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

Pyramidal Forms Of Cryptomeria

Posted by Hugh on November 19th, 2013

Japanese Cedar (Cryptomeria)

Needle foliage of cryptomeria

Cryptomeria, aka Japanese cedar, (Cryptomeria japonica) is an evergreen conifer native to China and Japan. It rated to be very long-lived (USDA hardiness zones 6 to 10). Some cultivars may be hardy in 5-b as well.

There are many forms of cryptomerias, ranging from dwarf globe-shaped shrubs to narrow pyramidal trees. Needle foliage may be green or golden sometimes contorted. Heights vary from 6 to 80 feet in height and 3 to 20 feet in width. All thrive in open full sun and good air circulation; they prefer an average moist well-drained acidic to neutral pH soil.

Pyramidal forms develop into beautiful evergreen privacy screens or hedges. Two to three year old established cryptomerias are superior to Leyland Cypress (x Cupressocyparis leylandii) in blizzard-proned and high wind areas. Young plants should be trained to a single leader. Cryptomerias suffer from few disease and pest problems. Prune off any discolored foliage as fungal blights cause inner foliage browning.

Five most popular pyramidal forms:
‘Yoshino’ is far and away the most popular cultivar, with a rapid growth rate (40 to 50 feet tall, 1/2 that in width) and bright green summer foliage; in zone 7 and areas north, typically foliage takes on a bronze winter tinge.

‘Ben Franklin’ grows slightly slower, more compact and darker green foliage than Yoshino. Similar height and width as Yoshino.

‘Radicans’ exhibits an upright, pyramidal form to 20 to 30 feet tall and 7 to 10 ft. wide in 12-15 years; popular choice in zone 7 gardens for its dark green non-bronzing foliage.

‘Black Dragon’ is 10 by 10 feet slow grower with dark green foliage.

‘Gyokuryu’ is “the Yoshino for small gardens” with a dense pyramidal form and dark green non-bronzing foliage; grows 5 to 6 feet in 10 years (10 to 15 feet in maybe 20 years).

Renewal Pruning Is An Easy Technique To Learn

Posted by Hugh on November 16th, 2013

Healthy Rhododendron Is Easy To Coppice

Renewal pruning is the practice of severely cutting back selected shrubs and trees. The task is simple. There are no books to read. Select a day from mid-February to early April (USDA hardiness zones 5-7). Cutback the entire shrub(s), leaving 3-5 inch tall cut stems or stubble. The cut stems will bud out in the spring along with adventitious buds below the soil line.

Renewal pruning can eliminate weather-damaged, diseased, and insect-riddled wood, particularly scale insects, without resorting to heavy pesticide use. All diseased and pest-ridden prunings should be removed from the property or burned. Healthy pruning wood can be ground up for mulch that is spread after 6 months or more composting.

Renewal pruning invigorates old shrubs, brightens foliage color, and increases fruit size and quality. Pruning tools needed: hand clippers, loppers, hand pruning saw, or chain saw. Do not use string trimmers (“weed-eaters”).

Renewal pruning may not the ideal practice for all shrubs.
• Summer flowering shrubs often recover and bloom the same year. Some spring flowering shrubs may not re-bloom for 1-2 years.
• Overgrown rhododendrons, hollies, pieris and mountain laurels respond better to a practice called “coppicing” in late September or early October in USDA hardiness zones 5-7.
• Plant health must be good. Weak, sickly shrubs may likely die when drastically cutback.
• Shrubs must be well-established for 3 to 4 years before renewal cutback.
• Don’t cutback grafted or budded plants in fear of losing the cultivar (above-ground portion) The root system may gain dominance.

Partial list of shrubs which respond to renewal pruning:

Glossy abelia (Abelia x grandifolia)
Butterfly bush (Buddleia davidii)
Beautyberry (Callicarpa spp.)
Blue mist shrub (Caryopteris x clandonensis)
Smoke tree (Cotinus coggygria)
Forsythia (Forsythia spp.)
Fothergilla (Fothergilla spp.)
Rose of Sharon (Hibiscus syriacus)
Smooth hydrangea (Hydrangea arborescens)
Pee Gee hydrangea (Hydrangea paniculata ‘Grandifolia’)
Oakleaf hydrangea (Hydrangea quercifolia)
Crape myrtle (Lagerstroemia indica x L. faurei)
Trumpet honeysuckle (Lonicera sempervirens)
Firethorn (Pyracantha spp.)
Sumac (Rhus spp.)
Rugosa rose (Rosa rugosa)
Pussy willow (Salix spp.)
Corkscrew willow (Salix matsudana)
Elderberry (Sambucus canadensis)
‘Hancock’ coralberry (Symphoricarpus orbiculatus ‘Hancock’)
Chaste tree (Vitex agnus-castus)
Weigela (Weigela florida)

Staghorn Sumac’s Reliable Fall-Winter Assets

Posted by Hugh on November 12th, 2013

Sumac Growing Along Roadside in Tennessee

Staghorn sumac (Rhus typhina) is known by several names, including velvet sumac and hairy sumac. This large shrub or small tree is native to northeastern U.S. and eastern Canada (USDA hardiness zones 3-8). Staghorn sumac often arrives uninvited into a landscape and its aggressive suckering root system makes it difficult to eradicate. For landscape use it should be limited to large properties with space for it to spread naturally.

