Honey fungus forms an underground network of bootlace-like threads called rhizomorphs, which attack the roots of susceptible plants – usually trees and shrubs.
A number of honey fungus (Armillaria) species are native to the UK, but it's Armillaria mellea and Armillaria gallica that are usually encountered. The plants most commonly affected by honey fungus include acer, beech, birch, holly, apple, hydrangea, viburnum, magnolia, pear, rhododendron, rose and lilac. Annuals, biennials and perennials are generally unaffected.
The first signs honey fungus might be present in your soil are a sparse crown, branch dieback, smaller than usual leaves, cracking and bleeding bark (particularly near soil level) and sometimes clumps of honey-coloured mushrooms. If you suspect honey fungus is present, have a look at the collar of the plant where the roots and stem meet, and look for signs of decay and white fungal material beneath the bark. Digging in the soil around affected plants will often reveal the dark, bootlace threads.
When honey fungus reaches a garden, the consequences can be dramatic, as it has the ability to kill old and majestic trees and shrubs, which can be a real issue for orchard owners.
Mycorrhizal fungi naturally present in the soil are thought to restrict the spread of honey fungus by protecting the roots of susceptible plants. You can ensure mycorrhizal fungal spores are able to reach the roots of susceptible plants by keeping the soil beneath trees and shrubs free of lawn, in a circle that roughly matches the canopy spread.
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While honey fungus will prevent you from growing many plants (at least for a few years), there are just as many, if not more, plants to replace them with. These include beautiful trees, shrubs and perennials.
Discover some of the many lovely plants resistant to honey fungus, below.
Bearing aromatic, golden fruits in autumn and blossom in spring, the quince (Cydonia oblonga) is a fantastic honey fungus-resistant tree. Best grown in a spot with full sun and moist, well-drained soil.
Commonly known as fragrant winter hazel, Corylopsis are deciduous shrubs that eventually reach the size of small and attractively branched trees. For winter scent, they bear fragrant pale yellow flowers that provide gorgeous colour right when it's needed – a great alternative for witch hazels (Hamamelis), which are susceptible to honey fungus.
Honey fungus unfortunately affects most acers, with the exception of Acer negundo. Fortunately, Stewartia pseudocamilla, the deciduous camellia, provides just as good a display of autumn colour as acers, and grows to the same beautiful proportions. In addition, it provides beautiful white flowers in spring.
The tupelo, Nyssa sylvatica, is an attractive deciduous tree native to the eastern regions of North America. It's primarily grown for its fiery autumn colour and in medium to large gardens it will grow to an impressive size. Best planted in the ground in its final position as it resents being transplanted due to its large taproot.
A stunning tree throughout the year, Parrotia persica has branches that start low down on the trunk, often giving this small tree an attractive multi-stem appearance. Before leaf break later in spring, gorgeous crimson flowers adorn the branches. Later, in autumn, the foliage puts on a real autumn show of reds, oranges and yellows before falling.
Phlomis are among the best plants for winter interest, providing tiered seedheads and evergreen foliage. While in bloom, the flowers are a magnet for pollinating insects, particularly bumblebees. Some of the most popular phlomis to grow include Phlomis russeliana, Phlomis longifolia and Phlomis tuberosa.
Like phlomis, perovskia is a member of the mint family, Lamiaceae, whose members seem to be generally resistant to honey fungus. It's a fantastic sub-shrub that provides plumes of lavender-coloured flowers in late summer and autumn, and holds its structure into winter. A good choice for poor soil.
You'll most often spot artemisias like 'Valerie Finnis' and 'Powis Castle' brightening up sunny borders with their silvery foliage. They're easy to grow, but do require full sun to stop them becoming lanky, and well-drained soil to prevent die-back.
Fortunately, box plants aren't troubled with honey fungus but they are currently prone to box blight and box tree caterpillar. However, if you've found your box plants affected by either blight or box moth, you could consider one of the many alternatives to box.
Fothergillas are robust, medium-sized shrubs from North America, with fragrant, bottlebrush flowers in spring and summer. What's more, before the leaves fall in autumn they turn vibrant shades of yellow, orange and red. Great for a moist, humus-rich soil in partial shade.
The Chilean myrtle, Luma apiculata, is a small evergreen tree, bearing fragrant white flowers in summer. It has all-year-round interest, as its cinnamon-coloured bark peels as it grows, revealing paler bark beneath.
Salvias have mercifully proven to be resistant to honey fungus. There are lots of beautiful types to grow, including herbaceous and shrubby types.