Archives For evergreen

Overcoming Winter Scorch

Tim Johnson —  April 29, 2014 — 9 Comments

Gardeners are facing bigger challenges than usual this spring due to a “perfect storm” of weather conditions that scorched evergreens, protected plant predators, elicited heavy use of road salts, and encouraged snow molds. The scorch or burn that has left patches of brown on arborvitae (Thuja), yews (Taxus), boxwoods (Buxus), and other evergreens is the worst and most widespread I’ve seen in my 29 years at the Chicago Botanic Garden. Branch damage from voles and rabbits is also particularly bad this year, and heavy and prolonged snow cover also promoted snow molds, creating bleached-out patches of lawn. Road salts put additional environmental stress on our landscaping.

PHOTO: A boxwood hedge with the outer foliage killed by winter damage.

Although slow-growing, this boxwood (Buxus microphylla) should make a full recovery.

The bad news is that more plant damage is likely to appear once the weather is consistently warm, though many plants will recover from the long, hard winter. While plants may have to be severely pruned or removed altogether, the polar vortex has given us a few important reminders about growing in the Chicago area and could ultimately make us all better gardeners.

PHOTO: A completely brown, winter burnt white cedar.

Winter was particularly hard on this Heatherbun white cedar (Chamaecyparis thyoides ‘Heatherbun’).

During the cold winter months, evergreens continue to lose water vapor through their leaves or needles. The leaves must replace the water by pulling it up from the roots. But when the ground is frozen, the plants’ roots cannot absorb water to resupply the leaves.

If the weather turns warm and sunny while the ground is frozen, evaporation from the leaves increases and the water cannot be replaced. The resulting symptoms, discolored or “burned” foliage, tend to show up quickly in spring, when days are sunny and warm.

Bright winter sun and strong winds can accelerate evaporation, and it’s typical to see the worst burning on the west- and south-facing sides of a bush or tree. Signs of winter burn include needles or leaves that have turned golden or brown. Sometimes a plant has an overall yellowish or off-green color. Leaves may appear bleached. Salt sprayed up by passing traffic can exacerbate the problem and accentuate damage on the road-facing side of the plant.

Many evergreens—particularly fast-growing varieties such as yews—will be fine after a light pruning. Deeply scorched plants will require heavy pruning, leaving unsightly “holes.” Slower growing evergreens may take years to recover from a severe winter burn, and gardeners must decide on a case-by-case basis whether it’s best to remove the specimen.

Unfortunately, some evergreens will be a total loss. This is especially true for plants grown at the edge of the hardiness zone. To determine whether a bush is going to make it, look for new buds or lightly scratch a branch to look for signs of green wood. Patience is often a virtue in gardening, so if you have any doubt about a plant’s viability, give it some time. 

PHOTO: A browned Bosnian pine, with fresh green growth at the tips of its branches.

This Emerald Arrow Bosnian pine (Pinus leucodermis ‘Emerald Arrow’) also shows hard winter damage.

The deep drifts of snow and prolonged snow cover were a boon to such plant predators as voles and rabbits. The blanket of snow shielded voles, mouse-sized creatures that travel under the snow, from hawks and other predators, leaving the creatures free to gnaw on branches and trunks. The drifts also provided a stepladder for rabbits, which feed on top of the snow, allowing them to reach higher into bushes. Signs of rabbit damage include a 45-degree cut in branches. Severe rabbit damage often looks like a bad pruning job, but gardeners can improve the situation by evening out the bush. Branches that have been girdled—or chewed all the way around—are likely to die and should be pruned back.

The sparkling white drifts also promoted snow molds, which can leave large patches of dead-looking lawn. Typically, lawns will bounce back after raking and light fertilizer. Lawns damaged by salt spray might not recover as quickly, and strips growing along roads might need to be replaced altogether.

PHOTO: Grass showing winter damage.

Grass showing winter damage will recover fairly quickly with attentive watering and care.

