Caring For Your Black Walnut Tree

The black walnut is a stately native of the United States east of the Rocky Mountains, with a huge crown and dark, ridged bark. Its nuts have been used for their oil and protein by indigenous people for at least 4,000 years, and its timber – durable and chocolate-brown – has for centuries been over-exploited for veneers and furniture.

Two-thirds of the annual black walnut harvest in the United States comes from Missouri. Their flavor is more intense than that often common, cultivated “English” kind but their tough, deeply corrugated shells are hard work for a casual snack – possibly an adaptation to dissuade rodents from polishing off the next generation of trees.

Walnut trees protect themselves with juglone, a natural herbicide that discourages competing plants, and tannin, an inspect repellent. For humans though, these chemicals work as dye and fixer, handily delivered in one package. During the American Civil War, walnut husks were used to dye homespun uniforms a brownish-grey for Confederate soldiers and to make the ink they used to scratch out letters to loved ones back home.

During World War I, black walnut was specified for aircraft propellers because it could withstand huge forces without fragmenting. By World War II, walnut has been so depleted that the US government ran a campaign to encourage private individuals to donate trees to the war effort. Simultaneously, powdered walnut shells were combined with nitroglycerine to make a form of dynamite. With such associations, it is perhaps appropriate that black walnut wood has also long been popular for upmarket coffins.

Walnut Tree

Weed Control for the Black Walnut Tree

Weeds that grow in your yard effect black walnut trees in the same way as it does with other plants. Weeds will rob your trees of vital moisture. light, and nutrients that it needs to stay healthy and grow. There are several things you can do to help prevent weeds from impacting the health of your walnut trees:

  • Cultivation is the best weed control method. Cultivate a shallow area around your tree and take precautions to not dig too deep, so that you don’t damage the roots.
  • Mowing periodically removes the top layer of the weeds. This allows more sunlight to get to your tree.
  • Mulching with plastic, sawdust, bark, or wood chips can control weeds. Make sure and do this each year!
  • Several chemicals are effective in controlling weeds in black walnut, particularly one
    preemergent herbicide, simazine, and five postemergent herbicides: atrazine, amitrol, dalapon, glyphosate, and 2,4-D. These are tolerated well by black walnut, generally available, inexpensive, and safe when handled and applied properly.

Ground Cover for the Black Walnut Tree

The ideal ground cover for a black walnut plantation would be similar to that in a
dense mature forest. Unfortunately, when a plantation is established, regardless of the type of site preparation, the walnut seedlings will not be tall or dense enough to shade out the vegetation that competes against them.

In general, it’s important to keep in mind that grasses will reduce the growth of a black walnut tree, while legumes will promote it. Here’s a couple of key things to think about when it comes to ground cover:

Here’s a couple of key things to think about when it comes to ground cover:

  • The ground cover should not compete with your tree
  • The ground cover should help control or prevent weeds
  • The ground cover should improve the soil
  • The ground cover should either prevent or control pests
  • The ground cover should be easy to maintain

Sources:

Walnut Council Org
Around the World in 80 Trees by Jonathan Drori

A Closer Look: Quaking Aspen

Any comprehensive survey of the Colorado’s treescape would not be complete without a solid mention of the quaking aspen. In fact, the quaking aspen is so bountiful in Colorado that it covers an area that spans 5 million acres of land – that’s 20 percent of the forested area throughout the state! This deciduous tree can be found at elevations of ranging from 6,500 to 11,500 feet, particularly west of the front range throughout the West Slope. Ideal growing conditions include moist, well-drained soil with a more acidic pH that is more often found at such high altitudes. For this reason, you are not likely to to see many quaking aspen in Denver, as conditions are not ideal for them to thrive.

In honor of this majestic native species, we couldn’t help but dedicate an article to our readers profiling the quaking aspen, and luckily came across some fantastic detail in the book Around The World In 80 Trees. We highly recommend reading through the entirety of the book (which is also beautifully illustrated), but in the meantime, enjoy this passage on the quaking aspen…

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The most widespread North American tree species, the quaking aspen, thrives in the high country of the west, especially in Colorado and Utah, where it is the state tree. A stand of aspen makes the heart leap. Its leaves flicker and shimmer, vivid green on top and pale grey underneath, becoming first yellow and then brilliant gold in autumn, glorious against clear mountain skies. The leaf stalks, or petioles, are long and flattened like ribbons so that leaves bend and twist in the slightest air, rustling with the soothing sound of a rippling stream. Nobody knows for sure why aspen leaves have evolved to quiver. One theory is that the flexibility of the stalks helps aspens to avoid having their leaves stripped by mountain winds. The constant movement might also allow light to filter through dense woods to the aspens’ pale trunks, which – tinged green with chlorophyll – can also photosynthesize.

