16-July London in Bloom: The Trees of July

The most common and most disliked of all our street trees is the common lime Tilia x europea syn. T. vulgaris. These are all over the city, in our gardens and streets, as well as avenues in our parks. Nearly all of the larger specimens were planted before the advent of cars, some even in the eighteenth century. This month they become heavily infested with aphids. These insects proceed to drop a sticky honeydew on to cars below, which then gets infected with a sooty mould causing black marks on the car.

Consequently, London’s motorists dislike parking beneath them. The tree itself is likely to be a natural hybrid between two common European limes, the small and the large-leaved lime i.e. Tilia cordata and T. platyphyllos. It is usually a sterile union, but occasionally viable seed is produced, although the seeds may take as long as a year and a half to germinate. Unfortunately, this lime also produces many ugly side shoots on its trunk, which neither of its parents do to any great extent. These tend to get cut off, giving many trees a rather mutilated appearance. On a more positive note, the flowers of many limes are scented and used to make the flower tea so loved by the French and by Proust especially.

There are a number of other less common limes also worth looking out for this month. Arguably the most beautiful are the silver lime T. tormentosa and silver pendant lime T. ‘Petiolaris’. The latter occasionally has bees rolling around beneath it having become intoxicated on the tree’s fermented nectar. Then there are the rather tortured-looking cultivars ‘tortuosa’ and ‘laciniata’ as well as fastigate or upright forms.

Still rarer, wild limes such as the American lime T. americana and T. henryana can be found in Hyde Park and the Mongolian lime T. mongolica in Cannizaro Park. The American lime is greatly favoured by the great spotted woodpecker, who pecks numerous holes into its trunk to suck its sap.

The false acacia or locust tree Robinia pseudoacacia is another common tree throughout London which is now covered in white flowers. Its English and Latin names are notoriously confusing. It is called an ‘acacia’ which it is not (hence false) as it has thorns and leaves similar to true acacias. Its generic name Robiniia comes from Jean and Vespasien Robin who were the French gardeners who planted the first trees of this type in Europe around 1600.

Its other English name of ‘locust tree’ comes from the seedpods which are similar to those of the true locust tree. These were said to have been eaten by John the Baptist when he was in the desert. These seedpods may even be the ‘locusts’ that were eaten by the Jews in the wilderness. Either way, the flowers are deliciously scented and much visited by bees.

Any magnolias seen in full flower now are mainly tulip trees which usually produce their flowers at a dizzy height whereas the more common bull magnolias are often seen growing up the front of old houses. Their large, plate-like flowers are popular, being so highly scented. Other rarer magnolias worth seeking out in gardens are Wilson’s magnolia M. wilsonii which has a dense central cluster of deep maroon stamens and the Chinese evergreen magnolia M. delavayi which has flowers that only open at night. There may also be one or two spring magnolias now producing a second flush of flowers.

The sweet chestnut Castanea sativa needs little introduction. It was first brought here by the Romans, who already had four or five eating varieties. It has been popular ever since and neglected coppices still exist around the edges of London.

It was grown originally to make hop poles, but where it is still harvested it is mainly now for the posts used in wired fencing. Older trees are often seen around country houses, where five hundred year old veterans can reach over thirty metres in height, with beautifully spiralled trunks. They are now producing their vast numbers of spermatic smelling catkins. Young Roman women ate sweet chestnuts when they were fasting. It is thought they may have been eaten to induce vomiting. A fine old sweet chestnut with a door in its bole, which has survived several arson attacks, can be seen in Carshalton Park.

Probably the most noticeable trees this month are the Indian bean trees Catalpa spp., which were unknown here before 1726. Because they produce such trumpets of flowers and need a little heat to thrive, they make for popular planting in central London. There is a fine old specimen coming to the end of its life in St James’s churchyard on Piccadilly. Fortunately, there are many more younger specimens dotted around Westminster, particularly in Parliament Square. Their white flowers are big and brassy with yellow and purple spotting. Three species may be encountered. The most common is the Indian bean tree Catalpa bignoniodes. The Western Catalpa C. speciosa which has less purple spotting and can be seen in Radnor Gardens, Twickenham and the Chinese Catalpa C. ovata in Chelsea Physic garden.

The golden rain tree or Pride of India Koelreuteria paniculata is now covered in golden yellow flowers, hence ‘golden rain’. It arrived by caravan from China in the mid eighteenth century. It has pink midribs on its leaves and bladder-like fruits which will come later. The Chinese used to make necklaces out of its seeds. A rare fastigate form can be found in the City of Westminster cemetery at Hanwell.

Other rarer trees in flower are best looked for in collections. Of particular interest are the Epaulette tree Pterostyrax hispida, Chinese Yellow-wood Cladrastis sinensis, Yellow-wood C. lutea and the Chinese Fringe tree Chionanthus virginicus all of which have clusters of white or creamy white flowers.

Although tender, they all deserve a wider planting as does Styrax obassia, S. japonica, Stewartia sinensis, S. pseudocamellia, S. monadelpha and Cornus contraversa. Most of these can be found in either Cannizaro, Richmond or Syon Park.