The autumn rain has awoken a lingering ghost in the garden. A tuft of honey fungus has sprouted where an apple tree once stood ten years ago. The common name given to three closely related species – A. mellea, A. bulbosa and A. ostoyae, honey fungus is feared by gardeners for its ability to kill a wide range of trees and shrubs. Yet, while it doesn’t taste of honey, the young caps with their white gills are edible when well cooked.

At this time of year, fungi spring up as if by magic, here one moment and collapsed in puddles of decay the next. While walking in the woods today, I came across peeling caps of fly agaric, the poisonous, red-and-white toadstool of fairy tales. Their appearance was another reminder of what lies hidden, ready to surface when conditions are right.

Neither animal nor plant, mushrooms and toadstools are the fruiting parts of mycelium, the fibrous white bodies of fungi buried in moist soil and rotting wood. Forest ecologist Suzanne Simard has discovered how trees use underground networks of fungi to communicate with each other and send each other nutrients, likening the systems to our own neural and social networks.

The reappearance of fungi at this time of year also fits with the traditional celebrations of Samhain or Halloween, when the veil between worlds of the dead and the living is believed to become less opaque, and the past returns to haunt us. In my own dreams in recent weeks, buried memories have been resurfacing and I have found myself waking in anger at perceived wrongs.

So, what to do about returning ghosts? Folklore advises us to treat them respectfully – and then, perhaps, they might just help us, rather than harm us. Now is the season to honour the past.