Roses respond well to care and feeding nearly year-round. When their basic requirements are met, they will produce two flushes of blooms each year, one in late spring and a second, longer flowering period in early fall. Soil nutrition, proper watering, disease control, regular fertilization, well-timed pruning and abundant sunlight all converge to support a profusion of blooms. Focusing fertilizer applications just before the spring and fall bloom periods will boost the bloom capacity of your roses, provided other care all year has been adequate.
Ensure that your roses are receiving ample direct sunlight daily. Give the roses a bare minimum of a half day of sun and preferably two-thirds to a full day. Light afternoon shade in summer or in hot climates is acceptable, however, as the sunlight tends to be more intense.
Top dress the soil and mulch around the rose plants once or twice per year with 3 to 5 lbs. of compost and well-aged livestock manure. Lay the mulch starting 6 inches from the trunk and extending a few inches to 1 foot past the outer drip line of the rose plant.
Water the roses regularly and deeply to keep the soil moist but not soaking wet at all times. Water the roses once every five to seven days, drenching the soil down to roughly 10 inches, when the weather is warm and there has been no rain. Scale back watering when rain is present. Apply the water at the base of the rose. Never wet the foliage and trunk if possible.
Feed your roses twice yearly with a synthetic or organic complete rose fertilizer with a guaranteed analysis of 10-10-5 or 15-10-10, or a product with the same ratio of macro-nutrients. Apply according to the label dosing directions. Do not exceed 1-1/4 lbs. of fertilizer in mid-spring and 1 lb. in late summer or early fall for every 100 square feet of rose plantings. Top dress the soil with fertilizer and nestle it into the top 1 inch of soil. Do not dig it in, as this can disturb the roots. Water deeply to distribute the nutrients into the root zone.
Prune your rose bushes in the spring after the last frost has passed but before the new buds swell. Prune climbing roses in the fall after flowering and when temperatures drop. Prune old-fashioned rambling roses just after the blooming period. Prune to encourage new flowering canes to develop. Deadhead spent blooms to ensure that the plant's energies go into flower production and aren't diverted to support rose hip and seed development.
Treat common pests and diseases when they are first noticed, as many can impact rose bloom by misshaping or stunting bud development. Treat black spot and mildew once per week with a fungicidal spray for roses, per label instructions. Spray aphids off the plant with a strong stream of water from a garden hose. Treat thrips and scale with rose-safe insecticides, per label instructions. Take a sample of your problem rose foliage in a sealed bag to a nursery center if you have doubts about the problem.