A step by step guide on how to grow oyster mushroom on straw

Species belonging to Pleurotus spp. (Basidiomycetes) resemble wood inhabiting mushrooms presenting wood-rotting abilities, degrading wood as saprophytes or facultative parasites growing on living or dead wood substrata on which produce a white rot. Pleurotus is more likely growing on deciduous trees and is rather rare on conifers.

Fruitbody morphological aspect: oyster shelf like cap 5-15(20) cm in diam of flesh like consistency with an eccentric-lateral stem of fibrous consistency. The cap color is variable, ranging from a species to another, and may be: white, cream, yellow, pink, reddish, grey, brown or dark grey.

Pleurotus ostreatus cultivation at home is very easy (known as the easiest to cultivate from all cultivated species). It grows on a wide range of substrates such as: paper, straw, leaves, and cotton residues, sawdust, etc which are rather present in rural areas.

Oyster mushrooms are rich in proteins (about 10-30%, fat, vitamins, miner-als, etc), they have a therapeutic effect with a major impact on human health (0% cholesterol, polysaccharides with antitumoral, anti-inflamatory, anti-bacterial, anti-viral, anti-oxidant and immunomodulating effects). In addition they are delicious and worldwide famous.

An important aspect worth considering here is that some Pleuortus species are thermophilic (they love higher temperature ~30-32 °C / 86-89.6 F) while some other species are cryophilic (lower temperatures such as ~8-15 °C / 46.4-59 F are more suitable for their development). Taking into account this, we may choose what species to cultivate and in what season.

Another important aspect is the sensitivity level of the mushroom; therefore we have more or less sensible species to the environmental factors present in the grow room. One thing is certain, these factors influence the mushroom developmental process, and are composed of biotic (e. g., competitive molds, flies, nematodes, or other competitive mushrooms for the same substrate), while a-biotic factors refer to developmental conditions such as: temperature, humidity, ventilation, and light. Both, abiotic and biotic factors and ways how to avoid (biotic) or adjust them (a-biotic) are discussed in detail in the Low-tech Small-scale Mushroom Farm Setup Training.

THE CULTIVATION PROCESS

Preparing the mushroom cultivation chamber

In order to avoid future culture contamination with various molds or insects the cultivation chamber obligatory has to be cleaned up. This procedure is necessary for the success of the cultivation process. The principle is simple: a clean product left in a place filled up with germs, has a high rate of contamination with germs; therefore a clean environment is necessary if we want to obtain success in our mushroom cultivation process.

Therefore you should wash the floors with water and soap, paint the walls and use germ killing substances such as: chlorine, or alcohol mixed up with water [100ml (0.0246 US gal) of chlorine to 10l (2.642 US gal) of tap water] that will be sprayed all over in the grow room. This treatment has to be applied before and after each mushroom cultivation cycle just to be sure that possible contamination from previous mushroom culture won’t affect future cultures.

The cultivation chamber may be any space destined for this purpose able to keep a high humidity level; however most chambers fail to keep humidity and this may result in dry substrates and poor mushroom fruitbody production. Since this cultivation method is classical and made without equipment the mushroom cultivation chamber should have some other requirements such as:

• if possible to be a place able to keep a constant temperature;
• a place able to allow a natural ventilation (e.g., by opening a window or a door);
•  a place able to allow sunlight entrance (e.g., through a window) or if this is not possible then this may be substituted by electrical lights;
• the floors should be made out of concrete or any other material except wood.

Basements are ideal for growing mushrooms especially because they do not fail in offering proper development conditions for mushroom fruitbody formation. Anyway, you may use any space that you have available for mushroom cultivation, just keep in mind the above mentioned.

Note: If you opt for an open space to grow mushrooms then you may use a plastic foil cover (as seen in the picture above) to avoid substrate water loss and mushroom fruitbody dryness. However, in spite of all these measures it is possible to grow mushrooms outside in open air if the outside environmental conditions are proper for this.

Material and tools needed for home mushroom cultivation

In order to grow mushrooms we will need to use the following:

• substrate ingredients (see substrate recipes) or the so called compost ingredients: straw (wheat, rye, or barley), woody materials (chips, sawdust, etc), paper (cardboard, newspaper, books), corn (corncobs, cornstalks), cotton wastes, coffee grounds, nut shells, dry leaves, hay, or any other type of agricultural wastes;
• mycelium (spawn or mushroom seeds);
• a fire source;
• tap water source;
• a pot, a metal barrel or any other recipient. This will be covered up with a lid;
• (a recipient built up by using a wire mesh);
• (a customized table -as seen in Fig.13: will be used for filling up the plas-tic bags with compost);
• a plastic foil;
• trash bags or customized column shape plastic bags;
• gypsum;
• water sprayer;
• disposable gloves.

