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Native Tree

OAK (Sessile)

Dair ghaelach

Quercus petraea



The traditional Irish oak is the sessile oak. It is the main species to be found in Ireland’s most familiar woodlands.

Sessile oak is found more commonly on poor acid soils, often in hilly regions. These woodlands can be found in Killarney, Co. Kerry, the Glen of the Downs, Co. Wicklow and Glenveagh, Co. Donegal, to name but a few.

They are important ecologically as habitats for hundreds of invertebrate species along with many species of birds and mammals. Sessile means that the acorns have no stalk while those of the pedunculate oak hang from long stalks.

Once widespread throughout Ireland, centuries of harvesting, with few trees being replaced, means that truly native oak can be hard to find, though there are small woods in most counties.

Very often, semi-natural oak woodlands contain a proportion of birch and ash, with hazel, holly and rowan scattered throughout the understorey.

Oak has been harvested for its fine timber for centuries and is much prized for its visual qualities and durability. It is commonly used in the making of furniture, for veneers and in the manufacture of casks.

The male flowers of oak are borne on rather inconspicuous catkins, which come out just before the leaves, but the seeds – acorns – are far more obvious. Oak trees do not produce a good crop every year, so it is worth gathering plenty in a good year.

FUN FACT: Ireland had a garden at a Japanese garden festival in Osaka, Japan. The Japanese asked the Irish Government about Ireland's national tree, but there was none. Mr. Haughey, who was the Taoiseach at the time, consulted with the Tree Council of Ireland and a short list of trees was drawn up. The sessile oak was selected, and a specimen was planted at Ardagh during the launch of National Tree Week in 1990.


Remember there is not a good crop of acorns every year, so be patient. Acorns can be collected while still on the tree if they are ripe. They can be picked when the acorn has turned brown and comes away from the cup fairly easily. When the seed is fully ripe there is usually a big fall of seed. It often happens on the morning following the first frost. In tree nurseries you can often hear the question “has the big fall happened yet?" It is also important to note that with oak (as with hazel and beech) there is a gradual fall of non-viable seed before the "big fall".


Sow straight away, if possible, as stored seed may lose viability. If necessary, store in a cool, well-ventilated place in a hessian bag. Protect against being eaten by mice. Shake the bag gently, every so often, if collection is on a large scale to prevent the acorns heating up. It is also very important that they are not allowed to dry out as they lose viability rapidly. In the New Year check every so often to see they are not beginning to shrivel. If the first signs are observed the seeds should be sprinkled with water to keep them plump until they are sown in the spring.


One method is to sow acorns soon after collection to a depth of 10cm, leave them over winter, and then in March rake off the top 5cm to leave a 5cm covering. This protects them from being eaten, and they should shoot in May. Otherwise store and plant in late March. Allow plenty of space for the seedlings which have big leaves even when very young.

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