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Troubleshooting Oyster Mushroom Kits

Updated: Jul 21

When Growing mushrooms you can run into some simple issues - much like any other crop or plant. Mushrooms are roughly 90% water and like a high-humidity environment. Depending on the mushroom strain they can be tolerant of temperature swings and other environmental factors.

This post will cover some of the most-common issues growers will experience with the common oyster mushroom. Whether an imported strain or NZ-native culture, the key issues are the same.

The Oyster Mushroom's Basic Needs: Some Fresh-air & Reading-level Light

Oyster Mushroom Grow Kit Troubleshooting - long stems & small caps
Severe lack of fresh air &/or light: otherwise healthy block!

Mushrooms are the opposite of plants in that they 'inhale' oxygen and 'exhale' CO2: much like us humans. Oyster mushrooms in particular produce a lot of CO2 as they grow, and need a steady supply of fresh air to develop normal fruit bodies. Unlike button mushrooms, that prefer darkness, oyster mushrooms require reading-level light (not direct sunlight) to get that nice deep-cap-colouring and proper formation.

Signs of Lack of Fresh Air/ Light & A Quick Fix - Repositioning

The first indicator of a lack of fresh air is when mushroom fruit bodies begin to grow with long stems & small caps -- as seen in the photo above. If they do not have sufficient reading-level light -- and a bit of fresh air, (say they are placed in a container or cabinet) -- they will produce very long, stringy stems with tiny caps or no cap at all. Once the mushrooms have gotten to this stage (like in the photo above), the best thing to do is remove the entire mushroom cluster by twisting it at the base. Then move the block to a more suitable environment and wait for the next flush. This won't effect your overall yield by much, as they will grow until they run out of nutrients.

Mushrooms grow at a very fast rate, doubling in size every 24 hours in ideal conditions. Because of rapid growth, the effects of environmental changes can often be seen within 24 hours -- if you act quickly the issue can often be solved while the mushroom is still growing. If you have moved the block and are not seeing a difference in cap size and the stems are still long and stringy, rip them off to start-over as a new flush will give you another chance.

What's that Yellow Liquid in my Oyster Grow Kit Bag?

Phoneix Oyster Mushroom Bag with Yellow Liquid Metabolites forming
Phoneix Oyster Mushroom Bag with Yellow Liquid Metabolites forming

When mushrooms grow through a substrate, they often secrete enzymes and digest the substrate externally -- they essentially have external stomachs. The yellow liquid patches are metabolites; which are a bi-product from the enzymes breaking down the substrate. These are sometimes produced to help fight-off an unwanted contaminant within the bag. If you see this, there is no need to worry as it is perfectly normal. The image to the left is of a healthy block from one of our >> 5-step oyster mushroom starter kits that is close to producing mushrooms.

Fun Fact: For the last 100 years most antibiotic drugs, such as penicillin, have been made from mushroom metabolites. There are records dating back to ancient Egypt documenting the application of mouldy bread to infected wounds. By 1943 large amounts of penicillin were being produced which many speculate won World War II.

What's the optimal point to harvest my Oyster Mushrooms?

Oyster Mushroom Grown to far
Oyster Mushrooms that are slightly over-ripe

Oyster mushroom grow very quickly, especially when the temperature is above 20 degrees. When to harvest is always a tricky one for new growers because of the growth speed. This mushroom kit shown to the right is just slightly over-ripe and ideally should have been harvested 12 or so hours before this. Harvesting at the right time gives a better tasting fruit body with superior texture and shelf life.

Oyster mushrooms begin to drop a lot of spores once they get to this stage, if left and not harvested they can literally change the colour of the floor with spores (like the photo below). If this happens just clean up the spores with a damp cloth and harvest a little earlier next time. Harvesting slightly earlier will save some nutrients for the next flush, meaning the total yield from the block over the life of the block will be the same just with more lots of smaller mushrooms.

