Acid loving plants, such as rhododendrons, azaleas, camellias, junipers and pin oaks, often need more iron. Sometimes sandy soils need micronutrients, but rarely clay soils. Certain micronutrients may be deficient in certain parts of the country. Boron is sometimes deficient in the Pacific Northwest. Many fertilizers are available to supply additional nutrients.
Some fertilizers only supply one nutrient.
Many supply N, P and K only. A few fertilizers include all of the macronutrients and micronutrients. The label on the package will tell which nutrients are included as well as the sources of the nutrients. The nutrients are identical whether they come from organic or synthetic sources, but the source will affect how fast the nutrients are available to plants. Ammonia sulfate and water soluble fertilizers release most of their nitrogen in a few days and may burn plants if too much is applied.