What have you added in the way of carbons? You need a good ratio of both items to get it cooking. Nitrogens alone will get hot briefly but it doesn't last or reach nearly the same temps plus it gets stinky. ;) So my guess is that your mix is carbon-poor.

Also, how wet is it? Too wet cools off. Should be damp/moist, not wet.

Dave

Just so we are on the same page here, by carbons, do you mean wood chips/sawdust/etc.?

Yes, so-called "browns". Although fresh sawdust and wood chips still have a lot of nitrogen in them. Any straw, paper, cardboard, dead leaves, etc.? You need roughly 3x as much carbon as nitrogens to get it cooking.

Dave

Compost in a tumbler reaching 120 degrees is pretty good and is not anything to worry about. Current research has shown that high temperatures are not what kills "weed" seeds during the composting process but the length of time composting took. I doubt a tumbler has enough volume of material to get much hotter than the 120 degrees you do have.

Do you know of any documentation sources for the current research you mentioned on composting? This is a community operation, so I will need to convince my neighbors that it is safe to put bindweed (for example) in the composter.

I read similar info that the rotting process kills seeds as well as the heat does. I read so much that I'm not sure of the source, but I THINK it was in 'Weeds: Control without Poisons' by Charles Walters (Acres U.S.A). See the link below and type 'weeds' in their search box.

Since you mention bindweed, it is one of the few things that I refuse to put into my compost pile. It is one of the few things that I place in a plastic bag and send to the landfill. The plant is probably very compostable, but the seeds are difficult to kill with lower compost temperatures, and they are resistant to rotting, and can stay in the soil for many years, defying heat, cold, microbes.

I know that many people say that everything is compostable, and under ideal circumstances, probably are. But my composting tends to be hit-or-miss, and I still get some weeds. I would hate to have something like bindweed be the one to 'get away'.

Generally speaking, if I run across something that I definitely would not want to let loose on my property, I put it in the black plastic bag that lines a particular container, and it goes to the dump. Bindweed, ivy, poison hemlock, and nightshade. If there are no flowers, I'll compost the tops and cut/twist/rip off the roots and put the roots in the bag.

For a community garden, I would tend to err on the side of caution.

Sue

Here is a link that might be useful: Acres U.S.A., A Voice for Eco-Agriculture