High and low light
Plant growth can be retarded by either too much or too little light.
Identification
Excess (high) light can cause foliage to become chlorotic even when temperatures are cool. Unlike sunburn, excess light usually does not cause necrosis (tissue death). Typical foliage color returns after plants receive appropriate light, but a prolonged light imbalance causes plants to become susceptible to other problems and possibly die.
Deficient (low) light often causes elongated, spindly shoots so plants become taller than normal but have thin stems. Foliage can become pale or dark, depending on the plant species. Leaves may become larger and thinner than normal and drop prematurely, beginning with the most shaded foliage.
Aeration deficit in the root zone and certain plant growth regulators can cause symptoms resembling those of deficient light. Aeration deficit, nutritional deficiency, and water deficit cause symptoms resembling high light damage.
Diagnose inappropriate light based on knowledge of the site's conditions in comparison with the plant's light adaptations.
Each plant is adapted to certain amounts of light, depending on its species and previous growing environment.
Solutions
Plant only species that are well adapted to the amount of light at the location. At sites receiving full sun, do not plant light-sensitive (shade-adapted) species such as Japanese aucuba, camellia, cast iron plant, Japanese aralia (Fatsia japonica), sweet box (Sarcococca spp.), and vine maple (Acer circinatum).
Avoid changing the environment in any way that significantly alters the amount of light received by established plants unless this is purposely done to remedy inappropriate light conditions. For example, planting overstory species can provide shade for plants sensitive to direct light. For more information consult publications such as Abiotic Disorders of Landscape Plants.
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