- Cornus kousa
- The Kousa Dogwood
- Kousa Dogwood Care: Tips For Growing Kousa Dogwood Trees
- Kousa Dogwood Varieties
- Tips for Growing Kousa Dogwood Trees
- Blue Ray Kousa Dogwood
- Brand New Blue Ray Kousa Dogwood lasts longer and looks more unique than other dogwoods.
- Planting & Care
- Kousa Dogwood Tree
- Kousa Dogwood Tree – Cornus Kousa For Sale Affordable, Grower Direct Prices Tennessee Wholesale Nursery
- Kousa dogwood
- Related posts:
- Attributes: Genus: Cornus Species: kousa Family: Cornaceae Country Or Region Of Origin: Sikkim, China to Temp. Eastern Asia Wildlife Value: Fruits and nesting sites attractive to songbirds. Squirrels eat fruits as well. Members of the genus Cornus support the following specialized bees: Andrena (Gonandrena) fragilis, Andrena (Gonandrena) integra, and Andrena (Gonandrena) platyparia. Play Value: Wildlife Food Source Particularly Resistant To (Insects/Diseases/Other Problems): Resistant to anthracnose and blights that native dogwoods are susceptible to. Mildly resistant to deer damage Edibility: Fruits are technically edible but are usually left for the birds. Dimensions: Height: 20 ft. 0 in. – 30 ft. 0 in. Width: 15 ft. 0 in. – 20 ft. 0 in.
- Whole Plant Traits: Plant Type: Edible Shrub Tree Leaf Characteristics: Deciduous Habit/Form: Erect Horizontal Rounded Spreading Vase Growth Rate: Slow Maintenance: Low Texture: Medium
- Fruit: Fruit Color: Green Pink Red/Burgundy Fruit Value To Gardener: Edible Showy Display/Harvest Time: Fall Summer Fruit Type: Berry Fruit Description: This plant has globular, pinkish-red to red fruit in late summer (though on ‘Greensleeves,’ fruit can be green at some points and a little pointy). The Kousa dogwood has berries that resemble raspberry fruit in autumn. ½-1″ diameter reddish syncarp hanging on a 2″ long stalk.
- Flowers: Flower Color: Pink White Flower Bloom Time: Spring Flower Shape: Cross Flower Size: 1-3 inches Flower Description: This plant has 2-4 in. white or pink tapered bracts. Flowers appear before leaves and bloom about 2-3 weeks after C. florida. They bloom around May (late spring) and into June. Showy part is 4 creamy, white pointed bracts. Actual flowers are inconspicuous.
- Leaves: Leaf Characteristics: Deciduous Leaf Color: Gold/Yellow Green Purple/Lavender Leaf Feel: Glossy Leaf Value To Gardener: Showy Deciduous Leaf Fall Color: Purple/Lavender Red/Burgundy Leaf Type: Simple Leaf Arrangement: Opposite Leaf Shape: Elliptical Ovate Leaf Margin: Entire Hairs Present: No Leaf Length: 1-3 inches Leaf Width: 1-3 inches Leaf Description: This plant has 2-4 in. long 1/4″-1 3/4″ wide, opposite, simple, and dark green leaves that have a reddish-purple to scarlet fall color. Cornus kousa ‘Greensleeves has glossy, slightly wavy, green leaves that are pointed at the ends. For Cornus kousa ‘Greensleeves, the top of the leaf’s venation is a yellowish-green which makes the venation obvious against the glossy green leaf; for Cornus kousa ‘Greensleeves, the leaf’s underside is a lighter green color than on top and the venation is prominent sticking out slightly and being a pale-green. The margins are entire and the base is cuneate with an acuminate apex. Elliptical/ovate, 2-4″ long, 1-2″ wide, acuminate, dark green above, glaucous below with yellowish tufts of hair. Distance between veins changes towards apex.
