Plane Tree: Planting, Pruning and Care

Description and Botany

The plane tree is a well-known tree frequently planted for the dense, cooling shade it provides. It is the sole representative of the Platanaceae family and comprises around 8 species, only a few of which are commercially available today. Its botanical name Platanus derives from the Greek “platanos“, itself from “platos“, meaning ‘broad and expansive’ – a reference to its potentially impressive dimensions. Beyond the California sycamore (Platanus racemosa) native to that state’s mountains, plane trees originate from various global regions depending on the species. The western plane or American sycamore (Platanus occidentalis) hails from eastern North America and northeastern Central America, while the oriental plane (Platanus orientalis) originates from southeastern Europe. Through importation and hybridisation, these gave rise in the 17th century to a hybrid species variably called Platanus (x) hybrida, Platanus (x) hispanica or Platanus (x) acerifolia. This spawned several cultivars, including Platanus ‘Malburg’ and Platanus ‘El Gordo’ to name but two. Most commonly called London plane or sycamore, this is the variety predominantly lining our roadsides, canals, or severely pollarded to shade Mediterranean terraces and squares. In the wild, it grows spontaneously along waterways and in deep valleys.

With rapid growth, it readily reaches 30-40m in height with a 15-25m spread, naturally suiting large spaces. However, more compact cultivars exist for gardens, such as Platanus (x) acerifolia ‘Alphen’s Globe’ which maximises at 10m x 6m with a spherical crown.

Exceptionally long-lived, these trees can survive centuries, even millennia, developing massive trunks of considerable girth. On the Greek island of Kos stands the Hippocrates Plane Tree – a Platanus orientalis estimated at 500-2000 years old with a 14m trunk circumference. Typically single-stemmed with a straight, massive trunk, the bark is greyish-beige and exfoliates in irregular plates (rhytidomes) revealing patches of green, yellow, pinkish and brown tones. This distinctive marbled effect provides ornamental value. When grown freely, its main branches are equally sturdy and upright. The deciduous foliage consists of large alternate leaves up to 20cm long on long petioles. Palmatilobate, they’re divided into 3-7 toothed lobes, resembling certain maple leaves. Young leaves are pubescent (covered in fine hairs), potentially problematic for allergy sufferers. Green in season, they turn yellow then brown before falling. Notably tough, plane leaves decompose very slowly.

The beautiful bark of plane trees: Platanus acerifolia ‘Alphen’s Globe’, Platanus hispanica ‘Malburg’, Platanus acerifolia, Platanus hispanica ‘El Gordo’

In late spring, inconspicuous flowering occurs as small flowers form spherical heads on long pendulous peduncles. Being monoecious, each tree bears both green male flowers and red female flowers. The latter develop into achenes forming small balls, initially green then light brown. Like the leaves, these fruits are covered in tiny hairs that create yellowish down when shed, potentially causing allergic reactions in sensitive individuals.

The plane’s root system is vigorous and may damage nearby structures. Its hard, dense pale wood resists moisture well, being used for joinery, boatbuilding and plywood. It also makes good firewood. Both leaves and bark are thought to have astringent properties.

Emerging leaves and fruits on a Platanus orientalis

The different species and varieties

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Planting

Where to plant?

A lover of sun and warmth, the plane tree also thrives in partial shade in any ordinary, deep soil, even chalky. While a mature specimen can withstand hot, dry summers, it prefers well-drained soil that doesn’t dry out completely. Highly resistant to pollution, it is often used as a street tree in urban areas. With a hardiness rating of -20°C to -25°C, it can be grown in most regions, except in very cold mountainous areas. Platanus racemosa, however, is more tender and struggles with harsh, prolonged winters.

When to plant?

The best planting time is autumn in most regions. In areas with particularly cold and wet winters, spring planting is preferable but requires regular monitoring of watering depending on weather conditions.

How to plant?

1) Soak the root ball in a large volume of water to saturate the substrate.

2) Meanwhile, dig a hole at least twice as wide and deep as the container holding your young plant.

3) Add a spadeful or bucket of compost and one or two handfuls of ground horn to the excavated soil and mix well.

4) Remove your plane tree from its pot and position it in the centre of the hole, ensuring the top of the root ball is level with the ground. Slightly higher planting is better than too deep, as the level will settle after watering.

5) In windy areas, install a stake (at the same time as placing the root ball) on the side opposite prevailing winds and secure the trunk without constricting it, using a flexible tie.

