Too much water in sawdust substrate?

Good day all

I spawned this sawdust fruiting block yesterday. (Ganoderma Lucidum)

5L hardwood sawdust (600g), 3L water, 100g wheat bran, 30g biochar and 20g gypsym

I am wondering if i used abit too much water? There is about 2cm of water at the bottom of the grow bag.
2 quart jars of Ganoderma Lucidum was used to inoculate.

I know mushrooms are 80-90% water so should i be worried??
My plan is to either drain the water if its too much and when the sub is fully colonized with tenacity - i will remove the whole grow bag. Leaving the reishi block exposed to airflow and humidity in my martha grow tent.

Hi @Merlyn,

Yes, unfortunately that is far too much water. There should never be any standing water in the substrate container, whether that be grain in jars or bulk substrate like sawdust in bags. Those pools of water prevent mycelial growth and encourage the growth of bacteria (among other contaminants).

If I were you, I’d wipe down the bag with 70% isopropyl alcohol, make a small incision at one of the bottom corners with a sterile scalpel blade, squeeze the bag to drain as much of the water as possible, wipe the incision with alcohol again and then cover it with micropore tape (or clear tape or duct tape).

The rule-of-thumb for bulk substrates is that there should be little-to-no water released when you grab a handful and squeeze. If a few drops are released, that’s OK. If a stream of water is released, your moisture level is too high.

As a general suggestion, I recommend using smaller amount of substrate and spawn while you are still in these early learning stages. For example, you could run your sawdust / woodchip substrate mix in 1 L jars or much smaller bags to dial-in your recipe and process. As Geoff Lawton says: nail it then scale it.

Sawdust is generally one of the more difficult substrates when it comes to getting the right moisture content. You’ll get there with practice. Could you outline your process for preparing the mix? I’m particularly interested in when and how you introduce the water.

Hi @glyph

Thanks for the feedback. I had a feeling there was too much water and already decided to make incisions in the bag with my syringe needle (about 3 holes - i felt the holes would be small enough to minimize contam)
However i think the scalpel idea you had would be alot more efficient - i was just worried about making the holes too big.

I thoroughly bleached down the bags before making the holes. Its hard to sqeeze out the last bit of standing water so im letting it drip for now.

Right now im just waiting for the last bit of moisture to escape before i seal it back up.

Basically my process involved just adding 60% water to the bag, sealing the bag and pressure cooking it.

Step 1:
Mixing ingredients. 5L sawdust (600g), 100g wheat bran, 40g of gypsum and biochar

Step 2:
I added 2.5L - 3L of water per bag. (I think 1.5 or 2 liters will suffice in the future)

I watched a video where someone on large scale just added water and didnt even bother getting it to field capacity. This is why i thought id give it a try.

I did not premix the water and the bag. I just adapted a pre-existing recipe to the quantity i wished to work with

Step 3:
Pressure cook at 10psi for 3 hours

Step 4:
Wait to cool down and inoculate with 1Liter (500g) of Reishi, Ganoderma Lucidum, grain spawn

Thankfully the biochar and water mixed up nicely so the water should stay fresh for longer while it drains. Later i will patch up the holes, every hour or so i spray down the bags just to eliminate any bacterial build up from outside - that may travel inside.

After its drained i will either patch up with tape, micropore tape or plastic cling wrap

In the future, i think i shall premix everything in a clean tote before packing into grow bags.
Doing all the mixing in the grow bag was difficult and messy.

I think I’ve also overhydrated my bags, and this is why I’m seeing this dark uncolonized region at the bottom of the bags:

The bags above were with 50% sawdust and 50% coffee. The bag below is with 90% sawdust and 10% coffee.

once the bags are mostly fully colonized like this, do you think it still makes sense to make a cut in the bottom to try to drain them? or should I just directly cut the bags open for fruiting and take them to the fruiting chamber, leaving that bottom area uncolonized?


I think I’ve also overhydrated my bags, and this is why I’m seeing this dark uncolonized region at the bottom of the bags

Agreed. That’s the tell-tale sign of over-hydration. The mycelium stalls at the point where there’s too much water to continue. The photos of the two mixes gives a really nice illustration of the relative moisture content of your coffee and sawdust substrates. Seems like the sawdust was probably slightly drier and was able to absorb some of the excess moisture from the coffee. Sawdust is one of the trickier substrates to get right in terms of moisture content.

In this case, since the mycelium is already well-developed in the upper region of each bag, I would cut the bags open for fruiting. The bags are difficult to drain sufficiently at this stage because you can’t squeeze the substrate easily (much easier to do when the mycelium hasn’t colonized the majority of the block yet). You are likely to introduce contaminants if you attempt to drain now.