“I’ve got some kind of creepy fungus all over my tree! Will it kill my tree?”

I get asked this A LOT. And so, I’ve created this post to offer a brief, but hopefully interesting discussion about the fascinating natural phenomena known as LICHENS (pronounced: “lye-kens”). More field photos below and you’ll find links to additional information near the bottom of this page.

But let’s first address the question concerning ARE LICHENS BAD FOR TREES?

The answer is “NO“

…they have not been shown to pose any significant harm to trees. Now you may breathe a sigh of relief!

Lichens are greenish, sometimes lettucy-looking, symbiotic growths made of fungi, yeast, and two types of algae. These grow as an interwoven mass appearing as a single individual which can develop into a sizeable “community” of lichens. Both the fungus and the alga provide something essential to the other for their survival but are not harmful to plants.

“But, WHY,” you may ask, “are these things growing on my tree(s)?”

Actually, they do not specifically pick on trees. Lichens can develop and grow on just about any stationary surface they can attach to, such as rocks, roofs, fence posts, gravestones, and even other lichens! And you can find lichens just about anywhere! As a matter of fact, there are an estimated 20,000 known species of lichens worldwide and come in a variety of colors, shapes, and sizes! They can grow flat or with a leafy lettuce appearance or other interesting (and sometimes gross-looking) structures. An increased amount of lichen on plants could indicate poor plant health because healthy, fast growing trees and shrubs are always shedding bark, making it difficult for lichen to attach. A season or more of severe drought, for instance, can slow a tree’s development allowing more time for lichens to form and populate.

Check out the photos of various lichen on different trees. (Note: The type of tree does not necessarily affect the type of lichens that grow on them.)

Moss is not lichens.	Lichens atop moss.

Hey! Are You “Lichen” What You See? LEARN MORE About Lichens Below!

• Lichens of North America – (Sharnoff’s photographic fieldwork) -This website grew out of the activities of Sylvia and Stephen Sharnoff, who did the photographic fieldwork for the book Lichens of North America, by Irwin M.Brodo and the Sharnoffs, published in November 2001 by Yale University Press.
• Lichen – (Encyclopædia Britannica) -Lichen, any of about 15,000 species of thallophytic plantlike organisms that consist of a symbiotic association of algae (usually green) or cyanobacteria and fungi (mostly ascomycetes and basidiomycetes). Lichens are found worldwide and occur in a variety of environmental conditions. A diverse group of organisms, they can colonize a wide range of surfaces and are frequently found on tree bark, exposed rock, and as a part of biological soil crust. Lichens have been used by humans as food and as sources of medicine and dye. They also provide two-thirds of the food supply for the caribou and reindeer that roam the far northern ranges.
• What Are Lichens? – (Live Science) – A lichen, or lichenized fungus, is actually organisms functioning as a single, stable unit. Lichens comprise a fungus living in a symbiotic relationship with an alga or cyanobacterium (or both in some instances). There are about 17,000 species of lichen worldwide.
• What Lichens Are Not – (USDA Forest Service) – Isn’t lichen that mossy stuff on rocks and trees? When people think of lichens, many of them think of them as a kind of moss. That could not be farther from the truth.
• Yeast Emerges as Hidden Third Partner in Lichen Symbiosis – (ScienceDaily) – For nearly 150 years, lichens have been the model organisms of symbiosis. Now researchers have uncovered an unexpected third partner embedded in the lichen cortex or ‘skin’ — yeast.

1. remember to do it,
2. know when & how much to do it,
3. and do it in a way that doesn’t discourage you from doing it.

• MULCHING AROUND TREES – Don’t forget that you need to check the mulch at least annually to monitor for new girdling roots, etc. (See: “Girdling Roots: The Silent Tree Killer”) Some soaker hose manufacturers may recommend removing them before winter’s freezing temperatures arrive because moisture retained in the hose may cause it to crack. Therefore, you may have to remember to reinstall the soaker hose the next spring.
• TREE TREATMENTS – If your trees are to receive (or recently received) any treatments to provide supplementary nutrients or to suppress insect pests infestations or disease infections, etc. then you need to ensure you provide them adequate water. This can help to reduce the potential for phototoxicity injury. [Note: Many pesticide labels caution applicators not to use their products when temperatures exceed 89°F (31.6°C). These also carry temperature precautions for storing chemicals.]

