Mushroom cultivation: introduction

What is it?

It’s the same as any other kind of cultivation – but mushrooms are not plants, and they’re more fiddly to grow. Mushrooms are grown from ‘spawn’ – mushroom tissue culture that has been produced from spores grown in sterile / laboratory conditions (contamination is a big problem at this stage). Spawn can be obtained from specialist suppliers, then added to a substrate (compost, a log, coffee grounds etc.) to spread their mycelium (thread-like root system) and produce a crop.

button mushrooms in a growing box

Button mushrooms in a growing box.

There are two major stages in mushroom growth. The first is the vegetative stage – the young, developing spawn is encouraged to feed and grow, to get to the second, fruiting stage, when the mushrooms can be harvested. So mushroom spawn suppliers provide the early vegetative stage, and it’s up to the grower to nurture it to the fruiting stage.

oyster mushroom tissue culture in a petri dish

Oyster mushroom tissue culture in a petri dish.

There are three types of mushrooms that can be cultivated:

  1. humus-inhabiting – can be grown in a mix of compost, horse manure, soil and straw; includes the classic button mushroom varieties, as well as others such as blewits or shaggy ink-caps
  2. wood-inhabiting – grown in logs, like shiitake, maitake (hen of the woods), ear fungus or monkey’s head fungus
  3. mycorrhizal – grown in association with tree roots; truffles, in other words

History

Humus-inhabiting: around 1650, in France, it was noticed that button mushrooms appeared naturally in the autumn after the melon crop. So they kept them damp and got another crop – of mushrooms. They died as soon as it became too cold though – and so they put them in trays and moved them to caves, where the season was extended by protecting them from the cold and the winds that evaporated the moisture from the soil. They were soon growing them year-round in a controlled environment in tunnels, and the mushroom industry was born. Britain followed in the early 19th century, and the US in the early 20th century.

shiitake mushrooms growing on a hardwood log

Shiitake mushrooms growing on a hardwood log.

Wood-inhabiting: there are written records of shiitake cultivation from around 1000 years ago in China. Cultivation was learnt from observation of wild specimens growing on oak or beech trees. They obtained spawn as best they could without contamination, and inoculated it into logs of the same species that they grew on in the wild.

Mycorrhizal: truffle cultivation has been complicated by the fact that in the wild, truffles only grow on the roots of a host tree. It was thought that they could only be collected from the wild – and in fact until the 20th century, it was thought that truffles were part of the tree. In 1972 in New Zealand, oak trees were planted with a view to inoculating their roots with truffle spawn. In Europe and North America there is a community of fungi associated with oak roots, all of which will compete with truffles and make cultivation very difficult. Oaks are not native to New Zealand, and so the truffle spawn had no competitors. By 1985, they were able to produce a consistent crop within 7 years – so still difficult but not impossible. They can now be cultivated anywhere, on the roots of oak or hazel – but it takes a lot of land as you have to plant the trees as well. A free-draining loam is required – clay soil isn’t good for truffles.

What are the benefits?

It can be a very interesting hobby with delicious results, that could easily become a profitable small business, due to the low cost of inputs and high value of the crop.

mushroom cultivation in a cave, Paris

Mushroom cultivation in a cave, Paris.

Production costs are low – for example humus-inhabiting species can be grown in coffee grounds that coffee shops would usually be more than happy for you to collect for free. Someone realised that coffee grounds have already been rendered sterile, and contain the cellulose and lignin that mushrooms need – the perfect substrate.

The substrate can be a waste product – like animal manure (although of course this is often used on gardens), or the coffee grounds mentioned above. There are lots of coffee shops and restaurants, there’s quite a lot of waste produced per cup, and millions of cups are consumed every day.

Mushrooms are very good for us. They are healthy and nutritious, and some species have medicinal properties. Reishi bracket fungus has been used to produce a medicinal tea for centuries, and now it’s used alongside conventional treatments for HIV, to help restore the immune system.

What can I do?

First think about what kind of mushroom-growing project you’re going for. Do some research on suppliers, what substrate you will need, and how to look after the spawn during the vegetative stage. Here is some advice for selected species:

v

Cultivated black truffle – Tuber melanosporum.