Staghorn sumacs are noted their greenish yellow flowers in early summer and persistent red fruit clusters (drupes) in the fall and winter months. Its excellent scarlet red fall foliage color rarely disappoints. Plant in full sun for best color, but will cope in any light. Bright green pinnate leaves and reddish-brown fuzzy stems make sumacs easy to id along any road at high speeds. Male and female flowers occur on separate plants (dioecious).

Staghorn sumac grows 15 to 25 feet high and 15-20 feet wide. A pinnately compound leaf may be up to 24 inches long, comprised of 13 to 27 long narrow leaflets. Leaflets are bright green with serrated margins and glossy underside. The deep red hairy drupe fruits attract many kinds of winter feeding birds and other wildlife.

In winter young leafless stems appear club-like, covered with a dusty pubescence. As branches and trunks age, they shed their pubescence and become smooth and shiny. Prominent C-shaped leaf scars are characteristic over the winter branches, each containing an orange bud in the middle.

Rabbits and deer leave sumacs alone. Established plants are heat and drought and prosper in air-polluted urban environments and shallow rocky soil. Untended plants colonize to form a thicket from underground root suckers and seed dispersal. Roots mat in for erosion control. Disease and pest problems rarely happen when planted in open areas.

China Fir Deserves A Look

Posted by Hugh on November 9th, 2013

China Fir at Knoxville Botanical Gardens in TN

To begin, China fir (Cunninghamia lanceolata) is not a true fir (genus: Abies). Branches are broadly pyramidal when young, and open up to become slightly pendulous as the tree ages. China fir grows broad at the base and spire-like on top. The tree often grows multi-stemmed to 75 feet in height and 20 to 30 feet in width (USDA hardiness zones 6b-9).

Both male and female flowers of China fir form on the tips of branches. Clusters of several tiny male flowers and individual greenish-yellow female flowers open in May. The 1 ½ inch diameter brown round cones mature on the end of twigs. As the tree ages the brown bark exfoliates in strips to reveal a reddish-brown inner bark.

China fir grows best in moist, acidic, well-drained soil. Plant in full sun, but China fir will tolerate partial shade (minimum 6-hours sunlight). China fir performs best when cozied up among other trees to afford it summery shade and protection from wintry winds. Lower branches tend to lose out as tree ages. Following a severe winter some branches may dieback and should be pruned out. Otherwise, this conifer has few disease and pest issues.

Its long 2 ½- to 3-inch green to blue-green shiny needles offer a lush look. The sharp-pointed needles are spirally arranged and slightly twisted at the base. The winter foliage takes on bronze color during the winter in the Southern Appalachian region (USDA hardiness zones 6 and 7).

Several blue needle forms are now available, most from seedling sources and designated ‘Glauca’. Hardier forms have been rated to –10 to -15° F. Its light-colored soft fragrant wood is treasured in China.

Three New Spreading Junipers Waking Up Landscapes

Posted by Hugh on November 9th, 2013

'Daub's Frosted' Juniper at UT Gardens in Knoxville

In times past Chinese junipers (Juniperus chinensis) were popular foundation shrubs and ground cover (USDA hardiness zones 4-9). They were popular choices in sunny locations for erosion control and around seashore areas. Three exciting cultivars have arrived on the landscape scene and should bring junipers back in vogue.

Angelica Blue Chinese juniper (J. chinensis ‘Angelica Blue’) grows 5 to 6 feet high and 6 to 7 feet wide with bright blue-green needles. Introduced by Angelica Nurseries, it exhibits a compact horizontal form.

Daub’s Frosted Chinese juniper (J. chinensis ‘Daub’s Frosted’) has a low ground-hugging habit that grows 1 to 2 feet high and 3 to 6 feet wide. It struts bluish green foliage frosted with new yellow tip growth in the spring.

Gold Lace Chinese juniper (J. chinensis ‘Gold Lace’) grows 4 feet high and 5 feet wide with vibrant gold foliage.

