Natural fertilizers come from once-living plant or animal matter. Meals made from fish, kelp, blood, cottonseed, bone and alfalfa are used to feed roses. They are often supplemented with aged manure from cows, rabbits, horses or chickens. Donald W. Trotter Ph.D, of the Organic Gardener, says natural rose foods can be used less often because they require decomposition by soil bacteria to be used by the rose. This slow process releases nutrients over a long period.
Inorganic (chemical) fertilizers provide instant sources of the three principle plant nutrients: nitrogen, phosphorus and potassium (N-P-K). Natural rose fertilizers, which must be broken down by bacteria and microrganisms to be available to plants, last longer in the soil but take longer to reach the roses. They also enrich the soil with micronutrients, which provide a balanced diet for rose bushes, according to Trotter. The Texas A&M Horticulture Extension recommends a combination of organic and instant chemical fertilizers to keep heavy-feeding roses healthy.
Rose fertilizers supply nitrogen for stem and leaf growth in early spring, phosphorous for flower and root development, and potassium for hardiness. A natural commercial or homemade fertilizer could contain a mix of fish meal, hoof and horn meal, seabird or bat guano, cottonseed oil, rock phosphates or bone meal and kelp meal, sulfate of potash magnesia or blood meal. A cup or two every four weeks will feed an established rose bush through the growing season. A handful or two of bone meal or superphosphate added to the bottom of the planting hole will feed a new rose's root system and help a young plant produce flowers.
Roses need more than nitrogen, phosphorus and potassium to be healthy and disease resistant. Calcium, magnesium and sulphur are secondary nutrients required by roses in smaller amounts than the major three. Micronutrients including iron, copper, cobalt, boron, chlorine, zinc, molybdenum and manganese are needed in even tinier amounts.
Natural fertilizers provide secondary and trace nutrients in commercial mixes or they can be custom mixed by gardeners with elements available at a garden center.
It's easy to feed roses fish emulsion, says Kitty Belendez of the Santa Clarita Valley Rose Society. Just mix 1 tbsp. in a gallon of water and pour around the rose. When gardens grow to 100 bushes, other application methods make monthly feeding easier. These include siphon devices attached to a faucet that carry fertilizer from a bucket through a garden hose to plants. Electric submersible pumps, which transfer fertilizer from a large tank through a hose to bushes, can be used for very large rose gardens.
Healthy soils keep roses fertilized and pest resistant. A few inches of a natural compost or mulch spread around the base of rose bushes annually will add organisms to enrich the soil for all roses, Trotter says. They also provide food for earthworms and beneficial bacteria to keep the soil healthy.