What Grows There :: Hugh Conlon, Horticulturalist, Garden Advisor, and Photographer

Downtown Street Trees With A Narrow Vertical Form

Posted by Hugh on December 6th, 2019

On the subject of land, Mark Twain wrote: “they’re not making any more of it”. This is particularly true in downtown urban areas where land to grow trees is usually very limited. Here are five tall trees that possess a striking vertical accent. Their upright branch habit does not take up much horizontal space. Trees are superb planting choices along wide avenues or boulevards. All five species adapt to the urban environment. They’re also fit into downtown pocket parks and small residential sites where there are no height restrictions like overhead utility lines.

During the first two years following planting, trees should be irrigated during dry spells (or every 2-3 weeks) from spring through late summer. All five picks are hardy in USDA hardiness zones 5-9.

‘Slender Silhouette’ Sweetgum (Liquidambar styraciflua ‘Slender Silhouette’) (USDA 5-9) is a narrow 35 to 50 feet tree that spreads only 8 feet wide. ‘Slender Silhouette’ produces very few nuisance gumball fruits so typical for other sweetgums. In some years, the yellow to red fall color is exceptionally nice. Bark develops deep furrows as the tree ages.

‘Beacon’ Swamp White Oak (Quercus bicolor Beacon) deserves more recognition. ‘Beacon’ is a tightly columnar upright branching, adapts to city environs, and mostly disease-free foliage. Fall color is yellow and persists for 2 to 4 weeks. Its mature height is 30 to 40 feet and 12 to 15 feet wide. Yes, this oak does produce acorns which can be a messy problem every 3 or 4 years unless picked up curbside.

‘Princeton Sentry’ Ginkgo (Ginkgo biloba ‘Princeton Sentry’) is a deciduous conifer (a true gymnosperm) that grows to 30-50 feet in height, although a rare mature 100 feet tree is possible after a century or more. Ginkgo’s two-lobed, triangular or fan-shaped green summer leaves are distinctive. It is a male (fruitless) variety. Fall foliage turns bright yellow and neatly fall to the ground to form a golden carpet around the tree.

‘Arnold’ tulip poplar (Liriodendron tulipifera ‘Arnold’) is a fastigiate grower to 50-60 feet tall and only 8 to 10 feet wide. Unusual light green and orange tulip-like flowers appear in late spring, most blooms hidden beneath the tree’s dense foliage. Fruits (seed pods) offer no value ornamentally. Its furrowed gray bark offers significant winter appeal.

Upright European hornbeam (Carpinus betulus ‘Fastigiata) displays a narrow, columnar form, especially when the tree is young. The tree’s middle (girth) gradually broadens into a tear drop or oval-vase shape with age. Mature tree size is 35 – 40 feet tall and 25 – 30 feet wide. Another hornbeam variety, ‘Frans Fontaine’ (40 ft. x 20 ft.), is also suitable for confined areas.

Space-Saving Vertical Shrubs

Posted by Hugh on December 1st, 2019

Try these slim and sleek varieties in a small space such as on patios or the front porch, in courtyards, or as a single specimens in narrow gardens or containers. Set them at the back of beds for space-saving walls and backdrops. Pot them up for container magic on the porch. All six plants grow best in full sun to part shade and well-drained soil. Shrubs requires little to no special care including pruning.

‘Sky Pencil’ holly flat-topped at High Point University

Landscape Uses: single specimen, allée, tall hedge, medium hedge, foundation plant, holiday foliage, containers. Choose any of the following:

‘Helmond Pillar’ Barberry (Berberis thunbergii ‘Helmond Pillar’) – deciduous shrub with a tight upright, columnar habit; features reddish-purple leaves (0.5 to 1.25 inches long) on spiny reddish brown stems. Mature size: 4-5 feet tall and 1-2 feet wide; highly drought tolerant and deer resistant. Alternative: ‘Sunjoy™ Golden Pillar’ Barberry– orange-red new foliage becomes bright gold in summer and orange-red in fall. Mature Size: 4 feet tall x 2 feet wide. USDA Hardiness zones: 4-9.
Roman Candle™ Podocarpus (Podocarpus macrophyllus ‘Miu’) – lovely Southern evergreen shrub with heat tolerant variegated creamy-white and green foliage; in a container, Roman Candle grows about 20 inches tall and 8 inches wide and is deer proof. Mature Size: 10-15 feet tall x 4-6 feet wide. Hardiness zones: 7b-10.
‘Sky Pencil’ Holly (Ilex crenata‘Sky Pencil’) – narrow, dense, multi-branched, columnar evergreen shrub with a rounded form. Mature Size: 5-10 feet tall and 1-2 feet wide. Hardiness zones: 6-8.
‘Dee Runk’ Boxwood (Buxus sempervirens ‘Dee Runk’) -broad-leafed evergreen with a very narrow, upright, pyramidal habit; oval, 1 inch long dark-green leaves. Mature Size: 10-12 feet high and 2-3 feet wide. Hardiness zones: 6-8.
October Magic® camellia – fits the tight garden spaces; deep green glossy foliage year-round along with pure white flowers. Mature Size: 4–5 feet high x 3–4 feet wide. Hardiness zones: 7 to 9.
‘Blue Point’ Juniper – maintains a dense, pyramidal form; prized for its lush blue-green foliage, looks good in formal garden landscape setting. Mature Size: 15 feet high x 3–5 feet wide. Hardiness zones: 4 to 9.

