Nitrogen (N) is critical for a plant’s growth and survival, or in other words, very simply put, nitrogen makes plants grow. When nitrogen is in balance in the soil the rose will have tall, strong canes, good blooms and rich dark leaves. If there is a lack of nitrogen that is available, the rose will have leaves of light green color, maybe even a yellowing. If there is an excess of nitrogen the rose will show weak, soft canes, small blooms and decreased resistance to disease. The availability of nitrogen to the rose is dependent on soil temperature, moisture and acidity. Adequate drainage will help keep the soil temperature and moisture levels appropriate for a rose to be able to take up the nitrogen. At the same time the correct pH level for roses, 6.0-6.8 will keep the acidity level where it should be for the rose’s ability to take up nitrogen.
Phosphorus (P) stimulates root growth, which in turn produces big blooms and quality plants. It can also hasten plant maturity and winter hardiness. The soil acidity is very important in making phosphorus available to the rose. Here in the western part of the United States, there is generally a high level of phosphorus in the soil. However, with too little phosphorus bloom production will drop. In severe cases the leaves at the bottom of the rose will turn a purplish red. Roses can benefit from bone meal, or superphosphate given at planting time.
Potassium (Potash) (K) promotes root growth, vigor and bloom color. It works a balancing effect on both nitrogen and phosphorus. It is important for starch formation and the development of chlorophyll by encouraging photosynthesis. Soil acidity has little influence on potassium, but certain types of clay soil can have a marked effect on potassium availability. A deficiency in potassium causes brown leaf margins, weak stems and blind shoots.
Utah Rose Society