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Composting in a Sack; When is it Finished?


March 8, 2021

Zipcode: 87144. It’s my first time composting and have a couple questions. I’m using a compost sack 100 gallon by Smartpots which I started late August last year.

I started with a bag of organic compost, added leaves, kitchen scraps mostly fruits and vegetables glass clippings, shredded paper.

I have been just adding each weekend and still halfway full. I guess this is cold composting?

1. Should I continue adding materials until it reaches to 100 gallon?

2. When can I expect for it to be all ready to use in my garden.

3. I have been folding the sack to close it. Should I leave it open?

Thank you!


Answer by JZ: Your question will be received by a few of my colleagues who may also respond.  Here are my thoughts.

Great to hear that you are composting.  Yes, you are cold composting.

What went into the sack first will decompose first, so your finished product will be at the bottom of the sack. The finished product will look like chocolate cakes crumbs, should have a pleasant earthy scent.

So here is one way to get to the finished product at the bottom of bag.  Spread out a tarp, then dump the contents on the tarp. Separate out what has not decomposed, then put it back into the bag and continue the process. Finished compost may be added to your garden soil at any time. Another way is to get down to the bottom with a hand scoop and remove the finished portion.

Sure you could continue to add organics, especially after you have harvested that which is already decomposed, by doing that you make space for more additions.

This method, if moisture is maintained will produce a finished product in 6-12 months.  The process slows some in the cold months, but will pick up come spring. So, yes you should continue to fold the top as this will reduce evaporation of moisture from the bag.

Consider adding some coarse materials as you build in the bag – finger size sticks, twigs, pine cones. This will decrease compaction of organics and help with convective air flow. This is described on page 5 & 6 of this brochure: ‎

Hope that this is helpful.  Let us know if you have questions.

From original questioner: This is very helpful. I’m learning a lot since we moved here from CA 3 years ago, learning the climate here in relation to planting zones, composting, etc.

I had to turn it last weekend, it felt the side close to the bottom was dry. Maybe I will dump the contents next month and see.

Is it okay to add Blood Meal? Someone gave me a bag.

Answer by JZ: Blood meal would be a source of nitrogen (green) you could blend small amounts with browns eg. used paper products, brown leaves. Maintaining moisture in composting setup is the challenge here in the high desert.  Keep up.

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