- Bark: Bark Color: Dark Brown Light Brown Surface/Attachment: Exfoliating Bark Description: The peeling brown bark on the mature tree trunks gives the bark an attractive mottled appearance. Looks espeically attractive if under light in the evening to take advantage of the exfoliating bark. Exfoliates with age, mottled gray/tan
- Stem: Stem Is Aromatic: No
- Landscape: Landscape Location: Small Space Landscape Theme: Butterfly Garden Children’s Garden Pollinator Garden Design Feature: Border Flowering Tree Mass Planting Specimen Street Tree Attracts: Bees Pollinators Songbirds Specialized Bees Resistance To Challenges: Deer
The Kousa Dogwood
Dogwood trees are well known for their delicate beauty in the landscape. Kousa dogwood not only meets the standard for attractiveness, it adds a hardiness that makes this species an excellent choice for home landscapes and urban areas.
This small tree makes its visual contribution year-round. In spring, it produces a heavenly array of star-like blooms. In summer, its intriguing canopy of layered branches provides some shade as well as beauty. In autumn, it offers a spectacular display of bright red color. It also produces berry-like fruits that are an attractive oddity edible to both humans and wildlife (though much preferred by the latter). Even in winter, this tree has an appeal all its own, not only in its stratified branch pattern, but in its bark that resembles a puzzle or camouflage.
Kousa dogwood is a native of Japan, China, Vietnam, Laos, and other eastern Asia countries. When planted with its popular American cousin, flowering dogwood, it has the pleasant habit of blooming, about the time flowering dogwood ends, and it retains its blossoms much longer. It also has strong, spreading branches and can survive the stresses of urban life. On top of all else, kousa is proving to be more resistant to diseases and insects than flowering dogwood, and may be better suited for growth at both the colder and hotter extremes of the native’s planting zones.
Read Which Small Trees will Work for your Yard
What’s in a Name
If you look for meaning in tree names, when it comes to the name “kousa” not much is found. Kousa is simply the Japanese word for dogwood and has been applied both as the scientific and common names of the species. The name dogwood is a bit more interesting. It derives from “dag” wood and the unpleasant use of the very hard wood for primitive weapons.
Eventually, botanists gave the genus the scientific name, Cornus, from the Latin cornu, again reflecting on the hard character of its wood, or a pointy horn or point. It is rather a grizzly name derivation for such a lovely tree.
Other common names sometimes applied to this species include Chinese dogwood, Japanese dogwood, Japanese flowering dogwood, and Japanese strawberry tree.
In the landscape
When selected carefully, a non-native species like kousa dogwood can add variety to the landscape and sometimes stand up better against pests that may trouble native species. It’s more cold hardy and disease resistant than the flowering dogwood, and somewhat drought resistant (hardiness zones 5-8). It’s slow-growing and reaches up to 25 feet at maturity, making it short enough to be planted under power lines.
In spring, it produces a heavenly array of star-like blooms. The white “petals” aren’t actually petals at all, they are modified leaves called bracts that surround the small, greenish-yellow, insignificant flowers.
In winter, this tree has an appeal all its own with bark that resembles a jigsaw puzzle. Note: to prevent bark damage, use mulch around base of the tree. Dogwood trees are often victims of lawnmower or weed cutter damage to the trunk.
Catch up on Burbank Plum: Named After a Genius
Kousa Dogwood Care: Tips For Growing Kousa Dogwood Trees
When looking for an attractive specimen tree for their landscaping design, many homeowners go no further when they come upon the Kousa dogwood (Cornus kousa). Its unique mottled peeling bark sets the stage for a wide branching canopy, thick branches of bright green leaves and drifts of white flowers every spring. Keep reading to get tips for growing Kousa dogwood trees and how to take care of Kousa dogwoods in the landscape.
Kousa dogwood trees begin life with an upright design, but their branches grow out horizontally as the trees mature. The result is an attractive canopy that will fill a large portion of the yard. Many people use them as a focal point by attaching small twinkle lights to the underside of the canopy, creating a magical look for evening relaxation.
Kousa Dogwood Varieties
There are a number of Kousa dogwood varieties, and the only basic difference is how each tree looks.
