Mushrooms are a wonderful addition to any garden, especially since mushrooms and plants often benefit from each other's presence. Another benefit to growing mushrooms outdoors is that it allows you to avoid having to pasteurize or sterilize substrates, all you need is a hydrated substrate, and a few jars of colonized spawn! Outdoor beds and logs are best inoculated in spring after the final frost of the season. It is possible to get fruits as early as the coming fall, but some species can take 2 to 3 seasons to produce fruits (primarily wood loving species that grow on logs).
Method 1: The Bed Method
This method can be used to grow mushrooms alongside plants in a garden, or fill a bed frame dedicated to mushrooms! Simply dig a hole that is roughly 8 inches deep between your plants, then make layers of substrate and spawn. Water your plants as normal, if using a dedicated frame, keep the ground moist/damp, but not flooded. This method is suitable for any species that can be grown in a monotub. For dedicated beds, you want to place the bed in a shady spot.
Method 2: Spawn Logs
This method is based of commercial Shittake cultivation in Asia. The idea with this method is to take a log, preferably within a week of being cut, and drilling holes (every 6 to 12 inches, I would do 8 staggered rows on an 8 inch diameter log) in it to insert plug spawn. The holes are then sealed with wax. The log can then either be laid on it's side and watered regularly, or used as the barrier of a garden frame. For vertical fruiting, you can also bury 2/3 of the log, and leave the other 1/3 sticking up like a post. This method also aids in retaining moisture.
To create spawn plugs, simply take wooden dowels, and cut them down to 1 inch lengths. Let these dowels soak in water for 24 hours, then remove them from the water and put them into jars and sterilize in the pressure cooker for 120 minutes. Inoculate as you would rye jars.
Another method of inoculation is to use sawdust spawn in the place of dowels. The disadvantage with sawdust spawn though is that it can easily come out of the holes, so when using this method, it is best to cut grooves into the logs with a saw, pack in the spawn tightly, then give the spawn time to branch onto the log before moving it.
Method 3: Indoor Substrate Relocation
Another method you can use is to relocate colonized substrates from indoors to the garden. Simply take a colonized substrate, such as an Oyster straw log, and place it in the garden where it will be shaded by plants. It's that easy! Contaminated substrates can be relocated in this manner, or used to kick off method 1.