Ever Blue

In the depths of winter, when the garden is mostly brown, the only thing better than a beautiful evergreen plant is one that is ever-blue!

Carex laxiculmus or Creeping Sedge is a low, clump-forming grass that stays blue all winter long. It is an excellent garden plant: durable, care free, deer resistant, and versatile. In its native habitat (moist woodlands in the Eastern US), Creeping Sedge is a slowly spreading ground cover in shady areas. It forms compact clumps with strappy blue-green leaves, about half an inch wide and a foot long. Once established, it sends out underground rhizomes that will pop up nearby to form new clumps. It is not very aggressive, and is easily controlled, but in a few years, it can form a lovely colony under trees and shrubs, or in a shady flower garden.

A winter colony of Creeping Sedge in a shade garden

Carex laxiculmus is easy to find in nurseries under the name ‘Hobb’ or “Bunny Blue” sedge, a trademarked name. Growers Lisa and Bobby Head of South Carolina trademarked the cultivar and named it “Bunny Blue.” The trademarked plant differs little from the native species, and in 2019, Neil Barger of New Moon Nursery reported that in side-by-side trials at New Moon, there was little discernable difference; but if anything, the species seemed to perform slightly better than the trademarked cultivar. Others believe that “Bunny Blue” is somewhat bluer in color than the species and more tolerant of dry soil. Though at the Nature Center we prefer planting straight species whenever possible, “Bunny Blue” is much easier to find, and we love it!

 Carex laxiculmus growing naturally in a forested area in Westchester County, New York

Although it is native to moist woodlands with rich soil, we have seen “Bunny Blue” sedge perform well even in thin, fairly dry soil. It is a good choice for underplanting trees. A small plant can be tucked in among sensitive tree roots, and it will send rhizomes out to find open spaces without disturbing or competing heavily with the tree’s root structure. “Bunny Blue” sedge is hardy in Zones 4 to 7, but can take the heat even in Zone 9 with enough shade and supplemental water.

“Bunny Blue” sedge makes a great “living mulch” when combined with other native shade-loving plants. Plant it with native ferns, Wild Ginger (Asarum canadensis), Foamflower (Tiarella cordifolia), and violets to protect tree roots and preserve soil moisture while providing habitat and food for wildlife. Use it instead of hosta and liriope in shade gardens, and instead of pachysandra, ivy, vinca, or winter-creeper under trees and shrubs.

In summer, “Bunny Blue” sedge, Maidenhair Fern, and Wild Ginger protect the dense surface roots of an old tree without disturbing the soil
 “Bunny Blue” sedge, newly-planted as “filler” in a shade garden, will gradually spread to open areas between other plants
The same new planting of “Bunny Blue” sedge in winter

Carex laxiculmus flowers in early summer, but the flowers are barely noticeable on fine stems rising just above the grassy clump. The lush foliage works well in rain gardens, and the spreading rhizomes are effective at controlling erosion on slopes or rain-washed areas. The lovely blue color works even in shady patio containers for color contrast with summer annuals. Plant it in the garden when summer ends!

“Bunny Blue” sedge in the spring shade garden

In late winter or early spring, you can cut back the foliage of “Bunny Blue” sedge to the base of the clump, or just snip off any tattered leaves. New growth will soon appear, adding a bit of blue to your otherwise green spring!

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For the Love of Trees: Part 3

Trees exhale for us so that we can inhale them to stay alive. 
Can we ever forget that?

Munia Khan

Caring for our trees properly begins with understanding how they live. We can avoid harmful mistakes if we understand what a tree needs for healthy roots, bark, and leaves. Human-caused damage to tree roots and bark is often accidental. [see “For the Love of Trees” Part 1 and Part 2] Unfortunately, the most common damage humans do to the leaf canopy is intentional. 

The practice of “topping” a mature tree — cutting the trunk and major branches to an arbitrary height – was once thought to reduce the likelihood of “top-heavy” trees falling in storms. But topping is actually counter-productive and dangerous. The result is a weakened tree that is more likely to fail — and fall.

Topping a tree drastically changes its shape, and ignores the reason nature has shaped trees the way they are. Tree branches reach upward and outward, away from the trunk, dividing again and again, becoming smaller at every division as they extend to the outermost twigs holding leaves. The purpose of this shape is to provide the maximum exposure for the largest number of leaves to absorb sunlight coming from above.