• “Heat & Drought Stress – Will Your Trees Survive?”
• Estimating Tree Water Requirements
• Watering Schedule example from the City of West Sacremento

[Last update: November 2025]

Quick Links to Topics Covered in This Article:

INTRODUCTION  •  17 Essential Elements
Using the Soil pH Chart  •  How a Soil Analysis Report Can Help You
How To Get Your Soil Tested

INTRODUCTION

Have you ever gone to a tree nursery and, to your glee, found what you thought to be the PERFECT tree for your home? Perhaps you saw it first in a magazine, on TV, or online, or maybe even caught it on sale at your local Walmart or Home Depot. Wherever you saw it, you impulsively purchase it for your property. In no time, you’ll have it in the ground and be taking selfies with it to brag to all your friends on social media!

After a few weeks, months, or years go by, you begin to notice it’s not looking as nice as it did when you planted it. “What happened? Why is it looking so sickly?” you wonder.

The 17 Essential Elements

Like most living organisms, a lack of any vital nutrients can have a negative health impact. Your trees are living organisms. Trees exhibit all the characteristics of life, such as growth, reproduction, responsiveness to their environment, and metabolism. They are made of cells, take in nutrients and water, and perform respiration and excretion. Therefore, KNOWING your soil can also help you to understand why existing trees may be failing in health. A soil analysis can help guide you to improve your soil management.

There are 17 essential elements for trees, based on the amounts needed, which are obtained from air, water, and soil, and are divided into macronutrients and micronutrients. Macronutrients are required in large amounts, while micronutrients, though needed in smaller quantities, are equally critical for survival and healthy growth.

• Basic Nutrients (Basic Macronutrients)
  These non-mineral elements are primarily supplied by air and water, rather than the soil.
  • Hydrogen (H): Comprises about 6% of a tree’s dry weight. Acquired from water, it is a key component of carbohydrates and other organic compounds that are essential for growth.
  • Carbon (C): Makes up about 45% of a tree’s dry weight. It is the foundation of all organic molecules and is used by trees to produce carbohydrates (a.k.a., sugars and starches) during photosynthesis.
  • Oxygen (O): Also makes up about 45% of a tree’s dry weight. It is obtained from water and carbon dioxide and is vital for cellular respiration, the process that releases energy for the plant to use.
• Macronutrients
  Trees require these six nutrients in relatively large amounts, which are supplied by the soil and often supplemented with fertilizers.
  • Nitrogen (N): Promotes strong foliage growth and green leaves because it is a key component of chlorophyll, the molecule central to photosynthesis. It is also essential for creating amino acids, nucleic acids (DNA and RNA), enzymes, and proteins. A deficiency results in yellowing (a.k.a., chlorosis) of older leaves and stunted growth.
  • Phosphorus (P): Crucial for converting sunlight into usable energy, a process vital for root growth, flowering, and seed development, phosphorus also plays a central role in the transfer and storage of energy within the plant. It helps trees recover from stress and increases their overall strength.
  • Potassium (K): Supports overall tree resilience by helping to regulate a tree’s water uptake and internal moisture levels, which improves its tolerance to drought, cold, and disease. It is also essential for activating the enzymes involved in photosynthesis and for strengthening cell walls.
  • Magnesium (Mg): As the central atom in the chlorophyll molecule, magnesium is critical for photosynthesis. It also helps regulate the transport of phosphorus and is involved in activating enzymes for carbohydrate and protein metabolism.
  • Sulfur (S): Important for synthesizing proteins, amino acids, and vitamins, sulfur is also involved in forming chlorophyll. It helps the tree resist diseases.
  • Calcium (Ca): As a key component of cell walls and membranes, calcium provides the structural integrity of the plant. It promotes root and shoot growth and improves disease resistance. It is also important for regulating the transport of nutrients.
• Micronutrients
  Trees need these eight soil-derived elements in very small, or trace, amounts. While needed in smaller quantities, these trace elements are critical for specific enzymatic functions. In excessive quantities, some can become toxic.
  • Boron (B): Important for cell wall formation, cell division, and the development of new growth, pollination, and fertilization, and also aids in the transport of sugars.
  • Chlorine (Cl): Necessary for the regulation of osmotic pressure, maintaining ionic balance, vital for photosynthesis and root growth, and also helps regulate water retention.
  • Manganese (Mn): This element activates enzymes involved in growth and photosynthesis, respiration, and nitrogen assimilation. It assists iron chlorophyll formation.
  • Iron (Fe): Necessary for producing chlorophyll, iron functions as a catalyst in energy transfer and is a component of many enzyme systems. A deficiency causes yellowing of the younger leaves (a.k.a., iron chlorosis).
  • Nickel (Ni): A component of the enzyme urease, and is necessary for nitrogen metabolism. Without it, urea can accumulate to toxic levels. Required to complete the life cycle of the tree and produce viable seeds.
  • Copper (Cu): Involved in photosynthesis, respiration, and the formation of cell walls, and also helps activate enzymes and increases disease resistance.
  • Zinc (Zn): Vital for enzyme function, protein synthesis, and hormone regulation, and is essential for plant growth and promoting root development, including the production of auxins.
  • Molybdenum (Mo): This element is essential for nitrogen metabolism and needed for the tree to utilize nitrogen effectively, helping enzymes convert nitrates into usable proteins.

