Chinese Chestnut Seedling Mycorrhization with Porcini

Badger Johnson, Southern Ohio Chestnut Company, Founder, southernohiochestnuts@gmail.com

All photo credits to Badger Johnson.

Editor’s Note: This article was previously published in January/February 2026 edition of The Mushroom Log, which is the newsletter of Ohio Mushroom Society. Small edits have since been made.

Author Badger Johnson holding a King Bolete mushroom (specifically Boletus variipes fagicola) freshly harvested from a Chinese chestnut orchard in Ohio. Prior to the chestnut orchard’s establishment, the site had been an oak-hickory woodland with residual American chestnut root sprouts in the understory. The site was cleared for coal mining, but in a strange twist of fate, the cleared site ended up being immediately planted to Chinese chestnuts, and then abandoned for a decade. This unusual sequence of events may have led to existing King Bolete mycelium in the soil, with its tree hosts removed, being forced to make a novel mycorrhizal pairing with the Chinese chestnut seedlings.

The project, titled "Chinese Chestnut Seedling Mycorrhization with Porcini" (grant FNC25-1458), is a farmer-led initiative funded by the Sustainable Agriculture Research and Education (SARE) program in the North Central region. Ohio Mushroom Society members are invited to get in touch with Badger Johnson at southernohiochestnuts@gmail.com.

We aim to develop reliable methods for inoculating Chinese chestnut (Castanea mollissima) seedlings with porcini mushrooms (Boletus sp., known as Porcini or King Boletes), specifically native North American species like Boletus variipes fagicola. The primary objective is to evaluate three inoculation techniques—mother tree, liquid culture, and spore solution. Desired effects from the inoculations include enhanced seedling growth, nutrient uptake, and drought resistance. Additionally, the project seeks to create a commercially viable porcini culture, potentially turning porcini into a high-value secondary crop in chestnut orchards. Expected outcomes include yields estimated at 36 lbs/acre/year dried, valued at $544–$5,346/acre annually based on market price. The project timeline spans from 2025 to early 2027, with inoculations starting in spring 2026, midpoint sampling after six months, and outplanting of 400 seedlings in spring/summer 2027.

Porcini form ectomycorrhizal partnerships with host trees, exchanging carbohydrates from the tree for soil nutrients and water. The project draws on the "Compatible Genera Generalization," hypothesizing that native Boletus species can pair with chestnuts due to shared fungal-host compatibility. No prior significant income from ectomycorrhizal mushrooms in North American orchards has been documented, making this a novel approach to boost agroforestry revenue, where porcini could exceed chestnut crop value in productive years.

Methods and Experimental Design

The project involves growing Chinese chestnut seedlings at Camp Washington Perennial Farm in Cincinnati, Ohio, using pots and air-pruning beds with a custom potting mix (5% sand, 15% compost, 20% perlite, 20% pine bark, 40% peat) optimized for acidic pH (<6.5), nitrogen from organic matter, and good drainage. Seedlings are randomly assigned to four groups of 100 each:

• Mother Tree Treatment**: Seedlings planted in root zones of known porcini-host trees, mulched, and protected with tree tubes for rabbit deterrence.

• Liquid Culture Treatment**: Seedlings submerged in a liquid mycelial culture derived from foraged porcini, then re-potted.

• Spore Solution Treatment**: Seedlings treated with a spore slurry from wild-harvested porcini, incorporating soil from under fruiting bodies.

• Control**: Seedlings in soilless potting medium in nursery beds, without inoculation.

Inoculations are planned for spring and summer 2026, with watering as needed. Six months post-inoculation, 10 seedlings per treatment will be sampled for fungal sequencing at Mycota Lab to confirm mycorrhization rates. All seedlings will be outplanted in spring/summer 2027 to assess long-term establishment and fruiting potential. The approach incorporates lessons from experts, such as using site indicator species like Amanita muscaria and moss (including but not limited to Thuidium delicatulum) to qualify suitable sites, and timing foraging for optimal conditions (September/October with 1–2 inches weekly rain and 80°F temperatures).

Progress to Date (As of January 30, 2026)

By mid-2025, foundational activities were underway. Members of the research team attended several Ohio Mushroom Society (OMS) foray to learn porcini identification. Mushrooms were foraged from sites in Pennsylvania (over-mature Christmas tree plantations) and Ohio (chestnut orchards), tentatively identified as Boletus variipes fagicola, and shipped to Thomas Lodge’s lab for inoculant development. Seedlings were germinated at Deer Orchard Nursery using air-pruning beds, though rates were lower than expected due to delayed planting and over-watering. This prompted considerations to shift inoculation to spring 2026 with earlier germination and less watering.

Inoculant progress included successful Petri dish cultures of King Boletes, as demonstrated in explanatory videos. We learned from Walter Sturgeon about a space under Norway Spruce with prior accidental porcini inoculation, via shavings and rinse-water from foraged porcini. This plus reading more in the literature, including a Chinese patent, yielded insights: mature trees inoculate faster and fruit sooner than seedlings, with annual harvests beginning under medium-sized trees. We have also learned from other chestnut growers that additional species of highly sought after mushrooms, sometimes found growing in chestnut orchards, have specific plant species that act as “site indicators”. These include the orchid Epipactis helleborine pointing towards Tuber (truffle) species, and Monotropa uniflora (Ghost Pipe) pointing towards Russula brevipes (short-stemmed brittlegill, host of lobster mushroom).

By January 2026, preparations advanced for the mother tree treatment. Chestnut seeds were stratified, an MOU signed with orchard owners, tree tubes purchased for protection, and a planting layout developed under 20 mother trees. The Cooper Orchard had porcini flushes which occurred in June and October of 2025. Larger June flushes correlated with steady precipitation (1–2 inches weekly), while October yields were smaller amid drought. Other species observed included Amanita muscaria guessowii and Baorangia bicolor. Mushroom samples from the October flush were sent to Mycota Lab for DNA barcoding to confirm Boletus variipes fagicola, supporting compatibility with Chinese chestnuts. This species is noted for its native Ohio occurrence, edibility (confirmed safe and delicious by tasters), and genetic similarity to Boletus edulis.

Challenges, Observations, and Future Outlook

Key challenges include inconsistent nut germination, ineffective soil pasteurization (allowing microbial contamination), slow mycelial growth, and the accidental consumption of samples. Host specificity remains a consideration, with Boletus edulis showing generalist behavior in Europe but conifer preferences in North America. Observations highlight environmental factors like rainfall influencing flushes and the value of mature orchards for quicker mycorrhization.

The project has confirmed native porcini viability with Chinese chestnut, established inoculation protocols, and gathered genotyping data to validate hypotheses. Inoculations under mother trees are slated for March 2026, with root tip examinations to verify mycelium presence across treatments in autumn 2026. If successful, inoculation could accelerate orchard establishment, providing dual revenue from nuts and mushrooms while advancing sustainable mycoforestry practices in the region.

Badger Johnson, Southern Ohio Chestnut Company, Founder, southernohiochestnuts@gmail.com