Bokashi, trench composting and in-ground digesters

Three ways to handle scraps that a bin leaves out or a household has no room for: ferment them in a bucket, bury them in a bed, or feed them to the soil through a cone. This chapter starts with the decision, and a written no is a finished answer.

Decide: ferment, bury or neither Understand

Most methods in this manual are composting: microbes and small animals break material down with air, water and a mix of browns and greens. This chapter covers three things that are not that, or not only that. Each exists because it solves a problem the bins in The slow pile, The hot pile and Worm bins leave open.

• Bokashi is a way to ferment food scraps in a sealed bucket with inoculated bran, so that foods a bin leaves out (meat, dairy, cooked food) can go in. Fermentation here means the scraps pickle in a sealed container without air instead of rotting. WSU Extension in Kitsap County says directly that bokashi is fermentation, not decomposition (WSU Kitsap's bokashi page). The output is not finished compost. It still has to be buried in soil or added to a pile.
• Trench composting is burying food scraps in a hole or trench in a garden bed and planting over it later. Sheet composting, also called lasagna composting, is building a new bed on top of the ground from layers of cardboard and compostable material.
• An in-ground digester is a purchased cone over a buried basket that takes cooked food and meat and feeds the surrounding soil. It is a product, and we describe it from one council's page.

The choice depends on four things, and the table puts them side by side. Times are ranges from the named source, under that source's conditions. Convention

Answer four questions in your own words before you pick a row.

1. Do you make food that your first method cannot take? If meat, dairy and cooked food go in the trash or to a drop-off that takes them, you may not need this chapter. Bokashi and a digester are the two options here that take them.
2. Is there soil for the output? A bed that can take buried material, a compost pile to add it to, or a soil factory on a balcony. Bokashi without a place to put the output ends at a full bucket.
3. Will you do the steps? Bokashi asks for bran with each addition, draining every few days, and a second bucket while the first ferments. A trench asks for digging, and not in frozen ground. If those do not suit your attention tier, the honest answer is no for now. Preference
4. Who decides? A trench or digester changes the ground, and a soil bin on a balcony can run into a lease. Ask the authority The who-decides section of Site and bin covers how to ask in writing.

Write the answer on your plan with the reason. "No, my city collects food scraps and I have no soil to bury in" is a good line. So is "yes, one bokashi bucket and a soil bin, because I cook with meat and I have a balcony." If you chose a drop-off or curbside program in Kitchen and collection, the program may already take what bokashi would; check its list before you buy a bucket.

How a bokashi bucket works

A bokashi system is a sealed container and bokashi bran, a wheat bran or rice hull carrier that holds the fermenting microbes (lactic acid bacteria and yeasts, by WSU Kitsap's description). RDCK, a regional district in British Columbia, describes a 5-gallon bucket with a lid and spigot as the usual container, and says kits cost $50 to $200 and that a home-made bucket is possible (RDCK's bokashi factsheet). The method as WSU Kitsap and NC State's Beaufort County center describe it (NC State Beaufort County's bokashi article):

1. Chop large scraps smaller. WSU Kitsap gives this as a way to speed fermentation.
2. Add scraps to the bucket, then sprinkle a handful of bran over them. Repeat with each addition.
3. Press the scraps down to push out air, and seal the lid. Both sources say fermentation needs the air kept out.
4. Drain the liquid every few days so the contents do not sit in it.
5. When the bucket is full, seal it and set it aside to ferment for about two weeks.

RDCK says you need at least two buckets, because a sealed bucket has to sit while you keep adding scraps somewhere else. USask's Saskatchewan Waste Reduction Council page says the same in practice: begin a different bucket when the first is full (USask's bokashi page). Convention

What goes in

WSU Kitsap lists fruit and vegetable scraps, cooked food, dairy, meat and small bones, and says to avoid soups, sauces and free liquids because they leave the bucket too wet. That is the default here. Other sources list a few more or fewer foods; the comparison is under Go deeper. If a scrap is liquid, let it drain or leave it out. Dog and cat waste and human waste are not bokashi inputs either; What goes in says why.

