Various types of rotating compost tumblers can be found on the market (such as the Back Porch Compost Tumbler, shown). Some rotate horizontally on a spit, others turn vertically on a spit or end-over-end. Some are huge orbs that roll along the ground, while others rotate on a base. To reach 140 degrees Fahrenheit or more, your organic waste should have mass of 3’ x 3’ x 3’ (27 cubic feet). Many commercial tumblers are smaller than that, so should not be expected to heat as high as 140 degrees.
Choosing a Location
Tumblers heat better when they receive direct sun for as much of the day as possible. Solar heat can be a key factor in heating a batch. Make sure there is plenty of space around the container for it to turn freely. If you have a compost tumbler on a spit, it will be too heavy to move once the batch has been loaded, so locate the tumbler where you want it for the duration of your batch.
If you expect a freeze during the duration of your hot batch process, put your tumbler in a protected area, but not in a wooden structure. If materials inside the tumbler are sufficiently moist during a freeze, contents may congeal into a large block of compost/ice that will be stuck inside the tumbler until the weather warms enough for it to thaw.
Collecting and Preparing Organic Waste
Collect enough organic materials to fill your tumbler 2/3 to 5/8 full. If you fill it more than 5/8 full, the materials inside will not be able to mix well when tumbling. About half of wastes by volume should be nitrogen, with the balance being carbon. (Since the tumbler is enclosed, you can experiment with a bit higher proportion of nitrogens than in a pile.) If you have a choice of nitrogens, choose those that naturally hold water well. For instance, manure and coffee grounds would be a better option than grass clippings.
Materials should be ground or chopped, mixed and moistened before being placed in the tumbler. It is good to have a variety of sizes and shapes in the wastes, but no overly-large pieces like limbs that could block content movements. Dampness should be that of a wrung-out sponge. Depending on your materials, you may or may not need to add water. For instance, if you are using fresh manure and sawdust, mixing may result in that moisture level. However, if you are using grass clippings and leaves, you could run a mulching mower over both types of material to chop and mix. Then soak the mixture in a wheelbarrow full of water to dampen them.
Place materials inside the tumbler and close.
Turning Your Compost Tumbler
Turn the tumbler as recommended by the instructions for your tumbler system. If that doesn’t work well for you, try turning more often and/or less often.
I find that turning my hot batch once a day works best for me, but you may have different results depending on your environment and the types of materials you typically use. Turning the unit too often can disturb decomposers and slow decomposition, while not turning often enough may create anaerobic bacteria conditions. Start with the turning recommendation made by your unit’s manufacturer, then experiment with more and less frequency to see what works best for you.
Check the contents of your tumbler regularly to ensure they are not drying out or clumping. Add water at first signs of dryness and untangle matted clumps. If you see compacted balls of waste materials, take them out and pull them apart. If contents of your hot batch get excessively dry, remove contents of tumbler, soak them in a wheelbarrow of water overnight, and replace.
Mary Tynes, Master Composter, www.mastercomposter.com
Image: Back Porch Compost Tumbler