To be honest, the title “spawn run” for this DIY mushroom growing post sounds like the latest release in a horror movie franchise. It’s not! In fact, it’s a whole lot of nothing, at least to the naked eye. We’ll get into that in a moment.

But first, to review the previous two phases:

Phase 1 of DIY mushroom log growing is Substrate Acquisition, where you find a suitable log which you’ll inoculate with mushroom spawn. This phase is all about judgement. Choosing the right log and the number of them for your desired harvest, pre-determining a space for keeping the logs, i.e. wood yard, are key steps.

Phase 2 of DIY mushroom log growing is inoculating that log properly, with the right tools and the mushroom spores of your choice. This phase is all about initiating the growing process and is labor intensive.

And now Phase 3 is allowing the inoculated log the time to fill with mushroom spores. The log at this point is doing all of the work.

What Is a Spawn Run?

The spawn run is the “run” of time between spawning and casing, or the time when the mycelium begin to grow throughout the log. It’s essentially the period of vegetative growth for the fungus. The length of time for the spawn run depends on what type of mushrooms you are growing, and it also depends on how you’re growing them—with quicker-turn commercial production techniques or via an inoculated log.

How to Stack Your Spawn Run Mushroom Logs

Spawn run mushroom logs should have as little contact with the ground—and even with each other—as possible. This means the logs should be stacked in a particular way called a crib stack. Begin with a foundation that will raise the stack off the ground. Two parallel posts or non-inoculated logs will suffice. The next layer will be two parallel spawn run logs set at a 90-degree angle to the foundation. The next layer will be another two logs set at 90 degrees, and so on until all the logs are stacked. If you’ve ever played with Lincoln Logs, you’ll totally have fun with this real-life reenactment. The finished stack should be held off the ground, and there should be little contact between layers of logs.

If you have only one or two logs, it’s perfectly fine to lean the logs at an angle against a fence or tree.

Where to Place Your Spawn Run Mushroom Logs

Remember, the one message my mushroom class instructor drilled into the class was that moisture management is of the utmost importance. This means your crib stack or leaning log needs to be placed in a shady/dappled shade location. My instructor’s crib stack is under a stand of pine trees, for example. My one mushroom log is leaning against the north side of a couple of trees. Perhaps you have a barn or structure with a north-facing wall that doesn’t get much light behind it. That’ll work.

Prolonged Hot Weather

Once you set up your spawn run logs, you can pretty much set and forget. It takes about 6-18 months for the mycelium to colonize the log and produce fruiting bodies, aka mushrooms. Your one task at this point is to keep your eye on the weather. If it is hot and dry for three weeks (hello, August) your log may lose too much moisture. And a dry log will kill your mushrooms. Consider soaking the log for at least 12 hours and up to 24 hours.

How do you soak a log? Well, it depends on the size of your log. A kiddie pool will work if the log fits in it. A bathtub works, too. My instructor, who has upwards of 400 logs, has built a raised bed-like container but with a rubberized lining. He fills it with water and can soak a dozen or so logs at a time.

Soaking logs is also a way to force the logs to form mushrooms. After that harvest you can soak the log again 6-8 weeks later for a succession of harvests. That’s how commercial growers of log-grown mushrooms stay on a production schedule.

That’s it for Phase 3. Stay tuned for Phase 4, in which we’ll discuss harvesting—and I’ll include a favorite recipe, too.