Holly is one of the toughest native plants we have in this country. It grows in exposed hedgerows, in the shade of old woodland, on the edges of bogs and along coastlines that would finish off most ornamental shrubs without a second thought. So when a mature holly in a garden starts dropping leaves at a rate that alarms the person looking at it, the instinct is to assume something serious has gone wrong. In most cases in Ireland right now, that instinct is right, but the conclusion people jump to, which is that the tree is dying, very often is not.

What I am seeing with increasing frequency in Irish gardens, and what I have seen in my own garden over the past couple of winters, is holly leaf blight. The scientific name is Phytophthora ilicis, which places it in the same family of fungus-like organisms responsible for a range of damaging root and stem diseases in Irish conditions. It is specific to holly, and it has become noticeably more common over the past two decades. The pattern of our winters here has a lot to do with that. Extended periods of cool, wet weather are exactly the conditions this organism favours. Spores splash upward from the soil surface and enter the leaf through the natural wounds left by the holly's own spines. In a wet Irish winter that can go on for months without relief, the disease gets a long, uninterrupted run.

The symptoms are worth knowing precisely so you are not misreading what you are looking at. On the leaves you will see dark blotches, purplish-black in colour, though on glossy dark holly foliage they can be difficult to spot at first. What is more obvious is the leaf drop itself. In a hedge, the defoliation tends to be arch-shaped, widest at the base and narrowing as it moves upward, because the initial infection comes from spore splash at ground level. Individual trees may lose a large proportion of their leaves, and smaller stems in badly affected areas can blacken and die back. If you are looking at a mature specimen holly and the leaves are coming off in quantity over winter and into spring, with dark blotching on what remains, this is almost certainly what you are dealing with.

I want to be direct about what this looks like at its worst, because I have been through it myself. In my own garden I have some really mature hollies that I value enormously. A couple of winters ago, the blight was particularly severe. By late winter I was genuinely questioning whether I was going to lose them. Nearly all of the leaves were gone. They looked, frankly, finished. The following summer, those same trees were in rude health. New growth came, the canopy filled back out and by autumn you would not have known anything had been wrong. The same pattern has repeated since. A difficult winter, a recovery in summer. That is the single most important thing I can tell you about this disease: in established hollies growing in open ground, the plant's recovery capacity is remarkable. Do not make irreversible decisions in February based on what a holly looks like in February.

There are practical steps worth taking alongside that patience. Collect fallen leaves from around the base of the tree regularly and dispose of them, do not compost them. The organism survives in infected plant material and fallen leaves lying on the soil surface simply feed it back into the system come the next wet period. Where you can see clearly affected stems that are blackening, cut those back to healthy wood and remove the prunings from the site. Keep the soil around the base of the tree in good condition. A well-fed, organically rich soil around an established holly gives the tree the resilience to fight back. A dressing of good biochar-enriched compost around the root zone supports that recovery without introducing anything artificial. One important caveat: if your hollies are in containers rather than open ground, the situation is different. A containerised holly that has lost most of its leaves could be suffering from drought stress even in a wet winter if the rain is not reaching the pot, or from root restriction if it has been in the same container too long. Rule those out first.

There is no chemical control available to home gardeners that will eliminate this problem, so do not spend money looking for one. The same damp conditions that drive fungal disease across the garden are behind holly leaf blight, and the response in every case is the same: support the plant's own health, reduce the sources of reinfection, and give it time. Holly is a native plant. It has been part of this landscape far longer than our gardens have existed. It has the biology to recover from this. Your job is to be patient, to clear away the fallen material, and to resist the urge to act dramatically. In most cases, if you see a mature holly through a bad winter, you will have a fine holly again by the following summer.