My Oyster Mushroom Block is producing a lot of spore mess

Phoneix Oyster mushrooms spore release
Phoneix Oyster mushrooms spore release

Oyster Mushrooms are one of the largest spore producing mushrooms of any commonly cultivated mushroom -- especially the velvet oyster, our native oyster mushroom! The NZ native oyster mushroom produces more spores than any I've seen. Left too long it will change the colour of your floors and benches -- this is why we commonly use the Phoenix oyster over NZ Native Oyster Cultures: the Phoenix oyster drops less spores and has a less chewy texture, but a little less flavour.

Oyster Mushroom Spores on bench top
Oyster Mushroom Spores on bench top

Mess from spores can easily be avoided by harvesting the mushrooms before spores begin to release. Generally spores begin to drop as the caps flatten out, so by harvesting when the edge of the cap is still curled down you can avoid this.

If you do happen to miss the harvest spores wipe off easily with a little warm water and a towel. For most people the spores are no issue but some people can experience allergies to the spores, so if you are sensitive be sure to harvest much earlier than you think. If you are a long term grower or growing in a commercial setting, be sure to grow in a well ventilated area so you are not continually exposed to spores for long periods of time. This type of prolonged high volume exposure can cause allergies to develop over time if care is not taken. Commercial growers usually wear masks in the fruiting room but this is not usually necessary for the home to hobby grower.

What's all the white stuff growing at the surface of my >> Oyster Mushroom Grow Kit?

Oyster mushroom kit ready to produce!
Oyster mushroom kit ready to produce!

Often before oyster mushrooms begin to produce the mushroom fruit body the mycelium will begin to consolidate on the surface under the plastic. This is 100% normal healthy activity and a good indication that your block may be ready to produce mushrooms any day now. If the sawdust in the holes has lightened in colour you can add 1/2 a teaspoon of tap water to each hole to re-hydrate the sawdust, you are not trying to add water to the block you are only dampening the small opening, this action mimics rain fall in the natural world and helps encourage mushrooms to form.

Should I water my Oyster Grow Kit?

A common mistake with new growers is the belief that the block needs to be watered like a plant, when mushroom blocks are mixed they consist of about 60-70% water, the mushroom will draw from this reserve over its fruiting life, adding water is actually somewhat difficult as mycelium is waterproof. If a block has fruited many times (2-4 months old) and is looking/feeling dry you can rehydrate it by submerging the block underwater for 12-24 hours. When you do this simply puncture a few holes in the bottom of the bag to allow excess water to drain out.

My Oyster Mushrooms are passable but a bit meh - what should I do to improve them?

This bunch on the right is 100% edible but some issues can be identified:

Oyster Mushrooms growing with insufficient light/humidity
Oyster Mushrooms growing with insufficient light/humidity
  • Long (ish) stems show a slight lack of fresh air but not a huge issue here.

  • Cap is almost 100% white where it should be a nice brown to dark brown: this is likely from a lack of light. Mushrooms like either filtered non-direct sunlight, or artificial light in the blue colour spectrum (6500k colour). Light is key for nice cap colour.

  • Slight yellowing on the edges of the mushroom, this is usually caused by two things. First, and most common, is the drying out of the mushroom as it is growing -- oyster mushrooms ideally like to grow in 80-95% humidity which can be hard to manage at home. We advise people to grow their oysters in the bathroom, as this is usually the most humid room in the house and almost always has filtered light. You can help with drying out by spraying a fine mist of water from a spray bottle. The second reason for yellowing can come from the misting using the spray bottle: if the mist is sprayed directly onto the cap it can cause the yellowing. Ideally you want to spray the mist from 30+cm away with the nozzle set to the finest droplet size possible - the mushrooms can be misted 2-5 times a day during dry weather. If your water supply is chlorinated you should leave the water out over-night, in an open pot, so the chlorine evaporates out of the water before using it on your mushrooms.

What's the green stuff growing on my Oyster Mushroom Kit?