Tree branches reach upward and outward to maximize sunlight on leaves
Small twigs at the end of each branch hold the vast number of leaves necessary to feed the tree.

Leaves need sunlight for photosynthesis — the miraculous process that turns sunshine, carbon dioxide, water, and soil into the oxygen we breathe. But oxygen is just a happy by-product of photosynthesis. The real purpose, as far as the tree is concerned, is to manufacture carbohydrates to feed the tree. Trees bring water and soil nutrients absorbed by the roots up through the living outer layers of the bark to the leaves. The carbohydrates manufactured by the leaves during photosynthesis are then carried back down to feed the living bark, including all the growing branches and twigs, and the roots. Topping is a brutal interruption of this process.

A healthy tree is balanced — both nutritionally and structurally. Nutrition is balanced because the root system absorbs just enough nutrients and water to supply the leaves, and the leaves manufacture enough carbohydrates to feed the growing trunk, branches, and roots. Structurally, the tree balances itself with a root system that grows strong and wide to anchor the heavy trunk and the weight of the leaf canopy. As the tree matures, the roots, trunk, and leaf canopy continue to grow in proportion to one another — and in balance.

Topping a tree, by removing most of its essential leaf canopy, suddenly and radically reduces the tree’s ability to manufacture enough nutrients to support its living trunk and root system.

Topping dramatically reduces the number of branches and twigs supporting leaves needed to feed the tree

A topped tree may begin putting out twiggy little branches, called “suckers” or “water sprouts” in an effort to quickly add more leaves. Even if leaves develop, however, the thin new branches are incapable of carrying enough nutrients back down to feed the mature tree trunk and roots. Deprived of the carbohydrates essential for survival, the roots farthest from the tree will wither and die, and the trunk will weaken, destabilizing the tree.

Water sprouts are not capable of carrying adequate nutrition from leaves to the rest of the tree
Trees topped to avoid power lines were unable to produce leaves at all and soon died
Photo: Guy Pardee
Topped evergreens do not easily generate new growth and rarely recover
Photo: Guy Pardee

There is a very strong consensus among modern tree experts that topping is a bad practice. So why do we see so many examples of topped trees all around us?

While most responsible tree companies refuse to top trees, or at least try to talk property owners out of it, homeowners often insist on topping and look for a tree service that will comply. Reasons given for topping trees include fear of trees falling, a desire to open up views, to increase light for lawn or solar panels, or simply to make trees shorter. All of these may be good reasons for appropriate tree pruning, which is completely different from topping. It is important to understand the difference.

Trees should be pruned to remove dead, weak, diseased, or crossing branches that can damage bark. Pruning by experienced, certified arborists is part of responsible tree care. And a qualified arborist can address aesthetic issues as well as tree health. Selective pruning at branch nodes can lighten the canopy, allowing more light underneath and improving air circulation. Careful thinning can reduce excessive weight on particularly vulnerable branches, or reduce the reach of branches too near buildings or power lines. Strategic removal of a few branches can open a “window” to a desired view. Before deciding on any of these options, discuss your concerns with a qualified, experienced arborist to determine the wisest approach. Sometimes, removing a tree in the wrong place is the better choice. 

If your tree company suggests topping, or “hat-racking” or “topping off” or “lopping” or “rounding over,” call another tree company. Trees subjected to any of these versions of topping will never look right, even if they manage to survive.

A once-graceful old magnolia became a twiggy mess with damaged bark after topping
An example of “hat-racking” distorts the classic shape of a Japanese maple

If your tree company suggests “crown reduction” to reduce the size of a tree, proceed with caution, and only after a very thorough discussion of exactly what is intended. A well-pruned tree will look natural. Fewer than 20% of the existing branches will be pruned back, and you should not be able to tell where they were. A “crown reduction” job that cuts back all or most of the branches is just another version of topping.

Extreme “crown reduction” looks grotesque and seriously damages the tree
Photo: Guy Pardee

Trees need their full complement of leaves to stay alive and to manufacture the very oxygen we breathe. Supporting them in that precious work is our responsibility.


For more on tree care, read these posts:
For the Love of Trees : Part 1
For the Love of Trees: Part 2

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For the Love of Trees: Part 2

“…if you want to save your world, you must save the trees.”