- “Gold Star” has a golden stripe down each leaf in the spring, which darkens to a solid green later in the summer.
- “Satomi” and “Stellar Pink” have pink flowers instead of white ones.
- “Moonbeam” has giant flowers almost 7 inches across and “Lustgarden Weeping” is a smaller version of the tree, often reaching about 8 feet tall while still spreading almost 15 feet wide.
Whatever Kousa dogwood cultivar you choose, it will have the same basic care needs as all the other varieties.
Tips for Growing Kousa Dogwood Trees
Kousa dogwood does much better when planted in the spring than in the fall, so wait until the last sign of frost has passed before putting in your new tree.
When it comes to planting dogwood Kousa trees, it all begins with the soil. Like most dogwoods, these trees enjoy a spot with rich, moist soil in full sun to partial shade. Dig a hole about three times the size of the root ball on your sapling, but keep the depth the same. Plant your Kousa dogwood trees at the same depth they were growing in the nursery.
Kousa dogwood trees aren’t very drought-tolerant, so make sure to keep the soil moist throughout the summer, especially in the first three years when the tree is establishing itself. Add a circle of organic mulch about 3 feet wide around the base of the tree to help retain moisture to the roots.
The bark of the Kousa dogwood is so attractive that you’ll want to selectively prune branches to show it off as part of your Kousa dogwood care. If the bark looks good, the mature branches are even better. The older the tree gets, the more the branches grow horizontally, giving the tree a spreading look that with a decorative canopy.
From the drifts of flowers in the spring to the abundant bright red berries late in the summer, Kousa dogwood trees are an ever-changing, attractive addition to almost any landscaping design.
Blue Ray Kousa Dogwood
Brand New Blue Ray Kousa Dogwood lasts longer and looks more unique than other dogwoods.
Brand New Blue Ray Kousa Dogwood—Get One Today!
You’re going to love the brand new Blue Ray Kousa Dogwood. It’s been adored by horticulturist for several years and is now being released to the public for the first time!
This dogwood guarantees you all the features you love about dogwoods with a few new surprises. Be one of the first people to grow a Blue Ray Kousa in your neighborhood—even town!
More Disease- and Pest-Resistant Than Others
According to the story of the Blue Ray Kousa’s heritage, Cultivator Ray Jackson originally planted this breed next to other varieties and was extremely impressed when Blue Ray Kousa did not get infected with the same diseases and pests that plagued the others growing right alongside it.
Its hardy growth qualities combined with its color influenced Ray to continue developing this Kousa Dogwood.
You’ll love how its disease- and pest-resistant qualities make it even easier to manage this low-maintenance species.
You’ll Flip for This Fancy Foliage!
Blue Ray Kousa is equally named after its cultivator and its unique colorful foliage. The showy leaves are bluish-green with burgundy tips. The ovate, 4-inch leaves slowly taper to a pointed end. Making the leaves equally curvy and dramatic.
You’ll be able to appreciate the bluish-green glow of this fully-covered, deciduous tree without being distracted by the flowers. The blooms only come forth in late spring, so you’ll have plenty of time to fully absorb the colorful foliage before it becomes a beautiful backdrop to the “flowers.”
This dogwood will stand out as an extraordinary addition to your yard.
Blue Ray Kousa Will Bring a Colorful Foliage Display in Fall, Too.
The blue-tinted leaves turn maroon as the season changes from summer to fall. The purplish-red color will stand out in your yard among the classic reds, yellows, and oranges. Warmly-toned, regal-looking foliage will adorn your yard as it gracefully falls from your majestic Japanese Dogwood tree.
Imagine that color blanketing your yard—you won’t want to rake it up!
You’ll Love That This Dogwood’s a Prolific Bloomer with Traditional Style.
If you like the traditional pearl-white blooms that make dogwoods eternally famous, then you’ll love it even more with Blue Ray Kousa! Your heavy-blooming dogwood will completely cover itself in a plethora of 3-inch wide, star-shaped blooms.
