How to Grow Humus Fungi

Method 1: On Compost Heaps

You can inoculate garden compost heaps with spawn. The composting process must be complete or the spawn will be killed by the combination of high temperatures and ammonia produced by the fermentation process. The temperature of the heap must be no higher than 25degreesC.

Remove the top 10cm or so from the top of the heap and mix spawn into it. About 150-200g of spawn will inoculate a heap with a surface area of 1 metre square. Replace the spawn/compost mix and firm it down to ensure that the spawn makes good contact with the rest of the compost. Put a layer of leaves about 5cm thick on top of the heap. After a few months the fungus will have colonised the heap and mushrooms will appear in the autumn.

Method 2: In Trenches

Dig a trench roughly 10cm deep and 40cm wide. Fill the trench with a layer of straw or well-rotted manure about 30-40cms thick (20-30cms above ground level) water as necessary and cover with a plastic sheet. Allow the straw to become soft, which may take a few weeks, depending on weather conditions. Peel back the plastic sheet and mix in the spawn at the same rate as described in the first method (150-200g per square metre of surface). Moisten the substrate if it seems at all dry. When the white fungal threads, known as the mycelium, have colonised most of the surface, remove the plastic and add a covering layer of soil or leaves about 5cm thick.

Method 3: In Plastic Sacks

It is possible to produce your own mushroom grow bags, which can be stood out in various positions in the garden, or in sheds and outbuildings. For the best results use a sterile substrate, which can easily be prepared from clean straw using the following method:

Cut clean, non-mouldy straw in 3-5cm lengths, about 1kg per bag is sufficient. Add a small quantity of ground limestone or chalk, about one tablespoon per kg, and put the straw into a cloth bag (a pillow case is good) or a fine wire mesh basket. Immerse the bag in hot water (65degreesC) for an hour to sterilise the straw. Ensure that work surfaces are clean. to prevent contamination, ideally they should be disinfected with bleach. (Other ways to sterilise straw: make a solution of builders' lime (calcium hydroxide) in water, 10g per 5 litres water, and immerse the straw in this for a couple of hours. Allow the straw to drain before adding the spawn. Household bleach can also be used the same way, 25ml of bleach to 5 litres water.) Allow the straw to cool to room temperature, then put it into a clean bin liner or mixing bowl. Add a large cupful of spawn (250-300ml) and mix it thoroughly. Put the inoculated straw into a clean plastic bag. A garbage bag is good. Pierce the bag about 50 times with a nail or knife sterilised with bleach or by passing it through a gas flame. Put the bag in a moist place at a temperature of about 20degreesC and leave to incubate for 2 to 3 weeks. To prevent drying out, it may be sensible to cover the bag with a plastic sheet, loosely placed to allow air flow. After incubation, make a series of slashes at the top of the bag and place it in a cool moist position, making sure it does not dry out. It will fruit in a short while.

Method 4: On the Lawn

Use the Plastic Sack method above to establish fungus on football-sized blocks of straw. For the best results these should be fully colonised. Bury the blocks intact, just under the surface of the grass. As the block decays, the lawn will subside a little and it will be necessary to fill the hole and reseed if appropriate.

Method 5: In Mulches

You can simply mix spawn into mulches applied around fruit and vegetables. If conditions are favourable this will produce a useful crop of mushrooms for several years. It is also worth putting the compost from exhausted bags or heaps down as a mulch. The mycelium often regrows and fruits.

Wood-inhabiting fungi can be cultivated using two main methods: on logs, or in bags of sawdust. The aim with both methods is to provide the fungus with a suitable food source and to adjust environmental conditions to favour rapid growth and fruiting. Sawdust bags are quicker to fruit than logs, but they have a shorter productive life.

The two main wood fungi are Oyster Mushroom and Shiitake (pron. Shii-tak'ay) which have been grown successfully for many decades now using these methods. Illustrated here are fruiting shiitake logs and sawdust bags.

Method 1: On Logs

Fell trees in late autumn or winter, between leaf fall and bud break in spring. At this time, sugar content of the wood is at its highest and the fungus uses this sugar to make rapid growth.

Select logs 10-25cm in diameter and cut them into pieces 50-80cm long. Try to ensure that the logs are free from disease and that the bark is damaged as little as possible, to prevent the entry of contaminant fungi. Store logs off the ground in a moist shady place, or cover them with shade netting, old carpets etc. to prevent excessive loss of moisture. You can store logs for a couple of months before inoculating, or inoculate soon after felling. If the wood has dried out appreciably before inoculation, it will need to be soaked for a day or two. Different fungi prefer different trees. Suitable woods for various species are:

Oyster mushrooms - Beech, Oak, Sycamore, Birh (most hardwood species are suitable). Pleurotus colombinus grows on conifer softwoods such as Scots Pine, Spruce and Larch.