What a working bucket looks like

WSU Kitsap says a working bucket smells sour, tangy and pickled, "not sulfur, rot, or ammonia." White mold is a good sign by WSU Kitsap's account, and USask agrees that white mold is not dangerous and means the process is working. Green, black or blue mold is a bad sign in WSU Kitsap's troubleshooting guide, with a fix of removing the affected material, adding bran and pressing down firmly, and discarding and restarting if mold dominates. A foul rather than pickled smell is also a signal in both WSU Kitsap and NC State Beaufort: add more bran. Test it Smell the bucket when you open it. Troubleshooting collects these signs with the other troubleshooting rows.

The liquid

Fermenting scraps release a liquid. WSU Kitsap and RDCK both say it can be diluted for plants or poured down a drain. None of the sources we read gives a dilution ratio, so this manual gives none. If you want to use the liquid on plants, we have no number to give you; the drain is the option both sources name that needs none. Jun and Lena in the example below pour it down the drain.

After the bucket: burial and the soil factory

A sealed bucket of fermented scraps finishes in soil or in a pile. This manual follows one source for the numbers, WSU Kitsap's, because it gives a depth, a mix, a wait and a table of conditions on one page, and the other sources' figures are under Go deeper. Convention

Burying in a bed

1. Dig a trench or hole 8 to 12 inches deep, wide enough to mix the scraps with soil, and not against the roots or trunk of a plant.
2. Spread the fermented scraps in a layer 1 to 2 inches thick and mix them with at least 2 to 3 times their volume of soil, so the result is not solid.
3. Cover completely so nothing shows, and firm the soil lightly.
4. Wait before planting. WSU Kitsap's minimum is 2 weeks and its ideal is 3 to 4 weeks, with cooler or compacted soil taking 3 to 4 weeks and containers 4 or more.

WSU Kitsap also lists what not to do: do not spread bokashi on the surface or use it as mulch, do not plant immediately, do not put a large volume in one hole, and do not leave it exposed to air. For trees and shrubs it gives holes 10 to 12 inches deep outside the drip line and says not to place bokashi against roots or trunks. A bed that already has plants can take a buried patch in an open section, with planting rotated into that section 3 to 4 weeks later.

The wait is the one number in this chapter you can check without a source. WSU Kitsap lists signs that the burial is done: the sour smell disappears within 1 to 2 weeks, the soil is darker and crumbly, and no odor lingers at the spot. If you can still smell the sour note, the wait is not over. Test it

Adding it to a compost pile

The other way to finish the output is a pile or bin you already run. WSU Kitsap says to add the fermented scraps as a green, bury them in the center, balance them with browns and cover completely. The pile's own rules apply: The slow pile covers the browns. RDCK calls bokashi "best used to compliment another composting system."

The soil factory

A household with a balcony or only containers can skip the ground. A soil factory is our name for a lidded bin of soil that fermented scraps are mixed into, so the soil finishes the job indoors or on a balcony. WSU Kitsap calls it a holding bin: fill a tote or bin with soil or finished compost, mix the fermented scraps in at 1 part scraps to 3 parts soil, keep it moist but not wet, and let it sit 3 to 6 weeks before using the soil in beds or containers. USask describes the same idea as a large tub of soil, with several inches of soil under and over the scraps, and says the scraps should be dissolved after 6 weeks. USask asks for garden soil and says not to use sterile potting soil, a detail we come back to in the example.

Containers need a longer wait than beds in WSU Kitsap's timing table: 4 or more weeks. A soil factory that is also the planting soil is a container, so we use that figure for it.

Two practical limits apply. A bin of soil with food scraps in it is something a landlord or building may read as stored refuse, so ask first (Site and bin). And the bin adds weight to a balcony; a 30-gallon bin of damp soil is heavy, so check the surface it sits on. Ask the authority

Trench and sheet composting

Trench composting skips the bucket. You bury raw kitchen scraps directly, and the soil does the work. It suits a household with a garden bed that can go unplanted for a season, little attention to give, and no meat or dairy in the buried scraps.

