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I recently discovered that many older Irish people considered it unlucky to pass an alder tree on a journey. If this were true, judging by the frequency with which alder grows in the West, we are all crocked.
Our native alder is the black alder, in Latin Alnus Glutinosa, and in Irish Fearnóg. A member of the birch family, this deciduous tree grows up to half a metre a year, quickly reaching its maximum height of 20 to 25 metres.
Very rapid 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, 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 tender plantings to become established within its cover.
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 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.
An established native 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, the tree 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. A tree, which in theory, adds more to the soil than it takes away is a rarity. Surely this is more than reason enough for you to take a chance and plant our native alder. Until next week, happy gardening and remember that a weed is just a plant in the wrong place.
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