Roses have a reputation as fussy plants to grow. However, when given a good application of compost, they are likely to thrive. Think of compost as a vitamin for your rose garden. When roses are healthy from a proper diet of nutrients, they are more resistant to diseases including powdered mildew, spots and blight. Roses can be 'top dressed,' with a mulch of compost, or they can be watered at the roots with compost tea.
Wait until compost has become 'finished,' before adding it to your roses. Finished compost will have no large clumps of undigested material, and will resemble rich, dark soil. You can test compost by planting radish seeds directly into the compost. If two-third of the seeds sprout and grow to maturity, your compost is finished. If you can't wait for your compost to finish (or to complete this test), use purchased compost.
Amend the soil of your rose bed before planting your roses by working compost 1 inch deep into the planting hole of the rose bed with a garden fork. Fill the hole with water and allow it to soak in. Then wait two days before planting your rose bush.
Create a compost tea by placing a small amount of compost in a burlap bag. Place the bag in a 5-gallon bucket and fill with water. Allow the bag to sit in the water until compost has permeated the water. Remove bag and dump compost back into pile. Spray this mixture on the leaves of your roses, and pour the remainder on the roots.
Spread compost around the root system of the plants with a shovel in the spring and fall. Turn it 3 inches deep into the soil with a rake.