In general, junipers grow in average well-drained soils with moderate moisture. Junipers are best planted in full open sunlight where air movement should reduce the threat of a disease outbreaks. Shady areas and wet soils are not where junipers belong. Pruning may be needed to maintain the height and spread of many vigorous cultivars.

Following a short one year establishment span, the new junipers listed above tolerate shallow dry soils and resist coastal salt and urban air pollutants. Juniper fruits may look like berries, but are actually small scaly cones.

Junipers suffer from no serious disease or pest problems. Avoid juniper tip and needle blights by selecting resistant cultivars and following proper irrigation practices. Occasional insect pests include aphids, bagworms, webworms, and scale. Deer have no taste for junipers.

Kentucky Coffee A Superior Large Native Tree

Posted by Hugh on November 4th, 2013

K Coffee Tree at Kingwood Center

Platy Bark of K-Coffee Tree

Kentucky coffeetree (Gymnocladus dioicus) is a large native tree found in 18 states, from New York west to Nebraska and from central Minnesota south to Oklahoma (zones 4 through 7). It reaches a mature height of 70 feet (some greater than 90 feet) with a spread of 50 feet. Established in 2-3 years, annual growth rate averages 12-15 inches, about the same as ginkgo or white oak.

Late appearing foliage emerges in mid- to late spring. Recessed vegetative buds push forth multi-pinnate compound leaves. A single leaf can be 2 to 3 feet long, producing between 70 and 100 leaflets. Fragrant olive-white flower panicles appear in late May in clusters of 8 to 12 inches long by 3 to 4 inches wide.

In autumn its lime-yellow to golden brown compound foliage falls to become a leaf raker’s nightmare. During the winter months, the totally naked upright branches take on the appearance of an arboreal horror from a Stephen King novel. K-coffeetree may be single or multi-trunked.

K-coffeetree grows in a wide variety of soil types and is tolerant of poorly drained (wet sites). No significant disease or insect pests mar the lush green tropical-like summer foliage. Bark is distinctively charcoal gray and shaggy, a trait more pronounced as the tree ages.

Spring pea-like flowers are dioecious, bearing either male or female flowers. Female trees bear clusters of distinctive bean pods measuring 5 to 10 inches long and 1 ½ to 2 inches wide on the tips of the branches. Flowers and pods are inconspicuous, mostly hidden within the dense foliage through late summer.

‘Espresso’ is a male cultivar with no seed pods to rake up. In colonial America the beans were harvested and a crude coffee extract was brewed, no threat to Folgers® and Maxwell House® today. The leaves and bean seeds are reportedly toxic to man and grazing cattle.

K-coffeetree is rarely sold in garden centers, but available on-line. It is notoriously difficult to transplant, but young 2-inch caliper nursery-grown trees thrive.

Burning Bush Turns Fire Engine Red In The Fall

Posted by Hugh on November 1st, 2013

Clipped hedge of Euonymus alata 'Compactus'

Be cautioned from the start that planting dwarf burning bush (Euonymus alata var. compactus) in some states in the U.S. is prohibited. This deciduous shrub is known for its awesome fire engine red fall foliage color (USDA hardiness zones 4 to 8). In shady areas fall leaf color tends to be more pinkish. Fall leaf color is spectacular most years, hence the common name “burning bush”.

This popular shrub grows in average well-drained soil and in full sun to part shade. ‘Compactus’ is not very compact, actually a vigorous grower. It tolerates heavy pruning, including tight hedging. If left unchecked, a single shrub grows mound-like, 10 feet tall and equal or greater in spread.

Small yellowish-green flowers appear in May but most are hidden within the dense foliage. Small red fruit capsules, less than ½ inch in diameter, appear in fall and most are not visible against the crimson red foliage.

Corky ridges (called ‘wings”) line the bark, a simple way to identify this shrub in the winter. The wings or ridges are not prominent on ‘Compactus’ and almost non-existent on very dwarf forms. Dwarf cultivars ‘Rudy Haag’ and Little Moses® may grow 3-4 feet tall and 4-5 feet wide in 15-20 years. Flowers of the latter two cultivars produce few, if any, viable seeds and are less of an invasive threat.

This utility shrub has few serious insect or disease problems. Occasionally, it becomes infested with dreaded euonymus scale, which is managed by applying dormant and summer oils (organic option) or any of several contact insecticides.

Dwarf burning bush is utilized as a single specimen or grouped together as hedges, privacy screens, or foundation shrubs.

Invite These “Bells” To Next Spring’s Garden Ball

Posted by Hugh on October 30th, 2013

Spanish Bluebells and Microbiota in Conlon Garden

Fall planting of many kinds of bulbs is a worthwhile long term investment of your time. Many bulbs (and corms) like daffodils and crocuses will naturalize where you plant them. They also bloom for long periods from late winter into spring. Bulbs bloom nice their first spring; flower heavier the second year; and multiply each succeeding year.

