Toadstools And Fungus In The Lawn

What's happening?

Most lawn toadstools are harmless and short-lived. They are the fruiting bodies of fungi digesting dead organic matter in the soil — buried roots, an old stump, thatch, timber left under a lawn — and they come up in mild damp weather and disappear again. Fairy rings show as arcs or circles of darker, faster-growing grass, sometimes with a dead band, caused by fungal activity altering the soil beneath. The one that genuinely matters is different: honey fungus is a parasitic fungus that attacks and kills the roots of woody plants, and the tell is not the toadstools but what is happening to the trees, shrubs and hedges nearby — sudden dieback, failure to leaf up, and white fungal sheets under the bark at the base of an affected plant. So the question to answer is not what the toadstool is; it is whether woody plants around it are dying.

What usually causes it?

• Fungi breaking down dead organic matter in the soil — buried roots, timber, thatch or an old stump
• Mild, damp autumn weather triggering fruiting bodies to appear across a lawn
• A tree stump or large roots left in the ground after felling, feeding decay fungi for years
• Fairy ring fungi altering the soil in an expanding arc, producing dark or dead bands in the sward
• Honey fungus present in the soil and attacking the roots of woody plants
• Buried construction timber, fence posts or shuttering left under a lawn
• A thick thatch layer and poor aeration giving surface fungi plenty to work on

When should you call a gardener?

Call a gardener where toadstools are recurring in quantity, where a fairy ring is spreading and killing the sward, or — most importantly — where woody plants near the fungus are dying back. Honey fungus needs confirming and managing, and that includes decisions about removing affected plants and their roots and what can safely be replanted. If a tree is involved and may have been weakened at the roots, get a tree surgeon to look at its stability rather than waiting for a gale.

What will the gardener actually do?

• Identify whether the fungus is harmless decay, a fairy ring, or honey fungus attacking living roots
• Inspect nearby trees, shrubs and hedges for dieback and check the bark at the base for fungal sheets
• Locate the food source — buried timber, roots or a stump — and remove it where practical
• Manage a fairy ring by aerating, scarifying and improving the affected sward
• Remove plants killed by honey fungus together with as much of their root system as possible, and advise on replanting with less susceptible species where it is confirmed
• Refer stability concerns on any affected tree to a tree surgeon rather than treating it as a lawn problem