The aspen hates shade. It can’t reproduce beneath its own canopy, let alone compete with a blanket of pines, but after a fire it can quickly repopulate fire-cleared ground before other species. That is why there are often whole groves of aspens of exactly the same height, having all sprouted simultaneously. Out west, where dry spells make life hard for seeds, aspens abstain from sexual reproduction and instead generate new tree stems directly by suckering. What look like separate trees may actually be genetically identical tree trunks rising from a common root system, collectively known as clone. In fact, the heaviest known living organism on the planet may be a single stand of quaking aspens in Utah, affectionately called Pando (Latin for “I spread”), which contains 45,000 trees, covers more than 40 hectares (100 acres) and probably weighs 6,500 tons. The colony (but not any individual tree) may be 80,000 years old.

The risk of reproducing this way is that plants may lack the genetic diversity to overcome disease or to adapt quickly to a changing environment. However, distinct aspen populations are remarkably diverse and can also revert to sexual reproduction; as a result, the species are very successful. Counter-intuitively, one of the main threats to large groups of aspen is the presence of protected areas and visitor centers with campsites. This is not because of what campers might do to the trees, but because fire in such places is more likely to be controlled or extinguished, giving the edge to competing shade-tolerant conifers.

Caring For Your Trees In Winter

As we write this article, it is officially the eve of winter. So what better way to honor the change of season than to discuss proper maintenance for caring for your trees in sub-freezing conditions! Remember, as your trees are not protected from the elements in the cold harsh winter, they remain especially vulnerable. This especially applies to smaller trees that are lacking deep root systems. In this article we discuss different methods for protecting your trees, and ensuring their health and longevity long into the future.

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Insulate your Trees

Applying roughly 2 inches of mulch to the base of a tree acts like a layer of warm insulation. This ultimately protects tree roots from extreme temperatures, while also serving to retain water in the soil. Although it may seem counterintuitive, it is preferred to wait until the ground freezes to apply mulch beneath the tree, so that mice or other rodents don’t end up making a home within the mulch.

Planning for Denver Weather Extremes

It is essential to keep newly planted trees watered even throughout the fall until the time when the ground starts freezing. May sure to bookmark in your calendar that Denver’s average first freeze typically falls around October 7th. Since Colorado is a specially prone to dramatic swings and temperature, it is not uncommon to experience warm spells that causes the ground to thaw. In case this does happen, continue watering a newly planted trees during these periods.

It should go without saying that even in the winter months, the Colorado sun can be direct and piercing. For this reason we recommend spraying broadleaf evergreen trees with anti-desiccant, which covers the leaves in a wax-like coating, and helps prevent loss of moisture.

Similarly, these extreme temperatures can cause the tree trunks to thaw out during the day, and to freeze in the evening. Unfortunately, this can cause the bark to crack and rupture, resulting in a condition known as sunscald. To reiterate, it is newly planted trees that are especially vulnerable under these conditions. In order to protect these trees, you can either paint your tree trunks white, or wrap them carefully in tree wrap, starting as close to the base of the tree as possible. Remove the wrapping in the spring as soon as freezing temperatures come to an end (in Denver, this is typically around April or May).

We found a concise video on how to wrap trees for winter protection here:

Protection from the Elements

Snow can in fact build up and accumulate on tree branches. Ultimately this can weigh them down and cause them to break. First, you can try gently pushing the snow off of low-hanging branches, while being careful not to break them. If the snow seems to have frozen into ice, try taking a garden hose with warm water and melting the ice down.

Critters such as rabbits and voles love to chew away at the inner and outer bark of trees, and if are allowed to do this for long enough, may cause permanent damage (i.e your newly planted trees may not survive). Protect yourself against these rodents by wrapping your trees with plastic tree guard (in the same manner as you would with tree wrap). Once the spring comes around, rodents will have better things to do than to gnaw on the bark of your trees, and it will be safe to remove the plastic tree guard at this point.

