Roses do best with uniform soil moisture throughout the growing season. The general rule of thumb suggests that one inch of water be applied per week during the growing season. The amount and frequency of application will depend on soil type. Sandy soils will need more frequent irrigation than heavier clay soils. Hot temperatures would call for more frequent irrigation, also. The use of soaker hoses in rose beds is highly encouraged. Water can be delivered in adequate amounts while keeping the foliage dry, preventing disease.
The use of mulch around roses to help retain soil moisture is a practice that is highly encouraged. Mulch will also help keep soils cool and help retard weed growth. Materials such as wood chips, straw, or dry grass clippings make good mulches. More decorative materials such as shredded hardwood bark or cocoa bean hulls could also be used. Mulches should be applied about 2-3 inches deep and replaced as needed. Because organic mulches tend to bind up nitrogen as they decompose, additional fertilizer may be needed to prevent nutrient deficiencies. Leave an un-mulched area about 6" in radius around the plant.
In order to maintain strong, healthy roses, it is important to establish an annual fertility program. Fertilization schedules vary depending on the types of roses being grown. For species roses, a spring application of general-purpose fertilizer is usually adequate for the season. General-purpose fertilizers such as 10-10-10 or 12-12-12 are used at about one-half to one cup per plant. Spread the fertilizer in a band starting six inches from the crown of the plant, going out to about 18 inches. Work it in lightly and water.
All other roses benefit from a second application about June 15 or at the end of the spring bloom period. For continuous-flowering or repeat-blooming roses, a third application in mid-July is suggested. No fertilizer should be applied after August 15 so as not to encourage soft, succulent growth that could be easily winter-damaged. Roses can be fall fertilized after the plants have gone dormant. Applying fertilizer at this time will not encourage growth but will be available as the plants start to grow in the spring. Also by using a fertilizer high in potassium winter hardiness tends to be increased.
Another fertilizer option is to use a timed or controlled release fertilizer (osmocote fertilizer pictured at right). These are dry, encapsulated fertilizers that release their nutrients slowly over the season, completing their work in 4, 6, or 8 months depending on the formulation. Nutrient release is dependent on the soil moisture and temperature. These materials are generally applied in May, using about 1/2 cup per plant. Several forms are commercially available.