How do nitrogenous fertilizers affect plants?

Fertilizers are compounds containing one or more essential plant nutrients that are formulated to be applied to plants through the soil. They can be organic or inorganic, with or without micronutrients. Nitrogenous fertilizers are important for maintaining healthy lawns, productive irrigated pastures, flowering plants, productive fruit and vegetable gardens, annual flower beds, and houseplants. The range of fertilizer products is virtually limitless.

Fertilizers help in many situations. However, nitrogen fertilizers do not need to be regularly applied to woody plants in ornamental landscapes. If fertilizers are used indiscriminately on woody ornamentals, the results can be negative, leading to pest susceptibility, reduced drought tolerance, and potential contamination of nearby rivers, streams, and groundwater resources. Excessive use of nitrogen fertilizers can lead to rapid plant growth, which in turn requires more irrigation and possibly increased pruning. Fast growing wood is also more prone to breakage. Although severed limbs should be removed with proper pruning, pruning wounds require additional energy to heal properly. If the wound does not heal properly, the disease can invade.

Nitrogenous fertilizers are particularly attractive because they promote lush green leaves and rapid growth. Before applying nitrogen fertilizer, you should evaluate the growth rate and general health of your plants. You can do this by looking at the amount of growth, leaf color, and leaf distribution on the plants each season. The first symptom of nitrogen deficiency is a uniform light green or yellow color on the oldest leaves. As the deficiency develops, the growing tips of the plants retain some green color, but the lower leaves are either yellow or have turned brown and have fallen off the plant.

Fertilize your garden plants regularly several times a year. These recommendations are outdated, misleading, or involve the seller's financial interests. Fertilize woody ornamentals only when specific nutrient deficiencies are observed. Native-adapted trees and shrubs will often benefit from supplemental irrigation during periods of drought, but will find the nutrients they need when properly planted and allowed to develop a well-distributed root system. Therefore, woody natives and drought-tolerant plants rarely require fertilizer.

Iron may be present in the soil but not fully utilized due to low alkalinity and soil temperature. Iron deficiency can be improved by foliar application of chelated iron to improve leaf color, but in most cases faded green leaves will "green" on their own once the soil warms. In some areas of northern Arizona where alkaline soils are found, some exotic landscape plants exhibit symptoms of iron deficiency in the spring. This is usually evident in red-tip heather. Iron deficiency symptoms are usually found when new leaves develop intervein chlorosis. Application of nitrogen fertilizer can exacerbate iron deficiency symptoms. The plant tries to grow more leaves with a limited supply of iron. Gardenias, rhododendrons, rhododendrons, birches and other acid-loving ornamental plants, in areas with alkaline soil, needle oak often show symptoms of iron deficiency. These plants should be avoided if soil with a pH of 8 or higher is present. Native and drought-tolerant plants have adaptations that allow them to grow and thrive in alkaline soil conditions. These adaptations include slow growth rates, root association with mycorrhizal fungi, and the ability to hold water for extended periods of time without precipitation.

Raised Planter Box

If you think you are observing symptoms of nutritional deficiencies, be sure to analyze the situation for evidence of insects or disease. Check the irrigation system to ensure proper operation. Mature woody landscape plants are best irrigated at infrequent depths to promote extensive root systems.