Roses love a sunny, well-drained bed full of loose, loamy, nutrient-rich soil. The decision over natural fertilizers versus chemicals is personal as both work well, according to Texas A&M University. Natural plant foods provide more micronutrients which are lacking in chemical formulas. The key is to water the roses well after adding fertilizer to dissolve the food into a form the plant can use, says Texas A&M landscape specialist Dr. Bill Welch.
Old and established roses that bloom once a season need fewer feedings than hybrid teas, floribundas and other continual bloomers and do well on one feeding in the spring. Hybrid teas are fed chemical or natural fertilizer at least three times a year. Established climbing roses need that at twice the strength.
Miniature roses are fed a diluted amount once a month.
Osmocote-type (slow release fertilizer) with a 14-14-14 analysis can feed a rose for the entire growing season. Applied just after the spring pruning, nitrogen will stimulate new stem growth and help the rose recover. Phosphate and potash will produce flowers and promote a strong root system as conditions warm up. Each rose bush gets 3 or 4 oz. sprinkled around the base, scratched lightly into the top inch or so of soil where it will release nutrients for three, six or nine months.
Chemical rose food is a balance of nitrogen, phosphorus and potassium (10-10-10 or 4-4-5) designed to sustain healthy foliage, roots and flowers. Large hybrid tea or rose bushes get 1 tbsp. dissolved in a gallon of water per feeding or an equivalent of dry food scratched into the soil. For the final feeding before the first fall frost, the nitrogen is eliminated (0-10-10) to slow growth before winter.
Natural fertilizers include well-rotted manure and fish emulsion, which add their own aroma to the garden while adding micronutrients like iron, manganese, copper, calcium, sulfur, zinc, molybdenum and boron to the soil, as well as nitrogen, phosphorus and potassium. Roses love a mixture of seaweed or fish emulsion, compost and composted manure, but these do not last as long in the soil as chemical or time-release fertilizers.
Established and old rose varieties that bloom once a year are fed once in early spring. For minimal care, modern repeat-bloom roses can be fed after pruning in the spring and in early fall. For continual, prize-winning blooms, many rosarians alternate natural and chemical fertilizers and feed their plants more often than once a month. They begin just before the last spring frost in their area by adding natural fertilizers to the soil. When the buds begin to swell, they apply chemical rose food. They fertilize at regular intervals throughout the growing season, ending six weeks before the first fall frost. They will give roses a supplemental liquid feeding after heavy rains to replenish nutrients that are washed away.