6) Water thoroughly, even if it’s raining. 10 to 15 litres at planting is beneficial.

7) Mulch around the base with a 10cm layer (straw, grass clippings, wood chips, flax straw, cocoa husks or any other organic mulch of your choice).

→ Thereafter, monitor watering to prevent the soil from drying out and ensure your plane tree establishes well. If needed, water deeply once a week rather than lightly and frequently. Once mature, it will rely on natural rainfall. Artificial fertilisation is unnecessary, but replenish organic mulch regularly in the early years.

Beautiful intertwined branches (Platanus acerifolia)

Pruning and maintenance

The plane tree tolerates pruning perfectly and many specimens are severely pruned to reduce wind resistance. However, repeated pruning can create entry points for certain pathogenous elements, the most common being anthracnose and canker. An insect known as the Sycamore Lace Bug (Corythucha ciliata) may also attack the leaves and weaken its host, leading to the tree’s death in the most severe cases.

Maintenance Pruning

The plane tree does not require specific maintenance or pruning. If necessary, in winter and on young, easily accessible specimens, remove poorly oriented branches growing inward as well as dead wood to shape its silhouette. For mature and very large specimens, it may be necessary to cut certain branches to limit wind resistance. In this case, call a professional arborist. Only they are equipped and trained to carry out proper, well-judged pruning on such trees.

Parasol Pruning

The plane tree lends itself well to parasol or arbour pruning to provide shade from the sun. Again, prune in winter to clearly identify the branch structure.

1) Allow the trunk to grow to the desired height.

2) Cut all secondary branches growing from the trunk up to the definite height. Use sharp, clean tools.

3) Select the scaffold branches. Choose 5 to 7 of the most horizontally growing branches, ensuring they are as evenly spaced as possible, and remove the others flush with the trunk.

4) Cut the crown or leading shoot of the tree at an angle to prevent water pooling on the cut surface.

5) On the scaffold branches, remove all small shoots growing vertically or poorly positioned.

6) Subsequently, prune any new branches growing upward or downward to encourage the scaffold branches to lengthen and thicken, as well as any shoots attempting to regrow a leading shoot at the top of the trunk.

→ Note that you’ll need a little patience before achieving a well-sized, fully functional parasol canopy.

Potential diseases and parasitic pests of the plane tree

Anthracnose

More resilient than its relatives, Platanus (x) acerifolia can nonetheless be affected by anthracnose. This fungal disease is caused by the fungus Gnomonia vegeta, which can attack all the cell of the tree. It tends to develop in spring, favoured by cool and damp conditions, and becomes less noticeable when warm and dry weather returns, ultimately having little worrying impact on mature specimens. Regions such as those around the Mediterranean offer less favourable conditions for this fungus to thrive. When infected, the leaf of the plane tree turn brown and fall prematurely. In some cases, certain branch may die back. Mature trees produce new foliage when drier and warmer weather returns. To limit the onset and spread of anthracnose, avoid heavy applications of nitrogen fertilisers, which weaken the tissues, and refrain from watering the foliage. Collect and dispose of fallen leaf to prevent contamination cycles. For young plant, preventive treatments with copper or horsetail decoction can be applied.

→ To learn more, read our article on Anthracnose.

Canker Stain of Plane Trees

Canker stain of plane trees is a far more serious disease, causing the death and felling of numerous trees each year, to the extent that prefectoral orders are issued in affected departments. The culprit is another fungus, Ceratocystis platani, which lodges in the vascular system and feeds on the sap of its host. The blocked vessels can no longer transport sap, leading to the plant drying out and dying. Highly contagious, this disease spreads rapidly to nearby trees. Warning signs appear as lesions on the trunk and branch, displaying blue-black or purple discolouration, nicknamed “blue flames”. The bark dries out, the leaf turn yellow, and the tree dies within just a few months. Incurable, this disease requires the prompt felling of the tree, with protective measures to prevent contamination of neighbouring trees. To prevent infection, disinfect tools before any intervention and avoid injuries that could provide entry points for the pathogenous agent.

