With established plants, I recommend fertilizing your roses with a mixture of Atlantis Fish Emulsion, mixed at the rate of two tablespoons per gallon of water. Use half a gallon per plant. Fish fertilizer provide an excellent source of nutrition for plants and the soil. When fish fertilizers are used, the plant receives a controlled level of nitrogen, a vital element necessary for the production of chlorophyll and maintaining the health of the plant.
Two weeks later, use Miracid, one tablespoon per gallon of water and use one half gallon per plant. I use Miracid because the soil in this area is very alkaline and roses do best at 6.2 to 6.5 Ph. Miracid lowers soil pH and makes nutrients more readily available. Many times when customers tell me that their roses are not flowering well, this is part of the problem.
Two weeks later, use Bayer All in One mixed at four ounces per gallon. Bayer All in One Rose and Flower Care contains a fertilizer, fungicide, and insecticide combined in one product so it feeds and protects against insects and diseases in one easy step. Just mix and pour around the base of the plant.
I keep this schedule all summer long, until the first week of September.
Another product you might want to consider is Rose-Tone by Espoma. Rose-tone provides slow release nutrients to keep your plants doing well. It is an organic product which will not harm beneficial insects like bees and ladybugs. You should use half a cup of Rose Tone per plant, every 45 days. Work it into the soil around the base of the plant.
Please remember to water your roses once a week in cooler weather and twice a week during warmer temperatures. Water around the base of the plant, not overhead. Overhead watering promotes black spot. You should water with a slow running hose for about 15 minutes.
I will be giving a presentation, The ABCs of growing Roses on May 25, 2017 at 6 pm at the greenhouse. The class is free and so is the handout. Hope to see you there.