Note: Newspaper or books are not recommended as substrate ingredients since oyster mushrooms; particularly Pleurotus ostreatus has the ability to accumulate polluted substances and heavy metals into its fruitbodies
The beginner mushroom cultivator may leave out of this list the wire mesh recipient or the customized table since these is not obligatory for the cultivation process.

Main ingredients of the mushroom cultivation substrate

Oyster mushrooms generally grow on a wide range of agricultural waste materials of which they decompose. Such waste materials may be easily found in our house backyard, in our own kitchen or in the paper and wood industry. It can be used any material that is consisting of cellulose and lignin, two basic constituents of wood and plant organisms.
Many woody materials consist also of resins and polyphenolic compounds (such as found in the conifer wood) that inhibit mycelium growth in some mush-rooms.

Therefore for oyster mushroom cultivation is not recommended to use as main grow substrate coniferous wood. By contrast, Pleurotus species grow on deciduous wood such as: beech, poplar, oak, birch, maple, and other such wood types.

Other largely used substrates include: straw (wheat, barley, rice, etc), cotton hulls, corn stalks, leaves, paper or other agricultural wastes.

For those living in the city oyster mushrooms can be grown on cardboard, nut shells, (e.g., peanut, sunflower), coffee grounds, hay, or dry leaves. All of these substrates are rich sources of nutrients for mushrooms and are readily available as wastes in our own yard or kitchen. Why throw them out? We have the chance to turn them into food.

Things to consider when choosing substrate material:

• I recommend you to use fresh materials (not older than 1 year);
•  the material shouldn’t be moldy or wet because of improper storage;
• the material should not have any color other than its native color;
• the material should be clean without any alien particles such as rocks or glass pieces;
• the substrate dimension is an important feature and is strongly connected with the spawn (mycelium) run through compost. For example the straw should be chopped into small pieces (1-1.5 cm/0.4-06 US in) or wood should be used as wood chips. Keep in mind: the bigger the substrate particle is, the slower the decomposition rate by mushrooms gets and this results in a longer time until mushroom fruitbody formation.

Note: If you don’t have any chopping machine around, no problem use the material as it is (for example use straw as it is). Wood may be also used as whole logs

Substrate recipe

I recommend to the beginner mushroom cultivator in his first trials of oyster mushroom cultivation to use a simple substrate recipe: composed of a single ingredient (e.g., wheat straw -the first recipe). Once familiar with the culture of mushrooms the beginner cultivator may play with a wide range of ingredients, including nutritional supplement additions. Finally through failure and success he or she will understand how the whole process works and will develop a real experience in time.

I will expose here some substrate recipes for oyster mushrooms cultivation from which you may choose:

1. wheat straw 95% + gypsum 5%
2. sawdust (beech, poplar, oak, walnut, horn-beam, maple,..) 95% + gypsum 5%
3. straw 60% + corn-cobs 35% + lime 5%
4. corn-cobs 90% + barley grain 7% + gypsum 3%
5. soybean stalks 60% + corn-cobs 36% + gypsum 4%.

We’re going to focus on how to grow oyster mushrooms on straw therefore let’s see how they’re grown on 95% wheat straw with 5% gypsum.

Next the material has to be chopped into pieces (if possible). In principle for a 100 kg/220 lbs of substrate you will need about 30-60 kg/66-132 lbs of dry material. The material is going to be soaked into water therefore its final weight will be around 100 kg/220 lbs.

Note: Weighting the material is not mandatory only if you want to know exactly the substrate quantity that you are going to process. Usually this is a necessary step when you estimate the overall mushroom production.

Substrate disinfection

there are several ways to disinfect your substrate before inoculation but here I will tell you only how to heat treat that. If you’re interested to find out some other cost effective methods like ‘the cold pasteurization method’ or how to start a mushroom growing business you have to invest in knowledge to get results faster and to not loose precious time and energy with futile trials. The Mushroom Cultivation Training  was created for total beginners interested to start their mushroom journey the right way.

