What’s The Difference Between Lichen and Moss?

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lichen

Lichen; iStock: mgfoto

Lichen and moss, often lumped together, tell you different things about your yard and environment. Let’s take lichen first.

Prior to the Clean Air Act, signed in 1967, finding lichen in the Midwest proved difficult because it couldn’t tolerate pollution. Its ubiquitous presence today shows how much cleaner our air has become in the last 50 years.

Lichen combines two organisms, algae and fungus, in a symbiotic relationship. Fungus protects the algae from strong sunlight and drying out, but cannot produce the needed nutrients to survive. Enter the algae. It contains chlorophyll, allowing it to photosynthesize and produce food and vitamins, which it then shares with the fungus. The type of algae and fungus determines the lichen’s color, ranging from yellow through multiple shades of green on into gray.

You find lichen growing on tree trunks and also inanimate objects such as buildings and yard art, especially during damp, humid weather, when it becomes more obvious. Lichen protects itself during drought by going dormant, but once moisture becomes available, it absorbs three to 35 times its weight in water.

Lichen does not harm trees, but might indicate a young tree has another problem. Juvenile trees grow fast, and lichen won’t stick to rapidly stretching bark. If lichen covers the trunk, it indicates there might be something else wrong, preventing the tree from maturing.

Moss exists as a very simple form of plant called a bryophyte. Not having a vascular system, it absorbs water and nutrients through its leaves. It can’t grow stems, so the plant just piles on top of itself and reproduces by spores instead of seeds. Unlike lichen, mosses grow on or close to the ground.

The presence of moss indicates you have one or more of three conditions present in your lawn. First, that area of your yard has inadequate drainage. Second, the lawn needs fertilizer, or finally, your soil is acidic. If you pull out the moss but don’t address the underlying condition, it will just grow back.

If you want to clear an area of moss, manual removal works best. Herbicides require a vascular system to move the chemical through the plant, which moss doesn’t have. Products containing iron in the form of ferrous sulfate or ferrous ammonium sulfate may somewhat control it.

Unlike lichen, moss not only grows in polluted air, but also can act as an inexpensive way to detect the presence of heavy metals in the air. People studying moss in Portland, Oregon, found heavy concentrations of cadmium and arsenic present in the moss of two neighborhoods containing glass factories. Glassmaking produces cadmium and arsenic as byproducts. The air quality tests showed 50 times the normal level of cadmium and 150 times the accepted levels of arsenic.

Instead of removing the moss from your problem area, try turning it into a moss garden instead. You already know moss thrives there.

Ask an Expert

Q: Why won’t my American bittersweet make berries?
A: Bittersweet vines (Celastrus scandens) are either male or female. Only the female plants produce flowers, which in turn become berries. Try planting one male plant for every three female plants, situated in full sun.

Q: A gardening friend gave me some money plant seeds. I planted them but they didn’t flower. Why?
A: Give it another year. Money plant (Lunaria annua), an herbaceous biennial, blooms the second year.

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