Cathy Ludden Around the Grounds, Native Plants

Mighty Arborvitae

Arborvitae gets no respect.

Though Arborvitae (Thuja occidentalis) may be the most-planted tree in suburban America, it has been given a diminished role unworthy of this majestic native tree. Planted by the thousands along property lines by developers, builders, and landscapers, rows of crowded Arborvitae trees, standing shoulder to shoulder, have become the de-facto fences of suburbia.

A typical builder installation of Arborvitae
Arborvitae “fence” on a property line

Without room to spread their branches or reach their natural height, Arborvitae is often topped and heavily pruned to form hedges. They handle this assignment very well, but Arborvitae can do so much more!

If you’ve only seen Arborvitae used as a hedge, it may surprise you to learn that in its natural habitat, it can grow 50 to 60 feet tall and live for hundreds of years! In fact, the largest known specimen is over 100 feet tall and more than 40 feet wide at the crown. The oldest living Arborvitae is thought to have germinated from seed in 952 A.D., and is now 1,071 years old! Based on ring counts on dead trees, there are verified specimens of Arborvitae that lived to be over 1,800 years old.

An ancient stand of Arborvitae on cliffs overlooking
Northern Lake Michigan
Photo: C.J. Earle

Arborvitae is one of the common names for Thuja occidentalis and means “tree of life” in Latin. It was named by the French sea captain, Jacques Cartier, when he was exploring Canada in 1536. After months at sea, Cartier’s crew, including two young members of the Huron native tribe who had been sailing with them, were all suffering from scurvy. On the way up the St. Lawrence River, Cartier dropped the two young men at their home village. When he later returned, he was astonished to find the two Hurons fully recovered from all symptoms of scurvy while his French sailors were still suffering. He asked the Huron elders to teach him the cure, and they showed him how to make a medicine, a tea rich in Vitamin C, from the foliage of Thuja occidentalis. Cartier brought the life-saving plant back to France, making it the first North American tree introduced to Europe.

The native habitat of Thuja occidentalis is swamps, low woods, and forest edges from northern Canada south to New York and Connecticut and west to Michigan and Northern Indiana. It is an
evergreen conifer, extremely cold hardy, and adapted to poor rocky soils all the way to the edge of the Canadian tundra. Sometimes called Northern White Cedar, Eastern White Cedar, or
Swamp Cedar, Arborvitae is not a true cedar in the Cedrus family, none of which are native to North America. But the fragrance of its foliage and bark, and the usefulness of its wood, are similar.

Arborvitae often grows in very thin, poor soil in northern
North America and is adapted to extreme cold. This forest of
Arborvitae is at the brink of the Niagara Escarpment in Northern Wisconsin.
Photo: C.J. Earle

The foliage of Arborvitae is flat and scale-like and has a spicy fragrance when crushed. Native peoples used it not only for medicine but also used the fragrant foliage as insect-repellant
bedding. They stripped the tree’s shredding bark to make rope and twine, and they found many uses for the rot-resistant wood, including canoe frames and roofing shingles.

Thuja occidentalis has significant value to wildlife. It is a favorite food of white-tailed deer, as suburban homeowners often discover to their dismay. Twigs and foliage of Arborvitae constitute as much as 10 to 25% of the winter diet of deer, who will browse it as high as they can reach. In northern forests, the tree also provides highly nutritious food for snowshoe hares, porcupines, red squirrels, and beavers. Many native birds find nesting sites in Arborvitae and insects to feed their young. The seeds are the preferred source of food for Pine Siskins, birds indigenous to the Northeastern US.

It is sadly ironic that one of the most-planted trees in suburbia is disappearing in the wild. Thuja occidentalis is listed as Threatened in Connecticut, Illinois, Kentucky, and Maryland and Endangered in Indiana, Massachusetts, and New Jersey. Development is the primary culprit as forests are cleared to make way for more suburban homes.

It is equally sad that the rows and rows of Arborvitae planted on suburban property lines are not nearly as valuable to wildlife as they should be. The most popular varieties of Arborvitae are cultivars or hybrids that offer little value to wildlife – other than deer. A cultivar called ‘Emerald Green’ Arborvitae was developed in the 1950s in Denmark, just in time for the rapid expansion of the US suburbs after WWII. It quickly became the ubiquitous hedge plant we see all around us. In a tight hedge, and with limited biological diversity due to clonal reproduction by nurseries, its value to insects and birds is limited.

Not Native

Another Arborvitae popular with builders is a hybrid called ‘Green Giant,’ which is a cross between a species indigenous to the Pacific Northwest and a Japanese species. As a hybrid between two non-natives, ‘Green Giant’ has very little value to insects or birds in this part of the country. If you can find the straight species of Thuja occidentalis (without a cultivar name), plant that. If not, ‘Emerald Green’ is a better choice than ‘Green Giant.’

