Q. What’s wrong with my compost pile?

This is a question we master gardeners hear often. Usually, the answer is straightforward, but occasionally we get some head-scratchers. This week I’ll cover some of the most common compost problems, what went wrong, and how to fix them.

One of the most common (and icky) issues is the wet, slimy, and stinky compost pile. The most common cause is an imbalance of “greens” and “browns.” Green material is nitrogen-rich and includes fresh grass clippings, non-dried plant material such as weeds and leaves, manure, and most kitchen waste. Brown material is carbon-rich and includes dried grass clippings, any dried plant material, straw, shredded paper, and sawdust. If there’s too much green material, the compost will tend to mat or clump tightly. 

Turning the pile and incorporating plenty of brown material will help things get back on track. This can be an unpleasant task, because you’ll have to break apart the soggy chunks of material. Once it’s done, the compost should begin heating up and the smell will dissipate.

During the rainy season, make sure the bin or pile is covered so it doesn’t get too wet from the rain.

During the hot summer months, a compost pile may dry out and become dusty. Although it won’t be stinky, this is not optimal either. The composting process needs some moisture, so you may have to water your pile. When you pick up a handful of material, it should be about as moist as a well squeezed-out sponge. If the pile has become very dry, it may take quite a bit of water to bring it back to the correct moisture level. If possible, mix in some high-nitrogen (green) material such as fresh grass clippings, steer or chicken manure. Once the compost has been rehydrated, it should heat up quickly. Ours usually reaches 160F within 24 hours. Use a compost thermometer, which has a long probe, to check the internal temperature.

Compost that is too wet or too dry will not heat up enough to kill insect eggs or deactivate weed seeds. If there are a lot of seedlings (squash and tomatoes seem to be the most common), just turn them under and they will break down. Insects and other creepy-crawlies (grubs, pill bugs, earwigs, and ants) will take up residence in a cool compost pile. Turning the pile and maintaining a proper moisture level will heat things up and the bugs will go elsewhere. If the compost is finished and there are still bugs, spread it out on a tarp in the warm sun. The bugs will crawl away to escape the heat. One summer we did this and within 15 minutes a huge flock of quail landed and devoured all the bugs. That was fun to watch!

Sometimes you’ll see unwanted animal visitors such as skunks, racoons, opossums, or rats. These guys will show up if there’s something in the compost that shouldn’t be there. Remember – don’t try to compost any meat, cheese, dog poop, or roadkill. If animals are a recurrent problem, invest in a rodent-proof compost bin and secure it when not in use.

Los Angeles County

[email protected]; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/

Orange County

[email protected]; 949-809-9760; http://mgorange.ucanr.edu/

Riverside County

[email protected]; 951-683-6491 ext. 231; https://ucanr.edu/sites/RiversideMG/

San Bernardino County

[email protected]; 909-387-2182; http://mgsb.ucanr.edu/