Both Nitrogen and Iron Fertilizers Contribute to Dark Green Plant Color

Q. Thanks to your previous advice I used an iron chelate, applied it to the soil in March, and got my plants to develop a dark green color rather than a yellowish green color.

Shrubs that the reader was speaking about. Not sure but they do look like desert natives.

A. There are many things that develop a yellowish color in plants besides needing an iron fertilizer or chelate. The plant you questioned appears to be native desert plant, a Texas sage. That is odd needing an iron fertilizer for native desert plants. They are usually accustomed to our soils and don’t need iron. Watering or a nitrogen fertilizer may be the issue.

Not sure but I do recommend iron chelates that contain EDDHA as the chelating agent. It works in all the different alkalinities of desert soils. EDTA and DTPA iron chelates don't.

Regardless, the two fertilizers that can create dark green leaves are nitrogen and iron. If that plant is native to the Western US, then yellowing leaves is more likely issues involving either nitrogen or watering too often. Nitrogen causes stem growth as well as dark green leaf color. Adding only an iron fertilizer or chelate causes the new growth to become green but does not stimulate new growth that much. When iron is involved, the yellowing occurs on newer growth. Yellowing due to a need for nitrogen occurs all over the plant. Also, the yellowing of leaves due to iron may be a yellow leaf color while the veins of the leaves stay a darker green.

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Winter yellowing I call bronzing of a shrub due to very cold temperatures for Las Vegas.

Two types of “overwatering” can occur; watering too often or giving the plant too much water all at once. It is easier for the plant to resist “overwatering” from the second kind than the first kind. It is easy to water desert native plants too often when placed on the same irrigation line as non-desert plants.

Mesquite leaf yellowing and leaf drop during winter cold temperatures.

Another reason for yellowing of plant leaves are cold temperatures. This type of yellowing is more of a “bronzish yellow” leaf color and happens during cold weather. Cold weather damage to mesquite leaves (yellowing or bronzing) is a common occurrence during cold weather just before the leaves may fall from the tree if it gets cold enough.

Soil Iron Fertilizer Applications End About April-May

As I mentioned before, we are nearing the end of any soil applications of iron fertilizers that work. You can still do it now but don’t expect glorious results like you would see when you apply it at the beginning of new growth (spring). 

Soil applied iron applications will end about April-May as new growth slows down and finishes.

These iron fertilizers and include Kerex, EDDHA iron chelates and any other iron fertilizers meant to be applied to the soil. 

Kerex iron application was made to the soil near this plum in April of 2015. Didnt work. Should have used EDDHA iron chelate or more of the Kerex or added compost AND then applied Kerex.

If there is not enough soil "organics" to decompose then any iron fertilizer will work. Decomposition of organics in the soil lowers its alkalinity and makes just about any iron fertilizer work. Bottom line, be careful greening up plants that have been growing in rock mulch more than three or four years.

Once early spring through early summer has passed, the only thing that cures leaf yellowing are the leaf sprays applied directly to yellowing leaves. 

This chelate is iron EDTA, not EDDHA. EDTA chelated iron works well IF the soil alkalinity (pH) is 7.6 or below. For any iron to work well also requires that nitrogen fertilizer is present. Always apply iron chelates with a well fertilized plant OR include a nitrogen fertilizer at the same time.

Iron sprays like this one are less expensive but you MUST adjust the water chemistry either by adding

 a cup of vinegar (acetic acid) to a gallon of water or use distilled/deionized water.

That’s a poor substitute for soil applications of iron, best done earlier in the season (late January- March) but sometimes the yellowing is so severe it must be done when it’s seen.

Sometimes the yellowing of plants is so severe that an iron application, either applied to the soil or sprayed on the leaves (or both), is necessary to prevent death or injury to the plant.

            Just remember the alkalinity of our tap water is very, very important to a spray’s effectiveness so either adjust the alkalinity of tap water with a cup of vinegar for each gallon or use distilled water for your iron spray.

            Regarding applications of fertilizer, do the trees really need it? It’s best to apply plant growth fertilizers in the spring but applying it now, if desperate, is still better than nothing. Applying fertilizers when trees don’t need it is a waste of fertilizer, a waste of money and unhealthy for the trees.

New growth in apricot. Excessive. Should be an average of about 18 inches.

 Look in several locations at the color of the leaves and the amount of new growth. If the leaves are a very dark green and new growth is exploding, your trees don’t need a fertilizer application. Save the fertilizer application for next February or, least wise, the November coming up.

Dense canopy of a fruit tree. Add no fertilizer this year.

Desert Horticulture: Iron Applications Differ in Timing and Product Used

 Iron applications are applied to the soil earlier in the year and sprayed on leaves later in the year. Learn why and how on this episode of Desert Horticulture.

Interveinal chlorosis (yellowing) on apricot growing on a desert soil.

Green Yellow Citrus Leaves in Winter

Q. My calamondin tree has yellowing leaves. I found this Liquinox iron and zinc plant fertilizer at Home Depot. My question is at this time of the year, can I apply it to my tree?

A. Yes, as a foliar spray. For those not knowing calamondin, it is sometimes called calamonsi in the Philippines. It is a citrus similar to a small lime. 

You would waste your money applying it to the soil unless the soil pH is about neutral (7). I looked at the label. Dilution, use distilled or RO water and apply with a spray bottle. Because it has Yucca extract in it you should not need a wetting agent to get it inside the leaves. Repeat sprays weekly. Might take 3 to 4 applications to see results but each spray it should get darker. Do not use tap water if the pH of the water is too high for this product. You need a pH of about 7 or lower for this to work right.

Will Green Light Chelate Cure Iron Chlorosis in Highly Alkaline Soils

Q. I used a product called Green Light. It contains chelated iron, copper and zinc for correcting plants that are yellow. Is this similar to the chelate you talk about for our soils?