Do not fertilize your roses with either a high nitrogen fertilizer or a balanced fertilizer (e.g. 10-10-10). The numbers are percentages of nitrogen, phosphorus and potassium respectively (N-P-K). Nitrogen promotes leaf growth, phosphorus increases flowering and root growth and potassium promotes the general vigor of the plant. The plant should not be encouraged to send up new tender shoots late in the season; they will only be killed off by the first frost.
Repeat bloomers flower beautifully in September and October in the New York area - use a foliar spray such as Monty's Joy Juice™ or Neptune's Harvest™. These foliar fertilizers are sprayed on the leaves of the roses. They give the plants an instant energy boost and produce lush rose bushes for late in the growing season.
Let the buds turn into hips. This will help protect the roses in cold weather. The hips will also provide food for wildlife in the fall and winter.
Roses are susceptible to black spot, a fungal problem that creates spots on the leaves and eventually defoliates the plant. The spores of the fungus will also overwinter in the soil around an infected plant. It is paramount to clean up all diseased foliage and to be meticulous about keeping the area around the rose free from infection.
This helps to protect the base of the rose during the cold winter months and acts like a winter parka. Finely-shredded, pine bark, mulch is good to use. It creates a nice thick blanket that doesn't get matted down into large clumps. Mound the mulch around the base of the rose to a depth of 6 to 8 inches. This is all we do to protect our roses in the Peggy Rockefeller Rose Garden.
Prune the rose once it goes dormant in the fall. This will simply entail cutting it back to a smaller size, so that it is easier to protect. Surround the rose with a cylinder of chicken wire and sturdy poles (rebar). Fill the cylinder to the top with dry leaves or straw and cover it with a solid top to prevent the protective mulch from compressing in the rain and snow (e.g. an old board or trash can lid with a rock on top to hold it down).
Leave just a small pile of mulch around the canes. Two weeks later, after the roses have adjusted, clear off the remainder of the mulch and top-dress the roses with compost and aged manure.
We fertilize our roses three times during the growing season in April, June and August with an organic fertilizer such as Rose Tone™. This regimine is supplemented with foliar feeds.
The winters are getting warmer in the New York area and our roses are sometimes blooming all the way into December. It is important to remember to stop deadheading at least a month before the the first hard frost.