There are few plants that stop people in their tracks in an Irish garden the way a mature tree fern does. The trunk — fibrous, ancient-looking, moss-covered — and the crown of long arching fronds above it give a garden a sense of scale and prehistory that almost nothing else achieves. And yet tree ferns are far more straightforward to grow in Ireland than most people assume, particularly in the west and south of the country where our mild, moist climate suits them almost perfectly. The questions people ask about them — how much to water, whether to protect them in winter, what the moss on the trunk means — usually come from a place of anxiety rather than a real problem. In most parts of Ireland the honest answer is to relax and let the plant do what it wants to do.

The species most widely grown in Irish gardens is Dicksonia antarctica, native to the cool, humid forests of south-eastern Australia and Tasmania. It is the hardiest of the tree ferns and by far the most reliable in Irish conditions. It grows slowly — typically two to three centimetres of trunk height per year — but it is long-lived, and a plant established for ten or fifteen years becomes genuinely dramatic. The trunk is not woody in the conventional sense. It is made up of densely packed root material, and this is important to understand because it changes how you care for the plant. The tree fern takes in moisture primarily through its trunk rather than through an extensive root system in the soil below. This is why watering the trunk directly, particularly in dry periods, matters more than watering the base.

During the growing season — roughly March through to October — tree ferns benefit from regular watering of the trunk in dry spells. If you are in a part of Ireland that gets consistent Atlantic rainfall, particularly along the west coast, you may find that nature provides enough and that supplementary watering is only needed during genuinely dry stretches in summer. In drier parts of the country, or in gardens where the tree fern is positioned under a canopy that intercepts rainfall, more regular watering of the trunk will be needed. Pour water directly onto the trunk and into the crown at the top — this is where the plant absorbs it most effectively. During winter, ease off on watering significantly. The plant is dormant or nearly so, and a trunk that stays waterlogged in cold wet conditions is more vulnerable than one that is simply kept moist.

The question of winter protection comes up constantly with tree ferns, and the answer depends heavily on where in Ireland you are gardening. In sheltered coastal gardens in the west and south — West Cork, Kerry, Clare, Connemara — Dicksonia antarctica will typically come through an Irish winter without any protection at all. The combination of mild temperatures, high humidity and shelter from the worst of the wind suits it very well. Further inland, at altitude, or in gardens exposed to sharp easterly winds, a degree of protection is worthwhile. The growing point is at the crown of the trunk, and it is this that needs protecting rather than the trunk itself. Packing the crown loosely with straw and tying the fronds together over it during the coldest spells — removing everything once temperatures rise again to allow air to circulate — is usually sufficient. Prolonged temperatures below minus four degrees Celsius are the real risk. A brief sharp frost on its own will rarely cause lasting damage to an established plant.

One thing that consistently worries new tree fern owners is the appearance of moss on the trunk. If you have a tree fern and you are noticing that the fibrous trunk has begun to colonise with moss, this is not a problem — it is a sign that the plant is in the right conditions. Moss on a tree fern trunk is a good example of symbiosis at work. The moss benefits from the moisture and stability the trunk provides. The tree fern benefits from the moss helping to retain moisture around the trunk surface. In a healthy Irish garden the two coexist naturally, and a moss-covered tree fern trunk is one of the most convincingly established-looking features a garden can have. There is nothing to treat, remove or worry about.

In terms of position, tree ferns want shelter and dappled light rather than full sun or deep shade. A position beside a west-facing wall, under a light tree canopy, or in a sheltered corner of the garden where they are protected from wind is ideal. Full exposure to drying easterly winds in spring is probably the single biggest threat to tree ferns in Irish gardens — it is not the cold itself but the desiccation that the cold wind causes that does the damage. The fronds, which can reach two to three metres in length on a mature plant, act like sails in a strong wind, and a plant that is rocking in its position is a plant under stress. Stake newly planted tree ferns until they have rooted firmly into their position, which typically takes a full growing season.