The winter may also present you with ideal opportunities to prune your trees. In the absence of foliage, it becomes much easier to spot areas where are your trees require pruning attention. Furthermore, given that many disease-causing organisms lay dormant in the winter, pruning your trees where appropriate may help to prevent the spread of disease. To learn more about pruning, see our article on Simple Pruning Techniques

Recycling Your Christmas Tree in Denver

That bittersweet time arrives every year, where we’re done decking the halls and roasting chestnuts over an open fire. That’s right – Christmas must inevitably come to an end as we turn a corner towards the new year. And along with this season of change, as we start packing up decorations and lights from the home, we must make the decision about how to dispose of our live Christmas tree (for you fake tree folks, this article does not apply!). But just because your tree will no longer be the centerpiece in your living room, doesn’t mean that the spirit of the tree can’t live on…

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Christmas Kindling

Thankfully there are ways to extend the life of your evergreen that will extend well beyond the holidays….

To start with, one option is to chop up your tree into firewood for an outdoor fire-pit. (Just remember that kindling from Christmas tree is not safe for indoor fires, as it can produce a chemical known as creosote which can build up and cause the fire to send out extremely hot sparks). What better way to prolong the holiday spirit than to warm yourself by an outdoor fire with a cup of hot cocoa and friends and family by your side!

Compost Your Tree

Another option is to use your tree trimmings as compost throughout your landscape. Using a thin layer of branches from your evergreens provides a solid base layer, allowing air to flow from the bottom of the compost pile. For this technique, you’ll simply stack the tree trimmings in a bin roughly 5-6 inches high, and then start adding your kitchen waste and other compostable items.

In a similar fashion, you can also repurpose some of the trimmings and lay them beneath your perennial plants to serve as protection from frost and temperature swings (which are notorious in Colorado!).

Recycle Your Tree

Before you go leaving your tree out by the curbside for disposal, did you know that many cities offer tree recycling programs? In fact, right here in Denver the city runs a program by Denver Recycles called Treecycle, where the city will turn your Christmas tree into mulch – for free! In turn, that mulch is made available to Denver residents at the Mulch Giveaway and Compost Sale in May.

Last year, the city collected 21,500 trees – holy recycling Santa! This coming 2020, the program will be running between January 6 -17, and you can read more details HERE. And not to worry, if you miss the aforementioned window to curbside your tree, there are also Treecycle drop off locations on 7354 E. Cherry Creek Drive South and 10450 Smith Rd. that will be open until January 31st. That gives you a full month and then some after Christmas to recycle your tree!

And if you’re reading this article from another city, make sure to do a Google search to see if your nearby city offers a similar program. Otherwise, you can use one of the options above to repurpose your tree. If none of these options apply to you, many Christmas tree shops will accept returned trees after the holidays, in most cases to use for their own mulching or recycling purposes. Make sure to contact the tree farm where you purchased your tree in advance to see if this is something that they offer.

Best Practices for Watering Trees and Shrubs

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Proper watering practices should not be dismissed when considering the health of your trees and shrubs. After all, water is the elixir of life! Here we explore the best means by which to water and soak your trees, while also considering methods for determining just how long you should water them for. So next time you start watering, consider these tips and tricks from The Homeowner’s Complete Tree & Shrub Handbook to keep your trees healthy and properly hydrated!…

Adequate water helps newly planted trees and shrubs recover from transplant shock so their roots can establish in the soil, a process that may take up to three years. If a tree is large at planting time, it will take longer to become established than a small tree does. Unless you plant drought-tolerant varieties, it’s especially important to water established plants in stressful times to help them maintain their vigor. Keeping them hydrated and healthy reduces the chances of stress-related pests and diseases.

Transplants need water on a regular basis when the top couple of inches of soil feel dry but before the deeper planting soil completely dries out. Water trees deeply at least once or twice a week with an irrigation bag (such as a TreeGator, a low-cost plastic bag that dispenses water automatically out of holes in the bottom) or a soaker hose, or leave a dribbling garden hose at the base of the plant. Continue watering long and deeply throughout the growing season and repeat the following year until the plant is well established and growing at a relatively constant rate. Establishing a newly planted tree depends upon both climate and planting conditions.

Soak It to Them!

A soaker hose is the most economical and efficient method for delivering moisture to transplanted trees and shrubs. Water seeps through tiny pores along the hose, penetrating the soil around the roots where the plant needs it most. Soaker hoses reduce the likelihood of transmitting disease by water splashing from one plant to another. Moreover, you can hide a soaker hose under a thin layer of mulch or topsoil, although clogs are less likely above ground.