Sycamore Lace Bug

Corythucha ciliata is an insect known by various names: sycamore lace bug, plane tree bug, or reticulated sycamore bug. Measuring 3 to 4 millimetres long, it is cream-white in colour. Its transparent wing are white and appear intricately patterned like embroidery. A black spot is visible on the forewing. This insect thrives in hot, dry weather and is particularly active in late spring and summer. The female lays numerous egg, mostly along the central vein of the leaf. Once hatched, the sap-feeding larvae disperse throughout the foliage. Symptoms may include leaf discolouration (turning yellow and eventually falling) and increased honeydew production dripping from the branch. Weakened, the tree becomes more susceptible to other pathogenous agents, particularly anthracnose and canker stain. While chemical treatments exist, at Promesse de Fleurs we encourage you to prioritise more environmentally friendly solutions. The use of nematodes (Steinernema) and lacewings (Chrysoperla), both natural predators of the sycamore lace bug, provides effective control. To prevent infestations, remove loose bark in late autumn to eliminate potential overwintering sites.

→ To learn more, read our article on the sycamore lace bug.

Propagate

The plane tree propagates easily by cuttings. Proceed in autumn, around October.

1) Take heel cuttings. This involves a piece of this year’s branch, about 20 cm long, “ripened” (meaning it has started to lignify and turn into harder wood) with a small piece of bark left at the base where it was attached.

2) Plant your cutting in a container deep enough to bury two-thirds of it.

3) Use a light and well-draining substrate, made of equal parts compost and coarse sand.

4) Water generously, without disturbing the cutting.

5) Shelter it until the following autumn.

6) Repot into an individual pot and let your young plant grow for another year before planting it out in the ground the following autumn.

Pair with

The plane tree is a majestic tree which, if left to grow freely, reaches impressive dimensions. Indeed, it can grow to 30-40m in height! Such use is therefore best suited to parks and very large gardens where it can be planted as a standalone specimen as a remarkable feature or in an avenue to frame a grand driveway.

The ultimate shade tree, it is sometimes pruned into a parasol shape to create a sheltered area for resting or dining away from the sun’s intensity. When trained this way, it can be kept to more manageable proportions. Finally, Platanus acerifolia ‘Alphen’s Globe’ is a variety that could be described as dwarf, reaching only around ten metres tall. Its crown develops into a rounded shape, adding a somewhat formal touch to a garden.

You can plant large drifts of early-flowering bulbs beneath your plane tree to create a colourful carpet with stunning effect. Daffodils, tulips, wild garlic and Cyclamen coum brighten spring with their sparkling corollas. For summer and autumn, consider Cyclamen hederifolium or Cyclamen cilicicum.

For perennials, certain hardy geraniums such as Geranium macrorrhizum or Geranium nodosum thrive in the shade of large trees, as do Pachysandra terminalis (in reasonably moist soil), periwinkle or ivy.

In a more formal garden, why not try dwarf bamboos such as Sasa or Pleioblastus, or if the soil remains moist, Hosta, ferns or Hakonechloa.

A Platanus hispanica ‘El Gordo’ with bamboos: Pseudosasa japonica (top) and Pleioblastus chino ‘Elegantissimus’ (bottom)

For bushes, Hydrangea appreciate the dappled shade provided by their neighbour, as do Japanese maples, Japanese andromedas, Aucuba, camellias or Fatsia, depending on the type of soil available.

The leaves of the plane tree turn yellow in autumn. Enhance this effect by pairing it with companions whose foliage ignites at this time, such as maples, Ginkgo or Liquidambar for large trees, or Mollis azaleas, winged spindle, Hydrangea quercifolia, serviceberry, Cotinus or certain dogwoods for bushes.

The beautiful autumn foliage of the plane tree is framed by the yellow of Ginkgo biloba, deep pink of winged spindle, glowing orange of Liquidambar and brown of Hydrangea quercifolia

Take advantage of the decorative mottled bark of the plane tree to create a colourful winter display. Pair it with the pristine white of a Himalayan birch, the amber-copper of a Prunus ‘Amber Beauty’, the cinnamon bark of an Acer griseum, the mahogany of a Tibetan cherry or the equally mottled bark of a Stewartia pseudocamellia. Complete the scene with the vibrant yellow, red or orange stems of ornamental-stemmed dogwoods and a few clumps of hellebores for midwinter flowering.

Winter tableau with the amber bark of Prunus ‘Amber Beauty’, white bark of Betula utilis jacquemontii, exfoliating bark of Acer griseum. Add flame-coloured bare stems of Cornus ‘Winterflame’ and clumps of hellebores.