Is this mold and if so is it a problem for my garden?

Question: I bought a load of compost from a local company. It didn't seem to have completed the compost process. I spread it on my garden and a few days later what looks like mold appeared (see photos). Is it mold and  should I be concerned?

responder: Donnetta Wilhelm Colorado Master Gardener  Replied July 06, 2023, 3:55 PM EDT
response: It would be helpful to know where you purchased this from and have the company provide you with the breakdown of what is in it. Is it plant-based, manure-based, biosolids (sewage sludge), etc.? Hopefully, you asked the company what the content of the compost mixture was which would help to better identify the substance.   These types of discolorations are generally fungi, or mycelium (the strands of fungus) that occur as plant material continues to break down and decompose. Fungi and bacteria play a very important role in soil health. What may 'look bad' doesn't necessarily mean that it is.  This could also be salts that are leaching. Most manures used in compost can be high in salt, which can leach through the soil.  It 'may' be a mold if the layer is exceptionally wet, but from the photos, it does not appear to be wet. There seems to be a lot of woody chunks in this mixture that may be breaking down or getting moldy if exceptionally wet.  If this is of major concern for the consumption of vegetable garden-to-table foods, you can submit a sample to the soil testing lab at CSU. You will need to let them know what you want it test for, including salt content. https://agsci.colostate.edu/soiltestinglab/  A couple of observations from your photo. 1) There are a lot of large wood chunks in the photo. Are you certain you purchased ‘compost’ and not ‘mulch’? 2) It is difficult to tell from the photo, but it looks like the compost is an extremely thick layer on top of the existing soil. Compost used as a soil amendment is good, but it needs to be turned into the soil. If you are using the compost as a mulch, top-dressing planting beds annually with only 1-inch of compost provides plants with a balanced source of nutrients.  Here are some CSU Fact Sheets on using soil amendments and mulches: https://extension.colostate.edu/topic-areas/yard-garden/choosing-a-soil-amendment/ https://cmg.extension.colostate.edu/Gardennotes/241.pdf https://landscapeforlife.colostate.edu/use-mulch/

responder: The Question Asker Replied July 07, 2023, 10:34 AM EDT
response: Thanks so much for your detailed reply. I wanted to answer the questions that you had.  I purchased the compost from A1 Organics in Sheridan, Colorado. It was billed as a green  compost with no animal manure. It was still really warm which made me wonder how long the compost had been aged. I wrote A1 Organics asking about their compost aging process but they haven't responded. I am using the Charles Dowding "no dig" method in my garden which calls for a top layer of compost.I have had great luck with this method using my own compost. Have only recently started using A1 as a compost source. I do have questions about the industrial scale of composting. Any suggestions about other sources for compost would be welcomed. Thanks again for your feedback!!!

responder: Donnetta Wilhelm Colorado Master Gardener  Replied July 07, 2023, 6:39 PM EDT
response: As Master Gardeners, we can't speak to the industrial scale of composting, nor can we speak to any company's compost aging process. I would wait for a response from your source, and hopefully that will answer some of your questions.  My only concern about using any no-dig method is if you don't fully know the contents of the elements or the process used to get that product, it may not be the best for your plants. Trusting outside sources can be tricky, speaking from experience. Soil tests are good for this very reason, so you know what you are getting.  There is a lot of misinformation about composts and mulches and gardening techniques. The University of Washington amasses a list of what they call 'myths' and have published those papers. There are several articles on composts, mulches, organic matter and soil amendments that might be of some interest to you. https://puyallup.wsu.edu/lcs/  Finally, we don't have lists for sources of compost or other yard materials. Denver Urban Gardens (DUG) has a Master Composter program that teaches on compost biology and microbiology, composting processes and procedures, field trips, guest lectures, and a in-depth look at the city-wide compost demonstration site. Perhaps their instructors might be able to give you better insight to your questions, or for $75 you can take the program. https://dug.org/master-composter/

responder: The Question Asker Replied July 07, 2023, 11:02 PM EDT
response: Thanks so much for your in-depth coverage. I really appreciate your assistance. On Fri, Jul 7, 2023 at 4:39 PM Ask Extension <<personal data hidden>> wrote: