Just like animals, plants need a number of nutrients to survive and thrive. These essential nutrients are broadly divided into two groups: nine macronutrients and 11 micronutrients. Macronutrients are needed in much greater quantities than micronutrients, which are often needed in minuscule amounts, though still necessary. Along with light and water, these nutrients are key to the plant's survival.
Plants require nine different macronutrients to survive. They include:
- Carbon (C): Required for the plant to form carbohydrates, proteins, and nucleic acids, among other compounds; the most abundant element in plant cells, accounting for about 50 percent of the cell
- Nitrogen (N): Part of proteins and nucleic acids; used to synthesize vitamins
- Hydrogen (H): Used with oxygen to form water
- Oxygen (O): Used with hydrogen for cellular respiration; required to store energy in the form of ATP
- Phosphorus (P): Used to synthesize nucleic acids and phospholipids; enables food energy to be converted into chemical energy
- Potassium (K): Helps to regulate stomatal opening and closing, which maintains a healthy water balance
- Sulfur (S): Part of amino acids such as cysteine and methionine
- Calcium (Ca): Regulates nutrient transport and supports enzyme functions
- Magnesium (Mg): Used in the photosynthetic process
Carbon, hydrogen, and oxygen are known as structural elements and are present in the atmosphere and growing environment. Calcium and magnesium work with micronutrients to balance the plant's ions.
Sulfur is often not included on the lists of "critical" major elements because it's so common. In most fertilizers, the other nutrients are delivered in the form of sulfate salts, which automatically includes sulfur. As a result, sulfur deficiency is extremely uncommon, and there is some debate over whether or not many plants even have upper tolerances for sulfur.
Plants get some of the required macronutrients from the soil it grows in, while other nutrients are obtained from fertilizer. Nitrogen, phosphorus and potassium are sometimes called the "fertilizer elements" because they are the familiar "N-P-K" identified on fertilizer labels. The NPK rating of a fertilizer identifies how much of the fertilizer by volume is comprised of these three elements. For example, a 10-10-10 balanced fertilizer would contain 10% each by volume of nitrogen, phosphorus, and potassium. Although each of these fertilizer elements has multiple roles, in general nitrogen encourages strong leaf growth, phosphorus encourages flowering and budding, and potassium encourages stronger root growth.
Both calcium and magnesium are crucial for many cellular functions in plants, as well as for fruit and flower formation. Be aware they might not always be present in your fertilizer mix or soil, although dolomite lime is a good way to deliver both. If you're growing houseplants, make sure your fertilizer is complete, with both calcium and magnesium present.
If a plant is deficient in any of the nutrients—particularly macronutrients—the plant's growth can suffer. A deficiency might show up as slow growth, stunted growth, or chlorosis, which is a decrease of the normal green color of a plant's leaves. In the case of a severe deficiency, the plant can show signs of cell death.