Fungi rule our lives whether we like it or not. We hate club root, onion white rot and honey fungus, but rely on mycorrhizal fungi to give our roses a helping hand. As ever, we categorise fungi as “good” or “bad”.

Most importantly, the ancient fungal kingdom played a critical role in creating the world we know. When algae emerged from the sea onto the bare rocky land of our planet about 600 million years ago, they began forming a symbiotic partnership with fungi.

From the outset, algae and fungi benefited from this association. Algae absorbed carbon dioxide from the atmosphere and broke it down into nutritious sugars.

Fungal hyphae, thin web-like strands penetrated the algae and absorbed some of the stored sugars in cells. They exchanged this for nutrients that they had scavenged from the rock. Over 50 million years, this allowed algae to grow tiny roots and soil began to build up as material decayed.

Research fellow Merlin Sheldrake says in the mind-blowingly fascinating Entangled Life (March 2020): “What we call plants are in fact fungi that have evolved to farm algae and algae that have evolved to farm fungi.”

This symbiotic relationship still continues. The soil is crammed with a vast network of fungal hyphae which serve and rely on around 90% of plants.

Hyphae are 50 times thinner than the thinnest plant roots and up to 100 times longer. So they access many more nutrients than plant roots ever could.

Individual plant and fungal species have come to rely on each other. Researchers recently compared how this applied to salt-water grasses and ones growing in hot, dry ground. After swapping the grasses round, both species stopped thriving because the new sites didn’t contain suitable fungal communities that let them cope with the new conditions.

We are only now realising how complex soil is and how much we rely on what took millions of years to accumulate. This means that digging over a piece of ground is like smashing up a china shop because complex fungal communities are damaged with every jab of the spade. And synthetic pesticides are equally lethal.

Perhaps inevitably, different fungi have evolved to benefit or damage our plants, and as gardeners know only too well, pathogenic fungi are the most damaging of all our plant diseases.

Mycorrhizae exchange nutrients with plants thereby benefiting each partner. Like these beneficials, pathogenic fungi insinuate their hyphae into root, stem or leaf tissues to absorb plant sugars. But there’s no exchange here: their hosts will be severely weakened or killed.

Some pathogens don’t kill their ready meal they want to keep consuming, but others, such as club root, go the whole hog. They thrive on dead and rotting plant debris, happily committing necrotrophy, or eating the dead.

These pathogens have led many gardeners to label all fungi as “bad”, forgetting we’d have no plants, soil or exist at all without this major kingdom of organisms.

By growing many similar plants together in our gardens we create perfect conditions for pathogens. There’s little consolation that scientists are discovering that many of our diseases aren’t actually fungi, but are now classified as “fungus-like”. They work in a very similar way but belong to a newly-identified kingdom of organisms.

They include downy mildew and 200 species of phytophthora. So our dreaded late potato blight isn’t a true fungus. Many tree diseases, like sudden oak death, first identified at RBGE Benmore in the 1960s are also phytophthora.

Half a million larch trees on Arran are about to be felled to stop the spread of Phytophthora ramorum. But they wouldn’t have been there without beneficial arbuscular mycorrhizae on their roots.

Plant of the week:

Salvia officinalis ‘Tricolor’ is a variety of culinary sage that has the traditional grey green leaves splashed with cream, pink and purple. Grow in a pot to avoid winter waterlogging.