Two bulbs that are underplanted are Spanish bluebells (Hyacinthoides hispanica) and summer snowflakes (Leucojum aestivum). They naturalize and thrive in compost rich moist soil. In zone 6 and further north, sow them in full sun; plant them where they receive afternoon shade in the hot Southeastern U.S.

Spanish bluebells (USDA hardiness zones 4 through 10) bloom in the late spring in full sun or partial shade. Their dainty bluebell flowers are supported on sturdy stems and are excellent as cut flowers. The cultivar ‘Excelsior’ is a rich darker blue than other cultivars, and stand slightly higher to 12 inches.

According to Becky Heath, co-owner of Brent and Becky’s Bulbs in Gloucester, VA, the popularity of summer snowflakes (USDA zones 4-8) have increased over the past 20 years. ‘Gravetye Giant’ is one of her favorites; they are exceptionally vigorous and naturalize rapidly. Their white lily of the valley blooms are large and showy in April / May garden. Plants grow 2 feet or more in full sun or part shade. The fragrant nodding white bells are tipped with light green dots.

Willow Oak Very Reliable As Street Or Park Tree

Posted by Hugh on October 28th, 2013

Willow Oak in TN parking lot

Mid-autumn foliage of willow oak

Willow oak (Quercus phellos) is medium to large, deciduous tree, part of the red oak group. It is noted for willow-like oak foliage and growth rate after a 2 year establishment period is moderate (USDA hardiness zones 5-9).

Willow oak grows 50-75 feet tall and 30-35 feet wide with a rounded top or canopy. Young trees tend to be pyramidal in form. Individual specimens may reach 90 or more feet under ideal site conditions. Its small ¼ – ½ inch nearly round acorns form almost every year, are not a major maintenance headache, and serve as an important food resource for wildlife.

Long stringy yellow-green long catkin flowers appear in April, a few days before leaves emerge. The unlobed 5-inch long leaves mimic those of willow trees (Salix spp.); leaves are tipped with a single 1-inch wide bristle. Green summer leaf color turns an undistinguished yellow-brown or dull gold very late in autumn. A young tree has a smooth grayish bark which darkens and becomes furrowed with age. From the latin word “phellos”, the species name means cork — because bark on older trees tends to be hard and corky.

Native to the Southeastern United States, willow oak prefers a moist bottomland, organically-rich, and well-drained soil. It tolerates light shade, but performs best in full sun. Willow oak can handle a wide range of soils including clay. Once established, it copes with summer drought well. Foliage is tolerant of urban air pollution.

Willow oak demonstrates good disease and pest resistance and is a long-lived and low-maintenance tree. In a landscape willow oak fits into large sites, such as in public parks or along wide roadways and avenues with good soil mass for adequate moisture. The narrow leathery leaves abscise very late in the fall and make a great loose mulch scattered under other landscape plants.

Better Red Fall Leaf Color On American Hornbeam

Posted by Hugh on October 21st, 2013

Firespire™ Hornbeam from Johnson Nursery, Menomonee Falls, Wisc

Fall Leaf Color of Firespire™ American hornbeam

American hornbeam (Carpinus caroliniana), aka ironwood or muscle wood, grows primarily in moist, slightly acidic soils along woodland rivers and streams (USDA hardiness zones 3-9). This native hornbeam adapts to either wet or dry ground as long as soil moisture drains adequately. It copes with tough urban conditions including on non-irrigated parking lots and on the outer edge of rain gardens. It grows equally well in full sun or partial shade.

Its autumn foliage turns intense shades of yellow, orange, and rarely scarlet, depending on soil pH and the provenance of the species. Over the past quarter century Johnson Nursery (primarily wholesale and retail locally) in Menomonee Falls, Wisconsin have selected several good fall red foliage forms. Firespire™ is a grafted clone with semi-upright branching and vibrant red fall color. ‘J N Strain’ is a known seed population which delivers above average red fall leaf color.

Ironwood blooms in spring as separate male and female catkins. In autumn female catkins form showy clusters of winged nutlets, that is an important food resource to numerous forest fauna. Its beech-like muscular bark covers the main trunk and branches as a singular trait in the winter garden.

American hornbeam grows 25-40 feet tall and variable in width depending on cultivar. It commonly grows multi-stemmed and is free of disease and pest problems. The rich green summer and colorful autumn foliage plus attractive gray muscular winter bark makes it an excellent small patio tree. Or mass several together to create a deciduous privacy screen.

American hornbeam is more difficult to transplant than its taller European counterpart (C. betulus).