Category: Around the Grounds

“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.

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.

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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.

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Sometimes you discover a product that performs so well, you just have to tell all your friends to try it. If you’re a gardener, the same thing can happen with a plant!

We are obsessed with Prairie Dropseed (Sporobolus heterolepsis), a little native grass that is carefree, beautiful, and versatile. We’ve planted it in multiple places at the Nature Center, and we’ve admired it in other public and private gardens. We definitely give it 5 stars!

Prairie Dropseed is an ornamental grass with fine-textured leaves that reach out from its center in graceful arches. The grass is small enough, and elegant enough, to form a well-behaved edge along a sidewalk or path. It reaches only 18-24 inches in height before blooming in mid-summer. The tiny flowers are on delicate stems that stretch 18 to 24 inches above the leaves and then branch into dancing seed clusters. Most surprising for a grass, the blooming stalks are fragrant! The scent is hard to define, and is variously described as being like popcorn, or green coffee beans, cilantro, or anise. The scent fades as the seeds ripen in fall.

Prairie Dropseed is native to American prairies and dry meadows and is found in at least 26 states from the Canadian border to Georgia and west as far as New Mexico, but it is most common in the Central Plains states. It is categorized as a “warm season bunch grass,” which means it starts turning green as the weather warms (late spring), and it forms “bunches,” tidy clumps that stay where you plant them. It does not spread itself by runners and, despite its name, does not easily spread by seed. The “dropseed” in the common name apparently refers to the fact that ripe seeds do fall to the ground where they may be eaten by birds and small mammals, but they do not seem to germinate easily. In our own experience, and based on reports from other gardeners, the plant does not self-sow in gardens, so you won’t see it popping up in other spots. 

Prairie Dropseed is happy in Zones 3 to 9. As a true prairie plant, it prefers dry, even rocky, soil in full or part sun. It never needs fertilizer, and is rarely bothered by deer or rabbits. Its roots are great for stabilizing slopes, and the plant needs so little care it is ideal for roadsides. It is relatively salt tolerant as well. And it is a great substitute for non-native “fountain grasses” (Pennisetum spp.) that are now recognized as invasive in the Northeastern US and other parts of the country.

The easiest way to establish Prairie Dropseed is from nursery-grown container plants or plugs. It may take a couple of seasons for the roots to form a dense clump, but once they have, Prairie Dropseed becomes very drought tolerant and care free.

We keep planting Prairie Dropseed in new places, and it does not disappoint. We planted it in the Pollinator Garden at the Nature Center, using it as an edger and a filler among flowering perennials. It makes a lovely unifying matrix, tying a flowerbed together visually, and covering the soil to eliminate the need for mulch. We’ve planted it in front of shrubs, in sunny flowerbeds, and at the edges of our Meadow. It is a winner in each site.

Prairie Dropseed turns gold in October, and continues to add structure to perennial beds even in winter. The seeds are eaten by migrating birds and persist long enough to supply food for winter birds as well. The plant is a host to several native leaf hopper insects, and small animals may take cover under the grass year around.

Prairie Dropseed is deciduous, which means that its leaves die off in winter, but they hold their shape even after being buried in snow. By late winter, the plants look rather quirky – somewhat like Cousin It of the Addams Family. In spring, when green shoots are starting to show, a quick haircut tidies things up.

A few weeks later, Prairie Dropseed leafs out again with fresh spring color, bringing the garden back to life. Totally a 5-star plant!

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.

Everybody loves hydrangeas. But especially at this time of year, it’s the Oakleaf Hydrangea that really steals the show. Just when other hydrangeas start dropping their leaves, Oakleaf Hydrangea (Hydrangea quercifolia) lights up the landscape with colors ranging from hot pink to deep burgundy. The shrub holds its leaves until very late in the fall, and the colors keep changing for weeks — so the show lasts well past Thanksgiving!

Oakleaf Hydrangea is a flowering shrub native to woodlands in the Southeastern US, from Georgia and Tennessee to Florida. It does very well in more northern gardens and is an excellent year-round landscape shrub in Zones 5 to 9, and even in Zone 4 with some protection. It prefers moist soil, but is surprisingly drought tolerant once established, especially with some afternoon shade. The fall color is best with more sun, so a morning sun/afternoon shade situation is ideal. Oakleaf Hydrangea is fast growing and can occupy a space 10-12 feet high and wide in just a few seasons. It is easily pruned for size, but should be pruned just after flowering to avoid cutting off the flower buds that form later in the season.

The scientific name “quercifolia” means “oak-shaped leaves.” The shrub is not related to oaks, but the leaves do resemble very large oak leaves. Interestingly, the leaves of the shrub grow significantly larger in shade than in sun. Deer resistance is questionable. Deer have not bothered the shrubs at the Nature Center, but neighbors report deer browsing, especially on younger plants.

Fall color may be the “hy-light,” but Oakleaf Hydrangea has advantages over non-native hydrangeas in other seasons as well. In spring, Oakleaf Hydrangea leafs out earlier than Asian mop-head hydrangeas (Hydrangea macrophylla) and seems to be less vulnerable to late spring ice storms. While mop-head hydrangeas suffer significant winter die-back, leaving lots of twiggy stems into late spring, Oakleaf Hydrangea fills in attractively and reliably by the end of May.

Oakleaf Hydrangea blooms in June with large cone-shaped clusters of white flowers. The 4-petaled outer flowers are sterile, and their only purpose is to attract pollinators to the tiny fertile flowers hiding underneath. A huge variety of bees and other tiny insects feed on the pollen produced by the smaller flowers.

While many gardeners love the big blue and pink flowers of mop-head hydrangeas, those flowers come at a price: they have been manipulated by growers to dramatically increase the number of colorful sterile blossoms, while eliminating entirely the tiny fertile flowers that feed pollinators. Have a closer look at mop-head hydrangeas and you will notice the complete absence of butterflies and bees. There is nothing for pollinators there.

After the fertile inner flowers of the Oakleaf Hydrangea have been pollinated, seeds form inside the flower clusters. At the same time, the sterile outer flowers begin to turn pink. It’s an enchanting sort of garden magic.

In November, Oakleaf Hydrangea lights up the late-season landscape as no other hydrangea can. When the leaves finally finish their show, they reluctantly fall, revealing cinnamon-brown bark on stems and twigs. As the shrub ages, the bark peels attractively, adding layers of warm brown color for winter interest, and forming a great shelter for winter birds.

Oakleaf Hydrangea really is a “hy-light” of the landscape all year long.

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.