Hybrid tea roses and other modern roses–such as grandiflora, floribunda, and polyantha roses–are heavy feeders and are considered high maintenance plants. More frequent fertilization assures the best growth for these breeds.
To ensure your roses will receive the proper amounts of nutrients, first test your soil to find its pH, texture, and existing mineral nutrient content. A pH range of 5.5 to 7 is ideal for roses. Texture should be balanced with sand, silt, and clay. Checking the mineral content helps determine what is needed in the fertilizer, although it is recommended you add organic material regardless of the mineral content.
Roses (and most plants) need certain minerals and nutrients, and the three most important are Nitrogen (N), Phosphorus (P), and Potassium (K). The three numbers on all fertilizer packages represent the ratio of these three nutrients (called the N-P-K ratio). All purpose garden fertilizer, for example, has a 10-10-10 ratio. While this is generally suitable for roses, most require a higher level of phosphorus. A 5-10-5 fertilizer is more appropriate for hybrid tea and other modern roses. In addition to these three nutrients, choose a fertilizer with micronutrients, such as Calcium (Ca), Sulfur (S), Copper (Cu), Magnesium (Mg), Zinc (Zn), Boron (B), and Iron (Fe). Some gardeners add Epsom Salts to the soil at the beginning of the growing season to ensure the roses get enough magnesium.
Fertilizers are either organic or inorganic. Organic fertilizers include manure, compost, and other plant or animal products (bone meal, kelp extract, etc.). Organic fertilizers usually do not have a balance of nutrients like inorganic fertilizers do, therefore it is very important to read and follow the manufacturer’s label. Also, due to the difference in nutrients, organic fertilizers need to be used on a more continual basis. A benefit to using organic fertilizer is it conditions your soil making it more plant-friendly over time. Inorganic fertilizers are man-made and are usually less expensive. They are available in different forms: Water soluble, granular, and slow-release and each one has slight variations in time of application.
When to apply fertilizer depends on if you are using organic or inorganic, as well as the climate. There is, however, a general time table to follow. Hybrid tea and modern roses are fertilized three times a year; approximately 4-6 weeks apart for each application. The first application occurs after pruning, usually in the early spring. The second application is during the first bloom, which is around late May or early June. Complete the third application in mid to late July. Fertilizing after July 31 is not recommended, as the new growth can succumb to frost.
Following the above steps will assure your roses are properly fed and are able to stave off disease. It’s important to remember to follow all instructions for any fertilizer you choose to use. Do this and you will be rewarded with beautiful plants.