Wait! Did you know that the blooms aren’t actually flowers? They’re leaves called bracts—the flowers are small, yellowish-green, and inconspicuously hidden in the center of the bracts.
The wavy bracts flow outward coming to a pointed, darker-tipped end—adding drama, just like the foliage does, to this well-loved, classic display.
Let this Japanese Flowering Dogwood bring a soft, beautiful appeal to your yard.
Don’t Knock the Wood, You’ll Love Its Look, Too.
The Blue Ray Kousa will still stand out as a favorite feature in winter (and every season, really!), because of its unusually appealing structure and bark. This dogwood has a thick canopy layered with branches. The branches shoot off the trunk almost horizontally—making the Blue Ray Kousa go from a vase-like shape to round as it matures.
The bark naturally exfoliates creating a camouflage-like patchwork of tan and gray all over.
You’ll be stunned at how the tough and artistically shaped structure combined with its soft flowering head makes Blue Ray Kousa a real attention getter.
Many Planting Options for You
This Kousa Dogwood can work well in any outside environment you choose. It will stand out beautifully near your street without the size interfering with power lines.
The arching, elegant architecture of the Blue Ray makes it a great focal point for your yard or near a sitting area. Or you could use it as a foundational feature near the front of your home—beckoning people to come inside.
The Blue Ray Kousa works well in traditional, woodland, and bird gardens. Birds love eating the red berries in summer!
If you’re artistically inclined, you could also cultivate a creative, miniature tree out of this dogwood using the art of bonsai. Just remember that Blue Ray should remain outside most of the time and only be brought in for display on special occasions, because it needs lots of sunshine.
There’s so much you can do with this appealing dogwood. BUT don’t dawdle on ideas when there’s ONLY a limited supply of this brand new variety. Buy the Blue Ray Kousa today and then, get to planning and planting!
Planting & Care
Location: Ray Jackson first started propagating the “Blue Ray” Kousa dogwood because of its unusual bluish coloration. Recently, the variety has become more widely available for sale to the general public.
The Kousa dogwood grows best in USDA plant hardiness zones 5 to 8. It is generally planted as an ornamental specimen because of its eye-catching flower display in May and June. It attains a height of 15 to 25 feet with as spread of 25 feet. Even in an optimum planting location, it grows relatively slow with only about 12 to 24 inches of new growth per year.
Planting Instructions: Avoid planting the Kousa dogwood in the fall. Plant in the early spring or mid-spring so the tree has ample time to establish a root system before winter.
Choose a planting location that offers full sun for best growth results. It prefers slightly acidic well-draining soil but will tolerate a neutral pH. It grows well in loamy, sandy, or clay soils and is somewhat drought resistant
The Kousa dogwood has a shallow root system so it is important to till the planting site prior to planting the tree. Till an area that is approximately three times as large as the tree’s root ball. Amend the soil with two inches of compost and till the compost into the soil.
Dig a hole that is twice as large in diameter as the tree’s root ball. The hole’s depth should be as deep as the root ball. Place the root ball into the hole and gently loosen the roots. Backfill the hole and press the soil firmly down to remove air pockets. Fill the hole halfway with soil and then water thoroughly to settle the soil. Finish filling the hole and again water thoroughly to further settle the soil. Apply a 2 to 3-inch layer of mulch around the tree to keep the soil moist and reduce weed growth. Avoid the mulch touching the trunk of the tree.
Fertilizing: It is recommended to test your soil for the pH and proper soil nutrients before planting your new tree. Fertilize the Kousa dogwood just as the tree’s foliage emerges and on into fall. Use a standard 12-4-8 or 16-4-8 synthetic fertilizer. Follow the directions on the fertilizer’s label for application instructions. Generally, use 2 pounds of fertilizer per 1 inch of trunk diameter. For a newly planted tree, fertilize in early spring and again mid-summer.
