If the leaves of your maple, oak and crabapple trees are turning lighter green or yellow and have dark green veins, it is because the soil is alkaline and the trees can’t absorb the needed iron. You have a couple options to save your beautiful mature trees. One is EDDHA iron (sprint 138), which you can purchase online. Simply mix a cup in three gallons of water and pour on the ground at the base of the tree once a month during the growing season until leaves return to dark green. Due to the alkaline nature of the soil, re-treatment will be needed when evidence of chlorosis (yellowing) returns. When leaves are just turning lighter green with veins becoming visible, re-greening will likely be visible in a couple months.Yellower trees take longer. Some, unfortunately, may be too far gone to save. Sulphur is another treatment option.

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More on Yellowing Trees

We are not tree experts. For those who don’t want to use a plant product without consulting an expert, we applaud your respect for the experts and encourage you to contact them as soon as possible. If your trees are showing chlorosis (yellowing), treating them sooner is more likely to result in restoring healthy dark leaves and will take fewer treatments.

Look closely at the color of your leaves. Many maple, oak and crabapple trees in the neighborhood that should have dark green leaves when they’re healthy are turning a lighter shade. They’re still beautiful—it’s easy to overlook that they are not healthy. We’ve found, when talking to neighbors, they don’t realize this change from dark green to lighter green to yellowish green to yellow is a sign of iron deficiency. Iron is a mineral essential for plants to make chlorophyll, which is needed for photosynthesis. Over time, the chlorosis gets worse and the trees get yellower. Many have already died.

We have personally jumped in on this cause for three reasons:

1. After seeing how many trees are showing chlorosis, we’re concerned that if these trees aren’t treated, the neighborhood could lose many large trees in the coming years.
2. We observed the results after one neighbor started treating all the yellowing trees on his block a couple years ago; they all now have healthy dark leaves.
3. Treatment options are affordable, easy and quick.

EDDHA Chelated Iron Treatment

The results we’ve observed came after use of a product labeled Sprint 138 Fully Chelated EDDHA Iron 6%. It’s available on Amazon, eBay and other sites. A 5 lb. bag can be purchased for about $120 and contains approximately 22 one-cup treatments (approximately $5.50 per cup). Other products online simply say EDDHA Chelated Iron 6%, but don’t say Sprint 138. We do not have information as to how or whether the Sprint 138 product differs from other products. We can only speak about the product we’ve observed now for a couple of seasons.

For the neighborhood trees we observed, one cup of the Sprint 138 product was mixed in 3 gallons of water and poured around the base of the tree. (The water turns your hands, your shoes and whatever it touches very red, but it does wash off with soap and water.) Ideally trees showing chlorosis should be treated at the beginning of the growing season and repeated once a month until the tree no longer shows signs of chlorosis. Treatment needs to be repeated when signs of chlorosis recur.

As noted in the article below, treatment later in the season is not as effective as at the beginning of the growing season. However, trees weakened by chlorosis may suffer during the winter, so treatment now may help trees go into the winter season a little healthier.

Treatment with Sulfur and Iron Sulfate

Another neighbor found his recently planted blueberry plants were showing chlorosis. Elemental sulfur added to the soil to make it less alkaline cured the chlorosis in a few weeks.

For large yellowing trees, a combination of sulfur and iron sulfate, less expensive and more commonly available products than EDDHA, should produce a result similar to EDDHA, but we have not had the opportunity to observe use of that on neighborhood trees.

For more information, check these links:

Iron Chlorosis of Woody Plants

Key points from this article:

Iron chlorosis refers to a yellowing caused by an iron deficiency in the leaf tissues. The primary symptoms of iron deficiency include interveinal chlorosis, i.e., a general yellowing of leaves with veins remaining green.

Plants use their stores of iron in new leaves as they create them so iron chlorosis shows first and more severely on the newer growth at branch tips. Leaves may be smaller than normal.

Any reduction in chlorophyll during the growing season reduces plant growth, vigor, and tolerance to stress conditions. Plants with reduced vigor from iron chlorosis are more prone to winter injury and winter injury may aggravate an iron chlorosis problem. Weakened plants also are more susceptible to other diseases and insect infestations

In Colorado’s high pH soils, the best method to prevent iron chlorosis is to select plant species tolerant of high soil pH and less affected by low iron availability. Avoid planting the more susceptible species (Table 1) on soils prone to iron chlorosis problems (pH above 7.5, compacted, clayey, or wet soils).

Table 1. Examples of Plants with High Susceptibility to Iron Chlorosis

Amur maple, Dawn redwood, Northern red oak, Apple, Douglas-fir, Peach, Arborvitae, Elm, Pear, Aspen,Flowering dogwoods, Pin oak, Azalea, Grape, Pine, Beech, Honeylocust, Raspberry, Birch, Horse chestnut, Red maple, Boxelder, Juniper, Rhododendron, Bumald spiraea, Linden, Silver maple, Cherry, London plane tree (sycamore), Spruce, Cotoneaster, Magnolia, Crabapple, Mountain-ash

Soil Applications of Iron Sulfate Plus Sulfur

Read the article for more info.

Soil application of Iron Chelates

Soil application of iron chelates may give a rapid response if the correct chelate is used and other contributing factors are minimal. Applications after May 1st are less likely to show results. Treatments may last less than a season to a couple of years. (Read the article for more info.)

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Iron Chlorosis in Trees

Key information from this article:

Iron chlorosis is a term describing leaf yellowing (lack of chlorophyll) due to insufficient iron. Iron is a mineral essential for plants to make chlorophyll, in turn needed for photosynthesis. Lack of iron in a tree may be due to a high iron need, less effective iron uptake, or insufficient usable iron in the soil. Colorado soils generally have adequate to high iron levels, as evidenced by the many red soils and rock formations. However, Colorado soils are mostly alkaline, causing most of the iron to be in an insoluble form not usable by plants.

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Iron Chlorosis

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Editor’s Note: A neighbor posted this on NextDoor in response to a comment about this article on yellow leaves:

We have treated with iron in the soil without much luck. My husband used this and our tree looks healthy now. You actually drill it into the tree. Scars are healed and leaves are green. Medicap 25-Pack FE Systemic Iron Tree Implants for Control of Iron Chlorosis, 3/8-Inch https://www.amazon.com/dp/B00DQUUSM6/ref=cm_sw_r_cp_api_i_-d0jFb1TX7EVE