A well-made hose resits cracking, clogging, decay, and frost damage, though you may want to check for clogs if you move the hose frequently. A high-quality, 60-foot black soaker hose with a 5/8 inch diameter sells for as little as $13. If your plant is at a distance from the source of water, attach a garden hose to your faucet and a soaker hose as the end of the garden hose. For large areas, you can attach a second soaker hose to the first, but make sure that water reaches the end of the second line. Fitting a Y-joint to your faucet lets you install a second hose to the water’s source.

Consider installing an irrigation system in order to automate sprinklers and soaker hoses. This way, you will know when you can deep-water a particular bed on a hot, droughty day in five minutes. For example, a second franklinia planted 10 feet from the first in a mixed border and never irrigated will survive as a small multi-stemmed shrub.

How Long to Water? It Depends…

The duration of watering also varies with root depth and composition. A tree planted in porous sandy soil may need more frequent watering than the same tree planted in slow-draining heavy clay where water pools on the soil surface. Gauge how much water your plants need by digging a small hole with a narrow trowel in the watering zone and checking after 15 minutes to see if water has reached the deeper roots. Note that most tree roots occur in the top 12 inches of soil. Check every few minutes to see if you need to keep watering for full saturation. Determine how long it takes for moisture to reach the entire root zone, then water your garden for that amount of time or set your automatic timer to run for the duration. Depending upon your region and the weather, you may want to water established trees as much as twice a week or as little as once every two weeks. Once established, trees planted in a moist open environment probably don’t need watering except during dry spells.

Water Efficiency

Planting the right plant in the right place is the first step to water efficiency. If you group plants requiring little water in one area and plants that needs lots of water in another space, then wasting this precious natural resource is less likely. Once trees and shrubs are established, they usually survive without extra moisture.

Why You Should “Limb Up” Your Trees

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“Limbing up” – also known as “raising the crown” – can help to form a handsome woodland scene, adding depth, diversity, and a unique sense of place to the home landscape. Limbing up can add aesthetic value to the home by selectively carving out spaces for people, plants, and architecture. Read on to learn more from the following passage in The Homeowner’s Complete Tree & Shrub Handbook...

Imagine a young 10-foot-tall Japanese stewartia grows in your front yard. You’ve chosen it about seven years ago for its yellow-centered white flowers, yellow to purple fall color, and flaking gray, tan, and orangey bark. Trouble is, you can’t see any of that bark because the tree was branched almost to the ground. You decide to limb it up while it is small, since you expect it to grow about 25 feet tall. You do the work yourself with hand pruners when the branches are less than 1 1/2 inches in diameter.

You also have a shade border with a sugar maple, a red maple, a pin oak, and some shade-tolerant shrubs and perennials. You had a problem with those trees some years ago, however. When you weeded newly planted primulas and barrenworts under the trees, you’d whack your head on the lowest branches. The trees were not fully mature but they were already big – about 25 feet tall for the 13-year-old sugar maple. For a big tree-pruning job like that, you turned to a certified arborist rather than doing it yourself. Over a few winters, they removed some branches and made a shade garden a joy to maintain. The trees are still full and beautiful, but you no longer have to worry about banging your head.

Limbing up, also known as raising the crown, frees space for people, other plants, and buildings. It can open a distant view and provide more sunlight to plants growing underneath the canopy. It also increases air circulation under the branches.

If you have aged conifers like the white pines, give them a second look. Sometimes the tops of old conifers shade out lower branches, which then diet and break off in storms. Although birds like to perch on those snagged limbs, you can achieve a more refined look if you remove the low dead growth.

Not every tree needs limbing up. While pin oaks, with its droopy lower branches, may keep you from gardening successfully, there are other trees that you may not need to touch. For example, the low twisted branches of Tortuosa European beeches create variety and visual interest in the landscape. Similarly, sourwoods are so perfect in their pattern of growth, beautifully droopy flower clusters, and long lasting burgundy fall color that you may not want to change a thing.

Raise a tree’s canopy in late winter or early spring before new growth starts. Beware of removing too many branches at any one time. Foliage collects energy necessary for healthy roots. A big reduction in leaves may stress a tree, making it prone to damage from disease or insects. Prolong the process of limbing up over several years if necessary, so that you can leave at least three-quarters of the crown intact with each pruning.

Limbing up trees increases the amount of light that reaches the ground. Do you grow dense-canopied trees in your lawn, surrounded by individual rings of mulch instead of grouping them in larger beds? Raising the crowns may help the turf below them to survive.

