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SustainabilityLesson 3 of 7

Worm bins and bokashi

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What you’ll learn

  • Which worms to buy and how big a bin you need
  • Bedding, feeding and the temperatures worms can take
  • Harvesting castings, and why the drained liquid stays off food crops
  • What bokashi is, and what the research says about it

The short version

  1. Worm bins take kitchen scraps indoors. Use red wigglers, about 1 sq ft of bin per pound of scraps a week. Keep the drained liquid off food crops.

  2. Bokashi ferments scraps; it isn't compost until it's buried for a few more weeks. The "effective microbes" sold for it haven't beaten sterilized versions in trials.

Worm bins

StepDetails
WormsRed wigglers (Eisenia fetida) from a known grower. Not nightcrawlers
Bin sizeAbout 1 sq ft of surface per lb of scraps a week, no deeper than about 1 ft; start with about 1 lb of worms per sq ft
BeddingShredded paper, cardboard or leaves, damp like a wrung-out sponge
TemperatureAbout 55–77°F is best; trouble below about 40°F or above about 84–90°F
FeedingBury small amounts under bedding; add more only when the last batch is mostly gone. Avoid meat, dairy and oils
HarvestEvery 3–6 months: move food to one side or use light to drive worms down
Using castingsUp to about ¼ of a potting mix; they can be salty

Does it work? In a meta-analysis, vermicompost raised yields an average of 26% compared with no vermicompost. Claims that castings beat regular compost several times over aren't backed by cited data.

Diagram coming soonWorm bin cutaway
Figure 1. Inside a worm bin.
Sources: NC State Extension, Oregon State University Extension and 4 more

Bokashi

Bokashi

  • What it is: fermentation, not composting. Pack scraps with inoculated bran in an airtight bucket and drain the liquid. Ferment about 2–5 weeks.

  • Finish it in soil: bury it, then plant 2–4 weeks later.

  • What the research says: the "Effective Microorganisms" did no better than a sterilized version in a 4-year field trial, so any benefit comes from the nutrients. It didn't reliably fight plant disease.

  • Safety: claims that it safely handles meat and dairy aren't backed by research. Wash your hands, and bury it deep enough that animals can't dig it up.

Diagram coming soonBokashi two-stage process
Figure 2. Bokashi is two steps: ferment, then bury.
Sources: Published research, Washington State University Extension

Resources

By zone

Worm bins work anywhere if you keep them between about 55 and 77°F. Here is what that means by zone.

3–4
Small piles freeze before heating. Start in May–June, or build a big pile in late summer to cure over winter. Worm bins go indoors (keep above about 55°F). Don't spread manure on frozen ground.
5–6
Larger piles (5 × 5 ft) keep working into winter. Apply raw manure in fall with a cover crop. Deep litter in winter coops.
7–8
Composting runs most of the year. Cover piles in heavy rain. Watch for jumping worms in bought mulch.
9–10
Heat speeds things up, but dryness slows them in the arid West: shade piles and water weekly. Worm bins need full shade. Go light on manure where soils are salty or alkaline.

Where this comes from

Every fact in this lesson was checked against 22 published sources, all from extension services, the USDA and research journals. Each section lists its own at the bottom.

See all 22 sources
Washington State University Extension
Colorado State University Extension
Iowa State University Extension
Oregon State University Extension
University of Alaska Fairbanks Extension
University of Illinois Extension
University of Maryland Extension
University of Minnesota Extension
University of Wisconsin Extension
Wisconsin Department of Natural Resources

Summary

The whole lesson on one page. Print it or come back to it.

Key information

  • Use red wigglers (Eisenia fetida); garden earthworms don't survive in bins.
  • About 1 sq ft of bin surface per pound of scraps a week, no more than about 1 ft deep.
  • Keep bins around 55–77°F with bedding damp as a wrung-out sponge.
  • Keep the liquid that drains out (leachate) off food crops.
  • Bokashi is fermentation; bury it a few weeks before planting. Its 'effective microbes' didn't beat a sterilized version in a 4-year trial.
  • Buy worms only from known growers: jumping worms travel in cheap bait and mulch.

Step by step

  1. 1.Pick an opaque bin with air holes, about 1 sq ft of surface per pound of scraps a week.
  2. 2.Fill with damp shredded paper, cardboard or leaves.
  3. 3.Add about 1 lb of red wigglers per square foot.
  4. 4.Bury small amounts of food under the bedding; add more when the last feeding is mostly gone.
  5. 5.Keep the bin at about 55–77°F, in shade in summer and indoors in cold winters.
  6. 6.Harvest castings every 3–6 months and use them as no more than a quarter of a potting mix.

Key graphics

Links to products

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