Compost not hot

I started with a compost tumbler last November.  I've been adding stuff all winter, and it has yet to get warm.  Most of what I add is kitchen scraps: vegetables, egg shells, and coffee grounds.  I fill up about a gallon a week with these scraps, and dump them in the composter.  I have a pile of mulched leaves and grass from the mowing last summer that I keep next to the composter.  Every time I dump in the kitchen scraps I add a handful or two of the leaf/dead grass material.  I first filled the left side of the two-bin composter, then started to fill the other side and let the first side cook.  But very soon I realized there wasn't enough material in the left bin, because it compacted down after a while, so I began adding to it again until it was fuller, then stopped and filled the right side.  Both sides were about full, but the material doesn't seem to be doing anything; there has never been any heat or even warmth in it.  I can't recognize individual items anymore, except eggshells, so I guess it's breaking down some, but how long should it take? Will it eventually compost even without heat? Should I do something different?  I'm not sure how to "end" filling a bin, because we keep making scraps and I have to put them somewhere, so I keep adding them.  But five months later I have no useable compost. . .at least it doesn't smell.

It takes a mass of moist material to generate a hot compost. A gazillion little microbes working away producing heat from their activity. Hot composting is good in that weed seeds and disease and insects are killed. Hot composting is around 140-160*F.

A small mass can't build up heat. But it can compost over time as you are finding. Once a side has been filled, don't keep adding more material. Yes, the volume has shrunk in half but that is just the process. The clock starts all over again each time new material is added. It may be that you actually produce an unusual amount of kitchen waste and could benefit with a compost cage, like 3'x3'x3', or more (and larger) tumblers.

It is recommended that home compost be sifted with a 1/4" hardware cloth screen. The larger, not-composted material can go back into the composter with more material for a second round of composting. PS Even some commercially bagged composts have a lot a un-composted material and benefit from screening.

Thank you, Sanderson! That makes a lot of sense, and assuages my doubts. Perhaps I do have useable compost in one side; I'll sift it and add the big stuff back.  I'm not ready to set up a bigger, unmovable bin so I'll just keep on with "cold" composting for now.  I didn't realize the heat is a function of mass. 

However, I do realize I'll never create enough compost on my own for mixing Mel's Mix! But I should have enough to add to my existing boxes when replanting. Good enough.

Guinevere wrote: I'm not ready to set up a bigger, unmovable bin so I'll just keep on with "cold" composting for now.  I didn't realize the heat is a function of mass.

Compost tumblers can and do make good compost at a fairly high temperature without a large volume. I have two Jora JK-270 twin compost tumblers which have a volume of approximately 35 gallons per side -- that is equivalent to an average galvanized garbage can -- and each side easily heats to 140ºF to 160ºF after filling with well balanced C:N material.

The primary key to composting, especially with hot composting in a compost tumbler, is the correct balance of the greens to the browns. If the compost is not heating, it usually means too much brown and not enough green. But, if the compost is "rotting" and has a foul smell it usually means to much green and not enough brown.

Do you have a compost thermometer? They are very helpful in knowing exactly what is happening in your compost.

Composting is a life-long learning experience. Robert Rodale got me started with composting in the early 1970's, and I have been doing it every year since. But, I'm still learning what works and what doesn't work with composting.

When I check the condition of a newly filled section of the compost tumbler, I find it hot and in need of turning.

OhioGardener wrote:Compost tumblers can and do make good compost at a fairly high temperature without a large volume. I have two Jora JK-270 twin compost tumblers which have a volume of approximately 35 gallons per side -- that is equivalent to an average galvanized garbage can -- and each side easily heats to 140ºF to 160ºF after filling with well balanced C:N material.

You are correct.  I had an 80-gallon tumbler and would fill it to the top with various browns and greens and water and it would take off.  You fill the units in one sitting, correct?  That will allow heat to build up.  Adding material over time doesn't seem to allow for "lift off".

Do you have a compost thermometer? They are very helpful in knowing exactly what is happening in your compost.

 Yes, invaluable for serious composters.

Composting is a life-long learning experience. Robert Rodale got me started with composting in the early 1970's, and I have been doing it every year since. But, I'm still learning what works and what doesn't work with composting.

When I check the condition of a newly filled section of the compost tumbler, I find it hot and in need of turning.

Nice!

sanderson wrote:

OhioGardener wrote:Compost tumblers can and do make good compost at a fairly high temperature without a large volume. I have two Jora JK-270 twin compost tumblers which have a volume of approximately 35 gallons per side -- that is equivalent to an average galvanized garbage can -- and each side easily heats to 140ºF to 160ºF after filling with well balanced C:N material.

You are correct.  I had an 80-gallon tumbler and would fill it to the top with various browns and greens and water and it would take off.  You fill the units in one sitting, correct?  That will allow heat to build up. Adding material over time doesn't seem to allow for "lift off".

Yes, and no. Sections where I add buckets full of juice bar pulp, coffee grounds, and pine pellets are completely filled at once. These sections immediately begin the heating process and quickly compost down. Usually within two days of filling that section the thermometer will show a temp of 120ºF to 140ºF.  These section of the tumbler usually are completely composted in about one month.

But, the section of the compost tumbler where I add the home kitchen scraps is gradually filled as daily scraps are added. I periodically also add some pine pellets to balance the C:N ratio. During this prolonged period of time it will do some "cold composting", but will not heat up a above maybe 90ºF to 100ºF.  Once the section is totally filled it is left to begin final composting. At this time it will begin heating up to complete the hot composting process. I monitor the temperature every day or two and turn it when necessary. These sections of the tumbler take longer to compost than the ones that are completely filled at once

Note: I only use the compost tumblers for pulp, vegetable scraps, etc., and have a 3-bay compost bin that I use for all cold composting things such as plant trimmings, leaves, grass clippings, etc..

OhioGardener wrote:But, the section of the compost tumbler where I add the home kitchen scraps is gradually filled as daily scraps are added. I periodically also add some pine pellets to balance the C:N ratio. During this prolonged period of time it will do some "cold composting", but will not heat up a above maybe 90ºF to 100ºF.  Once the section is totally filled it is left to begin final composting. At this time it will begin heating up to complete the hot composting process. I monitor the temperature every day or two and turn it when necessary. These sections of the tumbler take longer to compost than the ones that are completely filled at once

Probably this is what's happening with mine, since I keep adding.  Trouble is, the bin never really seems "full;" there's always room to add another bucket of scraps, so I think I keep the compost in the cold composting phase.  

I have to look up the proper ratio of green to brown, but I'm not really into doing a bunch of calculations every time I add material.  I tend to add two double handsful of leaves/grass (brown) for every bucket of kitchen scraps (green), and call it a day.  Maybe this is too much brown? Hard to know, but my material never gets smelly and slimy, so that's gotta be a good sign. 

I don't have a "composting" thermometer, but I have a digital temperature probe that works.  One side has a max of 64° and the other registers various temps in the 70's and 80's.  The colder side I am going to sift, and then I'll add the large material into the rest of the current batch, then stop adding to that side.  I'll see if it heats up when there's more mass undisturbed.