J.R.R. Tolkien

If you’ve ever counted the rings on a tree stump to determine a tree’s age, you have observed how trees grow: they add a new layer of wood in each growing season. The new growth doesn’t come from the center of the tree trunk — it all happens on the outer ring. The living part of a tree trunk is just inside the protective bark.

The living part of the tree is closest to the outside

Immediately under the bark is a layer of spongy tissue called the “phloem” (pronounced “flow-um”). The phloem carries carbohydrates, manufactured by the leaves during photosynthesis, downward to the rest of the tree. The upward flow of water and nutrients from the roots happens in the “xylem” or “sapwood,” just inside the phloem. Sandwiched between these two critical vascular layers is the “cambium,” only a few microscopic cells thick, which is the actively growing part of the trunk. The cambium produces a new layer of phloem on the outer edge, and a new layer of xylem on the inside, each season. 

As a tree ages, the xylem closest to the center of the tree hardens from the inner trunk outward with compounds that make the wood strong. The hard inner layer of the xylem, which is no longer alive and no longer carries water, is called “heartwood.” The older the tree, the more heartwood there is at the center, and that is the part of the tree we use for wood products. 

But the living part of the tree is in those outer layers, just under the bark. Looking at the tough exterior of an old tree, it is easy to forget that the tree’s essential life process is just a few millimeters below that rugged outer surface — and it’s very vulnerable to damage.

Cutting through the living tissue of a tree trunk all the way around the tree is called “girdling” and is a very effective way to kill a tree. Girdling cuts off the essential movement of nutrients up and down the tree, and severs the cambium, preventing growth. Girdling is sometimes used intentionally to kill trees before cutting them down. Unfortunately, it also sometimes happens unintentionally.

Understanding that the outer layer of a tree trunk or branch is the most vulnerable part should make us think more carefully about how we use trees and what we allow to interfere with a tree’s growth.

One common mistake is leaving tree support stakes in place too long. Unless a new tree is very top-heavy, it is usually unnecessary to stake it or use supports at planting. But if it is necessary, care should be taken to remove the supports well before the tree begins adding significant growth at the trunk.

Tree supports, if used at all, should be temporary and not made of material that will cut into bark – rope is not a good choice
A tree girdled by improper staking will not survive
Photo: Guy Pardee
Improper cabling can girdle a tree
Photo: Guy Pardee

Hanging swings, hammocks, and bird feeders from tree branches can also cause damage. Allowing tree trunks or branches to rest against power lines, big rocks, and fences is another hazard.

 A tree swing hangs from a branch on a rope
Power lines often interfere with tree growth and can girdle branches
The branch has grown around the rope, cutting off nutrient flow to the branch
Better to remove the branch before this happens
Tree trunks may be girdled by pavement and rocks that prevent the trunk from continuing outward growth

Another common error is incorrect planting that can result in a tree being girdled by its own roots. If a young tree has been in a nursery container too long, the roots may wrap around the base of the tree within the container. At planting, care should be taken to gently unwrap the roots and extend them away from the trunk in a hole wider than it is deep.

Tree trunk girdled by its own roots

Though trees may survive partial girdling by roots, they will be more vulnerable to storm damage and disease. Consult an experienced certified arborist to evaluate possible remedial action if the tree and girdling roots are in an advanced stage.

Although tree trunks merge with tree roots near the soil line, it is important to recognize that trunks and roots are not the same. Tree trunks “flare” at the base just above the root zone. If the flare is buried beneath the soil line, or by too much mulch, excess moisture can cause the protective outer bark to rot, exposing the living inner layers to mold, fungus, insects, and disease – effectively girdling the trunk at the soil line.

Healthy tree trunks “flare” outward at the base and should be above the soil line
Planting a tree too deep, or allowing mulch to cover the “flare,” can girdle a tree, eventually killing it

Lawnmowers, construction equipment, deer, and invasive vines all can damage trees by wounding the living outer layers of the trunk.

 Lawnmower damage can be prevented by providing a protected area between lawn and tree trunks
Invasive vines, including ivy, should be removed from tree trunks
Wrapping young trees with protective fabric can prevent deer damage, but don’t forget to remove it later!

Trees are strong enough, and adaptable enough, to share their life forces with other living things. They will work around a hole that supplies shelter for an owl or squirrel family. They can survive for decades with a virtually hollow interior because their living and growing happens on the outside. But it’s up to us to protect them from careless damage so they can continue to save the world.

