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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Wood chips, Mulching, Allelopathy

We've taken down some big cedars and chipped the branches. I've heard that cedar mulch can damage plants. What is your take on this? I already put it around some choice pines and some viburnums, but I could move it if need be.


Washington State University Extension horticulturist Linda Chalker-Scott has written about this very issue, and her scientific research on the subject says that cedar (both Thuja and true Cedrus) wood chips are not allelopathic (toxic) to plant tissue. Here is the article.
This author has further information on the general benefits of wood chips as mulch. Here is a newer Washington State University factsheet on the subject.

Date 2017-08-15
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Plant Answer Line Question

Keywords: Quirky, Myxomycetes, Wood chips

Please help me identify a killing substance in my garden that just appeared this year. I noticed it about a month ago, thinking it was animal barf. I cleared away the material and disposed of it along with the soil around it. A few weeks later I discovered yet another spot with this same substance. Upon closer inspection I found it had totally rotted my primrose and was continuing into the garden. It appears almost like a spreading mushroom with vents around it, hardens into something resembling cement, grayish white to an off yellow color. When I picked it up (with a sheet of plastic) it became brittle and released some sort of powder. Thinking it might be spores and could easily become airborne, I again bagged the material and kept it. I do not know how to contain it, or if it is hazardous to the rest of the garden. I have no idea where it came from but I do want to be rid of it.


What you are describing sounds very much like dog vomit slime mold, Fuligo septica. See if the links below are depicting the same thing you have observed:

Do you have wood chips or other wood-based mulch in your garden? This slime mold thrives on decaying wood. I've never heard of it harming plants, unless the plant matter is already decaying from other causes. I imagine it would be next to impossible to eradicate, unless you want to remove any woody material around your plants. It's possible that extreme heat (such as fire) might kill some of the spores, but it wouldn't be too good for your plants!

If you can tolerate it, it really is not known to devour and kill plants. Your primroses may have succumbed to something else, and the slime mold was just being opportunistic. See the following article by Kathryn Richardson, from Harvard University's Arnold Arboretum publication, Arnoldia:
"Dog vomit slime mold is motile, but moves quite slowly. It is not harmful to animals or plants and usually vanishes in a short period of time. This species and similar slime molds feed on bacteria, fungal spores, and smaller protozoa found on wood chips. Slime molds feed much like an amoeba feeds; they ingest their food and then digest it (unlike fungi, which digest and then ingest). If conditions are favorable, these slime molds will produce reproductive structures (sporangia) that produce spores. When conditions are unfavorable (loss of food, dry conditions), the plasmodium will form hard, dormant, protective structures called sclerotia. Inside the sclerotia the plasmodium will divide into cells containing up to four nuclei. When conditions become favorable each cell will form a new plasmodium. Dog vomit slime mold is primarily an aesthetic problem in mulched garden beds. It can be physically removed, but more is likely to return. So, before panicking and taking your dog to the veterinarian, take a closer look and consider that that stuff is likely just Fuligo septica working away at cleaning the mulch."

Date 2017-01-12
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Plant Answer Line Question

Keywords: Wood chips, Phytophthora

I have two 40' trees diseased with Phytophthora lateralis that I am having removed tomorrow. Can I chip the branches and spread them in my garden or will this spread the disease to other plants?


Although the following information from Washington State University Extension refers to a different species of Phytophthora, I imagine that the same precautions hold true.
"P. ramorum can be spread to other hosts through air, water, rain, soil and plant debris. People can move it via plants, plant material, soil, plant products, wood, woodchips, dirty shoes, and water. P. ramorum does best in cool, wet climates (like ours)."

A resource from Oregon State University confirms this for both commonly found species of Phytophthora fungus:

Generally, one does not need to worry about plant diseases being spread by wood chips, because "they cannot compete well with wood-decay fungi. Uncomposted plant materials can, however, carry two important diseases of woody plants: Port-Orford-cedar root rot, caused by Phytophthora lateralis, and Sudden Oak Death (Phytophthora ramorum). Many diseased Port-Orford-cedar trees are disposed of by chipping, and mulch made from these chips can spread disease to healthy plants."

Date 2017-12-09
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August 01 2017 12:36:01