Johnson-Su Bioreactor: Fungal Compost Without the Turning
If you’ve been trying to rebuild soil after a stretch of neglect, this is one system worth knowing well. The Johnson-Su bioreactor is a static, low-labor way to make fungal-dominant compost — the kind that actually helps restore structure and biology in depleted ground, rather than the faster, bacteria-heavy stuff most backyard piles produce.
The mental model
Dr. David Johnson (soil microbiologist) and Hui-Chun Su Johnson developed it at New Mexico State University. Their work showed that compost left undisturbed, kept consistently moist, and given steady passive air develops a much richer fungal network than compost that’s turned every week or two. Turning breaks the fungal threads you’re trying to grow. Fungal-dominant compost is what worn-out soils need most for aggregation, water holding, and nutrient cycling.
What we do with it here (Central New York / zone 5)
The build is straightforward and uses common materials. The widely used design from Johnson’s own guidelines is:
A cylindrical cage of 6" × 6" welded wire re-mesh (10-gauge), about 12'6" of it formed into a cylinder roughly 4 feet in diameter and 5 feet tall.
Landscape fabric lining the inside (one piece ~13' × 6' for the sides, plus two 6' × 6' pieces for base and top) so finer material stays put while air and moisture still move.
Six perforated 4" septic drain-field pipes, each about 6 feet long, stood vertically and spaced evenly before you fill — these carry oxygen into the core without any turning.
A standard shipping pallet as the base for drainage and bottom airflow.
Layer a diverse mix once — leaves, straw, wood chips, modest manure — aiming for a balanced carbon-to-nitrogen ratio. Soak it thoroughly so the whole mass is wet, not just damp. Target moisture is above 70 percent: a handful should glisten and feel like a well-wrung sponge. Then leave it alone.
Here in Oswego County the leaf fall and wood-chip season give us the carbon we need in autumn. (Suggested Sanctuary addition: if we are running one, note the actual fill date and any winter moisture checks we do with a tarp or drip line so the outer layers don’t freeze dry.) Check moisture a few times and re-wet the surface if it starts to dry; resist every urge to turn or dig into it. After the initial heat (thermophilic phase) drops, some growers add worms, but the core design does not require it.
What goes wrong
Moisture is the detail most people miss. Too dry and the fungal colonies stall. Too much fresh manure or nitrogen-heavy material and the pile can go anaerobic, get slimy, and draw flies. Materials that are too coarse or too fine both hurt airflow. And impatience: this is not a three-month hot pile. Nine months is the minimum; a full year is better for the microbial complexity you’re after. In zone 5, winter freeze-thaw is real, so plan for covering or occasional wetting so the outer edges don’t desiccate.
How it ties into larger design
The finished compost is used more like a microbial inoculant than bulk amendment. A little goes a long way:
Direct application to soil at whatever rate fits the planting.
Compost extract: a couple of handfuls in five gallons of water, agitated well, used as a drench or spray (research rates run as low as roughly one pound per acre).
Seed coating: a liter of slurry mixed with about 50 pounds of seed so the microbial community rides the seed into the ground.
It sits alongside other soil-rebuilding steps we already use — wood-chip mulch, cover, reduced tillage, and the slow work of succession on degraded spots. The point isn’t heroic labor. It’s a method that keeps working on the weeks you can’t get out there.
Seasonal next step
If you’re starting this fall, gather the leaves and chips now, build the cage on a dry weekend, fill and soak before the ground freezes hard. You’ll have mature inoculant by the following fall or the spring after. If spring is better for you, stage the materials over winter and build once the mud settles. Either way, start one cylinder this season; the land here rewards the patient timeline.
Further Reading
These are the sources I keep coming back to when someone asks how to build one right and what the finished material actually does. They’re practical, not sales copy.
Best Management Practices: Johnson-Su Composting Bioreactors — New Mexico State University / USDA-FSA — https://regenerationinternational.org/wp-content/uploads/2017/09/Johnson-Su-Bioreactor.pdf. The original construction and operating guide from the people who developed it; dimensions, moisture, and use rates in one place.
Johnson-Su Bioreactor overview — NM Healthy Soil Working Group — https://www.nmhealthysoil.org/2021/04/18/johnson-su-bioreactor-2/. Clear summary from the New Mexico soil-health community where the method started; good for seeing how others adapt it.
Building Biodiverse, Aerobic Composts Using the Johnson-Su Method — Land Stewardship Project Greenbook — https://wrl.mnpals.net/_flysystem/fedora/2025-08/Greenbook.Land%20Stewardship%20Project.pdf (or search “Land Stewardship Project Johnson-Su Greenbook”). Midwest farm trials with real recipes, what went wrong (too much manure, sludge, collapses), and management tips a grower can use.
On-Farm Testing of Johnson-Su Compost Extract — SARE project ONC23-119 — https://projects.sare.org/project-reports/onc23-119/. North-central on-farm work with extract on wheat and soy; shows how people are scaling the inoculant side and what DNA analysis found in the finished compost.
Place / living demonstration — New Mexico Healthy Soil Working Group field days and workshops (nmhealthysoil.org) remain the best place to see one built and filled in person. Closer to home, check your county Cornell Cooperative Extension or local Soil & Water Conservation District for soil-health workshops; several Northeast SARE and extension efforts have tested similar static fungal compost approaches.
On Our Website
If this method is part of rebuilding worn ground, these pieces sit next to it on the same shelf.
Soil Succession: From Barren Soil to a Thriving Forest Ecosystem — https://www.mindfullivingsanctuary.com/articles/soil-succession-from-barren-soil-to-a-thriving-forest-ecosystem. How the biology you’re inoculating actually moves a site from bare to more complex over years.
Transforming Degraded Properties in Cold Temperate Climates: A Guide to Soil Restoration — https://www.mindfullivingsanctuary.com/articles/transforming-degraded-properties-in-cold-temperate-climates-a-guide-to-soil-restoration. The bigger picture of what degraded zone-5 ground needs and the sequence of practices that stick.
Hugelkultur: Transforming Organic Waste into Fertile Garden Beds — https://www.mindfullivingsanctuary.com/articles/hugelkultur-transforming-organic-waste-into-fertile-garden-beds. Another way we put woody material and biology to work without constant turning.
Who’s in the Garden and What Are They Up To? — https://www.mindfullivingsanctuary.com/articles/whos-in-the-garden-and-what-are-they-up-to. The organisms — fungi included — that the inoculant is meant to support once it’s in the soil.
