Tony O’Neill, expert gardener and best-selling author of the famous “Simplify Vegetable Gardening,” “Composting Masterclass,” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify gardening. His mission? Helping you cultivate a thriving garden. More on Tony O’Neill
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Tumblers are an alternative to open hot composting piles, following a similar process and needing the same materials and elements. Adding a balance of brown (carbon) and green (nitrogen) materials at a 30:1 ratio and keeping the mix damp and aerated, tumblers can make quality compost.
Effective Composting Principles
Several factors help transform organic waste into soil-beneficial humus. Below is a list of factors that will help you create the perfect environment in your tumbler for decomposing your yard and kitchen waste into first-class compost.
Tumbles can provide the ideal environment for hot composting, the fastest, most effective composting process.
Still, unlike what some advertisers would like you to believe, it’s not merely a case of adding stuff to the tumbler and turning it occasionally.
Composting, in whatever format, requires you to create an environment where the microorganisms responsible for decomposition (bacteria, fungi, actinomycetes) can flourish.
Tumbler composting makes composting much easier than hand-turned piles.
- A heap with a 30:1 carbon-to-nitrogen ratio is the best mix for promoting microbial growth and proliferation while ensuring a product with the most carbon-stabilized carbon.
- A constant supply of at least 5% oxygen is needed to keep the microbes from dying.
- Enough water allows microbial activity and chemical reactions without affecting airflow. You can test the moisture level by squeezing a handful of wet compost as tightly as possible. If water flows out, it is too wet, and if no moisture is evident between your fingers, it is too dry.
- Temperatures should fluctuate between 60 and about 160°F (~15 to 71°C). More on this later. The upper range is vital in eliminating pathogens and weed seeds.
- The carbon- and nitrogen-rich substrates should be chopped up to increase the available surface area for the microbes to access. While this is important, so is avoiding compaction, so include some larger pieces to help boost airflow.
- The batch volume is critical as batches too small don’t allow enough heat to be generated. Size matters, so opt for a more significant bin (as long as you have enough waste to fill it). Your tumbler needs to be at least half full to start a batch.
Loading Your Compost Tumbler
The list of factors above is essential to creating a compost batch that works. You must combine brown plant matter (generally higher carbon) and green plant matter (higher in nitrogen) to achieve a 30:1 carbon-to-nitrogen ratio.
| Material | C: N Ratio |
|---|---|
| Kitchen waste | 14:1 |
| Coffee grinds | 29:1 |
| Vegetable garden waste | 37:1 |
| Prunings | 44:1 |
| Tree leaves | 47:1 |
| Dry grass | 81:1 |
| Sawdust | 638:1 |
The ideal C: N ratio to begin composting should range between 25:1 to 35:1. The higher the carbon content, the slower the process, while a high nitrogen content (a lower C: N ratio) is likely to cause some anaerobic conditions, easily identified by a foul smell.
If you shred the material, more surface space is exposed for microbial activity, allowing a better starting point and overall process effectiveness.
Guard against shedding everything too fine as this will limit airflow, creating an anaerobic environment – include a few larger pieces of varying sizes to help in the mixing process.
The Maths of C: N Ratios
It’s easier to calculate mixes than you think. Let’s, for example, say we have some kitchen waste we’ve gathered (14:1) and vegetable garden waste (37:1). We always start with what we know!
- We want a C: N ratio of 30:1
- Vegetable garden waste – 37:1
- Kitchen waste – 14:1
Given the above, we can calculate three values:
- The carbon difference between garden waste and kitchen waste is 37 – 14 = 23
- To calculate the percentage of garden waste needed:
- The difference between garden waste’s carbon ratio (37) and that of the target ratio (30) is expressed as a percentage difference of the difference between the two additives
- 1 – 7/23 = 70% garden waste
- The remaining 30% is the kitchen waste portion to create a 30:1 carbon-to-nitrogen ratio.
Managing your Tumbler Composting Process
1. Make sure you have the proper carbon-to-nitrogen starting ratio
As mentioned above, too much carbon and your microbial population with be slow to propagate as they need nitrogen for cellular growth. Stick to a starting ratio of 30:1.
2. Make sure your pile is big enough
Your tumbler must be at least half full to provide enough internal insulation to create sufficient microbial activity.
3. Use pile core temperatures as turning notifications
Turning too early slows the time needed to complete a batch of compost. Turning too late will also extend the time required to finish the set as microbes perish and your batch compacts.
Your first turning and mixing should be when the core temperature reaches 145⁰F (62⁰C) and turns only when the core temperature reaches 165°F (74°C).
Give the tumbler enough turns to mix the batch thoroughly. If the side incorporator is ineffective, manually mix the batch.
4. Keep the composting batch moist
Keep the whole batch moist but not wet. A more than 60% moisture level is in the danger zone for creating anaerobic conditions; less than 40% will affect microbial activity. Follow the guide above.
5. The Final Product
Compost is the color of dark chocolate and smells like rain on a hot day or freshly dug earth. Most of the content has decomposed but may need a week or two of curing before use.
In Closing
I hope that helps you speed up your process of creating what your soil longs for.
