Iron chlorosis treatment in Greeley, CO

What you are looking at

Leaves turn yellow while the veins stay distinctly green, producing a fine green network on a pale background. It shows worst on the newest growth at the top and outside of the canopy, because that is where the tree is trying hardest to build chlorophyll.

In advanced cases leaves go almost white, then scorch brown at the margins and drop early. Branches die back from the tips, and the tree gets progressively weaker each season.

This is the single most common tree complaint we get in Greeley, and almost everyone assumes it is a disease. It is not.

Why it happens here

Soils across the South Platte valley and most of Weld County are alkaline, commonly pH 7.5 to 8.2. Above about pH 7.2, iron converts to forms that plant roots cannot absorb.

The iron is there. There is plenty of it. The tree cannot get at it. That is the entire problem, and it is why adding ordinary iron sulphate to alkaline soil accomplishes very little — it locks up almost immediately.

Several local conditions make it worse: high soil moisture from lawn irrigation, compacted soil, high bicarbonate levels in irrigation water, and cool wet springs.

Which trees suffer in Greeley

Badly affected: silver maple, red maple, pin oak, river birch. These evolved in acidic eastern soils and are chronically unhappy here.

Sometimes affected: Autumn Blaze maple, cottonwood, aspen, some crabapples.

Rarely affected: bur oak, hackberry, Kentucky coffeetree, honeylocust, and most conifers. These are adapted to alkaline plains soil, which is exactly why they are better choices for new planting here.

Treatment options

Chelated iron soil application. The chelate holds iron in an available form despite the pH. EDDHA chelates work in the highest pH soils; cheaper EDTA and DTPA formulations are less effective above about pH 7.5. Effect within weeks, needs repeating.

Trunk injection. Iron delivered directly into the vascular system, bypassing soil chemistry entirely. Most reliable option for a badly affected mature tree, effective for two to three years. It does put wounds in the trunk, so it is not a first resort for a mildly affected tree.

Soil acidification. Elemental sulphur to lower pH in the root zone. Slow, partial, and works better as a long-term supporting measure than a treatment.

Foliar spray. Fast green-up, lasts one season, useful for a quick cosmetic improvement or a young tree.

Questions we get about this

Is iron chlorosis contagious?

No. It is not a disease and it does not spread. It is a soil chemistry problem, which is why several trees in the same area often show it at once.

Why did adding iron to the soil not work?

Ordinary iron sulphate locks up almost immediately in alkaline soil. You need a chelated form, and in soils above about pH 7.5 that means an EDDHA chelate rather than the cheaper EDTA products sold at garden centres.

How long until the tree greens up?

Soil-applied chelates typically show within two to four weeks in the growing season. Trunk injection is often faster and lasts two to three years. Foliar sprays green up quickly but only for that season.

Do I have to treat it forever?

For a susceptible species in alkaline soil, effectively yes. Treatment manages the symptom; it does not change the soil. For a large valuable shade tree that is usually worth it.

What should I plant that will not get it?

Bur oak, hackberry, Kentucky coffeetree and honeylocust all handle Greeley's alkaline soil well. Avoid pin oak, red and silver maple and river birch unless you are prepared to treat them indefinitely.