Adding Fruiting Trees and Shrubs to Your Landscape

In addition to flowers and awesome autumn hues, shrubs and trees can produce showy fruit that magnifies your garden’s charm. Technically, fruiting is the part o fa plant’s reproductive process that occurs after flowering. Fruit comes from the female part of a seed-bearing plant. It holds the fertilized seed or seeds of that plant’s next generation. Some plants have showy fruits to attract wild-life that eat the fruit and disperse its seeds. People, of course, also eat fruit, so shrubs with edible fruit may serve a dual purpose of enjoyment in our gardens. In fact, the word fruit derives from the Latin root, fructus, or enjoyment.


Shrubs that are nondescript for most of the year take on a new look when they fruit. Purple beautyberry’s tight clusters of bright purple fruit appear on a rather plain twiggy shrub in my shrub border. where I don’t pay it much attention until handsome purple berries appear in fall. Wow! The fruit quantity changes from year to year, but the color always delights me.

Likewise, driving a marshy stretch of highway near my home becomes a new experience in fall, when winterberry’s branches, naked of leaves but lush with bright red berries, transform the muck into a cloud of brilliant red. That inspired me to plant “Winter Red” winterberry, the berries of which may last all winter in my backyard. Imagine my surprise one one very cold Thanksgiving Day when I watch a flood of wild turkeys consume them. Besides red, you can also find winterberry in orange and yellow cultivars.


The fruit of some evergreen hollies stands out against the foliage, providing fall to winter interest. Ivory Queen inkberry has white fruit and evergreen leaves on a short plan suitable for a foundation planting.

Blue holly cultivars worth growing for abundant fruit include Blue Princess and Mesog China Girl. These fairly small hollies look great grouped in borders or used as n informal hedge. These fairly small hollies look great grouped in borders or used as an informal hedge.

Nellie Stevens holly is not as hardy as blue holly, but this popular cultivar ha a good fruit set. Although Meserve hybrids and most other hollies require a male plan for lavish fruiting, Nellie can fruit on its own, though it fruits better wth a male, particularly Edward Stevens participating in the process.


Planted alone, holly can make an outstanding garden specimen, particularly in winter, when there’s a little color to hold your attention. James G Eson altaclera holly grows 25 feet or more. From October to January it displays large, clear red berries against its shiny dark green leaves. Miss Helen, Comet Prancer, and fastest growing Carnival with orangey red fruit are showy American hollies that stand on their own. East Palatka and Fosters #2 holly make attractive fruiting screens, hedge, or specimens. Make sure you plan a male for fruiting and find the best for your climate.

*Source for this article was taken from The Homeowner’s Complete Tree and Shrub Handbook. For more information on adding visual interest to your yard, please visit some of these other helpful articles:

How Flowering Trees Can Improve Your Landscape
Use Tree Textures to Add Beauty to Your Landscape

How Flowering Trees Can Improve Your Landscape

In this article, you will find information about how flowering trees can add a unique contrast to your landscaping. This information is a continuation of our article about how you can use tree textures to add interest to your landscape, and is directly sourced from The Homeowner’s Complete Tree & Shrub Handbook. 

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Who can resist a southern magnolia blossom’s lemony sweet fragrance and outrageous beauty? Not I! They have baby smooth petals and a sublime scent. A backdrop of large leathery ever green leaves heightens the creamy blossoms sensual appeal.

Flowers are reproductive organs that attract what they need for pollination. A pollinated flower matures into a fruit containing the seeds for the specie’s next generation. If you grow trees for their flowers, be aware that flowering can be fast, a few days for most; if the tree has bracts the period of color may last for several weeks.

Flowers come at different times of year for different plants. Red maple’s red flowers blush the crown in spring before the leaves appear. A mass of female trees on a hill or along a drive transforms the view into a subtle, yet rich red haze. Even as red maples come into leaf, reddish fruits appear in clusters, prolonging the ruddy glow. (In a garden, some folks gripe that once those pretty spring flowers become abundant fruits they result in messy seedlings that need plucking one by one.) Steweartia’s lovely white flowers occur in summer when most other trees have finished blooming, and Franklinia’s delightful flowers appear in fall, just before frost.

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When you grow a tree for flowers, the blooms should be visible among the leaves and branches. Tulip tree produces large, cupped chartreuse and orange blossoms. The tuliplike flowers are striking, but the giant tree grows so fast that, unless your house is near the height of the tree’s canopy, you can hardly see the blossoms. I know because I had one that towered over my house where I live. Honestly, tulip trees are too big for most residential lots, but we like ours and kept it for its straight towering trunk, handsome light green leaves and yellow fall color. Another tree grown for its flowering clusters is fragrant styrax. This small flowering tree is quite pretty near a patio, but has droopy white bloom clusters sometimes seem hidden amid their leaves, which grow to 8 inches long and 6 inches wide. Even if you can’t always see the scented flowers, however, you can small them and appreciate the tree’s smooth, ruddy bark and exfoliating young stems.

