GROWING MUSHROOMS ON LOGS
Growing mushrooms on logs and tree stumps is by far the easiest way to cultivate wood-loving species such as oyster, shiitake and enoki, tawaka and more. It also requires a bit more patience. Where a straw bag or sawdust block may produce its first crop of mushrooms within 2 weeks to 2 months of inoculation. A mushroom log will take at least 6 months, and more commonly one to two years to produce its first flush of mushrooms.
The benefits of log culture is that they are low maintenance, can be kept outside year-round, and will continue to produce good crops of mushrooms for several years after they begin fruiting. They also don't require any specialised equipment. Just the logs themselves, a drill to make holes for the dowels, and some wax to seal the holes afterwards.
There are a few key requirements to consider when sourcing logs for your mushroom project. These are getting the right wood type, and cutting good quality logs of the right size.
The best kind of wood to use is deciduous hardwoods. Commonly used species include oak, beech, willow, birch, elm, and poplar. Growers in New Zealand have also had success on more commonly available or pest species including sycamore and gum. If you find a species of tree that's available to you and you aren't sure if it's suitable, just jump on google and check if it works for the type of mushroom you're hoping to grow. Oyster mushrooms, turkey tail and enoki are not as fussy as most other species - they will grow on basically anything!
QUALITY OF LOGS
It's best to try to choose logs which are clear, healthy wood with intact bark, not partially rotten. Rotted wood (with discoloured or soft patches in it) generally already has other fungi in it which will lower your chances of success. Lichen or moss on the outside of otherwise healthy logs is absolutely fine and nothing to worry about - this is on the surface whereas the mushrooms eat the wood inside.
Traditionally, such as in commercial scale Japanese mushroom log farms, logs for mushroom growing are cut during the winter or early spring, while the tree is dormant and with no leaves. It is thought that logs cut during dormancy, when lots of moisture is in the wood, have a marginal benefit to mushroom yields. Logs cut at other times of year still work absolutely fine as well, but may need an additional boost of water via soaking for a few hours if it is summer cut wood that does not have as much stored moisture in it.
SIZE OF LOGS
It’s also important to consider the size of logs you are harvesting. Larger logs take longer to colonise with mycelium, and therefore longer to produce their first crop of mushrooms. But they will continue producing crops any time environmental conditions are favourable, for several years. Smaller logs colonise faster and produce mushrooms faster, but they also fizz out faster once the mushroom organism has ‘spent’ all of the nutrients in the log. When a log is spent it will be soft and brittle, and will turn into soil shortly thereafter.
The ideal size of logs for growing mushrooms is 10 to 25cm in diameter, and 80 to 150cm long. One important consideration with regards to the length of the log is how easy is it for you to lift it and move it around. Wider logs may be cut at the shorter end of the scale simply for practicality sake, because you do not want to put your back out trying to shift around big heavy logs!
You can also inoculate tree stumps using the same techniques. Put dowels into the top part of the stump as well. Beause of the huge root mass underneath the ground, tree stumps can be a highly productive source of mushroom crops. It’s also a handy way of getting rid of the stump faster than it would have otherwise.
INOCULATING GROW LOGS
The process for inoculating grow logs is very simple. The basic idea is to get your mycelium coated dowels into the wood so that the mycelium can spread through the log. And then seal up the holes with wax.
Fresh cut logs (cut within the past month)
Mushroom culture dowels of an appropriate species for your wood type
A good electric drill
Some bees wax or soy wax
A double boiler (pot inside another pot) to melt the wax
A natural bristled brush or dauber to apply the wax to the logs
Figure out how many dowels you have and how many logs you want to inoculate. From there you’ll know how many dowels per log you have and can get a rough idea of how far to space them out. Ideal spacing of dowels is 10-15cm all around the log. As a rule of thumb a 20cm wide log that is 1 meter long will use about 30 dowels for a good inoculation. Wider logs need more dowels, thinner logs need less.
Once you’ve figured out your number of dowels per log, begin drilling holes in your log that are evenly spaced around the length and circumference of the log. Before you begin it can help to put a mark on the drill bit indicating the length of a dowel, so that you drill the holes to the right depth. You want the dowel to be flush with the bark or slightly inside the log. Dowels poking out of the log is not ideal.
After all the holes are drilled, begin tapping the dowels into the holes. You can use a hammer, mallet, or even just a rock or piece of wood. Don’t worry if some surplus mycelium ‘bunches up’ around the entrance to the hole – there's still plenty of mycelium living inside the wood of the dowel that will re-emerge.
Once all your dowels are tapped in, melt your bees or soy wax in a double boiler, and dab a blob of it over each dowel hole. This is to seal the holes, to help retain moisture in the log and also to prevent contaminating organisms or pests from entering the log.
CARE OF GROW LOGS
A mushroom grow log can take several months to a year or more to fully colonise with mycelium. During this time, while they are not fruiting, they can be stacked densely in a pile together. This helps to conserve moisture since there is not as much air flow. Stack your logs somewhere shaded and humid, such as under some trees or bushes. If the ground in the area is particularly ‘rich’ and has a lot of decaying organic matter, it can be good to elevate your logs off the ground, to prevent other fungi from invading. This can be done by putting the logs on a forklift pallet or just raised up with some bricks or cinder blocks.
It helps to water the logs from time to time, especially in the summer months, to help keep moisture levels up. A good soaking with the garden hose will suffice. A once or twice per year ‘dunk’ in a water tub or bath is a great way to recharge the logs moisture supply and a crop will often come soon after that. Logs should be soaked in water for 12 to 24 hours (not longer).
After 6 to 12 months you should notice by looking at the ends of the logs that they are becoming better colonised. At this point you can stack them in a more open format that allows for better air flow, and also gives space for the mushrooms to grow without getting squished. Two common methods are a ‘vertical lean’ where logs are leaned vertically against an object such as a fence or a large fallen log, with gaps of 20cm or so between them. The other method is a grid stack where two logs are laid down about 80cm apart, then two logs stacked on top of them going the other way (so that it looks like a # sign from above) and continue stacking like this as long as you feel that the stack is sturdy and stable.
From here, any time environmental conditions are right, usually in the spring and autumn, your logs may produce crops of mushrooms. Banging the logs with a mallet or dropping them on the ground a few times can stimulate them into fruiting through vibrational shock. Don’t panic if they don’t fruit straight away. Its not uncommon for logs to take 2 or more years to produce their first crop. But they can become highly productive after that.