Bay Area gardening: What to do about moldy compost in Walnut Creek

QI got free compost from the city of Walnut Creek about two months ago. I had it in the 33-gallon garbage cans with the lid on in the garage.

The top of the compost was moldy, so I scooped about 3 inches down and threw it away. Can I still use the rest of the compost? Is there anything I need to do with it before

I use it if it is still salvageable?

— Linda Hiatt,

Walnut Creek

A

Mold on compost is to be expected and is part of the decomposition process that turns green waste into garden gold.

The mold probably formed in the plastic containers because the compost heats up while decomposing, and that causes some condensation, which causes the mold.

In most cases, there is nothing to worry about. Just make sure to mix it well with the other compost or in the soil where you’re spreading it.

You’ll generally find three colors of mold on your compost. White mold is the most common and usually is found on compost that has a lot of wood in it. It’s usually a good sign that all the microbes and such are doing their jobs.

Green mold also is common, and it can be a sign that your compost had a lot of food products in it.

Pink, which sometimes looks orange, isn’t as good to find. It’s usually an indication that the compost has some cleaning products in it, and those can kill the organisms that are working to break down the material into good compost. The cleaner might have been in the compost when you got it, or could have been in the receptacle if you used soapy water to clean the bins before you put the compost in. Either way, it’s not the best thing you could put on your garden, so scrape the mold off and throw it away.

You should always wear a mask and gloves when handling moldy things, especially if you have an allergy or are sensitive to mold spores. Otherwise, you’re good to go.