Gardens grow some trees for flowers alone, including a few ornamental plums and cherries. Be careful which trees you choose as many cherrie and plums, which below ot the Rose Family, are prone to disease of that group. Even disease resistant varieties may attract tent caterpillars or Japanese beetles in areas where they are pests, the trees thus require regular picking or spraying. Prunus, my favorite cherry tree for its lush, tiny pink-on-pink flowers, yellow fall color and delicate airy habit, still gets Japanese beetles every July, but I grow it with a group of other shrubs that beetles do not bother.

What appear to be flowers may in fact be showy bracts, big petal like leaves that attract animals to the small flower clusters they surround. A wonderful ornamental known for its bracts is Kousa dogwood. It produces four pointed white bracts that turn pinkish with age surrounding a little greenish flower cluster at their center.

Use Tree Textures to Add Beauty to Your Landscape

Landscaping isn’t only about size or colors of your plants, it’s also important to consider unexpected textures on the bark and leaves of your tree. In this article, you will find information on how to add beauty to your landscape by paying attention to textures on your tree. This information is sourced from The Homeowner’s Complete Tree & Shrub Handbook. 

The Beauty of Bark

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I’m a sucker for bark. I go wobbly at the sight of a mature paperbark maple, a shagbark hickory makes me drool, and my jaw drops when I see a Pacific madrone. What is it about bark that excites us? Bark is always there, hiding just below the leaves, ready to reveal its beauty if I take the time to look.

Bark is a tree’s protective coat. Some bark looks decorative year round you can always see the arced plates of shagbark hickory, the ginger curls of paperbark maple, and the peely white skin of paper birch. But other barks reveal themselves best when trees or shrubs are bare. an example, the yellow-twig ash. Once those fabulous lemon-yellow autumn leaves fall to the ground, you can see butter-yellow young stems contrasting with the round black velvet leaf buds.

My favorite trees with colorful bark, however, are the strip bark maples – brilliant coral-stemmed moosewood and red snake bark maple. Moosewood’s gleaming red and white striped stems glow in a snowy winter landscape, while the bark of red snake bark maple has vertical strips in white and olive grey green with red shoots.

Red willow and shrubby dogwoods also come into their own after leaf drop. Native red-osier dogwood has red young stems in the winter. The cultivar “Cardinal” has brighter stems and more disease resistance than other popular varieties. Yellow-twig dogwood produces disease resistant, school bus yellow stems. Midwinter fire has flamelike stems of red orange and yellow. Remember new stem growth is the most colorful, so cut these shrubs to the base each spring or you’ll end up with dull bark.

Just as landscape texture refers to a tree’s visual nature, it may . also pertain to the sense of touch. Smooth, muscled beach bark thus differs by sight and touch from rough, plated bark of old sugar maples.

Evergreen Textures

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Now that we’ve talked about the bark of trees, let’s take a look at some of the other textures of trees that draw us in.

Textures effect our two senses of vision and touch. Coarse textured shrubs and trees have large leaves that create bold patterns of light and shade on a plant’s surface. Course plants leap forward in a landscape. On the other hand, trees and shrubs with fine-textured foliage have little contrast between light and dark. Their even surface can more easily fades into the background. Planting bold textured shrubs such as Oregon grape holly at teh back of a garden, makes it feel smaller while planting fine-textured plants like yew or pine enlarges the space.

To find additional information on landscaping, please visit our article on to properly landscape your yard by incorporating trees!

Common Insect Pests

In this article, you will find practical methods for identifying, preventing, and treating the following: Aphid, Gall, Lacebug, Leaf Miner, Scale, Spider Mite, Tent Caterpillar, and Wood Borer. This information is a continuation of our article on Common Tree and Plant Diseases, and is directly sourced from The Homeowner’s Complete Tree & Shrub Handbook. The second section of the article describes practical earth-friendly strategies to manage insects, while keeping your trees and shrubs healthy.

Being able to identify various insects can be instrumental in helping you prevent stress and disease to your trees and shrubs. For that reason, we recommend keeping these two articles handy as a reference!

