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Composting all my kitchen scraps in buckets ~20L results in:

  • large amount of compost compared to the amount of soil on the balcony (say 60L compost/year versus 200L of soil)
  • low temperature composting
  • unbalanced compost - only "greens" and no carbon sources.

I've just applied some of the foul smelling but hopefully fully degraded matter on TOP of some soil as it is too late to mix for fear of killing roots. And I notice pot drainage has decreased dramatically.

My source of soil is clay-y so I add sand to improve drainage. Assume the soil has been amended to drain well-but-not-too-well before adding the compost.

There's a lot more compost to add. Should I mix it with some sand to preserve current drainage parameters in the long run (5-10 years) or will it naturally degrade to nothing?


From the comments I see this is an X/Y problem. Unfortunately. Thanks guys!

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    Foul smelling? Uh.... not sure if that’s a good sign.
    – Stephie
    Jun 3 '21 at 12:22
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    If it was foul-smelling, it wasn't "compost." It was just a bucket full of rotting kitchen scraps. And "low temperature composting" isn't a thing. The middle of a properly working compost heap will reach a temperature of 40 to 50C (100 to 120F) .
    – alephzero
    Jun 3 '21 at 13:33
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    Clay + Sand = Cement, which may be the reason your pot drainage has decreased. Also - do you have gravel in the bottom of the pots? If so, you've created a perched water table, which also decreases drainage.
    – Jurp
    Jun 3 '21 at 19:21
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    For small-scale composting (or related methods), I recommend you look into a) tumbler-style composters, b) vermicompost, c) bokashi. Everything that is a version of “put scraps into a pile and wait” will need certain parameters, it may be a ratio of “brown to green”, temperature or the presence of a specific microbiology setup, to be successful. “Waste in a bucket” will almost certainly not give you the desired results.
    – Stephie
    Jun 4 '21 at 9:36
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Let's not fall into the trap of seeing this as an XY problem. XY just indicates that we have failed to find common ground in resolving the issue; XY is a sign that each party is retreating to their side for convenience sake - a classic cop out. You are trying to be kind to your plants and use up kitchen scraps responsibly - this is laudable, and we can help in that endeavour. The issues might be: creating the compost, drainage, and annual processing.

For drainage, adding sand to clay can help as long as the mix is kept moist. If clay, with or without sand, becomes dry it can become very hard and is extremely difficult to re-wet. In this sense it can become like cement, but cement is a quite different process whereby a chemical process is forced on a mineral substance to make it temporarily powdery, a process that slowly reverses itself when made wet. Sand can help re-wet a hard soil if thoroughly mixed in. And some clay is good for plants since it binds very well to nutrients and allows root hairs to access those nutrients.

Compost helps prevent hardening soils by keeping channels open in the soil for water to both flow through and be kept available to the plant at the same time as air pockets. So in that sense compost is better than sand to open up a clay soil, but the compost itself burns up quickly and needs to be constantly replaced.

Your current method for creating a useful product for plants is producing an anaerobic product, humus. While humus can be helpful in the very long term, what is needed for your plants in this case is compost, an aerobic product, and they are different. It sounds like your process is handling too much wet material and there is no way the excess moisture can escape. So we need to find a way of reducing that wetness, perhaps by adding dry material like shredded newspaper or wood dust, small chips, chopped straw, dry leaves, shavings that can absorb the excess water.

Thorough mixing of the components not only gets air into the mixture as it decomposes, it also allows you to see if it is yucky and smelly or not. There is a fine balance to be maintained, you may need to add more dry material or even water from time to time. Worm composting is instructive since worms will tell you if the mix is too wet or too dry.

Reprocessing your scraps through compost really requires making the compost and mixing in with your soils at the beginning of the season, planting up your pots and allowing the annual plants and soil to return to the composting process at the end of the year. This ensures that balcony plants are sitting in fresh compost every year. Long term plants need to go into larger pots with more of your soil+compost each year.

The result should be compost used up, good pot drainage and healthy plants.

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