The default trench

USask's trench page gives the plain version (USask's trench composting page): dig a hole or trench 12 to 18 inches deep and at least 6 inches away from the nearest plants, put kitchen waste, green plants or grass clippings in it, leave space at the top, and cover with 6 to 8 inches of soil. You can plant directly into the trench area after 3 to 6 months, and in an annual garden you can alternate the trench and the plants between years. USask excludes meat, bones, dairy and grease. Oregon State's EM 9480 gives the same trench size of 12 to 18 inches deep and wide (Oregon State's EM 9480). Nebraska Extension in Lancaster County also excludes meat, bones and fatty foods, and gives a shallower 12 to 15 inches with at least 8 inches of soil back over the top (Nebraska Lancaster County's trench page). Convention The default here is USask's 12 to 18 inches deep with a 6 to 8 inch cover. If you want one figure that satisfies both sources, a trench 12 to 15 inches deep with an 8-inch cover does.

• Cover an open trench. USask says to cover an open trench with a stout board to avoid accidents, or to dig a new hole for each batch.
• Winter. USask says trenching is hard in winter because the ground freezes, so new holes are hard to dig and the loose covering soil freezes solid. It offers two options: store kitchen waste frozen in a large outdoor container until spring, or use an indoor method such as a bokashi bucket.
• Where. A bed that will be planted next year is the spot this manual suggests, because the buried scraps feed it and the 3 to 6 month wait fits a bed that sits unplanted. Convention

How long the scraps take to break down varies a great deal. Nebraska says one month to one year. USask says you can plant after 3 to 6 months. The longer figure is the safer one to write on the plan. Convention

Sheet (lasagna) composting

Sheet composting builds the pile on the ground instead of in it. Oregon State's EM 9559 describes stacking consecutive layers of compostable material, about one to six inches each, on a base of overlapping plain cardboard, ending with a brown layer, and says a new bed should be ready to plant in approximately six months (Oregon State's sheet mulching and lasagna composting page). It makes little heat, so it is slow. It suits a household that is making a new bed and wants a way to build it from scraps and browns in one go. Oregon State says to use plain brown cardboard with tape and staples removed. The details of the layers are on that page; we do not restate them.

In-ground digesters

An in-ground digester is the cone-and-basket product you may see in council waste guides. It is a product fact, not a method with independent results. The only source we read on it is the Banyule City Council's user guide in Victoria, Australia (Banyule City Council's green cone user guide), plus one line in NC State's gardener handbook that meat, fish, bones and dairy can go in an in-ground digester such as the Green Cone (NC State's Extension Gardener Handbook, Composting). Product-specific

What Banyule says:

• What it takes. Fish, meat, poultry, bones, dairy, bread, pasta, cooked scraps, fruit and vegetables. It "is not a composter, and will not handle garden waste."
• Where it goes. A hole about 80 centimeters wide and 60 deep (about 31 by 24 inches) in good draining soil, or 90 by 70 centimeters in heavy clay or chalk, in as much sun as you can give it. Test drainage by pouring a bucket of water into the hole: if it disappears within 10 to 15 minutes, drainage is good.
• How much. The equivalent of a 4.5 liter container (about 1.2 gallons) every 1 to 2 days in summer and every 2 to 3 days in winter. For a family of four with average consumption, the basket needs emptying every 2 to 3 years.

It makes no compost you can harvest; the point of the cone is to feed the soil around the basket. We found no independent test of how well it works in a cold climate or in a small yard. If your household cooks with meat and has a sunny, well-drained yard it owns, it is one candidate. A renter would need a written yes before digging a hole that size. Ask the authority

Animals and buried food

Buried food smells to an animal that can dig. The sources say what is safer to bury, not that any burial stops a determined animal.