Shiitake - grows best on Oak, although other hardwoods may be used, such as Beech, Alder and Sweet Chestnut.

Disc Method

Wedge Method

Drill Hole Method

With a wide diameter drill bit (at least 1cm) make a series of holes in the log, about 20cm between each hole. Fill the holes with spawn and seal them. If using dowel plugs, select a bit that fits snugly, and make sure the hole is deep enough for the whole dowel.

With all these methods it is a good idea to seal the inoculation sites to prevent contamination, and to stop spore drying out, and to keep mice and slugs from eating it. The best method is to apply moulten wax to the inoculation sites. Cheese wax (if you can get it) is best because it has a low melting point so is less likely to damage the spawn (if you order our dowel kits, we include cheese wax and a special dauber). You can also seal with adhesive tape.

After the logs have been inoculated, the fungus begins to spread through and colonise the wood. This is known as the spawn run, and it takes place under warm, humid conditions. We offer the following suggestions:

Dig a pit in the ground big enough to take the logs standing vertically. Moisten the base of the pit and scatter a small amount of spawn on it. Stack the logs closely together and cover them with polythene sheeting or old fertiliser sacks.

Stack the logs in a shady spot and cover them with damp carpets, polythene sheeting etc.

Put the logs into fertiliser sacks, moisten, seal and place in a warm shed, garage or barn.

As the fungus develops, it generates heat, and it is a good idea to trap this heat by insulating the logs with straw or old carpets placed on top of the polythene sheeting. The incubation period varies from species to species. Oyster mushrooms take 6 months, Shiitake often takes longer, a year or more. Take care that the logs do not dry out too much, but don't allow them to become too wet, either, because that encourages the growth of contaminant fungi. Trial and error will allow you to develop a picture of each species' requirements. The basic aim is to keep the bark dry and wood itself adequately moist. Check the logs every few weeks. The spawn run is complete when both ends of the log show large patches of white fungal growth, the mass of fine fibres being known as mycelium. Shiitake mycelium often turns a cocoa brown colour on contact with the air. Logs covered with blue, black or yellow mycelium should be discarded because they have become infected with contaminant fungi which could spread to other logs.

Set logs out in their fruiting positions when the spawn run is complete. Select a spot in light shade with moist soil and place the logs so that about one third of their length is buried in the ground, with enough room between the logs to make it easy to harvest. Fruiting is initiated by the onset of autumn rains and mushrooms are produced in flushes; that is, numerous mushrooms appear all at one time. Depending on the type of wood used and the size of the log, mushrooms will appear for 3 to 5 years more. Logs may also be stood in pots of moist sand or in water in sheds and greenhouses and this may help to reduce slug damage.

Method 2: On Sawdust

It is easy to produce your own mushroom growing bags. The bags can be stood outside in various shady places in the garden, or in cellars, outbuildings etc. The sawdust must be prepared by disinfecting to get rid of competing fungi. Several methods are available:

Heat Treatment

Stand the sawdust for an hour in water at 65degreesC. Small quantities can be sterilised in a pressure cooker.

Lime Water

Make a solution of calcium hydroxide and water at the ratio of approximately 60g to 10 litres and use this to moisten the sawdust. Allow to soak for 2 hours, then drained for several hours before inoculating.

Make a dilute solution of household bleach by adding 25ml of bleach to 5 litres of water. Use as for lime water.

Inoculate with about 50-100g of spawn for 1kg moist sawdust. Add the spawn to the sawdust after it has drained sufficiently (or has properly cooled if you use heat treatment) and mix it thoroughly. Put the inoculated sawdust into clean plastic bags which have been pierced 50 times with a knife, knitting needle or nail sterilised with bleach or by passing through a flame. Tie the bag.

Incubate the bags in a warm place (approx. 20degreesC). The sawdust will appear white when it is fully colonized, although Shiitake mycelium may turn a cocoa brown colour. Incubation time varies according to species and temperature. Oyster mushrooms take a couple of weeks under optimum conditions; Shiitake a couple of months. Place the fully colonised bags in a cool, moist position in full light, but out of direct sunlight, and fruiting should occur after several weeks.