Lorraine Kiefer: Introduction to lichens, algae and moss

[Global] This dreary “gray all day” damp weather we have had for the last few weeks is too much like a British mystery movie for me. I long for some really sunny days. Seems there are always droplets on the branches when I look out. My husband reminds me that we always need rain with our sandy soil.

The time of year and the constant dampness has made lichens, moss and algae grow even more. People often call the nursery and ask about the gray growth on their trees. In winter when there are no leaves you can better see the moss, lichens and algae on the branches and trunks. Some folks like the look others do not. It’s like moss, some people lime their lawns to get rid of moss while others want the whole lawn to be moss. Our antique chicken coop has a moss roof that is so quaint to look at, but not good for the roof. But it does look like a cottage in a fairy tale.

I have been trying to read and learn about the lichen on branches so I have some information to tell folks. I found that the Royal Horticultural Society says, “Algae, lichens and moss often form green or grey, powdery or mossy, crusty growths on the stems, branches and trunks of trees and shrubs. While this can worry gardeners, these growths are harmless, although may occasionally indicate a lack of energy in the affected plant.”

Algae, lichens and moss often form green or grey, powdery or mossy, crusty growths on the stems, branches and trunks of trees and shrubs.

We often think of Britain as being damp and humid with frequent rain, but then New Jersey is also very humid, especially in summer. People often use overheard irrigation too much, keeping plants damp and wet all the time.

The Royal Horticultural Society also says, “Main causes: Humid, damp, still conditions and poor plant vigor. Algae are more noticeable after wet weather; mosses and lichens are present year-round, but are more noticeable in winter”

Lichen are not like other familiar plants in that lichen are made up of two organisms of very different types, a fungus and an alga, intimately associated with each other in a complex relationship called symbiosis. Each lichen species is one alga species plus one fungus species, each benefitting from their association. The alga makes the food for the lichen, while the fungus gives the pair support and soaks up moisture.

Actually, lichens are combinations of green algae and fungal tissue. The alga, a microscopic green plant, makes the food for the duo, while the fungus, a non-green plant, gives the pair support and soaks up moisture. Although they do not really hurt a tree or branch some people want them off. I once told a lady to mix bleach and water in a windex bottle and spray her little dogwood that had green on branches and trunk. I also told her to use soaker hoses instead of sprinklers to water, thus not making the plant so wet, She said by end of summer it was better.

I have done a lot of reading on this and found it does not hurt our plants. However, I picked up some other suggestions that make sense. One way is to gently scrub the bark of the tree with a soapy solution with a little bleach. You can use a scrub brush on a stick. Lichen is usually only lightly attached so comes off easily.

Several online sources say to use copper-sulfate. We use this on our roses to kill fungus in summer so I guess it attacks the fungus part of the lichens. You can also try sulfur to kill the fungus that makes up half of the lichen. Be careful that the lime sulfur is not applied to either the roots or the leaves of the tree, as this can damage the tree. It also burns evergreens.

Perhaps the best treatment for tree lichen is to change the environment where the tree lichens are growing. Lichens on trees grow best in cool, somewhat shady, moist locations. Thinning out tree branches overhead to allow more sun and air flow will help.

Also, if you use a sprinkler system, make sure that it does not spray the place where the lichen is growing, as you are essentially “watering” the tree lichen and helping it to survive. A soaker hose or drip line is better. You may want to consider changing to this type of watering this spring and summer. Meanwhile look closely at the beauty of the lichen on your tree branches or trunk, you may just enjoy their beautiful patterns and subtle coloring. There are also beautiful patches of lichen that grow on the forest floor. I collect these and use on wreaths.

If you care to venture out in your garden there are some plants that are blooming now. Several types of hellebores or Christmas rose are in bloom in some gardens. The mild temperatures have allowed their evergreen foliage to remain green and glossy so far this year. I walked around the garden last week taking photos of those lovely plants that look so pretty now.

In our back yard there is a fragrant winter sweet or Chimonanthus praecox a small tree that is in bloom now. It is a nice one to cut and bring in to enjoy in a vase on a table. You can also cut forsythia, quince and other flowering trees to force into bloom. Everyone loves a promise of spring. If you do not have a wintersweet plant one this spring.


Photo: Algae, lichens and moss often form green or grey, powdery or mossy, crusty growths on the stems, branches and trunks of trees and shrubs. Pictured here, lichen and moss. (Lorraine Kiefer)

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