Tree & Shrub Fertilization

Some of the trees and shrubs we plant in the landscape can benefit from fertilization, while native and desert-adapted plants rarely need any.  Let the nutrient needs of the species, the nutrients found in the soil, and your observations of the plants themselves be your guides.

•      Know the plants – not all plants have the same fertilization needs.

o   For example, a citrus tree needs regular fertilization to stay healthy, while a native mesquite rarely needs supplementation.

• ·         Don’t fertilize native or desert-adapted plants unless plant observation and/or a soil test indicates a deficiency.

o   If these plants appear healthy and have no pest or disease problems, no fertilizer is needed.

o   Some native/desert plants in urban areas may need supplementation due to soil depletion and compaction from construction and other activities that negatively affect the soil.

• ·         Non-native/non-adapted and medium to high water-use plants will need supplemental fertilization on a regular basis.

• ·         A soil test is recommended as a baseline to inform an accurate fertilization plan and schedule.

• ·         Timing – generally fertilize right before and during the growing season. Avoid fertilizing during times of extreme temperatures, dormancy or pruning stress.

• ·         Reduce fertilizer needs and improve soil structure and health by leaving some organic material like leaf and flower litter on the ground to enrich the soil.

• ·         Fertilizing plants beyond their basic needs:

o   May push fast, weak growth resulting in brittle limbs that are easily broken in storms.

o   Generates sudden plant growth with an insufficient root system to support this flush of top growth, leading to blow-overs.

o   Leads to unnecessary pruning, wasting time and fuel, and adding to air pollution.

o   Can adversely affect the environment due to run-off into bodies of water and groundwater.

o   Leads to high salt concentrations in the soil, causing stress on the plants and harming beneficial soil microorganisms.

o   Can be a waste of money.

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