Uniquely Different Red Dragon™ Contorted Filbert

Posted by Hugh on November 26th, 2019

Uniquely Different ‘Red Dragon’ Contorted Filbert

‘Red Dragon’ filbert in Columbus, Ohio garden

European filbert or hazelnut (Corylus avellana) is native to Europe, western Asia and northern Africa where it is often found growing in thickets and hedgerows. Red Dragon™ filbert is an outstanding red leaf selection of contorted filbert (C. avellana Red Dragon™). This unique landscape shrub grows 6 – 8 feet tall and 5 – 6 feet wide. It is a good addition to urban gardens (USDA hardiness zones 4-8).

This red–leaf shrub was developed by the Oregon State University filbert breeding program. Currently, gardeners are losing the popular green leaf variety C. avellana ‘Contorta’, aka “Harry Lauder’s Walking Stick’ to Eastern filbert blight. Red Dragon filbert demonstrates superior resistance to the disease. Red Dragon also replaces ‘Red Majestic’, another red leaf variety that is also vulnerable to Eastern filbert blight.

Contorted filbert grows best in moist, organically rich, well-drained soil and in full sun to partial shade. It tolerates average garden soils. Prompt removal of root suckers improves plant appearance, avoiding a messy buildup or thicket.

Autumn leaf drop exposes its contorted branches and ornate floral catkins in early days of spring. Filberts are monoecious, e.g. individual male and female catkins (flowers) develop on the same plant bloom in the early days of spring (March-April) before leaves emerge. The 2-3 inch long yellow male catkins (flowers) stand out. The 4-inch elliptical or ovate leaves have doubly serrate leaf margins.

Red Dragon filbert retains its burgundy red leaf color until early summer and turn dark green. The foliage is also partly curled. Leaves are coated with tiny hairs and appear dusty by the end of summer. Fall leaf color is variable, often with yellow shades. Smooth light bark is gray-brown.

Nuts appear in terminal clusters of 1-4 and are half covered in ragged husks. Nuts ripen in late August and September that the neighborhood squirrels and birds should enjoy.

Red Dragon filbert may also be grown in containers. Disease and pest problems are few. Japanese beetles may rigorously attack the foliage in some areas of the U.S. Scale may also occur.

‘Red Dragon’ is grafted cultivar and is sold by e-commerce nurseries online. Red Dragon filbert requires little or no pruning; removed all root suckers and keep the shrub well mulched. ‘Red Dragon’ is sold either grafted or not. It is through e-commerce nurseries online.

Trees That Age Gracefully

Posted by Hugh on November 21st, 2019

Trees transition from youth (seedling), middle age and old age (maturity) before requiring a chain saw and replacing. Some age gracefully, actually appreciating in $$ value. Many ginkgo, hickory, beeches, sugar maples, and Southern magnolias live 100 years plus. Oaks such as such as white (Q. alba) and live oak (Q. virginiana) mature in majesty over several hundred years.

It’s not hard to determine why some of these trees live more than one hundred years. Pedigree, heredity, germplasm, or whatever term you use to describe tree genetics is the key factor. Planting location, water and sunlight requirements, soil fertility, plant nutrition, and biological factors such as damaging diseases and insects, animal foraging, and air pollutants) are all key secondary determinants.

Location also refers to places where humans and trees interact. Examples: 1. Tree in an urban park setting should live and prosper longer versus one in a parking lot; 2. Tree planted along a busy avenue compared to one growing an asphalt desert (parking lot); 3. Tree in a National forest versus one growing in a Georgia swamp.