Thuja occidentalis is an amazing tree. It deserves to be more than a fence! Given enough room to take its natural form, Arborvitae merits a starring role in suburban landscapes.

Growing the way nature intended, Arborvitae takes its
rightful place with Oaks, White Pines, and Junipers in
Northeastern landscapes

In our last blog post [Privacy Without “O-fence“], we urged homeowners to diversify their hedges and privacy screens by planting a mix of native trees and shrubs to increase habitat and biodiversity. Too much of any one plant becomes a mono-culture, limiting resources for wildlife. Unfortunately, that is what has happened to this magnificent native tree.

Don’t limit Arborvitae to this poor fate

Think of Arborvitae as an easy-care, long-lived, medium-sized, native, hardy evergreen that will enhance your landscape as part of a diverse planting of trees, shrubs, and perennials. You won’t
be sorry!

Mighty Arborvitae

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.

Share this post:
TO SUBSCRIBE TO THE BLOG – AND NOTHING ELSE – ENTER YOUR EMAIL BELOW

Cathy Ludden Around the Grounds, Native Plants

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

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.

Cathy Ludden Around the Grounds, Native Plants

Oh, Say, Can You See…a White Pine?

Look out almost any window in suburban Westchester County, and chances are you can see an Eastern White Pine (Pinus strobus). This iconic evergreen is profoundly connected to the early history of the United States.

In 1605, English explorers sailing along the eastern coast of North America spied a solution to one of England’s most pressing problems: the lack of suitable trees for ships’ masts. Here, they saw seemingly infinite forests coming right up to the shoreline. And towering above the oaks, maples, beech, and birch trees were countless magnificent pines, so tall and straight that the explorers soon started calling them “mast trees.”

Forest of Eastern White Pine

England’s power in the 17th and 18th centuries depended largely upon the British Royal Navy. Warships needed enormous wooden masts, at least 3 feet in diameter and over 100 feet tall. England had long since been cleared of trees that size, giving France, Spain, and the Dutch a critical advantage in shipbuilding. The Royal Navy was forced to negotiate with Norway and the Baltics for timber, but the biggest trees available were no more than 27 inches in diameter and not close to the necessary height. Masts had to be pieced together, creating vulnerabilities in bad weather and warfare.

The Eastern White Pine grows tall and straight, reaching 130 feet or more. It is strong, but able to bend without snapping in stormy winds. It drops its lower branches as it matures, creating a smooth expanse ready for milling. Whole forests made of enormous “mast trees” were a shipbuilder’s paradise, and the Eastern White Pine became a major factor in England’s decision to colonize North America.

White Pines tower over other forest trees
White Pines grow tall and straight with few lower branches

As colonists expanded settlements in Massachusetts, New Hampshire, and Maine, it didn’t take them long to recognize that Eastern White Pine was extremely useful for building everything. The Royal Navy wanted to protect its supply of mast trees, so England declared that all White Pines with a diameter of 24 inches or more were property of the King. Penalties were assessed for cutting the King’s pines, and fines were collected by surveyors appointed by the Crown — until one night in 1771 in Weare, New Hampshire. 

Outraged at being fined for cutting trees on their own land, a group of “traitorous rebels,” colonists disguised with ash on their faces, dragged two British enforcement officers out of their beds, beat them with pine branch switches, tied them backwards onto their horses, and drove them out of town. It is thought that this act of rebellion, known as the “Pine Tree Riot,” was inspiration for the Boston Tea Party not long after. Both before and after the Revolution, White Pine was critical to the economy and development of America.

Today, this magnificent tree deserves our admiration for its beauty and its value to the ecosystem. Because of its vast height, it is a favorite nesting tree for bald eagles and hawks. Song birds, squirrels, and many other animals depend on the seeds in its pinecones. Its soft needles host the larvae of a dozen or more species of moths and butterflies.

White Pine cones are a valuable food source for wildlife
White Pine needles are fragrant, soft, and a host plant for butterflies and moths

As a landscape plant, Eastern White Pine is a gorgeous evergreen that smells divine and needs no special care. Though it is fast-growing, it can live to be hundreds of years old, so it needs some space. An arborist friend says White Pines are “self-pruning” because they drop branches as they mature. And those branches can be very heavy. It’s not a good idea to plant a White Pine too close to your house or other structures. Plant it where you can see its whole, unique shape from a window, and enjoy the fuzzy look of its needles. 

It’s also not a good idea to plant White Pines as a property-line screen. It may be tempting to plant rows of young pines for that purpose, but remember — they grow up to be “mast trees!”

Beautiful, but not a good privacy screen!

The Eastern White Pine is an iconic plant with a fascinating history. We recommend a book, White Pine: American History and the Tree That Made a Nation by Andrew Vietze for more information. And we also recommend planting Eastern White Pine if you have the chance.

A baby White Pine at the edge of the Nature Center’s Meadow

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.