Category: Native Plants

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.

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!

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.

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!

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!

THIS BLOG IS AUTHORED WEEKLY BY CATHY LUDDEN, CONSERVATIONIST AND NATIVE PLANT EDUCATOR; AND BOARD MEMBER, GREENBURGH NATURE CENTER. FOLLOW CATHY ON INSTAGRAM FOR MORE PHOTOS AND GARDENING TIPS @CATHYLUDDEN.

To subscribe to the blog — and nothing else — enter your email below.

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.

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.

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.

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.

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.

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.

THIS BLOG IS AUTHORED WEEKLY BY CATHY LUDDEN, CONSERVATIONIST AND NATIVE PLANT EDUCATOR; AND BOARD MEMBER, GREENBURGH NATURE CENTER. FOLLOW CATHY ON INSTAGRAM FOR MORE PHOTOS AND GARDENING TIPS @CATHYLUDDEN.

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

To subscribe to the blog — and nothing else — enter your email below.

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.

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.

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.

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!

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:

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.

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.

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.

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.

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.

THIS BLOG IS AUTHORED WEEKLY BY CATHY LUDDEN, CONSERVATIONIST AND NATIVE PLANT EDUCATOR; AND BOARD MEMBER, GREENBURGH NATURE CENTER. FOLLOW CATHY ON INSTAGRAM FOR MORE PHOTOS AND GARDENING TIPS @CATHYLUDDEN.

To subscribe to the blog — and nothing else — enter your email below.

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.

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 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.

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.

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.

THIS BLOG IS AUTHORED WEEKLY BY CATHY LUDDEN, CONSERVATIONIST AND NATIVE PLANT EDUCATOR; AND BOARD MEMBER, GREENBURGH NATURE CENTER. FOLLOW CATHY ON INSTAGRAM FOR MORE PHOTOS AND GARDENING TIPS @CATHYLUDDEN.

To subscribe to the blog — and nothing else — enter your email below.