Iron deficiency (iron chlorosis) is a common problem in Australian gardens and can cause serious problems to plant health and vigour. The symptoms however are easy to both recognise and treat.
Iron deficiency first appears as a ‘veiny’ look on new growth, with a darker green pigmentation retained on the leaf veins and the rest of the leaf developing a pale or yellowish green colour. Iron deficiency can be more common in pot plants as their roots are limited to the nutrients that are available in the pot.
Iron is essential for healthy plant growth and disease resistance. Iron can be lost from plants’ roots with excessive watering, long periods of rainfall and soil saturation, but the most common cause of iron deficiency is a high (or alkaline) soil pH.
Iron becomes soluble in water, and therefore available to plants, when the soil pH is acidic, or of a pH of 6 or lower. When the pH increases to 7 or higher, the iron in the soil solidifies and becomes ’locked up’ in the soil.
Some plants have a greater need for iron than others and will show symptoms of iron deficiency more quickly. These include azaleas, camellias, gardenias, hydrangeas, philodendrons, roses, citrus and fruit trees, many Australian native plants and lawns.
Some plants are known as ‘acid loving plants’ because of their demand for iron.
The good news is that correcting iron deficiency is easy, can be very quick and has a high rate of success.
The usual method is to apply Searles Iron Chelate (pronounced ‘keel-ate’) to the soil. This powder is dissolved in water and is easy to apply. It can also be applied to the leaves for quick uptake by the plant. Iron chelate is iron in a form that is instantly available to the plant and will not ‘lock up’ in the soil, even if it has a high pH. Repeat applications every few weeks may be advisable until the symptoms of iron deficiency disappear.
The other common cause of iron chlorosis is simply a lack or iron in the soil.
Iron chlorosis can also be caused by conditions that generally inhibit the uptake of nutrients by a plant such as compacted soil, poor drainage, waterlogging, persistent, excessively low temperatures, restricted root growth such as in potted culture, prolonged drought conditions and soil salinity. Iron chlorosis can also be caused by excessive use of fertiliser, such as those high in phosphorus. In fact, iron chlorosis is often the first stage of phosphorous toxicity in Australian natives and other phosphorus-sensitive plants.