Pruning: The Kousa dogwood only requires minimal or no pruning to look good. Prune the tree after flowering. Thin the dogwood to help light reach the interior and promote air circulation. Heavy pruning in the fall will not hurt the tree but you will not get any blooms the following spring.
69.95 Fast Growing Trees attract butterflies attracts birds disease resistant dogwood trees Planting Kit plants for bad soil shade lovers spacemaker small trees shrubs street trees Tree Spikes //cdn.shopify.com/s/files/1/0059/8835/2052/products/Blue_Ray_Kousa_Dogwood_450_MAIN.png?v=1549680725 //cdn.shopify.com/s/files/1/0059/8835/2052/products/Blue_Ray_Kousa_Dogwood_450_D2.png?v=1549680725 //cdn.shopify.com/s/files/1/0059/8835/2052/products/Blue_Ray_Kousa_Dogwood_450_D1.png?v=1549680725 13940919992372 2-3 ft. 49.95 69.95 //cdn.shopify.com/s/assets/no-image-2048-5e88c1b20e087fb7bbe9a3771824e743c244f437e4f8ba93bbf7b11b53f7824c.gif https://www.fast-growing-trees.com/products/blue-ray-kousa-dogwood-tree?variant=13940919992372 InStock 2-3 ft. 13940920025140 3-4 ft. 79.95 89.95 //cdn.shopify.com/s/assets/no-image-2048-5e88c1b20e087fb7bbe9a3771824e743c244f437e4f8ba93bbf7b11b53f7824c.gif https://www.fast-growing-trees.com/products/blue-ray-kousa-dogwood-tree?variant=13940920025140 InStock 3-4 ft. 13940920057908 4-5 ft. 109.95 109.95 //cdn.shopify.com/s/assets/no-image-2048-5e88c1b20e087fb7bbe9a3771824e743c244f437e4f8ba93bbf7b11b53f7824c.gif https://www.fast-growing-trees.com/products/blue-ray-kousa-dogwood-tree?variant=13940920057908 OutOfStock 4-5 ft.
Mystifying and beautiful, the “Magic Dogwood” – Cornus florida subspecies urbiniana – is a rare Mexican version of the common American Dogwood tree. Looking like exotic Chinese lanterns, these incredible blooms dazzle the eye by the hundreds each spring. Like snowflakes, no two are exactly alike. The plant is highly rare in cultivation, and genuine seeds & plants are rarely seen for sale.
The Magic Dogwood grows to about 20 feet tall here in San Francisco. The leaves are slightly bluer than the common species. In the spring, the tree puts on its show of decorative blooms, which are unusually large for Dogwoods. The white bracts are fused together at the ends to create an unusual, cage-like shape around the flowers. As you can see, the effect is truly spectacular. This is a naturally-occurring tree, not a cultivated hybrid!
The Magic Dogwood comes from the mountain forests of eastern Mexico, where it is rare. The climate there is spring-like year round, however the tree has been cold-hardy in Zone 6 here in the U.S. I recommend protecting it from frost the first 2-3 years. You may grow it in a pot and move indoors for the winter. It doesn’t seem to mind warm summers provided that nights aren’t too warm. The tree normally grows in the forest understory, so it appreciates some protection from strong afternoon sun.
Unfortunately counterfeit seeds are occasionally seen for sale. I guarantee that the plants and seeds i offer are the genuine “Magic Dogwood” shown here!
More tips on growing this plant
Kousa Dogwood Tree
Kousa Dogwood Tree – Cornus Kousa For Sale Affordable, Grower Direct Prices Tennessee Wholesale Nursery
Kousa Dogwood Trees are a lovely addition to landscapes and gardens. Gorgeous star-shaped blooms and layered branches catch the eye. Hardy in Zones 5-8, this ornamental grows up to 25 feet at a rate of one to two feet per year. It requires full sun to partial shade and average moisture in well-drained acidic, rich, sandy, and clay soils.
