By Alan Branhagen
The Arboretum displays an extensive Birch collection and rightfully so as a premier northern garden. Virtually all birch species are renowned in gardens for their showy exfoliating bark, which makes birches important components to gardens with ornamental appeal in wintertime.
Heritage River Birch (Photo: Alan Branhagen)
Most birch species are found at high elevations or northern latitudes, the exception being the river birch (Betula nigra) which is native in floodplains from southeast Minnesota to the Gulf. The paper birch (Betula papyrifera), with its exfoliating white bark is the northwoods icon. Yellow Birch (Betula alleghaniensis) with its unique copper-to silver-gold bark is more beloved abroad than here in its native United States where it is the longest living native birch. Minnesota’s only other native tree species is the steely-gray-trunked Heartleaf Birch (Betula cordata) mainly found on the North Shore. There is no record of it growing at the Arboretum. It may require a cooler climate.
Paper Birch (Photo: Mark MacLennan)
Yellow Birch (Photo: Alan Branhagen)
From the Northeast, two other birch species thrive at the Arboretum. The first is Sweet Birch (Betula lenta) with dark charcoal bark and high oil of wintergreen content in its bark and buds making it a favorite of brewers of root beer. The other is the Gray Birch (Betula populifolia) a smaller white-trunked birch commonly cultivated as the cultivar ‘Whitespire’ for its borer resistance.
Sweet Birch (Photo: Alan Branhagen)
The Arboretum also holds a few non-native birches including the Asian Black Birch (Betula dahurica) and Gold Birch (Betula ermanii) – both from a similar climate in Northeast Asia. Around the world, species from the Himalaya are beloved for their white to almost rose bark but these species cannot survive our coldest winters and often don’t like our hot, increasingly humid summers either.
Asian Black Birch (Photo: Alan Branhagen)
The recent book Winter Gardens by Cedric Pollet has provided much inspiration for a revival and new way of growing birches in home gardens. Out with the clump, in with the grove! Plant masses of closely spaced, single-trunked birch of various species for incredible drama in the landscape through our long winters.
River birch is the most widely grown birch for its flakey salmon-colored bark on young trunks: it is borer resistant and also heat tolerant. It’s bark character varies and some trees have exceptional bark that even looks unique at maturity (see the cultivar ‘Heritage’ in the Pilsbury Shade Tree walk here). Remember it does become a large shade tree with beautifully pendant branches so give it space. The arboretum has several smaller selections all I wish were more readily available to fit the smaller spaces people seem to plant these trees in and end up cursing them later. River birch also can suffer from chlorosis, turning yellow and ultimately dying in alkaline soil conditions.
Gold Birch (Photo: Alan Branhagen)
Paper birch is susceptible to the native bronze birch borer (look alike and related to the dreaded alien emerald ash borer) which attacks stressed trees. Many new selections of borer resistant paper birch are finally on the market, the most popular ‘Prairie Dream’ selected by North Dakota State University. Northern strains of the tree should definitely be avoided but the tree is native southward into Iowa and Illinois where it often grows on hot, dry south-facing hill prairies. These are the strains of paper birch that should be grown for the future and Arboretum researchers are looking at these trees.
The European white birch (Betula pendula) was once a very popular, white-barked birch with weeping forms and those with delicately cut or purple leaves. These trees have been virtually exterminated by the bronze birch borer, the last tree removed last year at the Arboretum for that very reason.
There is a native bush species of birch: bog birch (Betula pumila) which grows into a large mounded shrub. It grows wild in bogs, fens and other peaty wetlands. You can see this birch along our bog walk.
Native birch also support a wide range of beneficial insects so rate highly as a good choice for nature and ecosystem services as well. Unfortunately, Japanese beetles also like many of the varieties but as trees mature, the solely cosmetic impact becomes less. The winter seeds are eaten by many songbirds, especially goldfinches, pine siskins and redpolls.