This discussion happened on Shroomok Discord Growers Community, in ❓general-questions channel

In all the quotes, the original spelling and punctuation has been retained.

Let's discuss how spawn to bulk ratio influences the speed of mycelium growth and overall results!

🔴 Dino: I have a question, when it's time to mix with the bulk substrate, is there a disadvantage/advantage to use a sub 1:1 spawn:bulk ratio? Ex: 0.5:1

Discussion regarding the optimal ratio of grain spawn to bulk substrate for mushroom cultivation

🔵 User: Not necessarily bad but typically 1:2 - 1:3 is ideal

🔴 Dino: First of all, thanks for answering, I have gathered info on multiple forums and they all recommend anywhere between 1:1 and 1:4, but the definition of ideal is a bit blurry for me. Ideal in the sense that we can 'dilute' the spawn into larger volumes of bulk without affecting too much the yield of a single tub, effectively meaning I would 'waste' spawn if my spawn ratio is higher? Or ideal in the sense, that it's the ratio that maximizes the yield in any given tub?

I have also read that much higher bulk ratios increase the risk of contamination by increasing the time of colonization post spawn-to-bulk transfer, so that's a no go since my environment isn't as sterile as I would like it to be...

🔵 User: Well your theory on that is correct, the longer it takes for your myc to colonize the higher chances something else can grow first. If you are using coir it's borderline impossible to contam the sub by itself, now if your spawn isn't clean, well that's a diff story. What im saying is that typically contam is introduced via spawn since coir has little to no nutrients for contam to thrive on. Now in regards to your question regarding the ratio of spawn look at it this way....the whole point of using a 1:3 for example over a 1:1 is that your cakes/spawn provides enough nutrients for your tub. The increased amount of sub gives your mycellium more surface area to colonize. More mycellium means you can bear more fruits. On the low end (1:1) you get less mycellium area but faster colonization as compared to 1:3, etc. The opposite is true for higher ratios. You get more surface area to colonize but it colonizes slower. I typically do 1:2 or 1:3 as I find it is a good mean choice between colonization speeds and surface area. Hope that answered all your questions.

Also I would like to mention that colonization speed is primarily determined by genetics, but when I refer to colonization speed in this sense it is simply due to it having to colonize more area to achieve full colonization, however the rate of colonization is the same.

Ex. ) 2 cars traveling at the same speed but different distances will reach their destination at different times

🟠 User: Agree with the 1:3

🔴 Dino: Thank you, I get your point. So as long as I can cover the whole surface area with the right depth requirement for fruiting to occur, I should be good no matter the ratio, as long as it stays in the accepted ranges. The question was asked because I have 'too much' spawn compared to what is typically used in a 66qt mono tub. What I have seen is people using 3lbs of spawn + 3-6 lbs of bulk for this size of tub, since I have 4.5lbs of spawn, I was just wondering if using 3lbs of bulk (on the low end) was problematic, from what I understand, it shouldn't be

🔵 User: I dont think it would necessarily be problematic, more so a waste of spawn at that point

🔴 Dino: Exactly what I thought, might just use some to inoculate my next spawn bags and use one of my tubs with the extra spawn to see if there's a difference

To clarify, I have three bags destined to three tubs, one would be the experiment

🔵 User: Send it

🔴 Dino: Sure will, if everything won't crash in my face until the end, I will share my results with you guys! Oh that gives me an idea, maybe we can start a spreadsheet with everyone's experiments and draw our own analysis for optimal growth! Data is my specialty

🔵 User: That's been done already not here but there is a journal like that

🔴 Dino: Alright! Will look it up, thanks!