What can cause nutrient deficiencies or nutrient-deficient-like symptoms in your trees? Well… it could be any number of reasons:

• • Poor quality tree stock
  • Wrong Hardiness Zone
  • Transplant shock
  • Poor root establishment
  • Planted too deeply
  • Inadequate amounts of water
  • Repetitive mechanical injuries
  • Incompatible or poor soil conditions

Let’s take a few moments to consider the last item on this list: Incompatible or poor soil conditions, by examining the Soil pH Chart that follows.

Using the SOIL pH CHART

One of the biggest challenges in establishing some trees in Indiana clay soils is high alkalinity and compaction. Soil pH is a measure of the acidity or alkalinity of the soil, measured on a logarithmic scale from 0 to 14. A pH of 7 is neutral; values below 7 indicate increasing acidity, and values above 7 indicate increasing alkalinity.

Soil pH is defined chemically as the negative logarithm of the hydrogen ion (H⁺) concentration in the soil solution. It is a critical indicator of soil health because it governs the availability of nutrients to plants and affects the activity of beneficial soil microorganisms. Acidic soils (typically found in high rainfall areas) have a higher concentration of hydrogen ions. Alkaline (basic) soils (common in arid regions) have a lower concentration of hydrogen ions and a higher concentration of hydroxyl ions (OH⁻).

Optimal Range: Most plants thrive in slightly acidic to neutral soils (pH 6.0 to 7.0), where nutrient availability is highest. During the planning phase of tree selection, an overlooked first step is getting a soil test. Become familiar with the following Soil pH Chart. The range from Acidic to Alkaline soils can influence the success or failure of your tree(s).

FUN FACT: DID YOU KNOW?

When it comes to Soil pH Charts and soil guides, many focus on a scale of 4.0 to 10.0 instead of 0 to 14. Why? Because the 4.0 – 10 range encompasses virtually all naturally occurring and agriculturally relevant soil pH values. While the theoretical pH scale in water-based solutions extends from below 0 to above 14 (depending on the concentration), natural soils generally range from an extremely acidic pH of around 3.5 to a very alkaline pH of 10.0. Additionally, soils with a pH value close to 0 or 14 are exceptionally rare in nature. Such extreme conditions would require extremely strong acids or bases, which are not found in typical soil environments. Therefore, charts for gardening and agriculture aim to present the most practical information for plant growth and soil management. Since healthy plant growth is severely limited outside the 4 to 9 range due to nutrient deficiencies or toxicities (e.g., aluminum toxicity at low pH), focusing on the 0-10 or 4-10 range is sufficient for most practical purposes. NOW YOU KNOW!

