Birch trees are a common sight throughout Europe. The two principle species seen are Betula pubescens/Downy Birch (sometimes known as White Birch or European White Birch) and Betula pendula/Silver Birch (sometimes known as European Weeping Birch, European White Birch or Weeping Birch).
Both species outwardly look very similar and it is common for enthusiasts collecting wild (Yamadori) Birch for bonsai to automatically assume that their specimen is a Silver Birch/Betula pendula.
This short article is intended to help the bonsai enthusiast distinguish between the two main Birch species found in Europe so that they can correctly identify their own trees and bonsai. However, it should noted that there is little or no difference in care needs between the two species; they can be treated equally.
Both the Downy (B. pubescens) and Silver Birch (B. pendula) have white to silver bark in maturity. However, the bark of the Silver Birch will have a whiter appearance and black fissures (often near the base), Downy Birch has a more grey, smoother bark in maturity. Unfortunately, unless you have both species growing side-by-side for comparison, this information does not necessarily make accurate identification easier.
There is also a difference in leaf shape and texture between the two species, however, this is not necessarily easy to identify when a birch is studied in isolation. The leaves of Silver Birch (left) are roughly triangular, have a broader base and a pointed tip, and more sharply-serrated margins. Downy Birch (right) have more rounded, ovate leaves with less acutely pointed tips.
Downy Birch leaves have a grey underside (left) that are slightly hairy but in the main only when the leaf is young.
The easiest way of identifying a birch is to study the youngest shoots or new growth, particularly during the growing season.
The new shoots of a Silver Birch (left) are hairless and covered in 'warts' or glands. (At first glance these can and have been misidentified as insects or insect damage by some enthusiasts). Whereas the shoot of a Downy Birch (right) does not have these warts but is covered in minute hairs.
Silver and Downy Birch are widespread throughout Europe into Turkey and South West Asia, the Caucasus and are reportedly widespread throughout Canada. However, despite their dominance over such a wide area of the world and a wide tolerance of conditions in both species, there are subtle differences in the ideal growing conditions for each species.
Silver Birch tend to favour drier, faster draining soils and warmer summers. They tend to be more dominant in warmer southern climates. Downy Birch prefers a wetter soil and will happily grow with its feet in water at the side of rivers and in bogs and marshes. The Downy Birch prefers cooler northern climates and is even hardier than the Silver Birch, being found growing as far North as the Arctic circle.
Note that these are the preferred habitats of each species but both are very adaptable even in less than ideal conditions. As bonsai, I have experienced no difference in horticultural care-needs between the two species; both are happy to grow in identical soils and growing conditions.