It’s never good to lose a plant or shrub to the elements, but the polar vortex did provide the type of reality check that can lead to best gardening practices. In a relatively mild winter, Chicago-area gardeners may have success with plants growing at the edge of their hardiness, but these plants can be killed or severely damaged in typical USDA Zone 5 conditions. Perhaps you’ll think twice in the future before putting something less-than-hardy in the garden. Good mulching and watering habits, and planting in the spring to give plants an entire growing season to become established, will increase the vigor of your plants and may help minimize winter burn.

Another virtue of gardening is that it forces you to look forward. So keep last winter’s lessons in mind as you clean, prune, maintain, and perhaps replant this spring.

For more information about gardening post-polar vortex, go to our free public Plant Information Service: chicagobotanic.org/plantinfoservice

©2014 Chicago Botanic Garden and my.chicagobotanic.org

Christmas Tree Taxonomy

Kathy J. —  December 14, 2013 — Leave a comment
PHOTO: A student in class is examining evergreen needles.

Quick quiz: is this boy holding a twig of conifer, evergreen, or both?

Every winter, as a public garden, the Chicago Botanic Garden turns its educational programming attention—as well as its decorations—to the only plants that stay green through the season: the evergreens. We teach class after class of school children how to identify different kinds of evergreens by their needles and cones.

It’s a lesson in sorting and classifying plants—in other words: taxonomy. 

Conifer vs. Evergreen

Every year we remind students of the meanings of the words “evergreen” and “conifer”—they are not the same thing!—and every year, someone is confused. I blame Christmas trees.

PHOTO: Venn diagram showing a christmas tree in the intersection of the sets "evergreens" and "conifers."


The “Christmas Tree” intersects both of the sets “evergreens” and “conifers”—it’s both!

First, it’s important to understand that evergreens are any plants that remain green through the winter, like pine, spruce, fir, and Douglas fir. Conifers, on the other hand, are a classification of trees that produce seeds inside cones. These trees include pine, spruce, fir, and Douglas fir. Wait a minute…those are are the same trees!

You see, the problem is that our Christmas trees tend to be both evergreen and conifer, and as a result, many of us have forgotten the difference. To help us illustrate the definitions of the two terms, let’s look at some evergreens and conifers that do not fall into the intersection of those groups.

ILLUSTRATION: Charlie Brown and Snoopy with a sad-looking, needle-free tree sporting a single ornament.

Charlie Brown’s tree might have been a bald cypress.

One conifer that loses its needles, and therefore is not an evergreen, is the bald cypress. These can be very attractive when covered in snow. (The bald cypress trees growing in the Heritage Garden have been pruned at the top and look like candelabras.) The needles on these trees change color in fall—the same way deciduous trees like maples and oaks do—and drop to the ground, making them look, well, bald.

Boxwoods and rhododendrons are woody plants that keep their green leaves all winter, but they do not produce cones. Boxwoods are occasionally used in wreaths and can be found in many places around the Garden.

PHOTO: Closeup of a bald cypress branch in golden fall color.

Bald cypress (Taxodium distichum) is called “bald” for a reason—its needles change color and fall in autumn just like deciduous trees such as maples and oaks.

PHOTO: Boxwood in the Japanese Garden.

Boxwood in winter in the Malott Japanese Garden: these true evergreens may yellow a bit with winter, but keep their foliage.

Now here is where things actually do get confusing. Female yews produce a bright red “berry” that might make you think they are just evergreens. Actually, when you take a close look at the hard core at the center of this berry, you would see small, closed scales like those on any other “pine” cone. Yep. Juniper “berries” are also modified cones. That means yew and juniper are both evergreen and conifer.

PHOTO: Closeup of yew berries showing seed/nut inside the berry.

Yew berries (Taxus baccata)
Photo by Frank Vincentz, via Wikimedia Commons

So call your Christmas tree an evergreen or a conifer—you will be correct either way. But it’s worth remembering what the two terms mean. Recognizing how things are alike and different is the driving force behind taxonomy and is also fundamental to understanding the natural world.

Have a wonderful holiday season!


©2013 Chicago Botanic Garden and my.chicagobotanic.org

The horticulturists at the Garden created a new winter display in the Heritage Garden this year. As part of the Wonderland Express exhibition, they arranged willow branches and evergreens to great effect. See how it was done with this video, then come see it for yourself! http://www.chicagobotanic.org/wonderland.