Aphid

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Description: Aphids are sapsucking insects that come in many colors and textures from red, yellow, green, purple, brown, and black to whitish because of a light all-over secretion. Some have wings and some don’t, and many prefer congregating on the lower surface of leaves. What they have in common is their tiny size, pear-shaped bodies,
long legs, and long antennae. They tend to be group feeders on leaves and stems, but you’ll occasionally see a loner. Aphids probably won’t destroy your trees and shrubs, but sooty mold can turn the sticky honeydew they release black. You may also notice the foliage wilt, yellow, or distort.

Cause: Regular infestations.

Preventive Measures: You cant escape them: an aphid species is linked with almost every tree and shrub.

Treatment: Tree and shrub damage is usually more visual than life threatening. Live and let live, unless they really bother you or the infestation is severe. Hose foliage and stems with a powerful stream of water to displace them. If you want something more, spray your plant with insecticidal soap or horticultural oil. Many beneficial insects such as ants, lady beetles, and parasitic wasps will destroy aphids if you don’t destroy them first. Skip heavy-duty insecticides because they kill not just the bad guys but also the good.

Gall

Description: Galls are abnormal growths of plant tissue on leaves, twigs, and bark of trees. Oaks host most galls, but they also appear on other trees and shrubs.

Cause: Mites, wasps, aphids, and midge flies can all bring about galls. The insects that make galls are most active when trees leaf out in spring.

Preventive Measures: Keep trees healthy. Galls are not pretty but they don’t do permanent damage to your woody plants. You don’t know your trees have galls until
you see them, and spraying them won’t help because the gall shields the larvae.

Treatment: Hold off on chemical sprays. Sometimes tolerating a pest is the best thing to do. If the infestation is severe, you can prune out ugly twigs.

Lacebug

Description: Lacebugs get their name from their decorative wings and hood adorned with a lacy pattern of veins. These sapsucking pests about 1/8 inch long come in many species that affect a multitude of woody plants. They live on leaf bottoms, where they excrete spots of dark crud as they eat. Minor lacebug damage looks like yellowy dots on the upper leaf surface. Repeated severe infestations can kill a plant. Different species attack evergreen and deciduous plants, but damage is most common on evergreens.

Cause: Incorrect planting sites encourage some infestation of lace bugs.

Preventive Measures: Lace bugs thrive in sun. Set vulnerable plants such as azalea and andromeda in shade.

Treatment: In early spring. start checking under the leaves for eggs, newly hatched nymphs, and adults. Keep checking every couple of weeks, since several generations may hatch in a year. Dealing promptly with infestation prevents ugly damage from occurring. As with aphids, you can set upon lacebugs with a hose and give them a hard spray to displace and kill nymphs (immature insects) in spring. Encourage beneficial insects that prey on lace bugs by avoiding the use of chemical insecticides. Instead, drench leaves (especially the bottoms) with insecticidal soaps or horticultural oils to control the nymphs when they hatch.

Leaf Miner

Description: Leaf miners are similar to borers except that the latter go deeper into the plant. The larvae of leaf miners live inside leaves and their damage is visible as an irregular narrow whitish trail on the leaf surface. Most attacks are visible at the beginning and end of summer in mature foliage. Most woody plant families are susceptible to their raids.

Cause: Adult beetles and moths looking for suitable host for their larvae to develop.

Preventive Measures: Avoid stressing trees and shrubs with too much or too little water, and provide desirable conditions for their growth.

Treatment: Chemicals don’t work because the larvae are inside the plant. Anyway, leaf miners usually don’t cause permanent damage to most trees and shrubs.

Scale

Description: Scale insects feed on the sap of both evergreen and deciduous trees and
shrubs with mouth parts up to 8 times longer than their bodies. Scales hug their bodies tight to their food source and can be found on leaves, twigs, branches, and trunks. They can weaken and eventually kill the plant they infest, though that is not typical. Two kinds of scales exist, hard and soft. The latter makes honeydew while the former does not.

Cause: Scales occur on trees and shrubs that are stressed.

Preventive Measures: Maintain healthy trees and shrubs or drought. Avoid chemicals that harm lady beetles and that can survive an attack. Give your plants adequate
water and nutrition, especially when stressed by injury or drought. Avoid chemicals that harm lady beetles and parasitic wasps, their natural predators.

Treatment: Rub them off by hand or prune off severely infested branches. Because adults have a waxy coating that shields them from insecticides, you have to control them when they are overwintering or immature crawlers. Dormant oils work in early spring before trees and shrubs leaf out.

