There are several nutrients needed for proper plant growth. The first three are the non-mineral nutrients and are Hydrogen, Oxygen, and Carbon. Water (H2O), atmospheric Oxygen (O2), and Carbon Dioxide (CO2) supply these requirements for plant growth.
In photosynthesis, light energy is collected by chlorophyll in leaves, and part is used to split water (H2O) molecules into free oxygen gas (O2), and hydrogen (H). The hydrogen is bonded with carbon dioxide (CO2) to form the sugars the plant can then use to grow. The water is often added by itself or as part of a nutrient solution, and carbon dioxide are naturally present in fresh air (or is added to the garden as a gas).
In a natural setting, plants use nutrients to grow to maturity, then when they die they fall to the forest floor and return their nutrients to the soil, so new growth can use them to grow to maturity. One reason that composts are useful is that they are made from the decomposed building blocks of other plants (“animal” composts are plants processed through an animal first), and as such tend to have at least a little of all the required nutrients. When an animal dies in the forest, the scavengers eat the fats and meats, and the plants eat what remaining blood and bones they can get (blood tends to be high in N, bone high in P).
In a garden, often times the previous year’s plants have been cleared away, and are not decomposing into compost to return their nutrients to the soil. Even if they were, the nutrients removed along with the harvested portion of the plant would eventually show a loss of nutrients in the system.
In container gardens, the growth medium may be new and sterile, without any preexisting nutrients in them at all. To replace the missing nutrients, they are added to the system in the form of fertilizers.
Fertilizers supply replacement nutrients so they are available for use in plant growth. The first three are known as the primary nutrients, and are so important that they are listed on the front of nutrient packaging.
Nitrogen (N) is needed to make plant cells and the chlorophyll (the green in leaves) required for photosynthesis. Nitrogen compounds comprise from 40% to 50% of the dry matter of plant cells. It promotes large healthy foliage, absorption by roots, and proper plant development. Used in chlorophyll, amino acids, proteins, and nucleic acids. Nitrogen deficiency is the most common nutrient problem. “Growth” nutrients commonly have elevated levels of Nitrogen in them.
Organic nitrogen breaks down over time to become a form available to the plants. In contrast, synthetic nitrogen forms can become available to the plant very quickly, and are often made with an easily dissolved salt.
Nitrogen deficient leaves will contain relatively little chlorophyll, tend to be pale green to yellow in color, and plant growth is retarded. Nitrogen is very mobile in plants, and this enables it to be moved from older growth to young growing tips when supplies are short. This mobility of nitrogen explains why deficiency symptoms appear first in the older lower portions of the plants, working their way up to the growing tips.
Phosphorous (P) is required for photosynthesis, root development, and assists in blooming. It is also used to form nucleic acid which is an essential part of living cells. Compounds of phosphorus are used in respiration and the efficient use of nitrogen. It is important throughout the life cycle of the plant, but use is elevated during flowering. “Bloom” and “Flowering” nutrients often have elevated levels of Phosphorous in them.
Phosphorus deficiencies usually manifest as a generalized under-performance of the plant, leaf development is stunted, and buds size is reduced. Leaves may develop a bluish tint. Phosphorus assists in nitrogen uptake, so symptoms of phosphorus deficiency are often similar to a nitrogen deficiency.
Potassium (K) is required for photosynthesis, carbohydrate and protein creation. It assists with disease resistance, and is used in the “plumbing” of the plant: liquid movement within the plant, stems, roots etc. Many enzymic reactions require potassium, and it assists in silica uptake.and helps with fruit quality. “Bloom” and “Flowering” nutrients often have elevated levels of Potassium in them.
Potassium deficiency often shows as a yellowing/browning/dying of the leaf edges, curled over leaves, followed by yellowing spots in the interior of the leaf face. Discolored spots may appear on the undersides of leaves.
Potassium is mobile, so deficiency symptoms show first on lower leaves as flecking or mottling on the leaf margins. Prolonged deficiency results in cell death along the leaf margins and the plants can show signs of wilt. These symptoms first display in older leaves, and continue to work up through to the newer leaves if not corrected. Growth, root development, disease resistance, and bud size are reduced.
The next three are the secondary nutrients, and are Calcium (Ca), Magnesium (Mg) and Sulfur (S). Calcium-magnesium supplements can be used if needed, but sulfur deficiencies are rare since sulfur appears frequently in both synthetic and organic nutrients.
The final group are known as micronutrients, and are Boron (B), Copper (Cu), Iron (Fe), Chloride (Cl), Manganese (Mn), Molybdenum (Mo), nickel (Ni) Zinc (Zn). Micronutrients are only needed in very small quantities when compared to the other nutrients. Micronutrients may be either added as a separate additive, or included as part of a nutrient line.
One benefit of using a particular nutrient line, is that by following the manufacturer’s schedule the plant should receive enough of the above nutrients to grow. If designing a nutrient regimen, then attention should be paid to ensure that there are sources for each of the nutrients. Regardless of the exact sources of a garden’s nutrients, they can make the difference between a fair garden and an impressive one.