Are Fungi in Wood Chips Harmful?

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Robert Pavlis

This post, Fungi in Wood Chips, was prompted by a picture and discussion on a Facebook group called Australian Native Plant Enthusiasts (ref #3). The discussion was about the harmful fungi that appeared in wood chip mulch used in children’s playgrounds. Off course they posed no real danger–but people were scared. There are a lot of misconceptions about fungi growing in the garden and this post will look at the truth about fungi in wood chips.

Fungi in Wood Chips
Fungi in Wood Chips

Fungi in Wood Chips

Where do the fungi come from? Fungi is a type of organism that is neither an animal nor a plant. They grow just about everywhere, and a lot of different types grow in the soil. Normally we don’t see them, even when we dig in the garden. The reason for this is that they are just too small for us to see them easily. Think of them as very thin long strands of material. They do not have the ability to make food like plants, so they must get their food from other sources and a favorite food source of the type of fungi we are discussing is rotting things.

The wood chips we put into the garden soon start to decompose ie they rot. Fungi find this rotting wood and start to grow like crazy. They love this new home. Before long there are so many strands of fungi in one place that we are able to see it with our naked eye. When we turn over some pieces of wood we see white cottony material.

Where did the fungi come from? Fungi grow from spores which are everywhere; in the air and in the soil. It does not take long and they will find your wood chips.

Microbe Science for Gardeners Book, by Robert Pavlis

If you take a closer look at the wood chips you will find all kinds of different fungi, in various colors. It just happens that the white ones are easier to spot.

Fungi Myths

In this post I am only looking at the fungi found in rotting wood chips.

1) Soil Fungi Kill Plants

Soil contains a lot of different fungi and I am sure some fungi in soil have the ability to harm plants. However, the fungi in wood chips live on rotting wood, not on live plants. They will not kill or even harm your plants.

Note (Nov 2014): The last sentence above came from one of the references given below, but it is not entirely correct. Current research shows that most fungi living in wood mulch will not affect plants, but some do. This is discussed in the comments below and will be discussed in more detail in a future blog post.

2) It can’t be Good for Kids

The original post started because the fungi were found in a play ground and so there was concern for kids. They saw the white fluffy stuff, called it yucky, and assumed it must be bad for you.

Will it harm humans? Fungi are a type of mushroom and we all know that eating the wrong kind of mushroom can hurt us. But who is going to chomp down on a bunch of wood chips and suck out the fungi? I have not seen any evidence that the fungi cause a health.

3) This is Mycorrhizal Fungi

People are starting to become aware of mycorrhizal fungi and now every bit of white fluff in the soil is called mycorrhizal fungi. It is not likely that the white stuff you see in wood chips is mycorrhizal fungi. The fungi on rotting wood is a type that specializes in decomposing wood–it is a different type of fungi. Mycorrhizal fungi live deeper in the soil.

Benefits of Fungi

Ok, so the fungi will not hurt us or our plants, what good is it? Fungi decompose wood chips along with bacteria. As they decompose the wood they convert it to nutrients and put that into the soil, which benefit the plants. The decomposing process also improves soil structure, something most garden soils can benefit from.

The white strands you see is a natural process that is extremely important for soil and our plants. The fungi are native organisms and we should marvel at their efficiency and treat them with respect–leave them alone so they can help you garden.


1) The Myth of Pathogenic Wood Chips:

2) Fungi in Mulches and Compost:

3) Concerns about Fungi in wood Chips:

4) Photo Source: zen Sutherland


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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

28 thoughts on “Are Fungi in Wood Chips Harmful?”

  1. My fungi looks exactly as the picture in this article and IT IS killing my plants. The little spore things in the center are climbing or blowing or however they getting up the plants and staying on my basil, Wild onions that are in a pot and my strawberries to the point of picking bad leaves of EVERY day. I don’t want these removable tiny round center things on my edible plants. Now what?????

  2. I have a big layer of the wood chip fungus on my begonias! I don’t know what to do, I use a mini rake to pull them off. But they keep coming every 2 hours!

