Hardy Boxwood

When we first began the garden we have occupied for 30 years, a boxwood came with us. There are yellowed snapshots of it sitting in its large clay pot in a sea of raw mud at the back corner of the house, the first significant pixel of our garden-to-be.  It is still there, and it may well survive us, too, for boxwoods can live a long time. There are individual specimens in England and France, and in Virginia and Maryland, that can only be described as ageless.

Our particular boxwood, however, will need a bit of help. It may even need some sort of trust fund or endowment. I should say “they might,” for there are 15 progeny, all grown from cuttings of the original plant and now as large as their parent—about five feet wide and as tall. They are all English boxwood (Buxus sempervirens), which any good general garden reference will tell you is reliably hardy only to USDA?Zone 5, with protection. In the beginning of our garden we tended to skip over that hardiness part; North Hill, our Vermont garden, is located squarely in Zone 4 (or at least used to be), and that seemed to eliminate so many wonderful shrubs and trees. Instead, we took our chances.

We are not sorry, for these 16 boxwood have never been more than lightly pruned in spring, and they have all grown into magnificent dark green pillows. Three of them, including the parent plant, form a sort of loose barrier or dividing point between a little terrace just on the east side of the house. The others march in a regular rhythm up either side of a path planted with antique roses. They give form to that important section of the garden, since rose bushes, taken even at their best, never have much form of their own. That is what boxwoods are so very good at supplying.

But they ask a lot from us. Specifically, each must be protected in winter by its own huge, clumsy wooden box. Burlap will not do, because it does not offer enough wind protection, and the biggest limit to the hardiness of boxwood is not cold, but bitter wind and winter sun. So the advice is often given to locate boxwood on the north or west side of buildings, where shadows will fall on them all winter long. But that is no place for roses, and we wanted them growing together.

We have constructed boxes in place over the boxwoods, sheets of plywood held together by standard hooks and eyes, the kind on screen doors. It is a lot of work. But the alternative—to leave them to the mercy of our harsh climate without protection—would surely result in loss of much of the top growth, and even the death of the plants themselves.

HARDIER CHOICES
We once believed that there is no substitute for English box, but now we know better. It isn’t the much hardier Korean box (Buxus sinica var. insularis, formerly B. microphylla var. koreana), also called littleleaf box. We have also had plants of that from the garden’s beginning. They now form a tidy little hedge around three sides of a small terrace. They are beautiful at all seasons, even when their foliage turns a warm golden brown with the arrival of cold weather. Most people object to that, however, and so a form that remains green all winter has been developed, appropriately called ‘Wintergreen.’ It is a very fast grower, excellent for low hedges, but its leaves are as small as most Korean box—hardly more than one-third of an inch wide and long, and so it cannot compare in nobility with true English box, the leaves of which are almost three times as large.

The best alternative to English box is one of the remarkable hybrids developed by Sheridan Nurseries in Ontario, Canada, beginning in the late 1960s. They are all crosses of B. sempervirens with the much hardier B. microphylla, and all have the word green in their name: ‘Green Gem’, ‘Green Mound’, ‘Green Velvet’, and ‘Green Mountain’. They are all excellent plants. The first three are mounded and relatively slow-growing, and so they are useful for low dividing hedges in parterres and ornamental potagers. The last, ‘Green Mountain’, is upright and pyramidal and grows as rapidly as English box. It is perfect for free-standing specimens or for taller hedges.

We have had plants in the garden here in all exposures for 10 years without protection, and all have come through that many winters in good condition. That is more than we could say for B. sempervirens ‘Vardar Valley’, collected in a very cold part of Macedonia in 1934 and often praised not only for its hardiness but also for its hazy blue young foliage. Here, at least, it has withstood winter cold no better than ordinary English box.

A beautiful boxwood developed at Chicago Botanic Garden in Glencoe, Illinois, sometimes called Chicagoland Green and sometimes B. ´‘Glencoe’, has done wonderfully here, never suffering winter damage. We have three plants from the original test plants sent out years ago. From small rooted cuttings they have developed into upright, vase-shaped plants, each about four feet tall and of great beauty. But their leaves are small, and their growth tends naturally to be in loose, open sprays—wonderful in its way, but not a look-alike for the box we love best. Their wood can also be brittle under heavy snow, so plants are best cinched up by heavy twine in late autumn. That is a good precaution to take with any boxwood left uncovered for winter; it is heartbreaking, come spring, to find that a perfectly hardy specimen has been split apart by snow or ice.

BOXWOOD IN POTS
All the suavity that boxwood can bring to the open garden seems increased when it is grown in a pot. We have accumulated several such specimens, trimmed into large globes or pyramids that provide weight when used with groups of potted flowers and distinction when stood alone. (All potted boxwoods ask in winter is a cool, frost-free place to sleep, so we are apt to gather more.)

With patience, boxwoods can be trimmed into almost any shape, and so we also have three standards in pots, little mop-headed trees on slender stems. The smallest, now about 30 years old and only a foot and a half tall, is one of the original Korean box rootlings that just seemed to want to grow that way. Almost as old is a much larger standard of ‘Vardar Valley’, the cultivar that disappointed us so in the open garden. At four feet tall, with a head as round as a basketball, it carries an air of quiet sophistication wherever it stands.

Our favorite of the three standards is B. sempervirens ‘Elegantissima’, three and a half-foot tall, with small oval creamy white––edged leaves on dense short twigs. It was given to us as a cutting 20 years ago by the late Marshall Olbrich, co-founder of Western Hills Rare Plant Nursery. It is both beautiful in itself and also a living reminder of a very dear friend. ‘Elegantissima’ is the tenderest and most fragile of all English boxwood varieties, and so we take specially good care of it, in the hope that we can leave it in our turn to someone else.

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