One aspect of plant production over which growers can have great control is plant nutrition. Plant nutrition involves the absorption of nutrients for plant growth. The nutritional needs of greenhouse plants require close attention because the plants are wholly dependent on what is available in the growing medium Current fertilizer practices allow growers to adjust and deliver nutrients to maintain desired plant growth.
Plant growth is dependent on 17 essential elements, often referred to as nutrients. Three of the elements, oxygen, hydrogen, and carbon make up 89 percent of a plant’s tissue by dry weight. The plant through natural processes acquires these three elements. They are considered to be nonfertilizer nutrients. There is one exception to this. In some operations, carbon is provided to plants through the release of carbon dioxide gas into the greenhouse atmosphere.
Six of the 17 essential elements are required in greater quantity than the others. They are called macronutrients. The macronutrients are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Nitrogen, phosphorus, and potassium are considered to be primary nutrients because they are used in complete fertilizers. Calcium, magnesium, and sulfur are said to be secondary macronutrients because plants need moderate amounts. These secondary macronutrients may or may not be used in complete fertilizers.
The other eight essential elements are needed in small quantities. They are called micronutrients. Sometimes they are called trace elements. They are boron (B), copper (Cu), chlorine (Cl), iron (Fe), manganese (Mn), molybdenum (Mo), sodium (Na), nickel (Ni), and zinc (Zn). Six of these, boron, copper, iron, manganese, molybdenum, sodium, and zinc, are supplied to plants as fertilizers. Nickel and chlorine need not be added as a fertilizer. Plants obtain sufficient quantities of them through the medium or water
A fertilizer is any material added to growing medium that provides nutrients for plants. Adding nutrients in the form of fertilizers is necessary to improve plant growth and development. Fertilizers are particularly important with the use of soilless mixes. Because soilless mixes lack reserves of nutrients, the nutrients must be supplied regularly to the plants. Also, quick production of quality crops is achieved when all the nutrients required of plant growth are provided at the optimum rates.
Different plants have different nutrient level requirements. Also, plants have different nutrient requirements based on their stage of growth. For potted flowering plants, there are five stages of growth. In the first or juvenile stage, the plant is a young seedling or cutting. In the second stage, vegetative or leafy growth is encouraged. The vegetative stage is followed by the flower bud initiation stage, the flower bud development stage, and the flowering stages. Each stage calls for different rates of fertilizers. When in the vegetative, plants use more nitrogen, and when in the flowering stage, they require less nitrogen and more phosphorus.
There are two widely used methods to deliver fertilizers to greenhouse plants. One involves the use of water-soluble fertilizers with an injector system, whereby the plants are fertilized as they are watered The other involves the use of slow release fertilizers.