In urban areas tree longevity is generally alot shorter due to the hostile environment of a parking lot. Large trees find life difficult growing under utility lines and power poles. The important message here is to think before you plant.

Here is a short list of trees with long life maturities:

Paperbark maple (Acer griseum)

Full Moon maple (Acer japonicum ‘Aconitifolium’)

Japanese maple (Acer palmatum) – hundreds of beautiful cultivars

Sugar maple (Acer saccharum)

Manchu striped maple (Acer tegmentosum)

Three flowered maple (Acer triflorum)

American hornbeam (Carpinus caroliniana)

European hornbeam (Carpinus betulus)

Assorted hickory species (Carya spp.)

Atlas cedar (Cedrus atlantica)

Katsura tree (Cercidophyllum japonicum)

Alaska cedar (Chamaecyparis nootkatensis)

Chinese dogwood (Cornus kousa)

American beech (Fagus grandifolia)

European beech (Fagus sylvatica)

Ginkgo, Maidenhair tree (Ginkgo biloba)

Red Cedar (Juniperus virginiana)

Southern magnolia (Magnolia grandiflorum)

Dawn redwood (Metasequoia glyptostroboides)

Black gum, Tupelo tree (Nyssa sylvatica)

Persian ironwood (Parrotia persica)

Lacebark pine (Pinus bungeana)

American sycamore (Platanus occidentalis)

Douglas fir tree (Pseudotsuga menziesii)

Assorted oak species (Quercus spp.)

Redwood (Sequoia sempervirens)

Giant sequoia (Sequoia gigantean)

Bald cypress (Taxodium distichum)

American linden, Basswood (Tilia americana)

Assorted elms (Ulmus spp.)

American hornbeam (*Carpinus carolinana*)

Anise (Illicium) Shrubs Coming To Mid-South Gardens

Posted by Hugh on November 16th, 2019

Illicium x ‘Woodland Ruby’ at Biltmore Estates, Asheville, NC

There is lots of interest in this shrub group. Anise shrubs (Illicium spp.) are fast growing, evergreen shrubs (USDA zones 7 to 10). They exhibit a multi-stemmed, upright, compact growth habit. The green foliage of Florida anise (I. floridanum) is quite attractive and aromatic, smelling similar to anise spice when crushed. Their shiny, leathery leaves are olive green in color and the 1.5 inch wide dark red flowers appear in early spring.

In general, I. floridanum shrubs grow 10 to 15 feet tall and should be spaced at least 5 to 6 feet apart in the landscape. From Florida to Louisiana, its natural habitats are in wet, swampy areas or along wooded streams in humus-rich acidic soil. Some varieties have demonstrated winter hardiness further north into parts of Tennessee, N. & S. Carolina, and Virginia.

Illicium grows in partial to full shade, but reportedly can acclimate to full sun if irrigated. It prefers moist soil and kept properly mulched and watered during prolonged dry spells. Several cultivars are available including ‘Alba’ with white flowers and ‘Shady Lady,’ a variegated leaf form. Illicium ‘Woodland Ruby’ is an interspecific hybrid between I. floridanum ‘Alba’ and I. mexicanum, and produces showy blooms in spring and fall.

Yellow anise (I. parvifolium), aka small anise, is another Southeast U.S. native. In recent years its popularity has soared with the introduction of new gold leaf cultivars like ‘Florida Sunshine’ and Banana Appeal®. It is more tolerant of full sun and dry soils than other species.

The anise that is used as a spice is derived from a different species, Star Anise (Illicium verum), an evergreen found in southern China and Vietnam.

At the J C Raulston Arboretum in Raleigh, NC are 19 different accessions in its collection, including seven cultivars of Illicium floridanum.
All plant parts of Yellow Anise and Florida Anise are toxic.

New ‘Chastity’ Ornamental Pear

Posted by Hugh on November 11th, 2019

Chastity ™ ornamental pear (Photo by Dr. Tom Ranney)

Before you totally give up on ornamental pear trees (Pyrus calleryana) as invasive, a decision that I would never argue against, take a look at the new Chastity pear. NEW! NEW! NEW! on the market is Chastity pear, a triploid hybrid that is both very ornamental and highly infertile (USDA hardiness zones 5-9).

Chastity™ Pear was specifically bred by Dr. Tom Ranney of North Carolina State University. This hardy small tree is covered with white blossoms in early spring. Chastity pear grows to 35 feet tall and 25 feet wide. Fall leaf color is a vibrant orange to red. It is also highly resistant to fire blight.

