You don’t have to be a master sleuth to know something is amiss with your roses if half of the leaves turn brown and fall off, or all the new little leaves at the top of the plant take on a lemon-yellow color; it’s certainly not typical for a healthy rose. But what is causing it? Now that’s the dilemma. Many different plant problems can produce these symptoms often making it very difficult to diagnose them accurately. And that is doubly true for nutrient deficiencies.
The three macronutrients – nitrogen, phosphorus and potassium, are the ones gardeners routinely provide to their growing plants. The secondary nutrients - calcium, magnesium and sulfur are generally present in lesser concentrations in the soil followed by the seven micronutrients, also known as trace elements - boron, chlorine, copper, iron, manganese, molybdenum and zinc. If any nutrient is deficient or unavailable to plant roots, you may see symptoms showing up in the plant.
Knowing the general quality and composition of your soil, the pH, texture, and history can be very useful for predicting what nutrients may become deficient. But if you’re looking at the leaves on your plant and trying to figure out what’s wrong, it can be a bit tricky. Many micronutrients work together with other nutrients so a deficiency of one may appear like another. If more than one problem is present (i.e. water stress, disease, or insect damage) or if two nutrients are deficient simultaneously, you may not observe typical symptoms.
The chart below is a simple tool to aid in the identification of nutritional deficiencies in plants (not specific to roses); by focusing on two key attributes – chlorosis (yellowing or bleaching of normally green plant tissue usually caused by the loss of chlorophyll) and necrosis (death of tissue accompanied by dark brown discoloration, usually occurring in a well-defined part of a plant, such as the portion of a leaf), and where the damage occurs - on new or old leaves, you can potentially identify which nutrient is deficient.