Self-growing mycelium insulation mats from wood chips for cold frame add-ons protecting winter greens

To create these living insulation panels, you will first need to source the right materials. Acquire a bag of cold-hardy grain spawn, such as Pearl Oyster (Pleurotus ostreatus) or King Stropharia (Stropharia rugosoannulata), as these are aggressive colonizers that perform well in cooler temperatures. You will also need hardwood wood chips; avoid aromatic woods like cedar or pine which have antifungal properties. Aspen, poplar, or maple chips are ideal. The smaller the chips, the faster the mycelium will colonize them. For the mold, construct a simple wooden frame to the exact dimensions of the cold frame add-on panel you wish to create. A shallow depth of two to three inches is sufficient for an effective insulation mat.

The first step is preparing the wood chip substrate. Submerge the chips in a large container of non-chlorinated water for 12 to 24 hours to fully hydrate them. Next, you must pasteurize the chips to reduce competing molds and bacteria. An effective method is to drain the soaked chips and place them in an insulated cooler. Pour boiling water over them until they are covered, close the lid, and let them sit for at least 90 minutes. After pasteurization, drain the chips thoroughly. They should be damp to the touch but not dripping water when squeezed. Allow them to cool completely to room temperature before proceeding.

Once the chips are cool, you can begin inoculation. In a clean tote or directly in your wooden frame mold, break up the grain spawn with your hands until it is loose. Mix the spawn evenly throughout the damp wood chips. A good ratio is approximately one part spawn to ten parts wood chips by volume. Pack this mixture firmly and evenly into your pre-built frame. A tight pack encourages a dense, solid mycelial mat.

Now, the colonization phase begins. Cover the top of the packed frame with a sheet of plastic or a damp burlap sack to maintain high humidity. Place the frame in a dark, sheltered location like a garage or basement where temperatures are relatively stable, ideally between 60-75°F. Over the next two to four weeks, you will see white, web-like mycelium spreading and binding the wood chips together. The block is fully colonized when it is a solid, white, firm mass that holds its shape.

Before installation, you can harden the mat to make it more durable and less likely to produce mushrooms. Remove the plastic cover and expose it to more air circulation for a few days. This will cause the surface to become slightly dry and leathery without killing the organism. Once hardened, the mat can be carefully removed from its frame.

Install the finished mycelium mats by fitting them into the walls of your cold frame add-on structure or using them as an insulated insert under the main glazing on exceptionally cold nights. These living mats trap air within their dense network, providing an effective thermal buffer that slows heat loss and protects your winter greens from harsh temperature drops. The mat will continue to slowly digest the wood chips throughout the season. At the end of winter, the entire mat is fully compostable and can be added directly to your garden beds.