Tree Lichens Pose No Danger; Repotting Orchids Reduces Flowers | Print |  E-mail
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Thursday, 17 February 2011 16:24

By Buzz Bertolero

The Dirt Gardener

Q I have a bluish-green fungus-like growth on the branches of my apricot and plum trees. I’ve made two applications of copper sulfate, a week apart, but I haven’t seen any improvement. Can you recommend a treatment that will cure the trees of this problem?


A The bluish-gray-green growth is a plant called lichen. It is quite common to find it growing on trees in the Bay Area, especially near the coast and inland areas where there is a strong marine influence.


The one to three-inch bluish-gray-green patches are not a moss but a unique combination of individual alga and fungus species. The alga is a microscopic green plant that makes food for the duo.


The fungus is a bluish-gray structure that gives the pair support along with soaking up moisture from the air. Hence, tree lichen is unable to sustain itself during dry, warm conditions.


Lichens are able to make their own food with moisture and sunlight. They have no need to parasitize a host plant such as mistletoe, which will slowly kill a tree over a lengthy period. Lichens grow on the tree surface and do not penetrate any plant tissue. Instead, they make use of the trunk or limbs and branches for support.


It is often erroneously thought that the presence of the lichens indicates a declining tree. However, tree lichen will not cause any plant diseases nor will it kill a tree. The one exception is in wet tropical regions where it can be a problem. It’s more likely the lichen was there long before the tree became ill.


I’ve noticed that tree lichens do make a tree more picturesque. They add color, contrast, texture and natural beauty. It’s sort of like Spanish moss that hangs off many of the southern trees. On those overcast days, the blue-gray-green coloration is very attractive against the wet tree branches and stems.


A copper sulfate fungicide applied during the cool, wet winter months is ineffective. Instead, it’s recommended that it be applied after the rainy season has concluded; but, it will only control the fungus and not eradicate it. Tree lichen will reappear when the right conditions occur.


Note: I’ve posted a link to some images of tree lichens on my website — The link is at the bottom of the home page in the right-hand corner.


Q  We have several cymbidium orchids on our deck. I would like to divide and repot them, as they’re difficult to water. Why have I been advised not to divide them?


A Dividing and repotting cymbidium orchids affects the blooming cycle. They love to be crowded. The production of flower spikes is maximized when there is little room to grow; hence, there is little incentive to divide the plants.


Orchids can be repotted every two to three years, as the orchid soil mix will decompose. They can be repotted in the same container with new soil or in a larger pot; however, a larger container will delay the flowering cycle.


You should shake off what is left of the old soil, once the container has been removed and then repot with one of the commercial orchid soil mixes widely available.


The recommended time to repot or divide cymbidium orchids is after flowering.


Buzz Bertolero is a California Certified Nursery Professional. His web address is Mail in questions to 360 Civic Drive, Ste. “D,” Pleasant Hill, CA 94523, or send them via email to This e-mail address is being protected from spambots. You need JavaScript enabled to view it



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