Oyster mushrooms: Mix 500g oyster mushroom spawn with 2.5kg coffee grounds (fresh – use within 24 hours of collection). Keep in bags in a warm, dark place for 2-3 weeks, then make some slits in the sides and mist spray a couple of times per day for 1-2 weeks. A network of mycelium will spread and produce fruit that are ready for harvest in 3-4 days. You can then compost the coffee grounds. The cellulose and lignin will be gone, but they will still break down.

Button mushrooms: Source your spawn (you can’t do it yourself unless you have a lab) and your substrate. You could possibly get manure from a local farm or stables, but it will need to be treated as it will be full of microscopic contaminants. Get manure that has been dried for a few weeks, although it will still contain fungus spores and will need to be sterilised. The easiest way to do this is in a large, industrial pressure cooker. However, you must allow the sterilised manure to cool completely afterwards, otherwise it will kill the spawn. Add chopped (and sterilised) straw to the manure, and mix with the tissue culture (spawn) – around 1:10, spawn: substrate. Put this mix into trays around 6 inches (150mm) deep, but leave the top 1 inch (25mm) for a casing or topping layer of good quality compost from a garden centre (that will already have been sterilised). This layer will make sure that spores from the air don’t interfere with your mushroom spawn. Keep the trays moist, warm (between 15-28°C) and dark for a few weeks as mycelium starts to develop throughout the substrate. The fine white filaments will spread and feed on lignin and cellulose (the only food for mushrooms, whatever the substrate). After a few weeks, the fruiting bodies will push their way through the compost topping layer.

shiitake mushroom spawn delivered on dowels and grain

Shiitake mushroom spawn delivered on dowels and grain.

Shiitake: Spawn is usually supplied on wooden dowels, that provide lignin and cellulose. Dowels will arrive covered in furry white mycelium. Drill holes and inoculate logs with the dowels. Seal the holes with cheese wax – but not beeswax, because bees might arrive to reclaim it! If you don’t seal the hole, the spawn might dry out and die, or other fungus spores may get in and out-compete it. You can buy pre-inoculated logs, but this will work out more expensive – you can do it yourself.

king oyster mushrooms (Pleurotus eryngii) growing in coffee grounds through slits in a plastic bag

King oyster mushrooms (Pleurotus eryngii) growing in coffee grounds through slits in a plastic bag.

An important thing to remember with wood-inhabiting species is that you can’t use soft woods, as conifers contain a natural fungicide – not ideal when you’re trying to grow mushrooms. However, hardwoods are denser, making it more difficult for the mushrooms to produce mycelium. This means that the vegetative phase can last up to 18 months, giving more time for drying out or cross-contamination to occur. Leave the logs outside, under shrubbery so that they are in the shade and protected from frost and from winds that can accelerate evaporation. Moisten the logs in dry spells.

truffle plantation - Abruzzo, Italy

Truffle plantation – Abruzzo, Italy.

Truffles: Still a very specialist business with a much longer vegetative stage. But it’s a high-value crop that could suit an intrepid smallholder. You could plant maybe an acre of inoculated hazels (which grow much faster than oaks) and if you don’t manage to produce truffles, at least you can harvest wood and nuts.

Starting a mushroom-growing business

Button, oyster and even shiitake mushrooms are relatively easy to grow. Others are more difficult, but they tend to be more prized and therefore fetch a higher price. The more prized / exotic the species, the higher the chance of failure, but the higher the rewards if successful.

Beech Mushrooms (Hypsizygus tessellatus) growing on a sawdust block

Beech Mushrooms (Hypsizygus tessellatus) growing on a sawdust block.

There are some useful tricks to increase the chances of success of a mushroom-growing business. Some growers have found that a way to stimulate the fruiting phase is to induce environmental stress. In nature, fungi will exist in the vegetative phase, feeding, for several weeks, but if there is a sudden cold snap, they will fruit. They receive a genetic message that winter has arrived, and this may be the last chance they have to produce spores and pass on their genes. This effect can be recreated artificially. If after a week or so, mycelium is spreading through the substrate, put it in the fridge at 5°C for two days, then bring it out, and you can get fruiting bodies in half the usual time.

 

Thanks to Clifford Davy of Forest Foragers for information.


We'd love to hear your comments, tips and advice on this topic, and if you post a query, we'll try to get a specialist in our network to answer it for you.