What Is Chlorosis in Plants? Signs, Causes and pH

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What is chlorosis in plants? Chlorosis is the term for yellow leaves, and it is one of the most common reasons a landscape plant starts to decline without any obvious pest. The University of Maryland Extension resource says that “Chlorosis symptoms, caused by a deficiency of iron, appear as yellow leaves with prominent green veins.” The New Mexico State University extension page calls it “One of the most common landscape plant disorders in New Mexico is iron deficiency, also called iron chlorosis.” This article explains what chlorosis in plants is, how the iron shortage develops in the soil, what the usual causes are, and how to separate it from other problems.

Quick answer

Chlorosis is yellowing of leaves. The classic form shows yellow leaves with green veins, and the sources name iron deficiency as the cause.
Iron is most readily available in acidic soils, and when soil pH is above 6.5 the iron can be present but unusable.
Other causes named by the sources include poor root growth, root rot, over-fertilization, soil nematodes and poor drainage.
A soil test is the source-named way to check whether soil pH is too high.

How the iron shortage develops

Iron deficiency is the cause that both sources name. The UMD page gives the soil-side mechanism in one sentence: “Iron is most readily available in acidic soils between pH 4.5-6.0.” It then explains what happens when the pH rises: “When the soil pH is above 6.5, iron may be present in adequate amounts but is in an unusable form due to an excessive amount of calcium carbonate.” In practical terms, the soil can contain iron and the plant still cannot take it up in usable form.

The same page names where this often happens. It says that the problem “can occur when plants are placed too close to cement foundations or walkways.” Concrete is the context the source gives for high local pH, so a plant near a foundation or path is a likely place to look first.

The NMSU page adds that the iron problem is not always the only stress. It states that “In most cases, the plants are suffering only from iron deficiency either by itself or combined with other environmental stresses, such as water stress, hot and drying winds, and other nutrient deficiencies.” That matters because a plant under several stresses can show a mix of symptoms rather than a single clean pattern.

What the leaves look like

The NMSU extension describes the signature pattern directly: “The classic symptom of iron deficiency is interveinal chlorosis where the leaf turns yellow and the veins remain green.” The UMD page describes the same pattern in more detail: “Leaves will be light green with contrasting dark narrow green veins.” It adds that “Leaves may eventually show marginal scorching and bleaching.”

Timing is another clue. NMSU says that “Iron deficiency symptoms typically begin in spring when the plants are initially leafing out.” UMD says that “Deficiency symptoms are first seen in the young leaves.” Because new growth shows the problem first, a gardener may see yellow tips on fresh leaves while older leaves look normal.

Weather can change how strong the symptoms look. The UMD page says “Symptoms will be more severe during cool wet spring weather.” NMSU says that “Symptoms can be made worse when plants are in heavy, poorly drained soils.”

How chlorosis progresses

If the cause is not corrected, the sources describe a steady decline. NMSU states that “In very severe cases, leaves may turn white in color” and that “Over time, plants that remain untreated will start to die back (Figure 6), become unsightly in appearance, and may eventually die.” UMD adds that “Terminal dieback may occur under severe deficiency conditions.” and that “Shoot growth may be normal but small in diameter.”

The NMSU page also reports that severe leaves may develop necrotic spots. Those spots “can resemble a fungal infection, on the affected leaves,” which is why the sources suggest a diagnosis rather than a guess. A plant with spotted leaves should not be assumed to have only iron deficiency.

The NMSU page lists the plants most often sent for diagnosis, and the list includes “photinia, willows, mulberry, maples, sycamores, poplars, roses, apples, pears (especially ornamental), hawthorne, stone fruits, and pecan.” The list shows that the problem is not limited to one plant group.

Other causes to rule out

The UMD page is direct about alternatives. It says: “Other causes of chlorosis include poor root growth, root rot, root damage caused by over-fertilization or excessive deep cultivation, soil nematodes, and poor drainage.” Each of these points to a different fix, so the cause matters more than the yellow color alone.

