I want to plant a grove of birch trees, about 50 feet thick, alongside a road that borders my property. I’ll be starting with small whips. How close should they be planted, and how should they be pruned to achieve tall, straight growth? Are birches a good choice for this purpose? What natives are best for underplanting?
Michelle Cannon, Burlington, WI
Dr. Edward Hasselkus, professor emeritus of horticulture at the University of Wisconsin in Madison, replies: Your idea is the way birches are best used. The repeated white trunks in a birch grove are very striking. There are three white-barked birches I recommend: paper birch (Betula papyrifera), gray birch (B. populifolia), and B. platyphylla var. japonica ‘Whitespire’. White-barked birches should be planted on a north-facing slope where the soil is cool. If stressed by hot, dry soil, these birches are prone to bronze-birch-borer attack.
For tall, straight growth, start with single-stemmed whips, and space them irregularly from 6 to 20 feet apart to give your grove a natural look. As they grow, prune out lower branches as they become shaded out.
When young, the branches of these trees will be too low to accommodate shrubs as an understory. Start by mulching the birches with shredded bark or wood chips. Later, if you want to add a low-growing, native shrub, try dwarf bush honeysuckle (Diervilla lonicera). This deciduous plant is about 2-1/2 feet tall at maturity. Its foliage is bronze in spring and reddish-purple in fall, and small, yellow flowers appear in June and July.