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Why Aren’t My Compost Piles Breaking Down?

by Marla
(Napa Valley, CA)

We have 10-12 acres of landscaping on an estate in Napa Valley, California. We generate sizable portions of leaves, horse manure, grass cuttings, and small amounts of food scraps. We have 3 piles that are 10 feet tall by 20 feet wide, which are not deteriorating very quickly. What is your recommendation on how best to facilitate the more rapid deterioration of the organic materials to be turned into compost?

We have tractor end loaders available to move the materials. Do we need to aerate these piles? Should we inoculate them and water them as well? We just need help with composting piles and how to maintain them with the least amount of manpower.

Thank you very much.

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Sep 27, 2011
Back to Compost Fundamentals
by: Compost Junkie Dave

Wonderful question Marla.

In order to answer it, we need to get back to the fundamentals of what it takes to make a great compost pile. There are three key elements…

1. The Ingredients
2. Oxygen
3. Moisture

By the sounds of it, you’ve got the first two bang on. The only suggestion I’d have would be to potentially decrease the size of the materials included in your piles and make sure they’re mixed well. If you’ve got a loader, mixing shouldn’t be difficult. If there are a lot of larger materials present, which it doesn’t sound like there are, I’d say you may want to consider shredding them. The smaller the initial size of the material going into your compost, the faster it will be broken down by the microbes.

Now, we come to the most likely culprit…your moisture levels. Do the piles get rained on? When you reach in, grab a handful of the material, and squeeze it, does any water come out? It should. Not too much, but a little bit of compost “juice” is a good thing. If this isn’t the case, your solution is an easy one…as you mix the piles, add a significant amount of water to them. Please refer to our “hand squeeze-test” on our How to Compost page to get the desirable moisture levels. Also, you’ll want to make sure these moisture levels are maintained during the composting process.

One final tip to get your compost fires blazing…Try adding 1 quart/liter of black-strap molasses to each of your piles. The simple sugars in the molasses, as well as the micronutrients, will provide your microbes with instant food while the rest of your compost ingredients begin to breakdown. You can either dilute the molasses and apply it with a sprayer, or you can just pour the molasses onto the piles as you mix and water them.

Please let us know how this works.

Happy Composting!


Sep 30, 2011
SIze of piles
by: Elizabeth

I disagree with the previous comment about adequate oxygen. Unless you are turning your piles frequently, there will be little oxygen at the bottom of a 10 foot pile. A better measurement would be four feet high and 10 feet wide.
Turning will also allow you to incorporate moisture if needed (I agree that it probably is.

A last comment on your mix: the ingredients are good, but the proportions may be off. I suspect that leaves may be the largest single ingredient. If so, they piles will break down slowly as they are carbon heavy. You would do better in the future to pile leaves separately and let them do their own thing, using only enough in your compost piles to balance the nitrogen-rich manure and grass clippings.

Good luck.

Sep 30, 2011
by: Compost Junkie Dave

Thanks for your comments Elizabeth.

I must admit that I am wrong on this one. I’d forgotten to consider the shear size of these piles when answering Marla’s question.

Marla, please follow Elizabeth’s advice, in addition to my original advice, re adjusting the size of your piles, especially if you’re not going to have the time to be turning them.

Re the ingredients, Elizabeth and I are both working off assumptions, so it’s best if Marla is able to clarify the approximate proportions of ingredients within her piles.

Looking forward to hearing from you Marla.


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