Last week I discussed fertilizing roses every two to four weeks, alternating between organic fertilizers and inorganic ones. Let’s dive deeper into organic fertilizers.
All plants need the macronutrients: nitrogen, phosphorus and potassium. Nitrogen (N) is for healthy green growth. Phosphorus (P) encourages healthy roots and increases flower production.
Potassium (K) assists with the movement of water, nutrients and the sugars needs for a strong plant. K also improves drought resistance and pest resiliency. Plants, especially roses, also need micronutrients such as calcium, magnesium, sulfur, iron and more to thrive.
Some organic fertilizers are derived directly from plant or animal sources. Others come from rock minerals that are finely ground. Organic fertilizers usually have lower nutrient levels with more than just N, P, or K. The nutrients in these fertilizers usually have to be converted to forms plants can use by soil microbes. This process happens relatively slowly.
Organic fertilizers do not form a crust on the soil surface and by feeding the soil microbes, soil structure and workability are improved. This improves water movement into and through the soil. Often organics are slow-release so they rarely burn plants.
A downside to organic fertilizers is that they may cost more than conventional fertilizers and have lower nutrient percentages. In the case of manures, when organic matter is not fully composted, the soil microbes have to break it down and actually use existing soil N to do this. This can actually deplete the soil of N in the breakdown process, harming the plants.
A disadvantage to fresh manure as an organic fertilizer is that it can seriously burn plants. In addition, “Organic standards require: a 120-day waiting period between applying raw manure and harvesting crops that touch the soil (e.g., lettuce, onions, beets) and a 90-day wait for crops where the edible part does not contact the soil (e.g., corn, pole beans).
Oregon State Extension reports that blood meal has an analysis of 12.5% N, 1.5 P, and 0.6 K slowly releases that N over two to six weeks. Feather meal has a 12% N and breaks down more quickly. Rock phosphate (20% to 33% P) and bone meal (15% to 27% P) are both rich in phosphorus. Kelp meal (4% to 13% K), wood ash (3% to 7% K) and greensand (5% K) are good sources of potassium. Other organic products are cottonseed meal, seaweed extract, fish fertilizer, and alfalfa meal.
There are many prepacked organic rose fertilizers on the market. Or, make your own organic fertilizer “teas” with something like alfalfa.
— JoAnne Skelly is an Associate Professor and Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.
