Fertilizing your roses provides soil nutrients and amends deficient soil. Temperature, aeration, moisture, and soil PH are also very important, but if your soil lacks the nutrients that your plants need to grow, none of those things will matter. There are six macronutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S).There are seven micronutrients: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).
Most commercial fertilizers contain three key ingredients: Nitrogen (N), Phosphorous (P), and Potassium (K). Other elements, such as calcium, magnesium and sulfur also need to be present. iron, boron, chlorine, manganese, molybdenum, copper, and zinc are important too, but rarely need to be supplemented. Other necessary elements such as carbon, hydrogen, and oxygen are taken from the air and water, not from the soil.
The N, P, and K are the three ingredients represented by the numbers in the fertilizer name. For example, an all-purpose fertilizer might be called 10-10-10 because all three elements are present in equal proportions; 10 percent nitrogen, 10 percent phosphorus and 10 percent potassium. The rest of the bag is called ‘filler’.
Nitrogen (N) is most important for green growth in the spring. Later in the season, when your plants should be entering dormancy, green growth is unwanted, and nitrogen intake should be reduced. Also, too much nitrogen will prevent blooms from developing. N is water soluble and moves through the soil very quickly, so it must be replaced more often than the other elements. Sources: commercial fertilizer, Bloodmeal, manure.
Phosphorus (P) promotes root growth, fruit ripening, and seed development, and it is especially important for very young plants and right before plants go into dormancy for winter. Phosphorous naturally occurs in composting organic matter in the soil. Sources: commercial fertilizer, earthworms, compost.
Potassium (K) Often called 'potash', this element is important for development of fruit and leaves, and it is responsible for the overall health of the plant. The most obvious sign of deficiency is scorched leaves. Sources: commercial fertilizer, wood ash, seaweed meal, compost, manure.
Calcium (Ca) When calcium fertilizer is used it lowers the pH of the soil reducing the toxicity of the soil. It will stimulate the ammonium absorption by plants by as much as 100%. Some of the ammonium is changed to nitrate so the precipitated calcium gets resolubilized which increases the amount of calcium available for use in the soil. Photosynthesis increases and the amount of carbon dioxide captured by the plants is also increased. If you use a soluble calcium to stimulate plant growth you will see remarkable improvements in the survival rates of your plants through the winter but don't stop there, using it throughout the year will yield you impressive results through the growing season. In fact you can expect a considerable increase in yield from your garden.
Magnesium (Mg) Gardeners apply Epsom salts to tomatoes, peppers, and roses, hoping to produce more flowers, greener plants, and higher yields. This natural mineral, discovered in the well water of Epsom, England, has been used for hundreds of years, not only to fertilize plants but to treat a range of human and animal ailments. Who hasn't soaked sore feet in it at least once?
Chemically, Epsom salts is hydrated magnesium sulfate (about 10 percent magnesium and 13 percent sulfur). Magnesium is critical for seed germination and the production of chlorophyll, fruit, and nuts. Magnesium helps strengthen cell walls and improves plants' uptake of nitrogen, phosphorus, and sulfur. The causes and effects of magnesium deficiencies vary. Vegetables such as beans, peas, lettuce, and spinach can grow and produce good yields in soils with low magnesium levels, but plants such as tomatoes, peppers, and roses need high levels of magnesium for optimal growth. However, plants may not show the effects of magnesium deficiency until it's severe. Some common deficiency symptoms are yellowing of the leaves between the veins, leaf curling, stunted growth, and lack of sweetness in the fruit.
Magnesium tends to be lacking in old, weathered soils with low pH, notably in the Southeast and Pacific Northwest. Soils with a pH above 7 and soils high in calcium and potassium also generally have low magnesium levels. Calcium and potassium compete with magnesium for uptake by plant roots, and magnesium often loses. Sometimes, a soil test will show adequate magnesium levels in soil, but a plant grown in that soil may still be deficient because of that competition.
Gardeners add magnesium when they apply dolomitic lime to raise the soil's pH. However, this product (46 percent calcium carbonate, 38 percent magnesium carbonate) breaks down slowly, and the calcium can interfere with magnesium uptake. For soils with a pH above 7, many gardeners use Sul-Po-Mag (22 percent sulfur, 22 percent potassium, 11 percent magnesium) to increase magnesium. Although dolomitic lime and Sul-Po-Mag are inexpensive ways to add magnesium, Epsom salts' advantage over them is its high solubility.
Sulfur (S) Sulfur, a key element in plant growth, is critical to production of vitamins, amino acids (therefore protein), and enzymes. It's also the compound that gives vegetables such as broccoli and onions their flavors. Sulfur is seldom deficient in garden soils in North America because acid rain and commonly used animal manures contain sulfur, as do chemical fertilizers such as ammonium sulfate. Sulfur slowly breaks down (with help from oxygen from the air and water) to produce an acid that lowers the pH of the soil. The lower pH of the soil helps make the iron naturally in the soil more available to the grass as a nutrient. Iron helps provide a deep green color. The black clay soils in north Texas have a tendency to have a high pH and benefit from the use of sulfur. An excellent way to introduce sulfur to lawn is to use 'sulfur-coated urea' (SCU), which provides sulfur and nitrogen (the nitrogen is from the urea).
Boron (B), Boron is an essential micronutrient for growth and development of healthy plants. In small concentrations boron compounds are used as micronutrients in fertilizers, in large concentrations they are used as herbicides, algaecides and other pesticides. Boron is essential for maintaining a balance between sugar and starch and functions in the translocation of sugar and carbohydrates. Boron is also important in pollination and seed production, and is necessary for normal cell division, nitrogen metabolism and protein formation.
Boron is an essential element for plants’ development, growth, crop yielding and seed development by helping the transfer of water and nutrition in plants. Though plants’ boron requirement is very low in amount, their growth and crop yielding are severely affected when there is a boron deficiency in the soil.
Chlorine (Cl) Needed for photosynthesis; stimulates root growth and aids water circulation in plants
Copper (Cu) Copper deficiencies are mainly seen on sandy soils which are low in organic matter. Copper uptake decreases as soil pH increases. Increased phosphorus and iron availability in soils decreases copper uptake by plants. Small leaves with necrotic (dead) spots and brown areas near the leaf tips. Rosetting of the leaves and dieback of terminal shoots.
Iron (Fe) New leaves are the most symptomatic and when iron deficiency is most severe they can be all yellow or white but still have green veins. Overall you see yellow leaves with green veins leading to marginal scorching or browning of leaf tips. Tip leaves, especially basal areas of leaflets, intense chlorotic mottling; stem near tip also yellow. Fruits have poor color. Shoot diameter is small. Iron deficit often occurs when the soil pH is higher than 7.5 meaning it is more alkaline. Lack of Fe is common in plants living next to concrete walls, foundations etc.
Manganese (Mn) Manganese deficiency is similar to Nitrogen deficiency, leaves display marginal scorching, rolling and reduced width. Yellowing may also occur between leaf veins or total yellowing on youngest leaves.
Molybdenum (Mo) Molybdenum deficiency is only a problem with brassicas like broccoli, cauliflower, etc. in acid soil. Heads can fail to form properly, leaves will become thin, elongated and rippled.
Zinc (Zn) Zinc deficiencies are mainly found on sandy soils low in organic matter and on organic soils. Zinc deficiencies occur more often during cold, wet spring weather. New and intermediate leaves are small, yellow, sometimes with a grayish cast. Narrow and older leaves may drop. Small shoots may show resetting, followed by dieback.