Joined: 30 May 2006 Posts: 2162 Location: West of Ireland
Posted: Thu Feb 08, 2007 4:19 pm Post subject: Black Alder ... Alnus glutinosa ... Fearnóg
Black Alder ... Alnus glutinosa ... Fearnóg
I recently discovered that many older Irish people considered it unlucky to pass an alder tree on a journey.
If this were true, then we are all crocked, judging by the frequency with which alder grows throughout Ireland.
. Black Alder leaf, catkin and seed-bearing cone, photo / pic / image.
Back in black.
Our native alder is the black alder, Alnus glutinosa. A member of the birch family, this deciduous tree grows up to ½ a metre a year, quickly reaching its maximum height of 20-25 metres. Very quick to establish, and, once established, maddeningly difficult to root out of the ground again, these are two of the reasons that black alder works well as a soil maintainer and erosion reducer to the soils along our river banks.
If you spot a thriving group of Alder trees, you can reliably assume that its roots are sitting in soggy soil, possibly alongside a marsh, stream, river or lake, in situations such as this it is common for the trees to form a dense thicket. Our Alnus glutinosa is very tolerant of waterlogged situations, preferring a heavy soil and damp conditions to all others.
I sometimes jokingly refer to it as the ultimate tree for the wet and windy west. Yes, windy, that's right, as maritime exposure is no problem to the black alder. It can be grown as a windbreak or a hedge, quickly providing sheltered conditions, allowing further and tenderer plantings to become established within its cover.
The wind through the catkins.
The wind absorbing foliage of the alder, held amongst ascending branches, appears in April, with leaves that are broad, circular and irregularly margined. Their time on the tree lasts late into autumn, when they eventually shed, they do so without the fiery colour display we come to expect from other deciduous trees.
The flowers of the alder known as catkins, open in March to await pollination by the passing breezes. These catkins pollinate the female flowers, which grow as small green rounded cones, in clusters of four at the end of twigs. When they ripen, usually by October, they turn woody and release small flat reddish-brown seeds.
The then seedless cones remain as an interesting and decorative winter feature, hanging onto on the tree until the following spring. Alders are, to my knowledge, the only deciduous trees utilising tiny cones such as this to bear seeds.
For insects, moss and nitrogen, just add Alder.
An established Alder tree within your garden offers refuge for up to 90 species of insects, not to mention the many varieties of moss and lichen, which will aim to clothe moist area alders. Grass will even be allowed to grow in tandem with the alder, as unlike other trees it does not siphon nitrogen away from grass around it.
In fact, it actually makes nitrogen available to grass and other plants growing nearby, through the amazing nitrogen-fixing bacteria growing in its root nodules. These nodules add fertility to the soil wherever the alder grows, allowing the tree to tolerate poor soils, such as the clays found in many reclaimed lands.
In Ballyseedy Wood, near Tralee, you will have a good opportunity to see a native Irish alder which has reached more than 23 metres in height, with a trunk which is more than three metres round.
Click for map if you wish to visit and view.
Other interesting Black Alder facts.
During archaeological excavations at Dublin's Wood Quay, native alder wood was found in the form of posts and other turned items.
Alder is extremely prone to tearing if cut or machined with unsharpened tools. Alder is easily finished, sanded, and takes staining well.
Sawn alder wood is known to be susceptible to woodworm attack.
Alder is also susceptible to a form of Phytophthora disease (Alder Phytophthora).
Trees affected develop lesions on the bark of the stem, along with the production of a tarry or rusty exudate. The trees foliage may become small, sparse and yellowed. Trees affected normally die quite rapidly.
To avoid introduction of the disease, seed sources and alder plants of unknown or dubious origin should be avoided.
After a great summer of growth my poor black alder sapling is being absolutely ravaged by little caterpillar type grubs. They haven't touched the oak near by. Google suggests it's the Alder Flea Beetle. Is there anything I can do and will they kill the tree or spread? It's still only waist high or so.
Joined: 15 Jan 2011 Posts: 918 Location: north tipperary
Posted: Thu Sep 13, 2012 11:05 pm Post subject:
You could squish the caterpillars and give it a feed, but they're probably Alder specific,as you say, so I wouldn't worry about them spreading. Anyway, winter is coming, and it will go dormant soon. Make sure there is nothing growing within 2' of the stem, make sure it is watered well and regularly next year, and possibly mulch in spring with rotted muck/leaf mould/compost. I suspect that you'll end up with a fine healthy sapling, well able to cope with bug attacks.
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