Can I Apply Iron in the Winter?

Q. I have a dwarf lemon tree with many yellow leaves. Can I add iron at this time of year (December)?

This is not citrus but it is iron chlorosis. You can tell from the yellowing of the leaf while the veins remain green and appearing on the newest growth. It is possible to confuse it with manganese deficiency easily.

A. If you apply iron this time of year (December) it is best applied as a foliar spray rather than to the soil. If the leaf yellowing is not extensive you could wait until spring. Leaf yellowing reduces a plant’s ability to capture sunlight and produce energy to maintain its growth and health.

Iron chelate made for applying mixed with water. 

If you want to correct it now, you must apply iron to the leaves as a liquid or foliar spray. It is best to use an iron chelate mixed with water and add about 1 tablespoon of white vinegar if you use tap water to reduce the alkalinity. If you use distilled water, you will not need the vinegar.  To this water add the appropriate amount of iron chelate listed on the label. You should add a wetting agent to help the spray penetrate the leaves.

You can make your own wetting agent by using a liquid detergent like Dawn or Ivory Liquid at a rate of about 2 teaspoons per gallon added to the finished spray mix. It is not as refined as a commercial wetting agent but it will do the job.

A very safe wetting agent for better leaf penetration

You would apply this mixture of water, chelate and wetting agent to the leaves immediately after mixing it until the spray runs off the leaf surface. Let the leaves dry and repeat it a few days apart or until you see the leaf color change from yellow to a darker green.

Foliar sprays like these may require several applications to get the results you desire.  Citrus leaves have a very waxy surface and are difficult to penetrate with just plain water. If you use tap water then each time you prepare a new spray you should adjust the alkalinity of the water with vinegar and add a wetting agent.

Foliar sprays should always be freshly made, applied immediately and not stored for any length of time. Unfortunately homemade iron liquids, unlike commercial sprays, do not store very well. It might be cheaper in the long run to buy the liquid iron spray already made and make the application.

It is also possible citrus leaf yellowing could be a magnesium or manganese problem. Liquid iron sprays will not correct problems due to magnesium or manganese.