Compost Post Going to stop adding to this bin (50 gallons) which is just over half full. This will give it 4 weeks to finish breaking down before we need to use it. I keep the compost bin in the greenhouse in the winter so it can start breaking down. It is still in the greenhouse as we are still getting below freezing at night but I will be moving it out shortly. For the next month I will put our compost in second bin.