Long-held traditions

There is a certain grandeur to a tree avenue, which is probably why the tradition has endured for so long. Parallel lines of trees create a sense of stately calm, adding majesty to whatever architectural feature they unerringly lead the eye towards.

The avenue is a long-established means of training the eye to a specific feature – the avenue of sphinxes approaching Hatsepsut’s tomb still stands today, more than 3000 years after it was constructed. When it comes to trees, majestic species have often been employed to create imposing approaches to stately homes or resplendent walkways, with two rows of a single species planted either side of the avenue.

Bare-root and root-ball season lasts until March and is perhaps a shrewd and economical time to purchase large quantities of trees for avenues.

Avenues of trees remain one of the structural plantings with most impact in designed landscapes – but is it time to reconsider how we incorporate them within designs?

Landscapers cannot ignore the spectre of future tree diseases in their planning

Time for change?

One of the biggest potential problems with formal tree avenues as we know them is the fact that they are customarily planted with just one species, where uniformity adds to the splendour of the structure. Tree diseases have caused devastation to many quintessentially British trees, often targeting one particular species – from elm and ash to horse chestnut and, now, the English oak itself.

Landscapers cannot ignore the spectre of future tree diseases in their planning, so designing mixed tree avenues is a practical way to ensure that any diseases or pests are more likely to affect a smaller area. This makes it more easily controlled, with any damage able to be rectified more economically and without unduly injurious aesthetic impact.

There are other benefits, too. Biodiversity attracts a wider range of wildlife to an environment, and a range of species can be selected to provide a changing seasonal display of colours. The different heights and sizes of the trees also create a wonderfully textured and naturalistic effect which can be visually stunning.

What tree species are good for avenues?

There are several criteria for good avenue trees: a straight trunk, vertical top and free trunk height of at least two metres. Thought must be given to how the trees will be pruned as they reach maturity so as to maintain a trunk height of four metres or more and a balanced, dense branching in the crown.

Traditionally, relatively fast-growing trees with impressive forms and a grand height were selected. Popular species include Fagus sylvatica (beech) Tilia (lime), Populus (poplar) and Aesculus (horse chestnut).

However, a surprising number of trees work well in avenues. There are many considerations which will affect a landscaper’s choices, including the purpose of the avenue – for screening, ornamental value, marking a boundary, a recreational walkway, creating enclosed or protected spaces, providing shade or a combination of these. The project’s budget and timescale (including whether instant impact is required) and the landscape itself (function and level of formality) also play a part. For a mixed tree avenue, it’s important to be sure that the trees will thrive in similar conditions, too. Here are some species you may consider, depending on your landscape.

Sorbus aria (whitebeam)

This tree makes a stunning addition to an avenue, and creates a stunning aesthetic throughout the year, with leaves whose silvery white undersides give the appearance of shimmering in the wind. It boasts white blossoms in spring, and attractive red berries in autumn.

Betula (birch)

Betula utilis var. jacquemontii (West Himalayan birch)

The West Himalayan birch is notable for its striking white stems, which provide beautiful winter interest in naturalistic environments.

Betula nigra (river birch)

This birch thrives near water, making it an excellent choice for tree avenues lining a water feature in the landscape. Its orange stems are also particularly pleasing.

Tilia (Lime)

Lime trees have long been a staple of tree avenues, but there are many varieties to choose from.

Tilia platyphyllos (broad large-leaved lime)

A stately, large leaved Lime with lush year-round foliage.

Tilia cordata (small-leaved lime)

A wonderful tree for attracting bees, with fragrant blooms in summer and yellow foliage in autumn, this tree is great for commercial street avenues, with its architectural spire-like shape. Tilia cordata ‘Rancho’ is a good variety to try.

Tilia tomentosa (silver lime)

This Lime’s large dark green leaves have a silvery-white underside, which glimmer when moved by a breeze. Its summer flowers have a lovely scent, and in autumn its leaves turn an attractive shade of yellow.

Tilia x europaea ‘Pallida’ (common lime)

Displays the typical pyramidal habit  of Limes. Its flowers blossom in spring, and its fresh green foliage turns fiery shades of gold and orange in autumn.

Fagus sylvatica (Beech)

Mighty Beech trees make a majestic avenue, particularly in autumn, with their coppery leaves, which brown in winter before their spring regrowth of verdant green.

Acer (Maple)

Acer campestre ‘William Caldwell’ (field maple

With upright and compact growth up to 8m, and glorious vivid orange-red foliage in autumn, ‘William Caldwell’ is a spectacular selection for a visually marvellous avenue.

Acer platanoides (Norway maple)

This maple can grow up to 12m and its autumn colours are yellow and orange. In spring its yellow flowers cast their aroma into the air, making this tree a delight for avenues designed for pleasure walks.

Carpinus betulus ‘Fastigiata’ (common hornbeam)

A tall, deciduous tree, Carpinus betulus ‘Fastigiata’ has a compact, closed crown and a particularly vertical trunk. The leaves are a fresh green colour in spring and golden yellow in autumn. This flexible tree can be planted in sun or shade on all soil types, making it a great choice to mix with other species in an avenue.

Liquidambar styraciflua (sweet gum)

Liquidambar styraciflua is another species boasting intense autumnal colour. Foliage runs the gamut from red and yellow to orange and purple (the latter colour is enhanced when planted in a humid environment).

Platanus x acerifolia/Platanus x hispanica (London plane)

The London plane tree is a classic of tree avenues for a reason. Besides its beautiful flaking grey and cream bark, this magnificent tree is fairly undemanding, thriving in most soils and whether planted in sun or light shade.  

Quercus palustris (Pin oak  or Swamp oak)

Vivid lime green leaves turn equally vividly scarlet in autumn. The Pin oak can withstand a range of soil conditions (including temporary water-logging).

Taxus baccata (English Yew)

The long-lived English Yew makes a graceful addition to a tree avenue. With small, dark green, needle-like leaves which and grow from spiralling branches, Yew can be clipped into formal shapes or left to create a wilder, more natural look, depending on the environment.

For more formal environments, or to create a stylised, architectural effect, pleaching or topiary can be used for some species to great effect.

Commercial landscaping considerations

While mixed tree avenues have many benefits – creating modern, textured environments with the added bonus of extra environmental credentials, certain circumstances can mean single species tree avenues  could be the better choice. Often, this may be in the commercial sector.

Limited space below ground, in addition to roads and paving, does not make for an ideal environment for trees to flourish. Since different species have different growth rates and soil preferences, it may be best to eliminate competition for limited resources with just one tree variety, depending on the space available.

As a rule, it is best to select species able to thrive with full or partial paving for commercial tree avenues. Fruitless and thornfree varieties may also be sensible options in public spaces. The other key consideration is size. In commercial settings, the planting of trees often serves to offset the proliferation of tall buildings; publicly used areas also put trees at greater risk of vandalism. Therefore we recommend slightly larger trees for these settings (a good guide is a minimum girth size of 16-18cm for a tree avenue with immediate impact).

There remain clear benefits to both a mixed or single species approach to tree avenues, and landscapers must carefully consider the factors which hold most weight in any particular environment. What remains the same is the incredible architectural effect which a well planned tree avenue can have on a landscape.