Remove old leaves and mulch under plant and discard. Replace with fresh mulch. This will remove much of the blackspot that is in the garden and may lead to healthier roses next year. Cover crops are plants grown in bare areas to control weeds, to reduce erosion and to add organic matter and nutrients to the soil. Plant ryegrass, rye, wheat, oats, Austrian winter pea or clover as soon as possible.
Ryegrass is probably easiest to find.
Till in the cover crop 3 to 5 weeks before you plant. Call for more details on putting the cover on your garden. Adding compost and tilling it in also has a similar effect. There are several local sources of cheap compost. Call for a list.