Mushrooms and Fairy Rings in Your Lawn: What They Mean and What to Do

A ring of pale toadstools that wasn't there yesterday, or a curve of flat brown grass with unusually lush green just inside it: both are fungi in the soil, and neither is a lawn disease in the usual sense. Scattered toadstools need no treatment. A fairy ring cannot be cured with a bottle from the garden centre, but the dead patch it can cause is manageable with spiking, watering and feeding, and the only real cure is digging out a small ring. The one thing that needs action is poisoning risk: keep children and pets off fresh mushrooms, and never eat one from the lawn.

What's growing under your lawn

A mushroom or toadstool is not the organism itself. It is the fruiting body, the short-lived structure a fungus makes to release spores. The fungus lives underground as a network of fine threads (hyphae, together called mycelium) through the soil or through buried decaying organic matter such as old roots and stumps, and it is there all year, invisible. Fruiting bodies appear when conditions are right, overwhelmingly in late summer and autumn after rain in mild weather, which is why they seem to come from nowhere: the fungus was feeding for weeks, months or years beforehand.

Most garden fungi are either saprophytes or mycorrhizal. Saprophytes feed on dead plant and animal matter in the soil and release the nutrients back, which is ordinary, useful decomposition. Mycorrhizal fungi partner with the roots of living plants, including trees and shrubs, extending their reach for water and nutrients in exchange for sugars. Most toadstools on a lawn or in a flower bed are one or the other and do the plants around them no harm.

Ordinary toadstools: decomposition, not disease

A scattering of toadstools with no pattern is decomposition reaching the surface, and doing nothing is a fine response. Picking them off won't stop the fungus spreading, because the spores are airborne, travel long distances and are likely arriving from elsewhere anyway. There is no fungicide for them, and in nearly every case none would be needed. Removing them is still reasonable for tidiness or to keep pets and children away: take them off while still unopened, and wear gloves or wash your hands afterwards. Heavy thatch, poor drainage and compacted soil give decomposer fungi more to feed on, so scarifying and aerating a lawn that throws up toadstools every autumn reduces how many show, as it does with moss. A fork driven in to break up fungal matter helps where it is stopping water getting into the soil.

One case where tidying them away is the wrong instinct: an old, unfertilised lawn, paddock or graveyard with small, brightly coloured toadstools in scarlet, yellow or purple may be hosting waxcap fungi. Waxcaps are characteristic of ancient pastures, old lawns and graveyards, and a waxy-feeling cap and gills are the visual giveaway. Compare a photo with a proper ID guide, such as Plantlife's Scotland waxcap guide, rather than guessing from memory. It matters because the UK is one of Europe's strongholds for these species, several are classed as Threatened on the European Red List, and Scotland is one of the most important places for them. They need nutrient-poor soil that has gone unfertilised and undisturbed for years, and ploughing or fertilising ground like this causes an immediate loss of fungal diversity that takes over 50 years to recover. If a lawn or rough grass area has never been fed and regularly produces colourful toadstools, identify them before treating the ground for anything, and keep it unfed and undisturbed. Old churchyard, manse and estate lawns are the classic sites.

A few other fungi do cause real problems. Honey fungus (Armillaria species) is the most destructive fungal disease in UK gardens. It kills the roots of trees, shrubs and some perennials, and it produces honey-coloured mushroom clumps around dead stumps or over dead roots in late summer and autumn, sometimes well away from any visible source, because it spreads underground along black root-like cords (rhizomorphs) at up to 1m a year, reaching plants up to 30m from the source. Privet, birch, rhododendron, lilac and leyland cypress are especially vulnerable, and there is no chemical control. The honey fungus page covers identifying and managing it. It is a different problem from harmless lawn toadstools and from fairy rings, but the buried-wood mechanism is the same.

Fairy rings

A fairy ring is a single fungal colony expanding outward from a central starting point, so its effect on the grass or its toadstools shows as a ring or part-ring rather than scattered individuals. It typically expands about 30cm (a foot) a year, and a ring can persist for centuries in undisturbed turf. Turf professionals group rings into three types:

Any of these can produce toadstools when conditions suit, typically late summer and autumn, and for much of the year a ring may show only as one of the grass patterns with no mushrooms at all.

Why they are so hard to get rid of

No fungicide is available to gardeners for fairy rings in the UK. Some lawn-care companies offer professional-use products under strict regulation, so if you pay for that, check that the company is applying an approved product rather than an off-label one, and don't expect a guarantee.

The only method that removes a ring outright is physical: dig out the active advancing edge of the colony to at least 30cm deep, and wide enough to get ahead of where it has already spread, replace the soil, then returf or reseed. For anything beyond a small ring that is usually impractical. Where dead patches are the main problem, spike the area and water it, and feed the grass: this breaks up the colony's water-repellent effect on the soil, and wetting agents help water get in too. Heavy nitrogen feeding can green the grass enough to hide a Type 2 ring or the edge of a Type 1 ring without touching the fungus, so if a ring seems to vanish after a feed and later reappears, that is why. None of this kills the fungus, which is why rings so often persist for years whatever is done to the turf.

Is Scotland's climate making this more common?

Probably. These fungi fruit in response to moisture, mostly in the wetter, milder months, and much of Scotland, particularly the west, has plenty of both. Scotland's woodlands, grasslands, mountains and coasts hold more than 12,000 species of fungi. Nobody has compared how many Scottish lawns show fairy rings or toadstools with lawns further south, so treat it as likely rather than proven.

Ex-woodland and ex-farmland gardens

The buried-wood mechanism behind honey fungus also applies to a garden built on ground that once carried trees, hedgerows or farmland. Old roots, stumps and construction offcuts left buried during building are food for this kind of fungus, sometimes for years or decades afterwards. If your house is on an estate built in recent decades on what was farmland, woodland or a hedgerow line, you can reasonably expect more fungal activity than in an older, long-settled garden. Nobody has compared ex-woodland development sites in Scotland with ordinary gardens, so treat it as a likely explanation, not a diagnosis. If you find old stumps or roots, dig them out and watch nearby shrubs and trees for honey fungus.

Safety

Some garden fungi are poisonous, fly agaric (Amanita muscaria), the red cap with white spots, being one recognisable example, and there is no reliable way to tell a dangerous species from a harmless one by eye without real expertise. Don't eat anything growing in the lawn, watch young children and pets around a fresh crop, and either fence off the area or mow or remove the toadstools if there's a real risk of one being picked up and eaten. The Royal Botanic Gardens, Kew, answers general enquiries about mushroom and toadstool toxicity. The Scottish Wild Mushroom Code gives the basic rule for anyone tempted to eat wild fungi: only eat what you can positively identify yourself with a field guide, and leave anything you can't. If you suspect a child, adult or pet has eaten a wild mushroom, treat it as an emergency: go to A&E for a person or to a vet for a pet, and take a sample of the fungus with you rather than trying to identify it first.

Common questions

Dealing with a different lawn problem? See moss in your lawn, red thread, worm casts, chafer grubs, drought or the dog, iron sulphate overuse, and moles.

Sources