Kousa Dogwood Tree Flowers Bloom white clusters of bracts from mid-Spring to Summer and also grow Red Berries that grow to about 2cm to 3cm in diameter and can become more abundant towards the end of the season. The Berries are edible and taste very sweet. It is very tolerant of Drought and Restricted Water Conditions. Kousa Dogwood is also resistant to Dogwood diseases such as Anthracnose Disease which is caused by a Fungus. This is a beautiful dogwood tree for gardens and even lawns.
Buy Fast Growing Kousa Dogwood Tree
It grows to be fifteen to thirty feet tall and also twenty to twenty-five feet wide. During the spring it is covered with gorgeous white flowers that give way to berries. The berries are loved by squirrels and also a variety of birds. Kousa Dogwood Tree provides beautiful color and even an attractive appearance to all locations where they are planted. These trees also make great borders for lawns as they grow to maturity. These are a great addition to landscaping a garden and makes a yard stand out amongst the rest when they are in bloom. Kousa Dogwood Tree trunks of these trees are thin, but they are also reliable and hardy trees. They withstand winds and even storms very well. The leaves of this tree turn a dark red or burgundy during the fall months and look fantastic.
Affordable Kousa Dogwoods For Every Landscape
Dogwood Trees are among the most common trees that grow in almost every state. They often have blooms on them in the spring and summer, but you’ll usually notice leaves on Dogwood Trees even during the fall season before the leaves turn to a brilliant red or purple. When the tree showcases its colors in the spring, you’ll see white flowers that can sometimes appear light pink. These flowers are often one of the first signs that spring is arriving.
There isn’t a lot of care involved with Dogwood Trees. They are happy with sunlight and don’t require a lot of water in order to grow and display their flowers. Dogwood Trees can grow quickly from the time that they planted, especially if they are in an area that sees heavy amounts of rainfall. They often grow in zones 5 to 9 and can reach about 25 feet tall if they are not pruned back. The diameter of the trunk can span up to 12 inches depending on the nutrition that it receives. Dogwood Trees tend to grow about a foot a year and begin blooming in April or May. Branches of the tree grow in a rounded fashion to give the tree a circular appearance once the flowers bloom.
Kousa Dogwood Tree
The Kousa Dogwood Tree, (Cornus kousa) is a crowd favorite that produces white, starlike blooms that delicately adorn any spring landscape. It’s a small tree that delivers delicate beauty and yet, can hold its own against cold weather, drought, and a variety of pests. Come winter, the Kousa’s peeling bark takes on a striking appearance by creating a unique, jigsaw puzzle design.
The Kousa Dogwood Tree hails from eastern Asian countries like Japan, China, and Vietnam and is a relative of the American flowering dogwood. The Kousa is a hardier option than its cousin tree and grows slowly. It reaches heights of around 20 feet. The plant thrives best in USDA hardiness zones 5-8 and likes plenty of sunshine and water to maintain its exceptional beauty.
Fans of the Kousa Dogwood Tree are often attracted by its special form as it grows into a pleasing umbrella shape that envelops a property. Some homeowners attach tiny twinkle lights under the Kousa’s canopy to create a magical, nightly, focal point.
It’s a plant that delights all eyes through the seasons with dark green foliage in summer and little red, raspberry-looking fruit in autumn that birds enjoy nibbling on.
The Kousa Dogwood Tree is an excellent choice for those looking for elegant curb appeal and a smaller tree that reaches the perfect height for any landscape.
Tree & Plant Care
Although tolerant of neutral pH soils, it prefers acid soil and may develop chlorotic symptoms (pale green leaves) in high pH soils.
Shallow root system benefits with a few inches of mulch to moderate soil temperature.
Best in part shade conditions in a protected site.Flowers on old wood, prune after flowering.
Disease, pests and problems
Heavy clay soil can contains moisture, which can lead to root rots.
Borers and leaf spots
Disease, pest, and problem resistance
More resistant to drought than flowering dogwood.
Resistant to the anthracnose (Discula) that is common on flowering dogwood.
Native geographic location and habitat
Native to Asia.
Kousa dogwood (Cornus kousa) photo: John Hagstrom
Bark color and texture
Bark is gray-brown and slightly exfoliating.
