Do you have a little bit of space in the corner of your grow room? Then why not grow yourself some tasty Shiitake or Oyster mushrooms?  Our resident mycologist, John Robinson, explains how…

Growing your own mushrooms is easy.  And if you’re lucky enough to have access to an indoor growroom, then you already have the conditions necessary in order to provide a perfect environment for fruiting most tropical species of mushroom.  It’s surprisingly straightforward to get started and you can enjoy your first crop within weeks.

Before we talk about cultivation, let’s take a quick look at the mushroom lifecycle.  I imagine most of you urban gardeners will already be familiar with most of the terms I’ll use:

The Mushroom Lifecycle

The spore (”seed”)

Mushroom spores are the equivalent of seeds in plants and are released from mature mushrooms in their millions! Individual spores are microscopically small, but if you collect them by placing a cut mushroom cap on a piece of paper overnight you will see them as a fine dust (pictured right).

Mycelia growth (“vegetative growth”)

Under the right conditions, spores will germinate to form growing strands of mushroom mycelium (which is equivalent to the vegetative state of some plants). This growth continues until conditions become right for the formation of mushrooms (called fruiting – equivalent to the flowering stage of plants).

Fruiting (“flowering”)

When the growing mushroom mycelium receives the correct environmental triggers it begins to produce mushrooms. These triggers often include a reduction in temperature, exposure to light and a lowering of carbon dioxide levels. Mushrooms are often first visible as small “pinheads” which rapidly increase in size until they reach maturity, releasing spores and allowing the whole process to begin again.

Cultivation

The initial stage of mushroom cultivation usually involves the inoculation of a food source (called a substrate) that has been heat-treated to kill any competitor micro-organisms (making it sterile).

Historically this step has been a hit and miss affair for the small indoor cultivator. Jam jars filled with grain and plugged with cotton wool were cooked in granny’s pressure cooker. Even though the results can be excellent, quite a lot of trial and error is involved and contamination with green moulds or bacteria is common.

For the beginner, the easiest way to get started is with a kit containing sterile substrate that can be easily inoculated by injecting with a syringe containing spores or mushroom culture. Modern plastic containers and bags come with built-in air filters allow the growing mycelium to breath but don’t allow contamination in.

Inoculation and mycelia growth

A few days after inoculation with a syringe, fluffy white mycelia can be seen growing through the substrate. The fully colonised material on the right is referred to as mushroom “spawn”.

When all the substrate has turned white, it is ready for the next stage. Professionally made spawn of many species can also be purchased, making life even easier. However, this spawn is often only available at certain times of the year and the range of species can be quite limited.

Fruiting

At this point the mycelia can be encouraged to produce mushrooms immediately. Fruiting is usually initiated by exposure of the mycelia to light, lowering temperature and increasing ventilation. The simplest way to do this is by placing the mycelia in a bag with air filters, although you can construct a custom-built chamber. After a couple of weeks mushrooms will begin to appear as small pinheads, which quickly mature. This is the most direct and speedy way to produce mushrooms and a crop can be ready in 4-6 weeks.

Increasing Yields

Instead of fruiting immediately, larger and larger amounts of mycelia can be produced from this initial batch by transferring it to fresh sterile or semi-sterile (pasteurised) substrate. For example, a small amount of Shiitake grain spawn could be used to inoculate a larger block of coco coir.

Some species can also be encouraged to produce even more by the addition of a “casing” layer before fruiting. This will be covered in more detail in a forthcoming article.

Outdoor patches

Moving outdoors allows the preparation of larger beds or logs and potentially huge crops. However, our cool climate limits us to the cultivation of only temperate species. The Shaggy Ink Cap (Coprinus comatus – pictured below) and a member of the teethed fungi, the Lion’s Mane (Hericium erinaceus) are both suitable.

Mushroom FAQ

Q) What does inoculation mean?
The word “inoculation” refers to the placement of something to where it will grow or reproduce, such as the implantation of microorganisms or infectious material into a culture medium such as a brewer’s vat or Petri dish.

Q) Once I start growing mushrooms, will they just continue to grow and re-spore forever on the same bit of substrate as long as the conditions are right?
Most of the gourmet mushrooms occur in nature as wood-decomposers. Their mycelial network secretes enzymes which breakdown large molecules into simpler compounds, which can be absorbed. When cultivated, food is normally provided in the form of sterile grain, straw or wood chips and growth normally continues until the food source is used up. Often the water in the substrate runs out before nutrients, which is why adding more water after a crop can lead to further crops.

Q) Which mushroom is the most expensive?
White truffles usually cost £1000-1500 per kilo. In 2005 a specimen weighing over 1.2 kg was reportedly sold at a charity auction in Hong Kong for £60,000.

Q) What is the name of the world’s largest mushroom?
The world largest mushroom is a variant of the Honey Fungus (Armillaria ostoyae) found in the Malheur National Forest in the Blue Mountains of eastern Oregon, USA.  The underground mycelial network is estimated to cover over 2,200 acres (890 hectares) and be at least 2,400 years old, possibly older. By area it is the worlds largest organism. However, the organism with the greatest biomass (over 6,600 tons) is an Aspen tree called “Pando”. The Aspen tree forms large stands of genetically identical stems connected by a single underground root system.

Q) When is the best time to pick mushrooms?
The best time to harvest cultivated mushroom is just as the cap begins to open, before the release of spores. This keeps the area clean and free of spores. Large mushroom farms can produce so many spores that these can become a danger to health (any fine dust can damage the lungs and also some workers can develop specific allergies). This is not generally thought to be a problem for small-scale home growers.

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Well – that’ll do for this issue! Look out for articles in future issues of Urban Garden Magazine!  I will cover topics such as working with agar, taking spore prints, growing on bulk substrates and take a look at creating outdoor mushroom patches in more detail. If you have any questions, please post it as a comment below. Happy growing!