First, a little background. The U.S. Department of Agriculture (USDA) had introduced the callery pear cultivar ‘Bradford’ (in 1960). USDA stated that it is incapable of producing viable fruit (“self-incompatible”) which later proved to be untrue. The introduction of other USDA cultivars – ‘Whitehouse’, ‘Capitol’, ‘Redspire’ and ‘Chanticleer’ permitted cross pollination among the different varieties that resulted in fertile seed being produced, and results in its invasive traits.

On the good side all hybrid ornamental pears make reliable landscape trees. Trees withstands some tough environment conditions. Trees survive on poor infertile landscape sites as long as the soils are well-drained. Most varieties are short-lived, 15-25 years.

Other than invasiveness, the fruits can stains sidewalks and wood while attracting birds that further stain everything else (while spreading seed). Why is it 99.14% sterile? Researchers at North Carolina State University (NCSU) created a triploid (Callery pear is typically diploid) that is almost completely incapable of producing fertile fruit, and this trait (sterility) bred into Chastity pear is genetically stable. Thus, the new cultivar is unlikely to revert in the future.

Questions regarding branching strength of Chastity pear is not known at this time.

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Short Forms Of Cryptomerias

Posted by Hugh on November 6th, 2019

Japanese cedar, aka Sugi or Cryptomeria, (Cryptomeria japonica) is the national tree of Japan and also flourishes in China (USDA hardiness zones 5 to 8). It is one of the most variable conifers ranging from very dwarf rounded shrubs to large tree forms with golden or contorted leaves. It tolerates hot humid summers and prefers deep, moist, rich, acidic to neutral soil in full sun.

Handsome specimen of Cryptomeria ‘Elegans Nana’

Cryptomerias is utilized as a fast growing privacy screen in many areas of the U.S. (USDA hardiness zones 5-8). The cultivar ‘Yoshino’ is highly popular, but in many landscapes, it grows way too tall @ 30-40 feet (15-20 feet wide). Shorter tree and shrub cultivars are better choices for small to medium-sized gardens (see list below). Gold needle cultivars are available but not listed here.

Cryptomerias grow straight trunks with smaller sturdy lateral branches attached. The orange red bark peels away in vertical strips. Older trees are often limbed up to display their attractive bark. The short needles often develops a purple-bronze color in climatic zones where winters are more harsh. However, needles rapidly green-up in spring.

Cryptomerias are rarely troubled by pest and disease problems. Infrequently, a fungal blight and canker may cause needle browning on scattered branches. Prune out dead, broken, or discolored foliage when observed and remove clippings from the property.

This reliable evergreen is wind tolerant, even standing up to strong storms. Needles are also salt tolerant. Upright branches stand up well to snow loads. Cryptomerias make reliable privacy screens or windbreaks.

Intermediate And Dwarf Forms:

‘Black Dragon’ –medium height @ 10-12 feet high x 6 feet wide; deep green needle-like leaves.
‘Gyokuryu’ – compact upright pyramid habit @ 10-15 feet high; dark green foliage with only slight winter bronzing.
‘Globosa Nana’ – compact shrub form 2 to 3 feet high and wide, almost ball shaped.
‘Elegans Nana’ – globose compact form to 5-6 feet high.
‘Tansu’ – 2 x 3 feet dense compact form with rich green foliage.

There Is Nothing “Minor” About These Bulbs

Posted by Hugh on November 1st, 2019

Winter aconite (Eranthus)

Companion bulbs, often called “minor bulbs”, are early signs that spring is coming. Three of the most reliable are snowdrops, winter aconites and Glory of the snow. They bloom before crocus in winter.

Winter aconite (Eranthis hyemalis) returns with floral beauty less than three months after planting. Plants poke through the ground, grow and flower 3 to 6 inches high and wide. Bright yellow cup-shaped flowers appear in mid- to late winter. Green leaves emerge as the flowers begin to fade. All evidence of their presence has disappeared by late spring, and the bulbs have gone dormant.

Pure white, nodding, bell-like snowdrops (Galanthus nivalis) often peak through the winter snow in February. Leafless 3-4 inch stems support individual flowers. Plants grow only 4-6 inches high with 2-3 strap-like leaves.

Glory-of-the-Snow (Chionodoxa forbesii) is so-named because, in northerly areas, their bright blue six-petalled flowers poke up through the snow in the winter. Bulbs and seeds often spread very aggressively.