For more on tree care, make sure to read last week’s post,
For the Love of Trees

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For the Love of Trees: Part 1

“People who will not sustain trees
 will soon live in a world that will not sustain people.” 

Bryce Nelson

Trees convert carbon dioxide into oxygen, absorb vast amounts of stormwater, provide free cooling services, and supply food and shelter to thousands of insect, bird, and mammal species. And, if poets are to be believed, trees also soothe the human spirit. 

Mature trees in a well-landscaped yard are commonly estimated to increase the value of a house by 7 to 19 per cent. Nationwide surveys show that lush lawns and flower gardens, though appreciated, do not add to house prices. But big trees suggest stability and affluence. People want to live in neighborhoods with tree-lined streets and shady avenues.

Mature trees benefit the whole neighborhood
A native tulip tree is admired by local residents

It is a tragedy, therefore, when avoidable mistakes cost the lives of these valuable friends. Too often, humans seem to forget that trees are living things with their own needs. Trees are not inanimate posts — they need air, water, sunlight, minerals from soil, and room to grow.

This 80-year-old tree is dying because it has been treated like a post
Really?! New paving deprives it of everything!

Misconceptions about tree roots cause many avoidable tree deaths. Unintentional damage to root structure often explains why big trees fall in storms. 

Tree roots do not typically grow downward. The soil deep under a tree is compacted, often heavy with rocks and clay, and too dense to provide the oxygen and organic matter tree roots need. So, roots actually grow laterally, angling slightly downward, but staying close to the surface. If they hit a barrier, they will turn aside rather than going deeper.

Roots blocked by pavement turn back toward the soil, but stay close to the surface

In their first few years, young tree saplings do send roots, known as “tap roots,” straight down to stabilize the weight of their branches. But even tree species considered to have deep tap roots will soon direct most of their energy into developing lateral roots. As the tree matures and the tap root reaches compacted soil, it actually recedes. The lateral roots take over, anchoring the tree with a strong, wide base. The “critical root zone” is the area closest to the tree trunk and extending to the “drip line” – essentially the circumference of the tree’s leaf canopy. The roots in the critical root zone anchor the tree and keep it upright. 

When they reach 3 to 5 feet from the trunk, lateral roots begin to narrow and branch out, continuing to expand outward, ultimately reaching a distance equal to the height of the tree! These lateral roots send thousands of small “feeder roots” upward where the soil is lighter and better aerated. In fact, 90% or more of a tree’s roots are located in the top 12 to 24 inches of soil!

Tree roots grow wide and shallow rather than deep
From “Tree Root Systems,” Martin Dobson 1995
Roots grow close to the surface to absorb oxygen and nutrients

With an accurate picture of tree root structure, it is easier to understand how homeowners inadvertently cause tree damage. Anything we do in the top 12 to 24 inches of soil, from the tree’s trunk to a distance equal to the height of the tree, affects the tree!

Here are some common mistakes we see homeowners making:

Raised planter built over tree roots and filled with soil
Burying tree roots with more than an inch or two of soil can cause a tree to die within a few years

Some homeowners try to hide tree roots by building a raised planter filled with soil. But burying roots — with even a few inches of added soil — deprives delicate feeder roots of air and puts them too far from nutrients. Soil piled up around the tree trunk also damages the bark, causing it to rot and become more vulnerable to wood-boring insects. Raised tree planters may not kill a tree right away, but in a few years, the tree will decline and likely die. Damage to the critical stabilizing roots and the lower trunk make even the strongest tree likely to topple in a windstorm.

Soil or mulch “volcanos” piled on tree roots and close to the tree trunk have the same disastrous effect as raised planters

Other homeowners like to decorate around the base of trees by planting annuals there every year. Digging close to the tree year after year can result in repeated damage to roots in the critical root zone. A much better practice is under-planting with native perennials that will come back each year without requiring you to dig again. It is best to start with small plants and work carefully around delicate tree roots as you do the initial planting.

Under-planting trees with native perennials protects tree roots from repeated digging, lawnmowers, and moisture loss.

Another common reason for tree death is construction of walls, patios, and sidewalks within the critical root zone. Severing the major lateral roots responsible for stabilizing large trees increases the risk of trees falling in heavy wind.

