Read Part One here.
It’s mid- January as I write this article. My garden, and most likely yours too, is sleeping under a light covering of snow.
Also, after unseasonably warm weather in December and early January, we have now entered a cold stretch. Indeed, a few nights ago the temperature here in Goshen dropped to -17 F.
But, even so, as I gaze out of the window in my study, there is still plenty to catch my eye and hold my interest.
First I notice the structure and shapes — sometimes called “bones of the garden” — that I described in my previous article (“Sleeping Beauty: Part 1” that published in the Addison Independent on Jan. 6), including the gazebo and arbor, as well as groups of trees and shrubs, as well as the walls and steps.
My eye is especially drawn to a delightful small tree with intriguing exfoliating bark, that grows right outside my window. It goes by the unusual name of Seven-Son Flower (Heptacodium miconioides) and in late September it is covered with fragrant white flowers that are abuzz with bees. So the sight this little tree in mid-winter, with its sculptured shape and peeling bark against a snowy backdrop, is a second treat at this time of year.
In this article, “Sleeping Beauty: Part 2,” I will introduce many other plants which can enliven our gardens in every month of the year — including winter.
Of course, as we know, occasionally it can get very cold in Vermont. So, as we choose plants for our gardens, we need to select those that will survive the coldest temperatures we can expect to encounter at our particular location. This important concept is known as “plant hardiness” and I will start by discussing its meaning and how it can influence our choices.
How cold is “cold” for our plants?
The answer is that it all depends on the particular plant!
Some, like tomatoes and begonias, will die as soon as the temperatures drop below freezing.
But many kinds of plants thrive outdoors all year round, both in our forests and in our gardens, And the strategy they use to combat the cold depends on the type of plant.
With plants that we call perennials, the stalks and leaves die back each fall. But below ground, especially when thick snow creates an insulating blanket, the temperatures often remain actually slightly warmer than the air above. This helps their roots remain viable throughout the coldest weather, and it is one reason why we gardeners love a snowy winter.
By contrast woody plants — trees and shrubs — survive above ground all year long. But each fall — triggered by the ever-shortening days and cooler temperatures — they cease their active growth. In addition, to conserve valuable moisture, deciduous species will also drop their leaves.
At this point they then enter a state of dormancy, where the concentration of sugars in each cell markedly increases. This actually lowers the temperature at which the cell fluid will freeze (which would destroy the cell’s walls). It is like “nature’s antifreeze.”
But — most important of all — the actual temperature at which the cell fluids begin to freeze and cause the plant to die, is heavily dependent on the particular kind of plant. Thus, as gardeners, we need to know, for each type of plant, the minimum temperature it can tolerate.
This critical piece of information is designated the plant’s “hardiness rating.” (For instance, a rating of 3 means it can tolerate temperatures between -30 and -40 F).
But we also know that the coldest it is likely to get varies widely with location. Where I live I know that, for a few nights in any one winter, I can anticipate the temperature could drop below -20 F, meaning I live in hardiness zone 4B.
However, up in the northeastern part of Vermont, the temperatures may go as low as -30 F, which is designated as zone 3B.
But you live further out near Lake Champlain, you will probably only encounter to occasional night when the temperature drops to -10 F (zone 5B).
The USDA publishes a detailed map for every state showing the hardiness zones at each location. Check it to find the exact hardiness zone where you live, and then only select plants classified as hardy in your zone or lower. Thus I will buy plants designated for zone 4B or lower, but avoid any shown as only hardy in zone 5.
I love to see a few small trees planted to complement a house, perhaps a crab apple at the corner diagonal. (Just be sure to plant it far enough out so that it will have sufficient room to grow to maturity without the need for pruning). This really useful listing of crab apple cultivars (www.jfschmidt.com/pdfs/JFS_CRAB_CHART.pdf) shows the sizes and other characteristics of many different cultivars, including those that keep their fruit into the winter months.
The various species of serviceberries (Amelanchier) are all delicate small trees that, again, are perfectly sized to complement the house. And they too look lovely in the snow.
When we think about dressing up the garden for winter our thoughts quickly turn to evergreens.
Most garden-sized evergreen shrubs are specialized cultivars derived from genetic mutations of full-sized coniferous trees — primarily pine, spruce, hemlock and fir — all of which bear cones and have needle-shaped leaves. And today there are literally hundreds of hardy coniferous cultivars available for gardeners.
Garden-sized conifers are classified according to their growth rate and their growth pattern. Expect the smallest, those designated as “miniatures,” to grow less than three feet in 10 years, and those classified as “dwarf” to grow between 3-6 inches in 10 years. By contrast, in a decade those designated as “intermediate” will likely grow between 6-12 feet, whereas “large” cultivars will grow 12 feet or higher.
Furthermore some cultivars primarily grow outwards to create a wide mass, whereas others grow upwards as a single focal point.
So, to narrow down your choices as you consider which conifers you might use in your own garden, I suggest you consult with a specialty nursery such as Rockydale Gardens in Bristol, which offers a vast collection that you can see on their website.
Boxwoods are also delightful low-growing shrubs that have very small rounded leaves which remain green all winter long. They are extremely versatile in the garden since they can be readily pruned into particular shapes. For instance, I used a group of three boxwoods to create a four-foot high back-drop for an elegant metal bench that sits towards the front of one of my flowerbeds.
I have also planted pairs of boxwoods, pruned as rounded balls, to emphasize the top of a couple of stone stairways, plus a row to create a low hedge alongside the path up to our barn.
Two boxwood cultivars in particular are designated as hardy in Vermont. “Green Mountain” grows naturally as a pyramid and can make an accent, whereas “Green Velvet,” which forms a rounded shape, is excellent for creating a knee-high hedge.
I am also very partial to rhododendrons with their large shiny leaves and huge flowers in springtime. However, be warned! Especially during the winter months hungry deer may seek out available rhododendrons. So, if you do decide to plant a couple of bushes, plan on taking appropriate precautions, such as applying deer repellent spray and installing some fencing during the winter months.
Fruits and seeds
And finally, many plants keep their fruits or seeds into the winter, creating beautiful pictures for people, as well as tasty treats for birds and other wildlife during the coldest months of the year.
Many years ago I planted six female winterberry bushes (plus one compatible male for fertilization) around the back corner of our driveway. Winterberries, our native holly, drop their leaves in the fall. But their red fruit, which usually remains for much of the winter, not only makes a stunning picture in the snow, but also provides food for hungry birds.
Similarly the native Smooth Rose, (Rosa blanda), which also keeps its hips until late winter, is a wonderful addition to a wild hedgerow.
And, as I mentioned earlier, several crab apple cultivars also maintain their fruit into the winter.
And finally, I wait until spring before I cut back any perennials and grasses which have attractive seed-heads and strong stalks. Black-eyed Susans and purple cone flowers, which are also enjoyed by the chickadees and goldfinch, are among my favorites for their contributions to my winter garden scene.