The Magic and Mayhem of Winter

As a plant person, I never look forward to winter. No leaves, no flowers, and cold temperatures that keep me locked up inside the house. But the truth is we need winter if we are going to enjoy a beautiful spring. We think things are dead—or at least dormant—for months, but there is actually a lot going on that we can’t see. Most importantly, like us, many plants need rest so they can rise and shine in the spring.

All winters are not created equal, and each extreme has its own risks and benefits. The effects of harsh winter weather are obvious. If things get cold enough even the hardiest of plants can succumb. But cold winters kill off harmful insects and other pathogens, helping keep things in balance. Most weeds are annuals and are therefore not affected by winter temperatures. The seeds simply lie in wait until things warm up.

While many of us enjoy mild temperatures, the lack of a hard freeze usually results in large insect populations the following year—think mosquitos. And mild winters sometimes don’t kill off last year’s weed crop and give next year’s seeds an early start. Surprisingly, plants don’t necessarily love mild winters either. Think of it this way: the longer a plant’s enemies are kept at bay, the longer they are able to stay one jump ahead of the plants in the spring.

And the worst thing for a plant is a winter that can’t make up its mind. If things warm up too quickly, the plant thinks it’s spring and starts to grow again only to be shocked by a final winter freeze that kills off all the new tender buds resulting in fewer flowers and a spring that is simply just not as pretty.

Snow—Friend or Foe?

We all know how heavy snow and ice can damage shrubs and even mature trees. But did you know that snow (as opposed to ice) can actually protect your landscape during winter? As snow softly falls it traps air as it gently builds up on your shrubs providing insulation from freezing temperatures and harsh winds. The same is true for the snow on the ground. In this regard, it acts similarly to mulch. No wonder we call it a blanket of snow! 

Wind—the Enemy

Unlike snow, wind is never your friend, especially here in Cape May where it is seemingly ever-present. You would think we were in Chicago! Why is this so troublesome? Transpiration, i.e. evaporation. According to the New York Botanical Garden, “Winter wind is particularly damaging because plants are unable to replace the water they lose and become desiccated. The process is similar to an ice cube left in the freezer—although it doesn’t melt, it will gradually become smaller. In many areas, wind causes more winter plant desiccation than the sun.”

Survival Strategies

So how do plants survive winter? That depends, of course, on the plant. We all know annuals simply die and reseed—like most weeds. Perennials, on the other hand, go through a complex adaptive process that takes weeks to complete. In order to survive they enter a period of dormancy that is triggered by the angle of the sun, shorter days, and cooler temperatures. Metabolism slows, and exposed parts of the plant are allowed to die off. Depending on the perennial, this often means everything above ground. Water actually moves from within the plant cells to between them so that cell membranes do not rupture in freezing temperatures. (Think of what happens when celery freezes.) Sugars and salts that are left behind act as a kind of antifreeze by lowering the freezing point. Carbohydrates and other nutrients stored in the roots keep the plant alive all winter and provide the necessary nourishment to start growing again in the spring. Did you know that roots grow, even under the snow, if temps are not too low? 

Unlike perennials, all the above-ground parts of a tree need to survive except the leaves. Deciduous trees shed them to reduce water loss. The trunk of a tree is made up of cells that are (so are not at risk) and cells that are very much alive and carry water up and down the trunk. These are the ones that need protection and go through a similar process to that of perennials. The bark protects the trunk and acts as an insulator. Conifers (except Larch and Bald Cypress) do not need to shed their needles because of their narrow shape (less exposed surface area) and waxy coating.

Some bulbs need winter in order to bloom in the spring. They require a period of dormancy in which to rest, the length of which depends upon the variety of flowers. The cold protects the embryo of the bulb from emerging during winter and potentially killing off new growth.

Lend a Helping Hand

There are a number of things you can do to help your plants make it through a long, hard winter.

