Iron Chlorosis
By Dale Norrington, Master Gardener
Iron chlorosis generally refers to a condition in which plant chlorophyll is
damaged or destroyed due to insufficient iron.
Chlorosis disrupts the photosynthetic process through which plants
produce food and energy essential to life.
Chlorotic plants may lose vigor, become stunted, produce less and/or
inferior blooms and fruit, become more susceptible to pest and disease attack,
or die. Leaves appear pale green to
yellow while veins remain distinctly dark green. Symptoms may initially appear on young,
expanding leaves, progress to mature leaves or, in mild cases, disappear as
leaves mature.
Identification of iron deficiency as the cause of chlorosis can be problematic
because deficiency or excess of other elements, varying soil conditions which
may render elements unavailable to plants, and a variety of other abiotic and
biotic plant disorders can also cause chlorosis. Insufficient nitrogen, zinc, manganese, or
sulfur, and/ or excessive sodium or copper in soils are examples, as are
inadequate light, absorption of air pollutants including sulfur dioxide and
ozone, and insufficient soil mycorrhizal activity.
Type, texture, chemical characteristics including pH, and relative quantities
of air and water in pore spaces are among soil factors which influence mineral
availability for absorption. Minerals
can be present in soil yet unavailable to plants. Such is often the case with iron in alkaline
soils of the central coast.
If soil pH ranges between 6 and 8; fertilization is adequate, not excessive,
and includes appropriate quantities of primary, secondary, and micro-nutrients;
irrigation is adequate and not excessive; sufficient organic material is
incorporated into the soil; and tilling is avoided when soil is medium wet to
wet, then iron deficiency may be the cause of persistent chlorotic conditions,
and incorporation into the soil of chelated iron, commonly available from
horticultural supply facilities, is recommended. Product label information,
warnings, and directions should be read and followed carefully.