Grow mushrooms the EZ way.

How To Spawn To Bulk When Growing Mushrooms.

Layer of spawn in monotub


Spawning to bulk refers to the practice of mixing colonised mushroom spawn (such as grain spawn) with a nutritious substrate in an effort to expand the growth of the mycelium and eventually fruit into edible mushrooms. 

Spawning to bulk does not have to be a sterile procedure in the same way that creating grain spawn is. 

If you prepare your substrate in the correct way you should be able to spawn to bulk on a wiped down kitchen table with some gloves on.

Hopefully if you have never done this before you will come away with confidence in this stage of growing mushrooms as it can be a daunting step. 

In this post i will cover the following methods of spawning to bulk:

  • Spawning Grains to Bulk Substrate.
  • Spawning PF-tek (cakes) to Bulk Substrate.
  • Spawning to Outdoor Bed.

First let me start with some things you need to understand before spawning to bulk substrate.

Pasteurizing your Bulk Substrate – Quick Overview.

When spawning to bulk it is better to pasteurize your substrate instead of sterilizing it. This is because pasteruization leaves some good bacteria in the substrate which helps to fight off competing contaminants in the substrate. You can use the following methods to prepare your bulk substrate:

  • Hot Water Bath.
  • Cold Water Lime Bath.
  • Cold Water Ash Bath.
  • Oven Tek.

All of these techniques are covered in “How to pasteurize substrate at home” OR “How to pasteurize mushrooms without a pressure cooker”.

Unless you are growing using high levels of nutrition to the substrate (adding coffee or soy hulls) then sterilizing the substrate is not necessary.

When using sterilized substrate you must use a laminar flow hood with sterile technique .

Sterilizing your substrate without sterile condition will probably result in failure. Always pasteurize your bulk substrate if you are not in a lab environment.

Spawning To Bulk Substrate.

These techniques can be applied to grain spawn and sawdust spawn.

Spawning to bulk does not require sterile conditions, it can be performed in open air on a kitchen counter.

However it is still advised to take precautions to reduce the chance of contamination.

Step 1 – Prepare.

Put some rubber gloves on, a surgical mask and wipe down your surfaces with alcohol.

Wipe down the vessel you will place your spawn in with alcohol too (bucket, container, monotub).

Step 2 – Add Substrate.

Place a small layer of substrate about 1/4 of your substrate on the bottom of your growing vessel.

Try to spread this as evenly as possible removing any lumpy bits and compressing it slightly but leaving plenty of space for the mycelium to grow through.

Step 3 – Add Layer of Spawn.

Place a small layer of substrate about 1/4 of your substrate on the bottom of your growing vessel.

Try to spread this as evenly as possible removing any lumpy bits and compressing it slightly but leaving plenty of space for the mycelium to grow through.

Step 4 – Add Another Layer Of Substrate.

Place another layer on top of the spawn layer. Continue adding layers in a lasagne like fashion leaving a layer of bulk substrate as your final layer.

I like to spawn to bulk in this way because the spawn is surrounded by pasteurized material and can recover before reaching the vessel walls which may not be as “clean”.

Step 5 – Seal Vessel.

Cover your substrate with tin foil OR close off the spawn bag/bucket and leave it for 10-14 days it to fully colonize.

Spawning PF-Tek to Bulk Substrate.

Spawning pf tek to bulk is very easy and there are a few different techniques you can perform.

I will discuss the different options here for spawning PF-Tek to bulk substrate.

Step 1 – Prepare.

Put on your face mask and gloves, wipe your gloves down with alcohol. Wipe down you growing vessel with alcohol.

Step 2 – Add Layer Of Bulk Substrate.

Place a 1cm deep layer of substrate in the bottom of your container or grow bag.

Step 3 – Add PF-Tek Cake.

There are a few different options for how you add the PF-Tek spawn to bulk substrate, all of which are useful.

  1. Crush the cakes in your hands then mix them with the bulk substrate.
  2. Grate the cakes using a cheese grater over you bulk substrate. (wipe with alcohol first). 
  3. Cut the cakes into discs then lay the discs on top of the bulk substrate.

Step 4 – Add Another Layer Of Substrate.

Place a top later of bulk substrate on the top of the current so that the spawn is surrounded by pasteurized substrate.

Continue layering you substrate and spawn until you run out.

Spawning To Monotub.

Spawning to the monotub is basically the same as the methods described above method but you need to add the extra step of lining the monotub with a plastic bag to prevent side pins from forming.

Do this by taping a plastic bag (such as a shopping bag) to the sides of the mono tub about 3 inches from the bottom of the tub, underneath your fresh air exchange holes. You can find more details about that on my post on how to make a monotub.

Spawning To Outside Bed.

It is advised to use sawdust spawn for this method, due to the fact that birds will search out and eat grains if you throw them in your garden. 

Regardless this method is pretty straight forward just remember to keep the moisture levels up and use a species which is a really good coloniser outdoors like wine caps.

Step 1. Soak wood chips overnight in water then pour out excess water from your bucket.

Step 2. Next cut your sawdust spawn into a few brick sized pieces (maybe a little smaller than a brick) then place them onto the bed. 

Step 3. Covering the sawdust spawn with the woodchip allowed about 2-3 inches of woodchip to cover the sawdust spawn.

Step 4. Keep your wood chips moist with regular watering like you would with flowers.

If it is a wet season then the climate will do this automatically.

Your mushrooms should fruit automatically when the conditions are correct.

Hydration For Bulk Substrate.

Mushrooms require plenty of water to grow, this means the substrate you grow them from must be well hydrated so the mycelium can soak up water as they move through the grow cycle. 

So…how hydrated does the bulk substrate need to be?

The bulk substrate needs to be at “field capacity” to provide the correct hydration amount of water to grow mushrooms.

Field capacity can be attained in the following way:

Take a handful of pasteurized bulk substrate and squeeze it really hard, wait a few seconds then squeeze it again.

Your substrate will be at field capacity when you can hold it without any water coming out but when you squeeze it hard a small stream of water comes out.

You should now place it into your fruiting container or bag using the methods discussed below.

Now I will go over step by step guides of how to spawn in bulk when growing mushrooms. 

Fully colonized (100% engulfed in white mycelium) can be used to spawn to bulk substrate in semi-sterile condition.

This means you should wipe down your surface area and wear some gloves which have been wiped with alcohol before beginning; this can be competed in open air such as a kitchen counter if the area is properly cleaned.

Spawning To Bulk Temperature?

Optimal temperatures for bulk substrate are around 62-75f (16-23) so your bulk substrate should be room temperature before using it. 

If you spawn to bulk with higher temperatures in the 82f range you risk killing your mycelium through thermal death (think boiling them alive).

Sterilize Vermiculite Before Spawning To Bulk?

If you are using vermiculite as a casing layer for the top of a 100% colonized substrate then you do not have to worry about contamination and can just place the vermiculite on the top straight from the bag.

If you are adding it to your bulk substrate then you should add it in before the pasteurization process, therefore it will be pasteurised properly for a colonization stage.

I cant think of any other situation where you would be adding vermiculite to bulk substrate, but leave a comment if this doesn't answer your question and I will respond.

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