I was recently planting an ‘instant garden’ - dozens of plants of all types and sizes to make a formerly empty area instantly full and lush - and as I and my garden colleagues were digging compost into the new bed we smelled the most awful, rotten smell. We sniffed high and low and discovered to our dismay that the smell was coming from the compost! It was truly an atrocious smell and we were quite concerned about putting such foul material into our new garden bed. We examined the compost bags. They read ‘no poo,‘ proclaiming that the product was derived purely from ‘yard waste.‘ Well, it certainly smelled like ‘poo’ and rather fresh ‘poo’ at that.
Compost should smell earthy, like good soil. It’s made up of organic matter and a mixture of microbes that digest the organic matter to make nutrients available to plants. The microbes have certain requirements to thrive: not too hot or too cold (70°F - 140°F); moist but not soggy; food in the form of organic matter; and oxygen from the air.
So, what was wrong with our compost? To find out, I referred to the compost troubleshooting information in CSU Extension Garden Notes. An ammonia smell would indicate an imbalance in nitrogen and carbon. But that wasn’t the smell we experienced. We smelled a rotten odor and I learned that meant our compost had been deprived of oxygen, somehow. We asked some questions and it turned out that our bags of compost had been stored in very wet conditions for several days before we were ready to use them. The excess moisture had pushed out the air pockets and created anaerobic conditions for our microbes. The microbes weren’t getting one of their basic needs: oxygen. And they were letting us know by emitting a foul odor.
Now that we understood the cause of the odor, the solution was simple: let the compost dry out a bit (to the proper moisture level) and incorporate into it lots of air (i.e. oxygen). Luckily, our plan to incorporate the compost into our new garden bed fit the bill. We simply mixed the compost thoroughly into the soil, making sure to fluff the soil very well and incorporate plenty of air. Since our compost had been too wet, we let the bed dry out for a few days to restore the proper moisture level. When we returned several days later, the smell was gone. The compost had dried out to the proper moisture range and had received enough oxygen to restore the balance of microbes. We were lucky that our particular problem had a simple solution.
This mis-adventure taught me that we must take care of our compost as if it is alive - because it is! Compost needs moderate temperatures, moderate moisture and air to keep it healthy until it’s time to use it. And I also learned how important it is to have a reliable resource in the CSU Garden Notes, which gave us the precise diagnosis and corrective steps, so we were able to solve the problem quickly and efficiently. And I’m looking forward to our ‘instant garden’ having a healthy and beautiful future!