Italian Alder Trees – Alnus Cordata

Alnus cordata, or the Italian Alder, is a medium-sized deciduous tree originating from southern Italy and Corsica. Despite its Mediterranean roots, the Italian Alder is well-adapted to the UK’s climate and soils, making it a unique and valuable tree in the British landscape.

Typically, Italian Alder trees grow to heights of 20-25 metres, with a broad crown. The bark is a smooth grey that darkens with age. The tree’s leaves are distinctively heart-shaped (hence ‘cordata’), a feature that sets it apart from the native Alder species found in the UK. They are glossy green throughout the summer and stay green late into the autumn before falling.

The Italian Alder flowers in late winter or early spring, with male flowers appearing as yellow catkins and smaller reddish female flowers on the same tree (monoecious). Once pollinated by wind, the female flowers develop into small, woody cone-like fruits that persist on the tree throughout winter, providing a decorative feature and a food source for wildlife.

Italian Alders have a relatively fast growth rate and can live up to 60-80 years. They generally reach maturity within 20-30 years.

Compared to other trees native to England, the Italian Alder distinguishes itself with its heart-shaped, evergreen leaves, its ability to fix nitrogen (which enriches the soil), and its resilience in poor and compacted soil conditions. This adaptability makes the Italian Alder an ideal choice for urban planting and land reclamation projects.

In a British garden design context, the Italian Alder is a versatile choice. Its year-round green leaves provide structure and colour, especially in the autumn when other trees have lost their leaves. The tree’s upright form can be used for screening, or it can serve as a specimen tree due to its attractive foliage and catkins.

From a wildlife perspective, the Italian Alder’s catkins provide an early source of pollen for bees and other pollinators. The seeds within the cones are a food source for birds and small mammals during the winter months.

A notable fact about Italian Alders is their symbiotic relationship with nitrogen-fixing bacteria. These bacteria live in the tree’s roots and convert atmospheric nitrogen into a form that the tree can use, improving the fertility of the soil around the tree. This property makes the Italian Alder especially valuable in poor soils where other trees might struggle.

In conclusion, Alnus cordata, the Italian Alder, is a robust, adaptable, and attractive tree. Its resilience and soil-enhancing properties, along with its value to wildlife and its unique aesthetic qualities, make it an excellent addition to a British garden design.