This is a fungus called black spot. Left untreated, it can cause all the leaves on your roses to turn yellow and fall off. It will also affect nearby plants, as it spreads by spores. Remove ALL INFECTED material and throw it away or burn it. Do NOT leave it on the ground as this fungus is very hardy. It can survive winter and travels very easily, even after being removed from the affected plant. Spray your plants regularly (bi-weekly) in the growing season with a good fungicide (I like the Bayer products). You can also add a little bit of dish soap and baking soda to a spray bottle with water and spray the entire plant.
Northern gardeners need to know exactly what zone a rose is hardy to. Southern gardeners must also watch to see what zones are recommended for each particular variety, as some roses perform very poorly in hot and/or humid weather. Read the catalogs carefully and, if possible, purchase your roses from a local or regional grower. They will be able to advise you from experience about how a particular variety will perform in your area.
Pests and diseases: Prevention is the best way to avoid pest and disease problems. Start with disease-resistant varieties, keep plants in healthy condition (well fertilized and well watered), maintain good air circulation, keep foliage dry, and remove any diseased foliage or spent flowers. For Japanese beetle grubs, use beneficial nematodes or Milky Spore (Bacillus popilliae). Rose Rx is effective against scale, spidermites and aphids. For more information, see the Pest and Disease Finder.
There will be disappointments along the way, when many rose seeds fail to germinate, or perhaps they do germinate, only to die several weeks later from damp-off disease. Sometimes a rose seedling will turn out to be as ugly as sin, or very sickly, and you will reluctantly have to throw it away. Other times they will be just ho-hum, or look too much like its parent, and therefore have no value. But, just when you don't expect it, you might discover that one of your rose seedlings turns out to be very special.
Allow rose hips to develop by leaving dead flowers on the plant. The flowers are typically pollinated by insects, or pollinate themselves in some varieties, so there is no need to pollinate by hand unless you are breeding specific plants together. Leave the flowers on the rose plant without cutting them. After they wither, small fruits known as rose hips will develop in their place.
Soaking the seeds is a crucial step if your seeds will germinate properly and stay clear of any diseases. You MUST not mix the bleach with the hydrogen peroxide as this results in a chemical reaction. 3% peroxide for 24 hours is just fine. This is also a good time to perform the water float test. Remove all seeds that float as they might not be viable.
I am curious... it seems that you are just supposed to "soak" the cut stems for a week or more in water.... which is mostly what people normally do with cut roses. But whenever I put roses my boyfriend brings me in water, they just fade within a week or so. I'll "feed" the roses with either sugar in the water or with the packet of plant food that comes with them. I'll cut off a small bit at an angle from the bottom of the stem evert day or so. But after a week or so they start wilting and drooping, so at that point I just take them out and hang them upside down to dry.
I received some seeds as birthday present, the seller included a bonus packet of rose seeds. There’s no indication if they’ve been stratified. If I stratify them now, it will be July when they’re ready to plant. In this region (I’m ~50 miles north of Portland, Oregon)it might be mild or very hot. I’ve read that rose seed won’t sprout if it’s too hot – how well do rose seeds keep? Will they still be viable next Spring, or should i take a chance on the weather and start them now?
Select two roses that you want to cross-pollenate. The blooms should not be too tight, perhaps about one-half to 3/4 open. Carefully peel off all the petals. The rose stamens inside should look golden yellow and fresh. With sterile tweezers or cuticle scissors, carefully remove all the stamens at the base of the rose hip, so you do not damage the pollen sacs (anthers). Place the rose stamens into separate, clean film canisters, and place the canisters in a dry place, but not in direct sunlight.
Roses are usually grouped into one of two broad categories: old roses and modern roses. Old roses are those varieties discovered or developed prior to the introduction of the hybrid tea rose in 1867. But like everything else in the world of roses, when it comes to determining how a particular rose should be classified, it’s not always crystal clear.
One way to stratify the rose seeds is to place the cleaned seeds on a paper towel (a heavyweight brand such as Bounty). Then moisten the paper towel with a solution of half & half purified water and peroxide (to help prevent mold). Fold the paper towel closed, encasing all the rose seeds in the moistened paper towel. Then place the towel full of seeds into a plastic zippered bag. Mark the seed variety and date on the outside of the plastic bag with a permanent marker, and then place the bag into the refrigerator set at about 34-38 degrees. Never freeze the seeds, and do not let them dry out. The moistened paper towel should remain moist in the closed plastic bag for many weeks.
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!
Plant the seeds. Some store-bought seeds can be planted immediately. If you germinated your own seeds as described above, plant them as soon as they begin to sprout. Plant with the sprout pointed downward, as this is the root. Lightly cover them with soil, about 1/4 inch (6 mm) deep. Space seeds at least 2 inches (5 cm) apart to minimize competition.
Remove the seeds from the fridge. Try to do this around the time that the seeds would normally start to germinate, such as in early spring. Make sure that the environment outside of the fridge is about 70 degrees Fahrenheit. The seed will not sprout until you take them out of the fridge. Depending on the rose variety and individual seeds, the seeds could take anywhere from four to sixteen weeks to germinate. Often, 70% or more of the seeds never sprout at all.