If you are following a compass course through the woods, one sight that can sink your spirits in a hurry is an expanse of common juniper directly ahead. Juniper patches are not as painful to navigate as robust stands of blackberries, but the contorted horizontal branches, as much as 3 feet high and often 8 feet long, and interwoven with those of their brethren, are hell-bent on landing you flat on your face on their prickly needles. Trying to make your way through the bouncy branches of juniper has been compared to walking on bedsprings, but bedsprings are mercifully predictable compared to an unruly, sprawling jungle of juniper.
Extensive, impenetrable mats of juniper are not uncommon, and they might make you wonder if this could be yet another non-native super plant, well on its way to taking over the county. But as your eyes become accustomed to the bright light of a juniper opening, you will soon see clues showing that its dominance is ephemeral.
This low, light-dependent shrub can’t tolerate very much shade, even the shade from trees at the edges of its patch. As trees grow, juniper retreats; the dense mat of needles thins, gets spotted with brown, and then the poor shrub dies. Juniper skeletons persist for decades in the understory of forest stands that have grown in on abandoned pasture, reminding us of this fatal weakness.
Another vulnerable stage is when junipers are seedlings. They are slow-growing and master their environment only after establishing a good root system, a job that can take 5 to 10 years. That’s why its presence tells you that the soil beneath juniper is either naturally sandy and nutrient-poor or has been severely depleted by overgrazing – otherwise a host of other plants would have overtopped it in its infancy.
It does have the advantage of having resinous foliage that is unpalatable to browsers, an important trait for short-bodied colonizers of sunny land. Plus, once it has become well established, other herbaceous plants cannot begin to compete with it.
Common juniper is the most widely distributed woody plant on Earth and is found to Zone 2 in northern latitudes and south to mountainous areas at the latitude of the Mediterranean. After finding the shrub high on a mountain in Switzerland, landscape gardener Michael Dirr wrote: “Two things in life are inescapable: taxes and J. communis.” He might have found it, along with taxes, in Japan or most any other Asian country as well.
Common juniper has sharp-pointed, dished needles, usually about ¼-inch long. Each needle has a white stripe down the middle of the upper surface, but the shrub has a way of arranging its needles upside down. Looking down on a juniper, you see the green undersurfaces. When lifted, the undersides of the branches look whitish from all the little stripes. Typically, it grows in prostrate mats, keeping its wide-spreading branches within a few feet of the ground. Eastern red cedar, more common in southern New England, is the only other native juniper hereabouts, and it has the opposite approach to shape, preferring to be upright and columnar.
Male and female flowers are usually borne in early spring on separate plants. The berries that follow stay green for two or three years before finally ripening to blue-black. They have long been used to flavor gin and, especially in Scandinavia, in cooking meat.
Compared to the foliage, the berries are considerably more popular with wildlife. Although they are not high in nutritional value, the berries are often abundant and are rated as important food for the robin, bluebird, cedar waxwing, wild turkey, evening grosbeak, purple finch, and pine grosbeak. The berries are also eaten by the ruffed grouse, flicker, downy woodpecker, mockingbird, catbird, yellow-rumped warbler, and black-capped chickadee. Junipers produce excellent cover for nesting and resting birds; in winter, I have unintentionally caused grouse to explode from beneath the snow in juniper patches.
A trip through the digestive tract of a bird greatly increases the chance that a juniper seed will germinate. Although the seeds retain their viability for several years, the germination rate of seeds that have not been excreted by an animal is typically very low.
People often dislike juniper, believing that it ruins pastures and fields and because it is almost impossible to dig out when someone decides to try some mowing after years of neglect. But maybe they haven’t yet seen what for me is a frequent and welcome sight: a slender but strong sugar maple rising from the center of a big, old mat of juniper, protected from browsing deer by springy branches and prickles. These maples usually look so healthy as they reach upwards to shade the junipers to death. Could years of fallen juniper leaves have enriched the formerly hopeless soil, and could those deep, tough, hated juniper roots have mined deep for the very nutrients now enjoyed by the maples? I like to think so.
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