Lately, we have experienced hot, humid, and dry days with an occasional evening thunderstorm, or as some call it, the dog days of summer. Consistent moisture is critical for ornamental and edible plants as they bloom and produce the attractive flower or fruit desired. Besides water, the plants’ nutritional needs are also critical at bloom time. Because most of us do not have six inches of organic, rich topsoil, we have to supplement the soil through fertilization to meet the plants’ nutrient needs. This weekend was fertilization time for my annuals and some perennials and it made me think….do most gardeners understand their plants’ diet?
Healthy and productive plants need 17 nutrients. Three of these nutrients, carbon, hydrogen, and oxygen, are supplied through air and water. The remaining nutrients are delivered to the plant primarily by the soil. Soils can have high levels of some nutrients and low levels of others, which is why having the soil tested is critical. These 14 nutrients are known as macronutrients and micronutrients. Macronutrients include: nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium. Micronutrients include: boron, chlorine, cobalt, copper, iron, manganese, molybdenum, and zinc. If you are thinking this sounds familiar, look at the back of your multi-vitamin bottle and you will see many of these. All nutrients are important, and each has its purpose, with some being needed more than others. I will focus on the macronutrients.
Nitrogen is the one nutrient that is critical in most of the plants’ biological processes. Too much and the plant has plenty of green vine or leaves at the expense of the fruit. Too little and the plant will be stunted and fruit development will be delayed. Phosphorus is essential for both ends of the plant, as root and seed development need the nutrient. Potassium is necessary for development of stem strength and critical for the plant’s drought tolerance and winter hardiness. Calcium is required for root and leaf development and for plant cell elongation and division. Magnesium is a primary component of chlorophyll (green color in leaves) and involved heavily in photosynthesis. Sulfur is involved in development of enzymes and vitamins as well as organic compounds that give odor to garlic, mustard, and onions. Sulfur is the main component in deer repellent, and now you know why.
That’s just the macros; we haven’t even discussed the micros. Most of the nutrients, whether macro or micro, can be adjusted by fertilization. Calcium and magnesium levels are typically adjusted by adding lime to the soil. As you can see, adequate nutrients are absolutely required for plant development and plant health, i.e., the plant’s diet.
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