Leaf or needle arrangement, size, shape, and texture
Simple, opposite, 2 to 4 inch long with entire margins, elliptical shape; dark green leaves change to a burgundy-red in fall.
Flower arrangement, shape, and size
This tree blooms 2-3 weeks after native dogwoods.
True flowers are inconspicuous. 1 to 2 inch, white pointed bracts appear above the foliage and persist for several weeks.
Fruit, cone, nut, and seed descriptions
Large, attractive, 1 inch, raspberry-like fruit appear in August.
Cultivars and their differences
Champion’s Gold kousa dogwood (Cornus kousa ‘Losely’): Vase-shaped, 25 to 20 feet high and wide; white flowers; 3/4 inch red fruits
Heart Throb kousa dogwood (Cornus kousa ‘Schmred’): A rounded habit; 20 feet high and wide; deep dink flowers; 3/4 inch red fruits; deep red fall color
Milky Way Select kousa dogwood (Cornus kousa ‘Milky Way Select’): Rounded to wide vase shape; 15 feet high and wide; 3/4 inch red fruits; bright red fall color
Satomi kousa dogwood (Cornus kousa ‘Satomi’): Vase to rounded habit; 15 to 20 feet high and wide; rose pink flowers; red fall color
Summer Gold kousa dogwood (Cornus kousa ‘Summer Gold’): rounded to wide vase-shaped habit; variegated creamy white and green foliage; white flowers; pink to red fall color; 3/4 inch red fruits
for a general overview of the factors that influence how deep tree roots grow. Or, continue reading below to dig in to the science a bit deeper.
By James Urban, FASLA
Here’s an objection we face a lot when working on Silva Cell projects:
“Tree roots don’t grow more than 24″ (65 cm) below the surface, so soil volumes deeper than that are not viable.”
Not so! Let’s get debunking.
First, I should say that I am paraphrasing from our Director of Science + Design, Peter MacDonagh and our partner, Jim Urban, FASLA. This is Peter and Jim’s bailiwick, not mine, and I’m pulling together various work that they’ve compiled here.
The graphic above (sorry for the poor quality!) shows the response of 5 different species of trees in 2 different soil types: shallow and deep O/A horizons. The key here is that O/A soils are macropore-rich and have oxygen and water moving freely through the soil column (O refers to Organic, A refers to the topsoil). The hatched box indicates drought stress that each tree is under, and the trees in the study were small caliper.
Deep Tree Roots:
The mollisols (deep >20 feet prairie soil — all O/A soil horizons) have 2 broadleaf tree root depths in columns #2 & #4: 11 feet (Black Walnut) & 15 feet deep (White Oak). Both the Walnut & Oak have the least drought stress. The loams in the Silva Cell are functionally equivalent to mollisols. So, a 4 foot deep rooting space in O/A in Silva Cells will easily be utilized by tree roots.
Shallow Tree Roots:
The entisols (shallow <3 feet forest soils) have 3 tree root depths: 1.5 to 3.5 feet deep (Florida Dogwood, E Red Cedar, Sugar Maple). The E Red Cedar is an evergreen and not a typical choice for a street tree. The two broadleafs, the Dogwood and the Maple, are suffering significant drought stress.
The conclusion here is that tree roots follow the oxygen-rich macropores, whether they are in deep or shallow soils. The volume of this soil type determines above else how large the trees will grow.
Orjan Stahl has investigated roots and, while field investigating tree roots in Stockholm, has found over 300 instances of tree roots at 7 feet deep & over 170 instances of tree roots at 9 feet deep. Of the >500 trees investigated for root depth, roots at 7 and 9 feet deep were the most common depth. One tree had roots 23 feet deep. This is the largest root depth study to date, in terms of total numbers and variety of species. Based on this study, one can safely say that no trees will have any difficulty growing down 4 feet , the approximate depth of a 3 Silva Cell-deep system, in oxygen rich soils.
Photos via James Urban