How to grow mushrooms

Mushrooms are an unusual grow-your-own crop that’s increasing in popularity. Mushrooms take more effort than most crops to grow, but mushroom growing kits offer easier growing methods, and give you the opportunity to grow ‘gourmet’ varieties such as oyster and shittake, as well as the more usual button mushrooms.

Mushrooms can be grown indoors or outdoors in prepared beds or boxes, or on hardwood logs outdoors. Indoor growing in a controlled environment usually gives the best results. Outdoors, weather conditions have a strong influence on the success or failure of mushrooms grown in beds, although log-grown mushrooms tend to be more successful.

How to grow mushrooms

There’s a number of ways to grow mushrooms. You can buy mushroom spawn to grow in beds or boxes filled with manure or compost. Alternatively choose a ‘mushroom growing kit’ that usually includes the spawn and growing media (such as wood shavings or straw). If you have access to recently chopped logs, you can buy wooden dowels or plugs that have been impregnated with spawn, which you tap into pre-drilled holes in the log.

Where to grow mushrooms

Mushrooms are best grown under-cover, where temperature and moisture can be controlled. A shed, garage, garden cold frame or cellar will work well – anywhere out of the sun where it’s possible to give mushrooms their optimum growing temperature of around 15°C. (The temperature shouldn’t go below 10°C or above 20°C). Outside, grow mushrooms in beds, on compost heaps, or in logs, again away from sunlight.

Growing mushrooms in beds or boxes

A rich, fertile, moisture-retentive growing medium is needed for mushrooms. The traditional material for growing mushrooms is horse manure and you can buy this from your local garden centre or nearby stables. If the manure is fresh, pile it into a heap and fork it over to mix well every couple of days for a fortnight until the heap has cooled and settled.

Ensure the growing medium is moist. Spread the spawn across the surface and mix it 5-8cm deep, then cover with damp newspaper. After several weeks when white thread-like mycelium has appeared, take off the newspaper and cover the mycelium with a 2-3cm layer made up of 50 per cent garden soil or compost mixed with 50 per cent lime. Water as required to keep this evenly moist, using either a hose fitted with a spray attachment, or a watering can fitted with a fine rose. Mushrooms should start appearing from several weeks after sowing.

How to grow mushrooms on logs

Growing mushrooms on logs is easy as the logs need little attention once the dowels are inserted. However, you do need to supply and drill your own logs. These need to be hardwood, not conifers, and cut from healthy wood. Logs need to be freshly cut and the dowels implanted no more than six weeks after cutting. The best woods to use are oak, beech, hornbeam, chestnut, hazel, birch, maple or holly. Logs should have a diameter of 10-15cm and be 45-60cm long.

Drill holes along the length of the log, 15cm apart and in rows 8cm apart. Insert the impregnated dowels fully into each hole. Some kits come with sealing wax, so seal each one with wax if directed to. Place the log in a shady spot, under trees or shrubs, with one end on the ground and the other propped up, and ensure it stays moist. Mushrooms can take up to 18 months to appear.

How to grow oyster mushrooms

Buy a pack of oyster mushroom spawn, along with some straw. Soak the straw in water overnight to make sure it’s thoroughly damp, discarding excess water. Mix the mushroom spawn with the damp straw and then pack into a polythene bag such as a bin liner. Seal and leave for six weeks in a damp, sheltered spot between 20-25ºC, such as near your compost heap. As the straw breaks down, the mushroom spawn will grow into it, colonising the straw.

Here, Monty Don demonstrates how to grow oyster mushrooms in straw:

After six weeks the oyster mushroom spores will have colonised the straw in the plastic bag. Move the bags into a light, warm and moist environment, such as your greenhouse. Cut slits in the bag so the oyster mushrooms can grow through them.

Monty Don checks on the progress of his oyster mushrooms:

After two weeks, check the bag to see if oyster mushrooms have developed. The straw should continue to produce mushrooms for several weeks.