This DID YOU KNOW? is based on an online article by Guodong “David” Liu and Edward Hanlon (Publication #HS1207 (March 2024), IFAS Extension)

After a laboratory analysis, a soil test report will typically show specific soil nutrient content, soluble salts, and pH level.

NOTE: Typically, standard soil tests do not analyze for contaminants, such as bacteria, mold, fungi, herbicides, etc. Therefore, if soil contamination is a concern (say, for example, bacterial problems associated with Crown Gall disease, which affects roses, euonymus plants, willows, etc.), then more advanced analysis is needed, and that would require the help of a microbial services laboratory, which may charge a significantly higher lab processing fee.

When foliage lacks normal spring and summer coloration and displays pale or yellowish tones rather than green, it may be due to a nutrient deficiency condition known as Chlorosis.

Chlorosis is the yellowing of leaves in trees due to a lack of chlorophyll, which is caused by a deficiency in essential nutrients like iron, magnesium, or nitrogen. This impairs photosynthesis, leading to symptoms like pale green or yellowing leaves, and can progress to leaf scorching, twig dieback, and eventual tree death if untreated. The most prominent sign is leaves turning a pale green or yellow, often with darker green veins (interveinal chlorosis).

Common Nutrient Deficiencies and Contributing Factors Associated with Chlorosis:

• Iron deficiency: Typically causes interveinal chlorosis, starting on younger leaves, as the veins remain green while the tissue between them turns yellow.
• Nitrogen deficiency: Tends to cause older leaves to yellow uniformly.
• Magnesium deficiency: Often shows yellowing between the veins but may also turn the leaves bronzy-orange.
• High soil pH: Alkaline soils can make it difficult for trees to absorb iron and other nutrients, even if they are present.
• Poor soil conditions: Compacted or waterlogged soil can restrict root function and nutrient uptake.
• Root damage: Physical damage to roots from construction or disease can also cause chlorosis.

How a SOIL ANALYSIS REPORT Can Help You

• This is where the pH rating may be an important factor to note. What is the soil pH rating? Is it too low, too high, or just about right? In reference to the aforementioned Soil pH Chart, the optimal pH range for most plants on a rating scale from 0 to 14 is between 6.0 to 7.0, with 7.0 being neutral. In the example Analysis Results report below, the pH level of the soil sample submitted is 7.3 (circled in red) and considered high.
• The soil texture (or percentage of sand, silt, or clay) determines how much Sulfur (S) content is needed to lower the pH. When soil pH is high and Sulfur is low or insufficient to reduce the alkalinity of the soil, nutrient absorption by the roots of some trees may decrease. In the soil sample below, the Sulfur reading (in parts per million (ppm); see blue arrow) is 14 ppm. This indicates that Sulfur is high, but since the pH is also high. This could indicate a problem related to soil texture.

• Should you add more Iron (Fe) into the soil for your yellowing Pin Oak (or River Birch or White Pine, etc.) to help green up the foliage? Well, if the soil in this sample report above came from the property with those trees, we can see that the soil already has a very high concentration of Iron (see green arrow) at 154 ppm. Therefore, additional Iron is likely unnecessary.
• The same may apply if we were trying to resolve a Manganese (Mn) deficiency in a yellowing maple tree to help restore summer season color to the foliage. According to the Analysis Results example above, Manganese is 72 ppm is considered very high. (See orange arrow)

HOW TO GET YOUR SOIL TESTED

Related articles:

• Soil and Water pH – Part 1: What is pH?  https://ucnfa.ucdavis.edu/news/soil-and-water-ph
• Soil and Water pH – Part 2: How is nutrient availability affected by pH?  https://ucnfa.ucdavis.edu/news/get-cultured-part-2-soil-and-water-ph
• Soil and Water pH – Part 3: How do fertilizers affect pH?  https://ucnfa.ucdavis.edu/news/soil-and-water-ph-part-3
• Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH  http://edis.ifas.ufl.edu/hs1208
• Chelates – What are they and What do they do? (PDF) https://www.gchydro.com/pdf/GreenCoast%20Hydroponics-IS-NUT-0413-The%20Science%20Behind%20Chelates.pdf
• Predicting Soluble Nickel in Soils Using Soil Properties and Total Nickel  https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0133920