Fungi are amazing things, even if, in a gardeners world, they are more often seen as the bad guys than the good guys. Over 70,000 species of fungi have been identified so far and an additional 1,700 species are being discovered each year. Estimates suggest that there are over 1.5 million species in existence, which makes fungi second only to insects in terms of number of species. The biggest living organism on Earth is probably the tree root-rot fungus Armillaria ostoyae, of which there is an example in the Blue Mountains, Oregon, USA which covers almost 900 hectares (2,200 acres) and is estimated to be over 2,400 years old.

Most fungi are made up of filamentous structures called hyphae, a mass of which is called a mycelium. The hyphae grow from their tips and can produce more than a kilometre of new growth in 24 hours. Familiar fungi such as mushrooms, toadstools and puffballs are made up of mycelium. Some fungi form visible sclerotia (singular ’sclerotium’), compact, hardened masses of mycelium in a dormant state which store food in preparation for further growth in more favourable conditions. Stromata (singular ’stroma’) are another compacted form of mycelium, which is visible on the host plant and usually produces spores. Rope-like bunches made up of strands hyphae growing underground are known as rhizomorphs.

Fungi consume food by excreting an enzyme onto it which then releases smaller molecules which the fungi can absorb. They obtain food either as saprophytes (living off dead organisms), parasites (living off live organisms) or as mutualistic symbionts (obtaining food from a live organism but where the association is beneficial to both organisms).

Fungi reproduce by the formation of spores, which can be produced sexually or asexually. Different species of fungi produce different types of spores, such as conidia and uredospores. Spores can be carried great distances by the breeze or by water, so fungi spread very readily. Some species of fungus are identified by pustules growing on leaves or stems; these are bodies called ‘uredia’ or ‘uredinia’ which release spores.

Why fungi are great for gardeners

Fungi form important symbiotic relationships in the garden. Mycorrhizae are a type of fungi which grow with plant roots and dramatically extend the area of the root, and therefore the area from which water and nutrients can be absorbed. In return the fungi obtain sugars from the plant. Mycorrhizae form naturally around plant roots, but can be added upon planting to help the plant establish more quickly and effectively.

In addition, yeasts are a type of fungi. And yeasts make beer. And, perhaps second only to a cup of tea, nothing beats a cold beer after a hot day in the garden!

Why fungi aren’t so great for gardeners

Fungi are the most important cause of plant diseases. More than 5,000 species of fungi attack plants or crops. Notable fungal diseases include honey fungus, powdery mildew, downey mildew and grey mould.