By Mary Free, Extension Master Gardener
Do you recognize the plant on which the male eastern tailed-blue is perching? It is a heath–Erica vagans ‘Yellow John’ (Cornish heath)–native to parts of Europe. Heaths are desirable, low maintenance, evergreen shrubs that nurseries sometimes mistakenly label as heathers even though heaths have needle-like rather than scale-like foliage.
Heaths provide year-long interest in the landscape. They offer a wide range of foliage color (yellow, orange, bronze, crimson and different shades of green) that often intensifies or changes in winter. Bloom time and color also are variable. For example, ‘Yellow John’ produces white/lilac flowers from late summer into fall, while rose pink flowers appear on Erica erigena ‘Irish Dusk’ (Irish heath) from fall into spring. Both heaths are pictured thriving in early April 2010, after the snowiest winter on record for the DC area.
Four years later, the picture (late March 2014) is quite different. Although ‘Irish Dusk’ is supposedly hardy to Zone 7 (Arlington and Alexandria are in Zone 7a), it is somewhat brittle and can suffer foliage damage below 18 degrees. Unfortunately, it was injured from falling debris during the preceding summer and in its weakened condition succumbed to this winter’s bitter cold temperatures. Somewhat surprising, though, is that ‘Yellow John’ also is (mostly) devoid of foliage. It had flourished in the same spot for ten years and is hardy to Zone 5 (-20 degrees). So what happened to it?
If you grow ornamental shrubs (especially those that are marginal in winter hardiness like rosemary, lavender cotton, heaths, evergreen azaleas, etc.), then you may have observed the same problem: bark splitting. According to the North Carolina Cooperative Extension Service, “Cold injury appears as peeling, sloughing, splitting or cracking bark often near the soil surface. Injured plants or branches may die in early spring, late summer or several years later.”
The Purdue University Cooperative Extension Service lists three winter conditions that can cause cold, or low temperature, injury:
- winter temperatures are much below normal;
- temperatures are below normal in the early fall or late spring; or
- winter temperatures fluctuate during the dormant period so that dormancy is broken and plant tissues are damaged.
Since different species become tolerant (aka harden) to the effects of freezing to different degrees and harden and deharden at different rates, some species will have been affected by the low temperatures and rapid temperature fluctuations this past winter while others remained unscathed.
To try to prevent permanent damage to injured plants, prune out the affected areas to the unaffected growth once the threat of late spring freeze passes. [Luckily the shattered stems of Erica vagans can be pruned to the ground (new growth already can be seen emerging from the soil), although it may take years, if ever, to regain its previous form.] To prevent further stress, water injured plants during dry spells in the summer. The best solution, though, is to grow reliably hardy plants, preferably natives, that have a better chance of withstanding low or rapidly changing winter temperatures.
For advice on reducing winter damage, see Managing Winter Injury to Trees and Shrubs, Publication 426-500 from the Virginia Cooperative Extension.
For a list of native plants that thrive in our local conditions and benefit our local wildlife, see MGNV’s Tried and True Native Plant Selections for the Mid-Atlantic.