My mushroom kit has mould, is that a problem? | OGM! (2024)

May 24, 2022

mushroom growing tips

Being fungi, mushrooms and mould love the same growing environment. Here's what to do if mould rears it's ugly head.

This article is mainly written for people who have purchased one of our kits, but the advice will apply to any mushroom kit.

Mould is potentially the biggest threat to the mushroom grow kit. If it does rear its head, there are some things you can do to slow it down and possibly beat it.

Mould is one of the most opportunist and pervasive lifeforms on the planet. It’s even a problem on the International Space Station! Unfortunately, the same ideal conditions for growing mushrooms are also the ideal conditions for mould. They are both fungi.

However, many mushrooms like Shiitake & Oyster mushrooms have had millions of years perfecting the art of dealing with it. So, once the mushrooms’ mycelium has grown sufficiently, it will make it difficult for mould to grow. The danger period is usually in the first week after a mushroom kit has been made and the mushroom has had a chance to establish itself.

If you find mould growing in your mushroom bag, spores were most likely present when the bag was made. The mould would most likely affect all kits made from that batch. It’s unlikely that the mould was able to establish itself after manufacture.

Contents hide

1What to look for

2What to do if you see an outbreak

2.1Should I treat the mould directly by cutting it out or using a fungicide?

2.2Are the mushrooms still edible?

2.3Disposing of a completely contaminated bag

3Quick info on moulds

4Green moulds

4.1Black Moulds

4.2White moulds

5For people who have purchased from us

5.1Mushroom growth stages and potential for an outbreak

6Further reading

What to look for

  • The most common mould you will encounter is the green variety, so you would usually see a patch of green rather than the white of the mushroom mycelium. There are varieties of mould that are white, but generally, any white you see growing will be the mushroom.
  • If the mycelium of the mushrooms is strong, it will usually encircle (quarantine) the mould into a small space.
  • Look for a brown liquid (it may just appear as dots) around the edges. This liquid, often referred to as metabolites contains properties that will kill and digest the mould. They are part of the mushroom’s immune system. Interestingly these same properties are bio-available to our bodies, so form the basis of the mushroom’s legendary health benefits.
  • All going well you should notice the green become less vibrant, fade to a more yellow colour and slowly be replaced by the white of the mushroom’s mycelium.

What to do if you see an outbreak

In the unlikely event you get an outbreak, here are some tips:

  1. Put some tape over any holes directly over the outbreak. This will deny it oxygen and contain its spores inside the bag.
  2. Use a marker pen to put an outline of the outbreak. This will more easily indicate if it’s growing or receding.
  3. Move it to a different location. The current one may be too warm or too cold, favouring the mould rather than mushroom growth.
  4. Putting the kit outside, with the mould facing the sun (exposing it to UV) will help. The mushroom mycelium should tolerate this without too much damage.

Should I treat the mould directly by cutting it out or using a fungicide?

Usually, what you are seeing is only half of the picture. A bit like an iceberg most of the mould is growing alongside the mushroom’s mycelium deep inside the bag. There is little point in trying to treat it directly by cutting it out or dabbing it with bleach or hydrogen peroxide. Most likely you will encourage its spread and potentially weaken the mushroom’s own defensive mechanisms in dealing with it. The best you can do is move it into conditions that favour the mushroom’s growth.

Are the mushrooms still edible?

If mushrooms are growing, and the mold is contained within the bag – it will not usually affect the fruit bodies (the mushrooms themselves), so they should still be okay. The mould is not able to penetrate the mushrooms in the same way as it would a loaf of bread. However, cobweb mould grows on the surface, and can cover the fruit bodies with a fluffy white coating. This causes the mushrooms to rot quickly. If you suspect cobweb mold, discard the grow kit if you see this.

Disposing of a completely contaminated bag

If it gets to the point of needing to dispose of the kit, we recommend composting it or laying it as mulch in the garden. Just take care when opening the bag not to inhale any spores that may be present.