Mushroom contamination: Trichoderma growing in mushroom block
Trichoderma growing in mushroom block

The green mould is trichoderma. Trichoderma is in the fungi family and grows almost everywhere -- very common in soil, compost and on your bread when you leave it too long. For mushroom growers this is the most common form of contamination, it is a rapid grower and sometimes will out-compete mushroom mycelium. It is easily identifiable by the green-colouring of the spores. If your bag is over 20% green then it is best to move it outside to the garden and let the battle happen outside, sometimes you will still get some mushrooms! It is best to put it outside as you don't want the spores (green-colouring) to go through your bathroom or grow area where you may want to do future mushroom projects. Most of the time trichoderma occurs from poor cleaning of work surfaces, hands, utensils etc when mixing the mushroom substrate. If the trichoderma spot is small and isolated (say $2 coin size spots) then the mycelium will usually get very dense around this area and hold it at bay. If this happens it is fine to keep the bag inside and 'fruit' it like normal. If the spot is near a hole you can simply put a piece of tape over the hole to stop the spores getting out of the bag. If you notice any green colouring in a bag that is still in the incubation stage (weeks 0-3) be sure to check it daily, as trichoderma grows very quickly and will go from not visible to the untrained eye, to green and dropping spores, within 24-48 hours.

What should I do about Oyster Mushrooms growing under the plastic of my grow bag?

Oyster Mushrooms growing under the plastic
Oyster Mushrooms growing under the plastic

When a mushroom block begins to fruit it directs the mushrooms to where the fresh oxygenated air is -- remember the mushroom block is a living organism and it is aware of its external environment. It is able to detect the differences in CO2 concentrations throughout the bag and this helps orientate the bulk of the mushrooms to push out of the holes in search of fresh air. In nature, this would be the most probable spot for spores to be released and travel far for reproduction. Sometimes mushrooms will begin to form under the plastic as well as near the holes as you can see in the picture to the right, if this happens it is usually best not to try open the bag and leave them. Most of the time, they will stop growing and re-allocate the energy to mushrooms that are in better quality air. The easiest way to avoid this happening is to twist the bag up as tight as possible when making the block, removing as many air pockets as possible.

Mushrooms that have started growing very long and stringy like in the picture above will not from into normal mushrooms and cannot be saved. Because of this, it is best not to open large holes in the bag to help them, we are trying to preserve as much of the water in the block as possible. Remember, mushrooms are 90% water so any evaporated water is a loss in edible fresh mushrooms. Keeping the holes small minimises water loss through evaporation. Mycelium is waterproof, so pouring water from the top like a plant does not work very well. If a block has been fruited many times and begins getting too dry, you can submerge it underwater for 12-24 hours to help re-hydrate it. This can usually only be done a few times before contaminants begin to grow on the older weaker mycelium. This is the ending stage of the mushroom life cycle. At this stage the plastic bag can be removed and the old block can be placed in a shaded spot in the garden to produce a few more if you are lucky.

How can I Grow a Steady Supply of Oyster Mushrooms?

If you want a steady supply of mushrooms you would make up a new block every 3-4ish weeks. With new and old blocks you begin to form a rotation of fresh blocks beginning to fruit and old blocks being retired to the garden. At the mushroom farm we produce fresh blocks every week to keep a constant supply of fresh mushrooms. As a block gets older the amount of mushroom it produces becomes less and less, usually the first 2 flushes are by far the biggest, 3rd and 4th flushes much smaller and 5th flush onward only producing a handful or so of small mushrooms. Our goal with the beginner-grower's >> 5-step oyster mushroom DIY kit (which most of these pictures are from) is to make it affordable for the average person to be able to easily grow fresh nutritious mushrooms at home as a somewhat consistent supply. We also sell >> refill kits for the 5 step oyster mushroom kit here - (includes a very economical subscription option).

If you have any questions with your kit or another product please don't be shy and send us an email through the contact us feature near the bottom of the front page!

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