Want more flowers on your rose bushes? If so then you need to provide them an extra boost through fertilization. Proper fertilization develops strong vigorous canes that will end in a big fat plump bud with a nice flower.
Most local soils have plenty of phosphorus and potassium, so the recommendation of using a balanced fertilizer such as 13-13-13 or 10-10-10 is outdated. The old recommendation was to apply about 1/2 cup of this type of fertilizer per plant 3 to 4 times per growing season between mid-April and mid-August.
Newer recommendations are more environmentally friendly, as it reduces the use of unnecessary fertilizer containing phosphorus and potassium. Nitrogen, the first number on a bag of fertilizer, is the key nutrient for established roses. Using a higher rate of nitrogen and low amounts of phosphorus and potassium are best. Examples of fertilizers to use are 27-3-3 or 25-5-5.
Instead of using the 1/2 cup rate, use only about 1/8 cup per plant using the same schedule. This supplies the same amount of nitrogen as the traditional application but does not build up high and unnecessary levels of phosphorus and potassium. If your roses are grouped in a bed then you will want to reduce the rate, as the roots are all sharing the same soil. Maybe use the above rate for each two closely spaced plants.
Landscape or shrub roses may really not need any additional fertilizer. These plants are more vigorous than the old hybrid tea types. As a result they will normally flower all summer long on naturally occurring nutrients in the soil. If you like, they can be given a boost with a mid-April application to get the shrub roses off to a good start.
For you organic growers out there, blood meal and alfalfa are excellent rose fertilizers. These are higher in nitrogen while being low in the phosphorus and potassium. You can apply about 1 cup or so each time to provide about the same rate as man-made fertilizers.
Fertilizer placement should be made out and around the plant at the drip line. Avoid placing the fertilizer at the base of the plant. Rose roots are out and around the plant. Be careful when working the fertilizer into the soil. Do not dig deeply into the soil, as this will damage the rose roots. If the plants are mulched, pull the mulch away, apply the fertilizer and then replace. Water it into the soil to complete the task.