Mushroom compost - Ask Extension
I bought some spent mushroom compost from a local bark, soil and rock center. I don't know how long it's been aged. I've been reading online that mush...
Knowledgebase
Mushroom compost #870158
Asked May 26, 2024, 1:43 PM EDT
I bought some spent mushroom compost from a local bark, soil and rock center. I don't know how long it's been aged. I've been reading online that mushroom compost is very alkaline. I had wanted to use it as a top dressing on my flower and shrub beds but now I'm not sure if it's a good idea. Should I mix something with it to lower the pH? Should I wait and let it age more? I have 3 yards and would like to make sure it won't harm my shrubs. I think it might be ok mixed in the native soil for my annuals. What do you recommend?
Benton County Oregon
Expert Response
The alkalinity of mushroom compost comes from the presence of calcium carbonate. While some plants will not appreciate the higher pH (blueberry, fuchsia, ferns, ...), it should not cause problems with shrubs, trees and perennials not considered acid-loving. You might begin with a modest 1/2" surface application.
Yes, mixing it into the soil should moderate this effect. You could have the compost tested for pH. Only send a sample to a lab that indicates that it tests compost. Find certified laboratories testing compost here:
Yes, mixing it into the soil should moderate this effect. You could have the compost tested for pH. Only send a sample to a lab that indicates that it tests compost. Find certified laboratories testing compost here:
U.S. Composting Council Seal of Testing Assurance Certified Laboratories https://www.compostingcouncil.org/page/CertifiedLabs