Construction of a wall cut off too many lateral roots and killed this tree
Excavation exposes masses of lateral roots causing tree damage
Careful construction, with hand-digging of trenches to avoid important roots, can save trees

Routine use of heavy equipment, including riding lawn mowers, can compact soil and damage tree roots. By protecting the entire critical root zone around the tree, either with under planting or good quality mulch, damage from mowers, foot traffic, and heavy equipment can be easily avoided.

Wise tree protection can be attractive and easy to maintain

With everything trees do for us, it is worth taking basic steps to save them. We should do it for the love of trees!

Next week in part 2, we’ll take a look at a few other common mistakes that can harm trees.


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My Favorite Tree

Ten years ago, I planted a Willow Oak. At the time, I didn’t really know enough about it to make the minimum 100-year commitment expected with oak trees. I had never actually seen a Willow Oak in person, only photos. In retrospect, planting that tree was a bit like deciding to get married before a first date. The tree looked good in photos, but we had never met.

According to its “on-line profile,” Willow Oak (Quercus phellos) is native to stream banks and wet meadows in the eastern US from the southern tip of New York to Florida, and inland to southern Illinois, Oklahoma, and Texas. So, where I live, north of New York City, Willow Oak technically is not native. And it’s definitely not common. But I had heard that Willow Oaks are very popular as far north as Pennsylvania and southern New Jersey, and I figured with ranges pressing northward due to global warming, it should work. The hardiness rating of Zones 6 to 9 included my area, so I decided to commit.

At first sight, you might not even guess that this glorious tree is an oak, but it is a member of the red oak family. Typical oak leaves are divided into lobes with pointed or rounded tips, but Willow Oak leaves are long, narrow, and undivided – somewhat like willow leaves.

An array of various oak leaves with Willow Oak at the bottom
Willow Oak leaves in fall

The long slender leaves of Willow Oak are part of its charm. They cast a dappled shade in summer and dance lightly in the wind. In the fall, the unusual leaves of Willow Oak make me the envy of my neighborhood. While leaf blowers roar and leaf bags pile up everywhere, I can completely ignore the Willow Oak leaves falling on my lawn and driveway. They just seem to disappear!

Willow Oak leaves are no problem on lawn

Willow Oaks are surprisingly fast growing. For the first several years, their energy is dedicated to developing a shallow, fibrous root structure; but after that, they can add 2 feet per year in height. Ultimately, they will reach 60 to 80 feet or more with a majestic spread of 30 to 60 feet. They are easier to transplant than typical oak species with tap roots, so if you’re in a hurry, you can start with a larger tree. Knowing that much, I chose a young tree, already about 15 feet tall with a trunk diameter of 2.5 to 3 inches, rather than a smaller sapling. Ten years later, my tree is well over 30 feet tall with a trunk diameter of 15 inches.

Willow Oak planted in 2012
The same tree in 2022

The shallow root structure of Willow Oak makes sense for a tree that evolved in low-lying flood zones and along streams, but it also makes sense for a specimen tree planted in irrigated lawn. Willow Oak is ideal for suburban lawns and parks, and makes an excellent street tree if enough room is provided for its roots to expand laterally. Unlike oak species with deep tap roots, Willow Oak will buckle pavement if planted too close to sidewalks or driveways, but with enough space, it is a great tree for front yards.

Although it needs ample water when young, once established, Willow Oak is fairly drought tolerant. Full sun is essential, and Willow Oak prefers acidic soil. It is a favorite shade tree in the South, where it is valued for its storm-resistance. It withstands flooding and heavy clay soil, as well as urban pollution, heat, and strong wind. Given the right place, a Willow Oak can survive well over 100 years.

Willow Oak in Autumn

Like all native oak trees, Willow Oak has exceptional wildlife value. The leaves host hundreds of species of butterflies and moths, as well as many other beneficial insects, including fireflies. A mature oak provides habitat and food for all of our native song birds and many small mammals. My Willow Oak is still a baby, so it doesn’t produce acorns yet. It takes 15 to 20 years for the tree to start producing acorns, and the acorns take two years to ripen before they fall. The acorns are small, about a half-inch long, and they are a favorite food of blue jays, squirrels, and chipmunks. 

I look forward to a long and happy life together with my favorite tree, and it makes me happy to think it will supply beauty, shade, food, and shelter to other living things long after I’m gone.

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