaves, they remain wet and can succumb to a fungus disease. Along the same lines, make sure the condensation can escape from the plastic or the stem will rot.
Cover the stem with plastic or a mason jar. To cover the stem with plastic, insert two eight-inch (20-cm) sticks or wires into the soil on either side of the stem to prop up the plastic. Cover the pot and stem with a clear plastic bag, and affix the bag to the pot with an elastic or twine. With a mason jar, simply place a large mason jar over the stem.
To get the best success, yor rose seed will need a period of stratification (a cold period of about 6-12 weeks). Its a good idea to time this so that it coincides with when they would naturally start to grow in spring – probably around early March, depending on weather conditions. I would look to sowing them in late November/ December and popping them outdoors or if we have a mild winter then stick them in the fridge!
I too, have tried the cut rose flower method, but haven't yet been successful--perhaps because there are chemical additives that the roses have soaked up, or because there are no nodes (which are the points where new shoots grow out), or because the stems have spent much of their energy producing the flowers...BUT, perhaps if the flowers were immediately cut off and some rooting hormones applied to the bottom cut ends, that may work.
Grandma's Mason Jar: For the beginner this is probably the easiest way to take rose cuttings. Not much equipment is needed, just a clear quart-size glass jar and some cuttings from your favorite rose. For you modern sodapop lovers, a 2-liter plastic bottle with the bottom cut off will work just as well. Cut a piece of rose stem about 6 inches long, remove the bottom set of leaves, and just stick the stem into the ground (or into a pot) a couple inches deep, and cover with a jar or bottle. You will need to periodically water the soil around the jar, otherwise the rose stem will dry out. It will take a couple of months for the rose stem to take root and begin leafing out with its new growth. The best time of year is spring or early fall. If you live in a mild climate, then winter and summer can also be successful for rooting roses. Intense summer heat of 100 degrees is not conducive for taking rose cuttings, nor are 32 degree or below winters.
Black Spot: Rose plant leaves with black spots that eventually turn yellow have black spot. This is often caused by water splashing on leaves, especially in rainy weather. Leaves may require a protective fungicide coating, which would start in the summer before leaf spots started until first frost. Thoroughly clean up debris in the fall, and prune out all diseased canes.
Be aware of your variety’s needs. Rose care will depend a lot on the variety you’re raising. Some roses like William Baffin and Lady Hillingdon climbing roses are more drought tolerant, for example, while others need more water. Some varieties can withstand less sunlight than others. Rose varieties should also be pruned differently depending on the variety and your climate area.
If you order bare-root roses from a mail-order company, order early (late winter or early spring). The roses are usually shipped in the spring because bare roots when plants are fully dormant, well before they have leafed out. They’ll look like a bundle of sticks on arrival. Note that they are not dead—simply dormant. Check that the packing material is moist and keep them in a cool dark place until ready to plant.
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