How to Get Compost in a Tumbler Bin to Heat Up

Answer by JH: Steve, wow, I'm impressed by such a serious approach to composting. The following response can be summarized quickly as this: If you are hoping to have a hot compost operation which is how I read your question, then the pile must heat up to 150 degrees. To achieve this, sufficient nitrogen is required. The easy rule of thumb is to combine 2 parts carbon to 1 part nitrogen by weight. It also may be necessary to keep the contents of your tumbler moistened more than they have been - the pile should be 50% moisture - similar to wet coffee grounds, damp but not dripping  - and not just at the beginning but at all times. If your tumbler has numerous holes or vents, there may be too much evaporation happening in which case you simply need to cover the openings - i.e. with caulk, duct tape, etc. - to keep a constant moisture level in the tumbler. If you still are not successful in achieving 150 degrees within 48 hrs or so, then it is some combination of these things - the 2:1 C:N ratio, the moisture level, or airflow. If the pile does heat up sufficiently and then drops under 150, simply add nitrogen, maintain the moisture level and it should reach the desired temp again.

Some other comments about the ingredients used -- unless you got the ammonium sulfate for free, it is an expensive way to add nitrogen to a compost operation. What I can find on this substance is that it is only 21% nitrogen. Free coffee grounds, grass clippings or other sources would be better options to increase the nitrogen. Also, both the mushroom compost and worm castings are already decomposed and ready for use as a soil amendment so are not functional additions. However, the mushroom compost may still be too hot, too high in salt to use on many plants and if so, must cure before use as a soil amendment. The compost activator isn't necessary if you have the right C:N mix. But it won't hurt although if there is insufficient nitrogen then the activator can't fully activate. Bone meal is high in phosphorous and is used as a soil amendment for plants needing this nutrient. As such it isn't useful in compost.

Finally, if the mixture has a tendency to form into dry clumps, this will be prevented by not only a proper and consistent moisture level but also by including bulking material to keep airflow throughout the ingredients. Pine cones, pine needles, wood chips, twigs, corncobs, and such will do the trick.

Feel free to visit our website, nmcomposters.org where we have a variety of resource materials including a pamphlet on desert composting. We also offer a variety of classes throughout the year and a schedule of these classes is available at the site.

Don't be discouraged - compost happens. A little tweaking will have your pile heating up.

Answer by JZ: 

1. The minimum size for a hot composting operation is a cubic yard.  My  calculation is that you have ( hopefully correct) 80 gallons = 0.46 cubic yard.  So most likely there is not enough mass/volume to insulate the heat that is developing.  So you may have to increase the volume/mass of ingredients.

2. Coarse bulking material should be added to the mix eg. sticks, twigs, pine cones, corn cobs.

This is recalcitrant carbon which creates “ fluff “ in the operations thus avoiding compaction of wet organics, then provide for air penetration throughout the ingredients.  You could add 5 -10 gallons of bulking, then mix in with the greens & browns.  Bulking material need not be counted in the final C:N ratio of the total mix. Since it decomposes slowly, it will be screened-out when you harvest your finished compost., then may be re-used in next batch

3.  The total mix of ingredients ideally should have a C:N ratio of 25 : 1.  You can get within the

a range of this ratio by adding one part nitrogenous material to every 2 parts carbonaceous material, That is 2:1 by weight.  If you wish to be more scientific you may consult a composting mix calculator.

4. Ammonium sulfate - this is an inorganic salt,  it is a nitrogen source, but because it is a salt it is not “kind” to decomposing microorganisms.  Personally I would not use it.  The other organic nitrogen sources you added are fine: kitchen scrap, coffee, manures, bone & blood meal. Consider also alfalfa meal/ pellets.

5. Once you have increased the volume of your batch and added coarse bulking material, be sure to maintain 50% moisture at all times.   This is similar to the moisture level of brewed coffee grounds.

6.  You may have to reset-up your operation so that you have a cubic yard.  The tumbler could be used as a passive static system (cold), which takes longer but produces fine humus.

7. You are welcome to visit our hot composting bin set-up in North parking lot of the BernCo Extension office.  They are currently static - not generating appreciable test.

8. Read our brochure about desert composting both hot and cold.

9. You are welcome to attend any of our free classes. 

Let us know if this has been helpful to you and if you have more questions.

Response from Questioner: Thank you everyone for your quick response and informative ideas!!! I will start your recommendations this week with the weather week forecast in the mid 50's. I'll give a follow up on  how things go.

Again, THANKS TO EVERYONE!

Answer by JZ: Great work.  Once again is your total volume a cubic yard ?  3’x3’x3' . My guess is that you have enough nitrogen.   Turning a tumbler causes the wet organics to form balls.  Suggest you break up the balls, then not tumble it.  Then see what happens. Purchased steer manure often comes from confined animal feed lots (CAFO’s ) - will likely contain some salt.  If you could get manure locally, would be better.