Quick info on moulds

Green moulds

The most common green variety that you may encounter is Trichoderma but could be from other varieties like Penicillium, Cladosporium or Aspergillus. These are generally easy to spot and perform remedial action. These moulds are fairly common in peoples homes, hiding in bread bins and other damp warm spaces but could also be growing on carpets, furniture, clothing, wallpaper or wood.

Black Moulds

When it’s too hot, sometimes the black ‘pinhead’ mould (Rhizopus stolonifer) may present itself. This is a common mould in people’s homes and is often seen on stale bread or in warm damp spaces like bathrooms. It is also a mould that can pose a health concern, mainly to people with compromised immune systems.

In our experience, both Oyster and Shiitake mushrooms will usually combat this type of mould if you move the kit into a cooler location.

White moulds

White moulds are generally less of a problem, but difficult to identify as they look similar to the mushrooms mycelium. Examples of white mould include Koji (Aspergillus oryzae) which is used in food production, or Cobweb mould (Hypomyces rosellus).

Cobweb mould grows very quickly. It not only competes with the mushrooms for nutrients, it also feeds on the mushrooms themselves. This type of mould starts as white, with a fairly thin covering (it mainly stays on the surface) but turns grey after a few days.

Brightly coloured or Pink & Purple moulds

There are some more exotic moulds that appear in hues of many colours (like the Purple mould Tuberculina Maxima). However, many of the moulds mentioned above can also appear in different colours based on conditions or the stage the mould is in, so may appear or change to Pink, Orange or just about any colour. If you see this happening it’s probably best to discard the kit as it’s likely beyond rescue.

For people who have purchased from us

If it looks like it’s spreading or the outbreak happens in the first 2 weeks – contact us on the live chat and attach a photo of the mould plus one of the batch numbers on the bag.

For every batch we make, with about 15 mini-farms per batch, we also make a small control bag kept in the lab. This way we can monitor what’s been sent out. This allows us to know if there are any problems with the batch – as the entire batch would be affected. We also use the control bag to compare against other stages, like the time it takes to pin etc

Mushroom growth stages and potential for an outbreak

  • Week 1: The danger zone is in the first week. If you see mould at this stage please contact us. If it’s an outbreak that we are responsible for, we will replace the bag.
  • Week 2: Generally the mycelium will have grown sufficiently to take care of any mould that may be present. However, if the grow kit is not in an ideal location (it is stressed) it may be weakened, and a small patch may present. In this case, the tips above should contain it until the mycelium has developed enough strength to deal with it.
  • Week 3: It should be well and truly out of the danger zone, and getting ready to fruit. Mould at this stage is rare, so a sign now would indicate that it’s in a bad location and highly stressed.
  • After soaking: Be careful when rehydrating the bag. If it’s soaked too long (more than 8 hours) or over-hydrated you may damage the mycelium and mould may take the opportunity to grow.

Further reading

If you’re interested to learn more, who isn’t? Here are some links

My mushroom kit has mould, is that a problem? | OGM! (2024)


My mushroom kit has mould, is that a problem? | OGM!? ›

The danger period is usually in the first week after a mushroom kit has been made and the mushroom has had a chance to establish itself. If you find mould growing in your mushroom bag, spores were most likely present when the bag was made.

Why is my mushroom kit growing mold? ›

If there's any area on the kit that has exposed substrate (if the white mycelium isn't really strong in that area) it could become susceptible to mould. Patchy mycelium can be caused by damage to the mycelium either during transit or on opening, from heat damage, over-watering or from storing the kit for too long.

How do I know if my mushroom kit is bad? ›

Off-odors: A strong, foul odor emanating from the growing containers or growing medium. Abnormal growth: Mushrooms that grow abnormally, such as those that are misshapen or stunted. Presence of molds: The appearance of molds, such as white or blue-green growths on the surface of the mushrooms or growing medium.

