It is always a difficult decision when you have to plant a tree in the garden. After all, unlike petunias and even shrubs, they will be in the garden (with luck) for decades rather than months or just years. And while it is easy enough to dig up a petunia or choisya if you find you have made a mistake, a tree is more of a problem to remove. A tree will make a great impact on your plot and can transform it, in bad ways as well as good, bringing with it the inevitable shade. We all want trees that look good all year but it is oh so easy, since most people reawaken in spring, along with their gardens, to plant a tree in March or April and be seduced by the beauty of cherries or magnolias. Planting at this time of year, which is the best time because the soil will get a chance to settle around the roots before growth in spring, also gives you a better chance to assess the beauty of the tree in winter. My default position for a tree for all-year colour is always Acer griseum – it has it all (apart from floral beauty) but it is a bit slow in its teenage years and is usually only available at a small size. I may now have to change my favourite small (to medium) tree to Alnus incana ‘Aurea’, a tree that has a lot to commend itself.
I planted a group of five last spring so they are now 18 months in the garden. They are in rather thin soil and I underplanted with cornus cuttings. Last year the alnus (alder) struggled a bit in the dry summer but have settled down now and at the moment they look lovely. This is a yellow-leaved form of the grey alder and the leaves, when planted in full sun, are rich, butter yellow as they open and through most of summer, though they do get a bit scorched if the soil is very dry. The tree is rather upright in habit and the yellow leaves look good all summer but you almost wish for winter when the leaves fall to reveal the twigs which are shades of orange, rust and brown. The male catkins start to develop in late summer but really show themselves off in autumn and winter and are a rich combination of pink and orange. The female catkins, which will grow into those delightful ‘pixie’ cones can be seen in the photos behind the larger male cones on the twigs.
In spring these catkkins expand and hang in profusion over the tree. On a sunny day, like today, the tree is delightfully bright when the garden is looking rather dull. This tree reaches about 8m high in time, rather less across and tolerates all but very dry soils and is informal enough to plant in rural landscapes yet neat enough for an urban garden. It was awarded the Royal Horticultural Society Award of Garden Merit in 1995. Alnus incana is native to much of the colder parts of the Northern Hemisphere so this is a hardy tree. Like most alnus it can ‘fix’ nitrogen in its roots so will grow in nutritionally poor soils though obviously, this golden form will prefer decent conditions in your garden to do well.