  3. I built my first garden last year and this fungi attacked the roots of my cilantro and killed it. It started to pop up all over the rest of the garden and made me nervous it was going to kill my other plants. I know it’s natural and healthy for the garden to have this but I would really rather not worry about any of my plants dying this year. Any recommendations?

  4. Hey Robert, what do you think of tossing sawdust on topsoil as a mulch? I guess fungus would grow quicker but I dont know if theres any downside compared to wood chips.

  5. What type of fungus IS this in the pic? Its so odd looking..a friend in NJ has the exact same type and we are trying to find the name of it…?

  6. I live in India. I have observed if I leave wood chips in my garden, it’s attacked by termites rather than fungi. In no time, I would see sand dunes kind of structure building up on walls. Are termites good for plant life or are they as pernicious to them as they are to home furniture?

    • I am sure there are many kinds of termites. The ones we have in North America do not seem to be attracted to wood chips. They do like dark wet places, so if termites are a problem it is a good idea to keep the chips a couple of feet away from the house. Termites don’t eat or damage plants as far as I know.

  7. But who’s going to munch on a bunch of wood chips and suck the fungi out of them?? Kids….kids do! I’ve seen many toddlers put wood chips in their mouths and suck/chew on them. You get them to spit it out and the second you let them return to playing they go straight back to gnawing on the wood chips. So you didn’t really answer the question on if it is actually dangerous for children since you just assume they don’t ingest it.

    • I think I did answer the question when i said “Will it harm humans? Fungi are a type of mushroom and we all know that eating the wrong kind of mushroom can hurt us. But who is going to chomp down on a bunch of wood chips and suck out the fungi? I have not seen any evidence that the fungi cause a health.”

  8. Hi, like the article. Just wanted to clear up a couple of points.

    Nitrogen lock up is the result of bacterial decomposition of wood and so you’ll be fine if you don’t dig the chips in.

    If the pile has been left to cool but seems to steam when you dig in to it this is a spore cloud and will cause lung infections (have done this myself and took a long time to cure).



    • You are absolutely correct about the nitrogen lock up. It only occurs in a few mm (fraction of an inch) around the wood chip.

      Sitting wood chip piles as well as compost piles will grow all kinds of things including fungi. Fungi will produce spores and in large amounts it looks much like smoke, as you point out. This can be a medical hazard for some people and with enough exposure you can be infected. It is not a common problem, nor is it usually severe or fatal. Once the wood chips are spread on the ground they generally do not produce enough spores to be a problem.

      Fungi spores are everywhere and we breath them in all the time.

  9. According to the fruit tree handbook by ben pike, page 135, he mentions leaving wood in the garden can lead to honey fungas. (Mushroom apperance). I put decaying bark as a mulch 3 weeks on some newly planted fruit trees and am now noticing this honey fungas. Who is right? Should I remove the bark??

  10. Can’t believe anyone would be so idiotic to think it might be harmful
    I love how a heap of chipped wood heats up and smells absolutely wonderful (don’t know if there is ever a risk of fire but it gets really hot) I just love the smell!
    Interesting how when used as a mulch you can get a temporary depletion of nitrogen when the hyphae explore down a few inches – easily corrected of course with a little fertiliser or if not inclined to use fertiliser do nothing!
    I think in getting your point over that most fungi are harmless or beneficial you neglect the fact that some fungi do cause plant disease and at the very least contribute to plant death.

    • I’ve seen several reports about piles of wood chips combusting on their own. The piles are usually fairly high, over 4 feet tall. Anything under 4 feet tall (120 cm) seems to be safe from fire.

      the studies I’ve seen indicate that nitrogen depletion only takes place at the interface with soil–a few mm at most. This has been explained by the fact that bacteria are responsible for most of the composting and use of nitrogen. You bring up an interesting point–fungi would reach deeper into the soil and in theory they would remove nitrogen from lower levels. That is not what is seen in field trials. If you have references showing different results, I’d be interested in them.

      You are correct fungi other than the ones being discussed in this post can cause plant problems–I thought I would leave that for a future post.


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