Spider Mite

Description: Mites are in the spider family. These teeny red, brown, or spotted sapsuckers damage leaf tissues. Fine webbing will appear on deciduous trees with large infestations. Leaves become spotty, yellow, and then brown before dropping. Common
hosts include spruces, arborvitaes, raspberries, roses, crabapples, and shrubby cinquefoils. To see if you have mites, tap a branch while holding a sheet of white paper
under it. If you see moving dots, you have spider mites.

Cause: Hot, dry, and dusty conditions grow their populations, while wet or humid weather lowers them.

Preventive Measures: Keep trees and shrubs healthy because spider mites thrive on stressed plants.

Treatment: While infestations are light, you can control them by spraying plants with hard jets of water. Do this whenever mite damage is apparent and repeat it weekly for at least 3 weeks. Use repeated applications of insecticidal soap or horticultural oil to further lower mite populations.

Tent Caterpillar

Description: You know them-those ugly, white, larvae-holding, silken webs or tents hung up in tree branches. The caterpillars eat the leaves of deciduous trees. They attack many kinds of trees but like rose, alder, birch, willow, ash, and apple more than most. Although they don’t kill trees, they can weaken them and make them vulnerable to other problems. Vigorous trees withstand an attack and releaf quickly.

Cause: Periodic infestations.

Preventive Measures: Keeping trees healthy helps them survive an infestation.

Treatment: Eliminate egg cases from trees. They are made of a foamy-looking gray to brown hard substance and are about 1% inches long. Remove the cases with pruners or
by hand. Get rid of hatched caterpillars by eliminating their nests from the limbs.

Wood Borer

Description: These insects, typically moths and beetles, grow under the bark of trees and shrubs, mining the inner bark in an immature, larval state. Most borers are drawn to dead, stressed, or dying trees. The beetles are dark brown, black, or red with tiny hard bodies. Many species attack conifers but the European elm bark beetle is a transmitting agent for the Dutch elm disease fungus that decimated the American elm (Ulmus americana) population in North America. Other examples of borers are longhorned beetles and carpenterworms, which become moths. Sawdust on the ground and sap mixed with sawdust oozing from little holes are signs that bark beetles have emerged from the trunk of conifers.

Cause: Trees stressed by drought, disease, and physical damage are more prone to wood borers than robust trees and shrubs.

Preventive measures: Keep shrubs and trees in tiptop health. Plant pest-resistant species and take good care of landscape shrubs and trees. Don’t over- or underwater
them, and make sure their growing conditions are conducive to maximum vigor. Baby new transplants.

Treatment: Cut off and get rid of infested branches to prevent the spread of the beetles. If the trunk shows lots of beetle damage, you may have to dispense with whole trees to save nearby trees. A certified arborist will know the right time to prune diseased branches from different types of trees.

Earth Friendly Remedies

Bordeaux mix can kill some disease-causing bacteria and fungi that affect both woody ornamentals and trees and shrubs grown for fruits or nuts. Bordeaux is good to use full strength as a long-lasting fungicide in fall, winter, and spring before a plant breaks dormancy; you can also use it at reduced strength after spring growth begins. You need proper safety gear (goggles and protective clothing) to apply this mixture, which you can buy prepackaged or make fresh. One gallon of Bordeaux mix requires blending 3 1/3 tablespoons of copper sulfate and 10 tablespoons of hydrated lime with 1 gallon of water. It should be used right after mixing. Bordeaux mix can control some mildews, fireblight, and apple scab.

Fixed copper fungicides, which are different copper compounds mixed with water, are safer to apply and safer to use on tender plants. You can also buy these ready made.

Insecticidal soaps kill vulnerable soft-bodied insects on contact. For efficacy, you have to ensure thorough coverage of affected plants, including stems and upper and lower leaf surfaces. The application may work better if you spray early in the morning or in the evening to prevent quick evaporation. These soaps are people-safe when you follow the package directions. As with any insecticide, use only when absolutely necessary.

Horticultural oils, which are made of refined petroleum or plant oils mixed with water, control many pesky insects on plants but tend to have limited effects on beneficial insects. Oils can kill aphids, mites, caterpillars, and scales on woody ornamentals as well as help prevent powdery mildew and rust. Dormant oil is horticultural oil used on trees and shrubs during their dormant season. Summer oil is safe to use on mature leaves during the growing season. Sometimes oils can injure sensitive species, such as juniper, hickory, black walnut, redbud, smoketree, some azaleas, spruce, Douglas fir, and Japanese cedar or cryptomeria, and Japanese, sugar, and red maples. Always follow package directions when spraying these products.