Plants require certain mineral elements for healthy growth. Deficiencies reduce shoot growth and leaf size and cause foliage to discolor, fade, and distort, sometimes in a characteristic pattern that can help you identify the cause. Fewer leaves, flowers, and fruit may be produced. Severely deficient plants may exhibit dieback, remain undersized, and be predisposed to other maladies.
Sufficient micronutrients (e.g., iron, manganese, and zinc) are usually present in landscape soils, but they may be deficient in sandy soils. Deficient macronutrients (nitrogen, phosphorus, and potassium) are more common in containers and planter boxes and when growing fruit and nut trees, palms, and profusely flowering shrubs (e.g., roses). However, except for nitrogen, most nutrient deficiency symptoms are not due to a deficiency of nutrients in soil; they usually result from other causes, commonly adverse soil conditions and anything that makes roots unhealthy. For example pH, whether soil is acidic or alkaline and how much so, affects nutrient availability to roots.
Identification
Common causes of deficiency symptoms include aeration deficit and poor drainage, high pH of irrigation water or soil (especially with plants adapted to acidic soil e.g., azaleas and rhododendrons), and inappropriate irrigation. Other causes that limit nutrient uptake and can result in deficiency symptoms include mechanical (physical) injury to roots, soil-dwelling nematodes, root decay pathogens, and anything else that injures roots or restricts root growth (e.g., hard pan layers, insufficient soil volume).
With certain exceptions (e.g., fruit and nut trees, palms, plants in containers, and perhaps roses and certain other heavily flowering shrubs), fertilization of established woody plants is not recommended unless specific knowledge of the local soil or a soil analysis indicates soil nutrients are insufficient. Applying nitrogen to young trees and shrubs can help plants reach a desirable size sooner, but fertilizing with nitrogen increases plants' need for irrigation and pruning and can cause plants to outgrow the available space. Adding nutrients will not improve the appearance of foliage already damaged by other causes and may divert attention from solving the true cause of unhealthy plants.
Solutions
Choose plants well-adapted to the conditions at that site. Plant properly and provide plants a good growing environment and proper cultural care. See Common Nutrient Deficiency Symptoms for a summary of deficiency effects on plants. To confirm a deficiency and learn how to remedy it see:
- iron deficiency
- magnesium deficiency
- manganese deficiency
- nitrogen deficiency
- phosphorus deficiency
- potassium deficiency
- zinc deficiency
Note that too high of mineral content can damage plants as discussed for:
- boron and other specific ions
- conditions favoring salt damage to plants
- nitrogen excess
- nutrient and mineral excesses, salinity, or salt toxicity
- pH problems
Consult publications such as Abiotic Disorders of Landscape Plants and Fertilizing Landscape Trees (PDF) for more information on prevention, diagnosis, testing, and remediation of nutrient deficiencies.
Adapted from the publications above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