To heat treat your substrate pick one of the following:

1. Direct flame heating: The material is placed into a container (usually a metal barrel, or an improvised boiler) half filled with water and it is soaked by using a grill placed on the top of it which is designed to keep the material under water, then everything is covered up with a lid for an appropriate heat treatment.
2. Scalding the material into hot water: the same procedure as described above should be used here too.

Place the straw in a barrel until the temperature reaches 80-85 ºC / 176-185 F and try to maintain this temperature for about 2 to 4 hours. If the treatment temperature is lower, then allow more time for heat treatment process. This way occurs the so called ‘substrate pasteurization’ and this step is important because kills competing fungi and bacteria present into the substrate mass. However this temperature doesn’t kill some bacteria species useful for the mushroom cultivation process.

Note: Another heat treatment procedure is to sterilize the material by boiling it for several hours or rising the temperature to 121ºC / 249.8 F for about 30 minutes to 1 hour. However, this procedure is not suitable for backyard mushroom cultivation.

Preparing the substrate for inoculation

The house backyard mushroom cultivation is a concept based on ideas and lots of improvised tools in order to make the whole process easier. One of such improvised tools is the wire mesh container which is filled up with material and soaked under water during heat treatment. This has the ad-vantage that allows water flow immediately after heat treatment. Thus through a rope system it can be lifted up from the boiler and kept in the air while water is licking away. It also has the advantage of removing all material from the barrel after heat treatment.

All operations that we undertake from now on (draining, inoculation, etc) should be performed in clean conditions in order to avoid substrate competitors like molds, germs and bacteria; otherwise all of our work until now could be compromised. This is why containers and all tools that the pasteurized material enters in contact with should be clean enough to ensure mushroom cultivation success.

A first step is to clean up container surfaces with 90º alcohol or some other germ killing substances (however, these should be oyster fungus friendly substances designated only against competing fungi or bacteria).

Wash hands with soap and water, then spray them with alcohol or use a pair of gloves.
After pasteurization, allow material to cool down preferably on a clean concrete surface covered up with a clean plastic wrap, or a specially designed table for this purpose. Disperse the material on the table in a layer of 20-30 cm / 7.9-11.8 US inch thick in order to cool quickly.

Check the substrate before inoculation:

• The material when squeezed into our hands should not show any water drops;
• The smell should indicate a freshly humidified substrate and should not have any sour odor indication the start of decomposition process.

Note: How will you know if you did the right thing so far?
Water should not accumulate at the bottom of the plastic bag that is going to be introduced in (waste bag, customized plastic bag, or other container type).
Checking substrate moisture content -the old school way: ok means few to no water drops.

When the substrate temperature drops down to cca. 20-25 ºC / 68-77 F the material is cool enough to be weighted and inoculated with mushroom mycelium (spawn).
In order to know the exact quantity of substrate, it is recommended to weight materials in a wet state separately and then to mix them up.

Adding amendments and mycelium to the substrate

1. Immediately after mixing up the substrate ingredients you’re good to add to the substrate mix up to 5% gypsum, then mix well and next you’re ready to inoculate the substrate with spawn.

2. Now take a pair of disposal gloves on your hands and carefully take the mycelium out of the jar or bag. Care should be taken not to damage the hyphae of mycelium surrounding the grain kernels or other support on which it is growing. Mycelium is a living organism, therefore if damaged the mycelium won’t be able to spread throughout the substrate and this will result in low mushroom yield.

3. Now weight the mycelium (mushroom spawn) and use the desired quantity (usually 2-3% = 2-3 kg / 4.4.-6.6 lbs to 100kg /220 lbs of compost)

4. Next add the weighted mycelium quantity to the readily pasteurized and cooled substrate that has been mixed up with gypsum. Mix everything together and disperse the mycelium in the whole substrate mass.

Note: If you will increase the amount of mycelium added to the substrate from 1.25% to 5% automatically the mushroom production will increase to about 30-50%. In addition this will reduce the time necessary for spawn to colonize the substrate during incubation and will prevent contamination by competing molds, bacteria or insect occurrence in the substrate.

Otherwise, the competing species might take control of part (10-20%) of your bags filled up with inoculated substrate. When this happens, the oyster mushroom mycelium stops or reduces its development. However, such situations occur, even if you did everything right, so there’s no need to panic if you find 10-20% of your bags are infected with molds or such contaminants.

Don’t get discouraged, but try to think of what did you do wrong or how could you improve your mushrooming experience. From time to time even the experienced mushroom growers are dealing with such situations.