1. Remove weeds and clean up any diseased or damaged foliage.
2. Mulch, but don’t smother your precious plants (especially their trunks) and be mindful of what you are mulching. Not all plants like as much as others.
3. Wrap shrubs that are sensitive to wind in burlap at least when they are young. I prefer to install temporary stakes around the plant or just on the exposed side and then attach the burlap to the stakes rather than wrapping the plant, thus allowing better air circulation. Burlap is the preferred material because it allows air to pass through but will keep the wind out. Install the windbreaks in the fall and be sure to remove them as soon as the temperatures stay above fifty degrees for a few weeks—ideally right before the last frost.
4. Don’t forget to water. Some winters can be very dry and most likely the irrigation system you relied upon in the summer has been turned off. Just like in the summer, water slowly at the base but only when temperatures are above 40°. And don’t water too late in the day to avoid the possibility of freezing temperatures at night.
5. Shake off snow. Heavy wet snow can be very dangerous. Lend your shrubs a helping hand by gently shaking their branches after the storm passes. It will help prevent breakage and protect the shape of your plant, especially narrow evergreens like arborvitae.
6. Plant natives. They are naturally the best-suited plants for your environment.

Magical Changes

Imagine a plant with white-tipped green leaves that produces white berries tinged with blue or green in the fall and stems that turn bright red after the leaves fall and stay that way until spring when it starts all over again. Sound impossible? Let me introduce you to variegated red twigged dogwood. The botanical name says it all—Cornus alba ‘Elegantissima’. 

Coral Bark Japanese Maple is another amazing specimen that is spectacular in winter after its leaves fall and its coral-red bark is revealed. It too provides year-round interest. Its leaves emerge pinkish yellow, turn light green in summer, and back to a soft yellow in the fall.

There are also a number of broadleaf evergreens that can add a pop of red to your winter landscape. If planted in full sun, Nandina deepens to a rich red in winter. Look for newer varieties like Gulf Stream and Obsession, both of which produce fewer flowers and berries thus reducing their invasive tendencies. Often forgotten, Glossy Abelia turns a rich shade of burgundy with bright red highlights and both Scarletta and Rainbow Leucothoe become increasingly red as winter progresses.

Lastly, Bergenia ‘Bressingham Ruby’ (a perennial) is shiny green in summer with rosy-red flower clusters in early spring but in winter it magically turns a rich maroon-red.

How about some red flowers? Yes, in winter! Add a Sasanqua Camellia like Yuletide or Kramer’s Supreme to your garden. Sasanquas bloom later than Japonicas—from December to March depending on the variety.

And don’t forget berries. Not only do we like to look at them, but the birds love them, too. There are so many choices: Hollies like Blue Princess or Red Beauty; Viburnums like Red Balloon® or Cardinal Candy®; and my personal favorite, Winterberries like Red Sprite, Berry Poppins®, Berry Heavy®, and Little Goblin®.

Master Gardener Sharon Walker puts it best, “Perhaps we can view our own winter dormancy not merely as something to get through until spring finds us back in our gardens but rather as a period of restoration, a time for regrouping and rest in preparation for the season to come.”

Rhododendron: Nature’s Thermometer

Ever wonder why the leaves on your rhododendron are curling up? If it happens during the summer, your shrub may be in trouble—suffering from lack of water or damage that cuts off its circulatory system.  Too much water can also be problematic. Rhodis should never be planted in a wet location – although we rarely have to worry about that here due to our sandy soil. Wind too can be a factor. Leaves curl to lessen the surface area exposed to the wind in an effort to minimize evaporation.

In winter, curling leaves may just be normal. The leaves on a rhododendron are thermostatic, i.e. they move in response to changing temperatures, in the same way, crocuses and tulips open and close each day. In fact, you can almost tell the temperature by reading the leaves.

Leaves are flat and horizontal when temperatures are above 40°. At 32°, they droop, at 25° they begin to curl and will be tightly curled below 20°. At 18°, they freeze unless covered by a blanket of snow that acts as insulation. In fact, if they are snow-covered, they may not curl at all!