Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Plants Looking Poorly - Iron May be the Solution
Is your azalea, ixora, gardenia, Japanese privet or hibiscus plant yellowing and sickly looking? Horticulturists and gardeners in the know would prescribe iron, the same thing physicians at times prescribe for run-down people. Iron is a tonic for plants, as well as for people.
Plants lacking iron quickly become chlorotic, that is the leaves turn yellow between the veins and may eventually die and drop off. This can happen even when plenty of fertilizer has been added to the soil. Iron may be present in the soil, but may be unavailable to the plant. This normally occurs in alkaline soil. Under such situations, iron often combines with other chemicals in the soil and becomes "bound" or "tied up" so that plants such as azaleas, ixora, gardenias and others can't get it. In most cases, the addition of fertilizer without a change in soil pH will not rectify the situation.
The solution to this problem would be either add iron or to add an acidifying agent to the soil. If iron is added, it has to be in a form plants can use. Such a form is called an iron chelate. This form of iron does not get locked up with other soil chemicals and is available to plants. They are sold under various trade names and in various formulations and can be applied to the foliage or to the soil.
The recovery of plants from an iron-anemic condition can be amazingly fast. A sickly, yellow plant sprayed with iron chelates can revert to lush green condition in as little as 48 hours. When sprayed on plants, chelated iron is absorbed by the leaves. Some chelates can be mixed with water and poured over the soil and taken up through the roots. When this is done, treated plants will return to their normal green color within a week if iron is lacking.
The other solution to iron deficiency problems is to treat the soil with an acidifying agent such as elemental sulfur or aluminum sulfate. These materials, when applied in the proper amounts, will correct the basic cause of iron deficiency which is soil alkalinity. Use sulfur at the rate of l pound per 100 square feet of area per application and do not use more than two to three applications per year. Sulfur must be washed into the soil immediately after application or it will severely burn grass or shallow plant roots. Aluminum sulfate can be applied at the rate of one-fourth pound per square yard of bed area. Do not apply aluminum sulfate more often than one time in a 12-month period. Repeated use of aluminum sulfate can lead to a toxic condition.
Iron sulfate can be used to supply iron to plants. This material is usually applied to the soil and serves not only to supply iron but also to reduce soil alkalinity.
For soil treatment around trees, shrubs, vines, and flowers, the solution is made by dissolving one pound of iron sulfate per gallon of water. For dormant trees, use one gallon of the solution for each foot of the diameter of the drip line. This rate should be cut in half during the growing season. Put solution in shallow holes just deep enough to hold one gallon of solution (one-half gallon during growing season) around the drip line of the tree at intervals of about three feet. The holes should be filled with water once or twice, letting the water soak away. Then refill the holes with soil. Orchid trees respond especially well to iron.
Shrubs and vines can be treated by digging a trench four to six inches deep around the drip line of the plant and pouring in from two to five gallons of iron sulfate solution, depending on the size of the plant.
For lawns, iron may be applied in summer to provide dark green color without stimulating excessive grass growth. Apply ferrous sulfate (liquid iron) at the rate of 2 ounces in 3 to 5 gallons of water per 1000 square feet of lawn. Stronger solutions could burn the grass. Bahia lawns will often respond nicely to iron particularly when planted on soils with a pH of 6.5 or above.
You might want to try this simple remedy to help restore your run-down plants back to health by giving them an iron tonic. Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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