What to do if mycelium has mold? ›

If the mould area is only small, smaller than a 50 cent coin for example, the mycelium may contain it itself or you can remove it. Ideally, if you have it available, spray the small patch of mould with isopropyl alcohol (rubbing alcohol) to kill it before removing it.

Can mushroom grow kits go bad? ›

Most mushroom kits will store for 3-6 months in the fridge if necessary. To store your kit, keep it in the fridge. This puts the mycelium into hibernation and will prevent it escaping the box early. Don't keep it somewhere it could exceed 30 degrees Celsius.

Can mycelium eat mold? ›

Week 2: Generally the mycelium will have grown sufficiently to take care of any mould that may be present. However, if the grow kit is not in an ideal location (it is stressed) it may be weakened, and a small patch may present.

Is moldy mushroom safe? ›

If the color has noticeably changed on your mushrooms, or if they have begun growing any dark spots or fuzzy mold, they should be headed for the compost heap. Most mushrooms are barely, if at all, scented, so a foul odor can be another telltale sign that your mushrooms have gone bad.

What does unhealthy mycelium look like? ›

The presence of bacteria is often made evident by the production of slime. Slimy patches on your grain or mycelium signify excess moisture and possible bacterial contamination. You might also notice brown and yellow stains, as well as crusty or gel-like textures.

What kills Trichoderma spores? ›

Phenolic disinfectants are the most suppressive to the growth of Trichoderma mycelium, and of these, Disolite is more effective in killing Trichoderma spores than Environ or Prophyl at the same dilution rate.

What does mushroom mold look like? ›

What is the mold that grows on mushrooms? Various mold species can grow on mushrooms, including Aspergillus, Penicillium, and Cladosporium. These molds can vary in color and appearance, ranging from black to green, white, or gray.

Does mushroom mycelium look like mold? ›

This should be a real concern, especially for those with a diagnosed mold allergy or respiratory problem, but often mushrooms that look problematic are perfectly safe and tasty. That's because mushroom mycelium can look somewhat like mold! So you should look more closely at you mushrooms before you discard them.

What is the white stuff in mushroom grow kit? ›

The white stuff is mycelium, which is the vegetative body of mushrooms. Think of it as the roots to a plants. The mycelium colonizes the substrate block, which is made up of locally sourced sawdust and organic soybean hulls, and once fully colonized the entire grow block will appear white.

Should mushroom kits be kept in dark? ›

All our kits are recommended to be grown in a room with enough light that you can read a book by during the day. Because mushrooms don't photosynthesis the light doesn't need to be natural, they'll get all their nutrition from the substrate block, and will just use the light to initiate growth.

How often should I water my mushroom kit? ›

Humidity is a key factor for successful mushroom growth. Spray the area around your kit with a few pumps of water whenever you have a chance, at least 2-3 times a day.

What is the white stuff on my mushroom grow kit? ›

The white layer on your substrate block is mycelium, which is the main part of the fungus that produces your mushrooms! By scraping mycelium on the surface of your substrate, you are stimulating the organism and kickstarting mushroom growth.

Is mushroom poisoning caused by molds? ›

No, it is due to the toxin produced by the fungi, which are in the same family as molds. Mushroom poisoning is caused by the consumption of raw or cooked mushrooms, which are higher-species of fungi. There is no general rule of thumb for distinguishing edible mushrooms from poisonous toadstools.

How do you clean mushroom mold? ›

For small mold infestations, you can attempt DIY mold removal using a solution of water and mild detergent or a mixture of water and white vinegar. Scrub the affected area thoroughly and dry it completely to prevent mold from returning.

What does contaminated mycelium look like? ›

If you spot green, blue, grey, or black patches on or in your fruiting box, your culture is most likely contaminated. Do keep in mind, however, that small blue stains in the mycelium may just be bruising and not mould. Especially where the rye presses the mycelium against the grow box, you may see some blue spots.

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