Poor drainage links the cause list to soil structure. NMSU says that “Symptoms can be made worse when plants are in heavy, poorly drained soils.” For a soil drainage check, see how to assess soil drainage, which covers the same basic question at home.

The UMD text also warns that visual symptoms can be misleading. It says that “nutrient symptoms are very difficult to distinguish from other symptoms associated with insects or disease, other adverse soil conditions such as compaction or discontinuous texture layers, and improper irrigation practices.” Yellow leaves alone are therefore a starting point for diagnosis, not the answer.

Why a soil test comes first

Both sources point toward testing before treatment. The UMD page says that “A soil test can determine if the pH is too high.” It also notes that “Soil tests are also an important tool for deficiency diagnosis.” A test answers the pH question directly, which is the main variable the sources name.

The UMD page describes two broad responses once pH is confirmed. For acidifying the soil, it says that “Soil amendments that acidify the soil, such as iron sulfate or sulfur, are the best long term solution.” For a faster response on the leaves, it says that “Foliar sprays of iron sulfate or chelated iron can reduce symptoms.” The page also notes that “Some fertilizers such as ammonium sulfate will also acidify the soil.” This article does not recommend any product. For a simple pH check at home, see how to test garden soil pH at home.

Because the sources place the symptoms in the young leaves first, a useful habit is to compare new growth with older growth over a few weeks. The sources do not give a fixed schedule, so the timing here is only a practical observation based on the NMSU and UMD descriptions.

How we chose

The two sources were chosen because both are university extension pages that explain the term and its causes directly. Each page was requested with curl, without redirects, and returned HTTP 200 on 2026-10-27. Quotes were copied from the fetched text. Claims that the sources did not state were left out.

What we could not verify

What the sources do not say

The sources do not give one soil pH value that applies to every plant species, so this article does not state a species-specific target. They also do not give rates for any amendment, and they do not describe the chemistry of chelation in detail. Those points are outside what the fetched text covers.

The sources also do not describe how long the color takes to return after a correction. The UMD page says only that foliar sprays “can reduce symptoms,” so any recovery timeline is not verified here.

Frequently asked questions

Is chlorosis the same as a plant disease?

Not necessarily. The UMD page names iron deficiency as the usual cause, and it lists root rot as one of several other causes. The NMSU page also says that the affected plants “are suffering only from iron deficiency either by itself or combined with other environmental stresses.” A disease is only one possibility on the list.

Why does chlorosis show up in spring?

The NMSU page says that “Iron deficiency symptoms typically begin in spring when the plants are initially leafing out.” The UMD page says that “Symptoms will be more severe during cool wet spring weather.” Both sources connect the start of the symptoms to the spring growth period.

Does soil pH cause chlorosis?

The UMD page says that “These symptoms are usually caused by high soil pH.” It also says that “When the soil pH is above 6.5, iron may be present in adequate amounts but is in an unusable form.” High pH is therefore the main soil cause named in the sources.

Can poor drainage cause chlorosis?

Yes, according to the UMD page, which lists “poor drainage” among the “Other causes of chlorosis.” The NMSU page adds that symptoms “can be made worse when plants are in heavy, poorly drained soils.”

Do all yellow leaves mean iron deficiency?

No. The UMD page says that nutrient symptoms “are very difficult to distinguish from other symptoms associated with insects or disease.” A yellow leaf can have several causes, so the sources recommend a diagnosis before treatment.

Sources

New Mexico State University, extension publication page on iron chlorosis, https://pubs.nmsu.edu/_h/H171/index.html (HTTP 200, opened 2026-10-27).
University of Maryland Extension, resource page on nutrient deficiency in trees and shrubs, https://extension.umd.edu/resource/nutrient-deficiency-trees-and-shrubs (HTTP 200, opened 2026-10-27).