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Home Composting Workshop

Big thanks to Jesus & Shova from the County of San Mateo Office of Sustainability and the hospitality of the Los Prados Community Garden for putting on an afternoon home composting workshop.  It was so good to see the new 3 bin composting setup - that volunteers built a few weeks ago - being put to good use.

Today's discussion covered both "hot" composting and worm composting.  Here are a few notes:

Worm Bin Basics:

  • Worms don't eat food scraps - instead they feed upward on the bacteria that is breaking down the food waste - making the stacked worm bins ideal 
  • Coffee grinds are very acidic - so a little goes a long way in giving worms grit to help in digestion.  Oyster powder is also good, as is fine grain sand
  • Important to keep the bin in a place that can maintain a moderate temperature - out of direct sunlight
  • Coconut coir is a common material for use in the bottom, bedding layer of each worm bin tray
  • Worm bin leachate, the liquid that collects in the very bottom of bin, is extremely valuable plant food
  • What not to feed your worms
    • meat, fish, poultry
    • dairy
    • oil or greasy food
    • starchy foods
    • animal feces
    • citrus
    • spicy peppers, onions, garlic

"Hot" Composting:

  • Question: Should your compost bin have a floor - or should it just sit on top of the soil?Answer: You'll get more microbial activity if you leave the bottom of the bin open to the soil
  • The "hot" is not from the sun or external temperature, but from the amount of microbial activity within the compost pile
    • Note: we actually moved the Los Prados bin to reduce the amount of sun exposure - which will help the bins retain humidity
  • Question: Should the compost material be as small as possible?  Answer: No - you need pockets of air within the compost pile to provide sufficient oxygen.  Adding egg crate material can help provide room for air within the pile
  • The Big 4:
    • Browns
    • Greens
    • Air
    • Water
  • Question: What is the optimal proportion of browns to greens?  Answer: 60% browns to 40% greens - but keep in mind that exact math doesn't apply to living things
  • Browns:
    • leaves (brown)
    • hay & straw
    • paper & cardboard
    • woody prunings
    • egg shells
    • saw dust
    • tea bags
  • Greens:
    • leaves (green)
    • grass clippings
    • coffee grounds
    • young hedge clippings
    • fruit & veggie peels
    • herbivore manure
    • green plant cuttings
  • Question: When is the compost done?  Answer: it depends on how the compost will be used.  Typically the length of time is measured in months.  To use compost as an amendment to soil (black color with no woody pieces) will take longer than for use as a filler in planting beds.

Cheers & GROW San Mateo!


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