Question
Six months-plus ago, I bought a Lemon Hemlock approx. one foot high, repotted it about three months ago into a 12-inch diameter pot.  I had it sitting in indirect light, and saw that the branches were becoming yellow and light brown; I thought it might be dying and placed by my west-facing window in very good light.  It seemed to be reviving after a few days.  Then this morning I noticed a bright almost-fluorescent yellow long-necked mushroom (actually a very pretty color!) approx. two inches long growing (almost overnight) just inside the outer rim of the pot.  I haven't noticed any spores in the soil, but had planned to remove some of the topsoil and replace it with new.  Is this mushroom harmful to the plant?  Hopefully the plant will survive until you reply, but I plan to remove the mushroom today and clean out the soil.  My question: Could there be any residual effects to the tree?

Answer
Hi Darlyne,

I have never heard of a "lemon hemlock" tree and could not find a single reference to one on the Internet. So I don't know what you have or who told you that is what it is.

If it is a hemlock species, then  you cannot winter it indoors because it requires sub-freezing temps to survive. If it is a lemon tree, then it must have maximum indoor light - right in front of an uncovered south facing window.

A 12-inch pot is too large for a 12" tall plant of any species. So, it was not a good idea to repot it. There is now an increased risk of root rot because of the excess soil it is now potted in. The extra soil acts like a sponge absorbing and retaining water for too long and depriving the roots of oxygen. Root rot and inadequate light are much bigger threats to your plant than the mushrooms.

Mushrooms are a type of fungus and they are harmless to your plant. They arrived when you used non-sterile potting soil. Fungus spores are so tiny they cannot be seen with the naked eye. If you want to get rid of the mushrooms, the best approach is to un-do the repotting you did by removing all the soil that you added and none of the soil from the existing rootball. Then, put the original rootball back into the original or same-sized pot. Doing this will eliminate the fungi and also the risk of root rot.

Now you understand why I often say that unnecessary repotting is the single most common cause of plant problems. Had you not repotted, you would not be here posing this question.

Let me repeat: Do NOT remove any of the soil from the original rootball in a zealous attempt to remove fungus spores. If you do that, you will damage many of the vital tiny root-hairs most folks don't even notice.

I have written a detailed article on repotting that I will email for free to you (or anyone else) who emails a request to me at [email protected]. I have also written an indoor plant care book in a PDF format that I can sell you if you contact me at my email address.

Please let me know if any of this is unclear or if you have any additional questions.

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Will Creed, Interior Landscaper
Horticultural Help, NYC

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