The London Plane Tree is a sycamore hybrid that is widely planted as a street tree and park tree for its ornamental, flaking bark, its large size and ease of growth and its toughness and durability in urban conditions. It is used to line city and suburban streets and it provides shade with its large leaves and wide-spreading branches. Platanus × acerifolia is a hybrid cross between American sycamore (P. occidentalis) and Oriental planetree (P. orientalis). The original cross may have occurred as early as the 1640s, after which this tree became widely planted in London and other major European cities because of its perceived tolerance for urban pollution. City planting spread to America where this hybrid today is common in such distant locations as Brooklyn, New York and San Francisco, California. This hybrid can be very difficult to distinguish from its American parent. Distinguishing features include: (1) Leaves have deeper sinuses and (2) fruiting balls appear in pairs. Like its American parent, it typically grows as a single-trunk tree to 75-100’ (less frequently to 120’) tall with horizontal branching and a rounded habit. Trunk diameter typically ranges from 3-8’. The signature ornamental feature of this huge tree is its brown bark which exfoliates in irregular pieces to reveal creamy white inner bark. Mature trees typically display mottled white bark that facilitates identification from great distances. The large 3-5 lobed medium to dark green leaves (4-9” wide) have coarse marginal teeth. In fall, foliage typically turns an undistinguished yellow-brown. Small, non-showy, monoecious flowers appear in small rounded clusters in April. Male flowers are yellowish and female flowers are reddish. Female flowers give way to fuzzy, long-stalked, spherical fruiting balls (to 1 3/8” diameter) that ripen to brown in October and persist into early winter. Fruiting balls appear in pairs. Each fruiting ball consists of numerous, densely-packed, tiny seed-like fruits (achenes). Fruiting balls gradually disintegrate as fall progresses, dispursing their seeds, often in downy tufts, with the wind. Easily grown in average, medium to wet, well-drained soils in full sun. Tolerates light shade. Prefers rich, humusy, consistently moist soils. Generally tolerant of most urban pollutants. Hardy in zones 4-8.
Growing Instructions for the London Plane Tree
The seeds have a period of dormancy. They can be planted outdoors in the fall or winter for spring germination or they can be cold stratified to simulate winter conditions and to break their dormancy at any time of the year. 1. Place the seeds in a plastic bag and seal it. Store the bag in a refrigerator for 2-3 months. 2. The seeds like moist, well-drained soil. Fill a pot with a mixture of half potting soil and half sand or vermiculite. Water the mixture so that it is moist but not wet. 3. Sow the seeds on the soil and cover them with a thin layer of soil about ¼ inch thick. The seeds need light to germinate. 4. Water the container and leave it to drain. 5. Put the pot in a warm, sunny area. 6. Water the pot regularly so that the soil is moist but not wet. 7. The seedlings can be transplanted when they are a few inches tall.