• Depth. NC State Beaufort says to bury bokashi at least 8 inches deep to avoid attracting animals; the bokashi maker Organko says 25 to 30 centimeters (about 10 to 12 inches) and gives the same reason. The maker's page is a product source. Product-specific
• What you bury. Nebraska says meat, bones and fatty foods have a high potential to attract wildlife, rodents, dogs, cats and flies. USask excludes them from a trench for the same reason. Bokashi is the exception: the sources we read accept meat and dairy in a bucket. RDCK says properly managed bokashi should not be attractive to animals when it is added to soil or a composter. We found no study that measures this.
• Fences. The University of Maryland's composting page says trench composting works best in fenced gardens that exclude raccoons, possums and groundhogs (University of Maryland Extension's How to Make Compost at Home).
• Bear country. Vermont Fish & Wildlife says to keep meat scraps and bones out of an outdoor compost system and lists a pit or trench as one option, with freezing for a drop-off and the trash as others (Vermont Fish & Wildlife's Composting in Bear Country). Follow your own state wildlife agency's page. This manual does not say what will keep a bear away.

If a buried trench gets dug up, rake the scraps back, cover them with more soil, and write it on the log. Then ask whether the place or the contents need to change. Site and bin covers rodents and wildlife.

See it: Jun and Lena, and Tomás See it

Free demonstrations of the choices in this chapter, from sources we fetched on 2026-10-26:

• WSU Kitsap's bokashi page: the full burial table and a troubleshooting guide for the bucket.
• USask's trench composting page: a short page that includes what to do over winter.
• Banyule's green cone user guide: sizing and drainage test for an in-ground digester.

Practice: decide, then start one Practice

Minimum: write a yes or no on the plan with a reason, and for a yes, put one bucket or trench in the log with its date. Time: about 20 minutes once for the decision; one evening for a first bucket or trench. Materials: your saved setup, the table in decide, the system plan and the bin log; for a bucket, a lidded bucket, bran and a plate or lid that fits snugly; for a trench, a spade and a board to cover it.

1. Answer the four questions in decide. One sentence each.
2. Write yes or no on the plan, with the reason. A no needs one line of reason and a review date.
3. For a yes, start the bucket or dig the trench. For a bucket, follow the five steps in how a bucket works. For a trench, follow the default in trench.
4. Add a row to the bin log. Date, "Bokashi bucket 1" or "Trench 1", the gallons added, and in notes the date it can be buried (bucket: two weeks after sealing) or planted over (trench: three to six months).
5. Write the burial or planting date on the plan. If you will bury the bucket in a bed or a soil factory, write the wait (2 to 4 weeks by WSU Kitsap's table, 4 or more for containers) and where.

Your system Your system

Check your work Check your work

Criteria

• Does the plan say yes or no to fermenting or burying, with a reason about your space, your food and your attention?
• For a yes, does the log show the bucket or trench, its start date, and the date it can be buried or planted over?
• Does the plan say where the fermented scraps will go (soil, a pile or a soil factory) and who decides, if someone does?
• If you chose bokashi, did you write that the output is not planted into directly?

Worked example

Jun and Lena's plan says yes to bokashi and a soil factory, names the manager's written answer, lists two buckets and the soil bin, and gives two dates: sealing plus two weeks to mix into the bin, and mixing plus four weeks to plant. Tomás writes a dated no with a reason and a review date. Both pass. Noor Haddad, whose apartment has no balcony and whose program takes no meat or dairy, writes "no, no soil to bury in; cooked food with oil or dairy goes in the trash; review in Your compost system," which also passes.

Common mistakes

• Planting into the bucket's output. The sources say to wait, and the sour smell is the sign the wait is not over.
• Burying a lot in one place. WSU Kitsap says not to concentrate a large volume in one hole. Spread it out and mix it with soil.
• Putting meat in a trench. Trench sources exclude it. Bokashi is the option here that takes it.
• Using a number for the liquid. No source we read gives one. The drain is the default.
• Writing only the start date. The log needs the date the bucket can be buried or the trench planted over, or there is nothing to check later.

What is still unresolved

Whether your soil or soil bin finishes the scraps in the wait you wrote is settled by looking and smelling at the end of it. Whether the building or landlord allows a soil bin or a hole is settled by their written answer. How well home bokashi works in general is not settled by any independent study we found.

Knowledge check and scenario

Checklist

• The plan says yes or no to fermenting or burying, with a reason; for a yes, the log shows the bucket or trench, its date and the date it can be buried or planted over.
• I know bokashi output is not planted into directly, and I wrote the wait I am following.
• I read how the sources differ on fermentation time, depth and waiting. (Go deeper; optional)