Bulbs are planted 3-4 inches apart and 2-4 inches deep in the fall. Sow in large numbers for maximum flowering impact under trees and shrub and in perennial beds. They should receive full day winter sunlight. All three companion bulbs are critter proof, not bothered by deer and voles. All are hardy in USDA hardiness zones 3–7. They often naturalize and the planting can last a lifetime.

All companion bulbs prefer compost-rich soil that is well-drained and moderately moist. Before planting pre-soak the bulbs overnight to hasten germination.

Snowdrops, winter aconites, and Glory of the snow are native to southern and eastern Europe.

Marcescence (Retaining Leaves Fall And Winter)

Posted by Hugh on October 31st, 2019

Through the fall and winter seasons, certain landscape and woodland trees retain their dead brown leaves on branches. Beech (Fagus spp.) and oak (Quercus spp.) are two common examples. Winter winds and precipitation will eventually force leaves to drop. Plant scientists term the retention of leaves as “marcescence”. There are many theories as to why this phenomena occurs.

Beech (*Fagus grandifolia*) hedge at NC Arboretum in Asheville, NC

True, most deciduous landscape trees shed their leaves in autumn. Cellular, physiological, and environmental changes are key factors. Growth regulator changes occur at the leaf abscission layer (the base of the leaf stalk or petiole. This process results in falling leaves. However, some hardwood trees retain their leaves throughout most of the winter season. For some gardeners, leaf retention is wonderful, but a few dislike having to rake leaves in the fall and again in early spring.

One is the first trees to evolve on planet Earth were evergreens such as (pines (Pinus), spruces (Picea), hemlocks (Tsuga), and firs (Abies). Other deciduous conifers such as bald cypress (Taxodium), dawn redwood (Metasequoia), and ginkgo (Ginkgo) soon followed. These trees encountered thousands of years of changing environmental and growing conditions. Next on the ecological chart were the broad-leafed hardwood trees which developed new ways of shedding their leaves. Short-lived trees like birch (Betula), maple (Acer), cherry (Prunus), and aspen (Populus) came next.

Beeches (Fagus) and oaks (Quercus) seemed to find a middle ground between evergreen and deciduous. Their leaves died, but did not drop in the fall. Evergreen and marcescent species increased their photosynthetic time and reduced nutrient losses by holding their leaves.

Young or newly planted trees often hold their leaves later into autumn. Once they become established in 1-3 years, leaf drop occurs at normal times, usually 3-4 weeks earlier. Marcescent foliage is also considered a deterrent to twig browsing by large four legged herbivores like deer and moose.

Lots Of Choices In European Hornbeams

Posted by Hugh on October 26th, 2019

European hornbeam

European hornbeam (Carpinus betulus),, aka ironwood and musclewood, is an underused tree in the U.S. It makes an excellent urban street and park tree. It develops a full, dense canopy and has very few maintenance requirements (USDA hardiness 4-7).

European hornbeams are planted across Europe for their formal upright form as street trees, privacy screens, and windbreaks. Seedling trees typically measure 40-60 feet high with a pyramidal to broad rounded canopy. Several cultivars are available, but some (like weeping and dwarf forms) may be difficult to purchase in U.S. nursery commerce.

Its dense summer foliage is medium green, leaves up to 4 inches in length, and exhibit little susceptibility to disease and insect problems. Flowers (catkins) are visible in early spring before the foliage emerges. Male catkins are yellowish and female catkins are greenish. Fruits are small nutlets in 3-lobed bracts that appear in late summer.

Hornbeams adapt to a wide range of soils and grow best in full sun. Trees tolerate hot and dry conditions once established in the landscape, but prosper in cool well mulched ground. Trees tolerate occasional wetness and slightly alkaline soil pH. Annual feeding of young trees with a slow-release fertilizer is highly recommended.

Dense, compact and narrow when young, they develop a wide oval crown with maturity. Long, thick, dark green foliage with prominent veining finish a pleasing yellow-orange in autumn. Trunks have smooth gray bark and distinctive muscular fluted bark.

Hornbeams are an excellent choice for hedging and windbreaks, particularly upright growing forms. Trees are mostly free of disease and pest issues. Powdery mildew may occur after a wet summer and Japanese beetles may sometimes chew on summer foliage. Little or no pruning is generally needed.

Found on the streets of U.S. cities are three upright branched European hornbeam cultivars: ‘Fastigiata’, ‘Columnaris’, and ‘Frans Fontaine’. Refer to other blogs for cultivar descriptions.