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

Redbuds With Awesome Summer Foliage

Posted by Hugh on March 16th, 2020

**The Rising Sun™** redbud at The University of Tennessee Gardens in Knoxville

Native redbuds Cercis canadensis) is native to eastern and central North America (USDA hardiness zones 4-8). This small tree is a highly dependable small flowering tree. Redbud is typically a relatively short-lived tree, perhaps 20-30 years at best. Depending on variety, their lavender / pink/ white pea-like flowers emerge in early spring, usually a week or two before our native dogwoods (Cornus florida).

Fifty years ago, most U.S. gardeners were unwilling to buy redbuds. Over the past 25 years numerous varieties flaunting colorful foliage continue to arrive at local garden centers, the green heart-shaped redbud foliage is not valued for their foliage tree. The introduction of ‘Forest Pansy’ redbud in 1950 changed the way we utilized this wonderful native tree in the landscape. What followed has been “A Redbud Revolution”.

Listed in the colorful foliage category are nine modern day redbud varieties. At the end I have included two cultivars with unusual thick glossy leaves:

‘Alley Kat’ – green & white splotched foliage

Carolina Sweetheart™ (‘NCCC1’) – spring foliage emerges rich maroon, and slowly changes to shades of white, green, hot pink; ending green with faded white margins in late summer.

Flame Thrower™ – new leaves start out burgundy-red, turn bright yellow and green as foliage ages.

‘Hearts of Gold’ – spring’s golden yellow leaves turn to chartreuses in summer. Leaves may sunburn (scorch) during hot dry summer.

Merlot™ – fade-resistant dark burgundy foliage

‘Pink Pom Poms’ (PPAF) – thick, glossy green foliage and dark pink-purple, double pom pom-like flowers.

Ruby Falls® – weeping form with purplish red foliage.

The Rising Sun™ – apricot/gold foliage that rarely burns in the summer heat.

‘Whitewater’ ̶ weeping form with leaves that emerge mainly white with minimal flecks of green; foliage matures mostly green with flecks of white.

Thick High Gloss Green Foliage (C. canadensis var. texensis)
‘Texas White’ (white flowers)
‘Oklahoma’ (lavender-pink flowers)

‘Oklahoma’ (lavender-pink flowers)A

Smoketrees For Their Multi-Seasonal Appeal

Posted by Hugh on March 11th, 2020

Smoketree or smokebush (Cotinus coggygria) is a large shrub or small tree native from southern Europe to central China (USDA hardiness zones 5-8). Over time it typically matures to 10-15 feet high and wide. Depending on cultivar (see list below), smoketrees have oval leaves tinted in rich purple, gold, or green shades. Generally, they grow as multi-stemmed shrubs, but many gardeners choose to train them as small landscape trees.

Truly, the uniqueness of smoketrees are their wonderful flower clusters which offer the illusion of clouds of smoke. Individual flowers are actually insignificant. Additionally gold and purple-leaved cultivars are available along with green-leaved selections.

Smoketrees are best grown in full sun and in well-drained soil. Standard varieties can reach 10 feet to 15 feet in height. Pruning is key to keep their multiple stems in check and prevent a gangly plant appearance. Plant a single smoketree as an accent feature or group several as a tall deciduous shrub border or privacy screen.

Fall color is a mix of yellow, orange, and red shades. Those varieties with standout seasonal leaf color, like Golden Spirit® or ‘Royal Purple’, are grown solely for their foliage. In the fall all growth is cut back (coppiced) to 6-12 inches above the ground. New colorful shoots grow 4- and 6-feet tall in one growing season with no flowering.

This tree/shrub has proven to be a reliable performer in the garden, holding up well in hot, dry conditions once the plant is established. To repeat the billowy summertime blooms put on a real show for 3-4 weeks. What follows is the fluffy clouds then disperse throughout the yard and your neighbors. Some may find this objectionable.

Leading cultivars:

Golden Spirit® (‘Ancot’) grows with unique golden foliage that fades to lime green in summer before showing shades of orange and red in autumn; 10 feet tall and 6 feet wide.

‘Grace’ offers rich burgundy-purple foliage in spring and summer then orange-red fall color; grows 15 feet tall and wide.

‘Nordine’ is an exceptionally hardy form with burgundy leaves that develop red and orange shades in fall; 15 feet tall and wide.

‘Pink Champagne’ bears pink smoky flowers along with round deep green leaves that turns a mix of scarlet and orange in fall; 10 feet tall and 10 feet wide.

‘Royal Purple’ bear clusters of purple puffy flowers and red-purple foliage which turns scarlet in fall; 15 feet tall and 12 feet wide.

‘Velvet Cloak’ struts dark purple-red foliage, fading pale purple foliage may dull somewhat in late summer, and turns a fall mix of scarlet, orange and russet; 12 feet tall and wide.

Six Perennials For Dry Shade

Posted by Hugh on March 6th, 2020

Many of the following perennials tolerate dry shade but flourish in moist, well-drained soil. Each typically displays the richest foliage colors with a couple of hours of direct sunlight a day. All hold up well to dry conditions and are deer and rabbit resistant.

*Epimedium perralchicum* ‘Frohnleiten’ makes a wonderful groundcover

Barrenworts (aka Bishop’s cap, Fairy Wings) (Epimedium spp.) represent over 70 cultivars and new hybrid selections are arriving every year. No two cultivars seem alike in flowering and foliage traits. Species will vary from 6 to 20 inches in height and 10 to 24 inches in spread. Fairy wings, depending on species, may be evergreen or deciduous.

Sacred lilies (Rohdea japonica) are mostly evergreen perennials that grow 8-24 inches high depending on cultivar. Well-established clumps produce short-stemmed, creamy to greenish, white bell shaped flowers. Blooms, mostly inconspicuous, are mostly hidden within the dense leathery foliage. Red or orange ornamental berries follow in autumn and last through most of the winter. Plants prefer humus-rich well-drained soil, but cope with moderate periods of drought. (zones (5)6-10).

Ajuga (aka bugleweed) is a groundcover perennial with pretty spring floral spikes of cobalt-blue flowers and lovely foliage. Popular varieties include ‘Burgundy Glow’ (silvery green leaves splotched with pink/ burgundy/ white); Chocolate Chip (small, narrow green leaves spotted burgundy purple); Black Scallop (large purple leaves with high gloss). (Zones 3-9).

Lenten roses (Helleborus x orientalis) are so easy and so pretty in dry shady gardens with well-drained soil. Exquisite bowl- or saucer-shape flowers in white (often speckled), pinks, yellows, or maroon bloom for three months from mid-winter into spring. Their evergreen foliage is deer-resistant.

Geranium *macrorrhorizum* ‘Bevan’s Variety’

Bigleaf cranesbill (Geranium macrorrhorizum) is a resilient ground cover for dry shade. Its deeply lobed green foliage takes on shades of reddish-orange in fall. Popular varieties- ‘Bevans’ and ‘Ingwersen’s Variety’- bear pale pink blooms appear in spring. (zones 3-8).

Lilyturf (Liriope muscari) is an easy to grow perennial that tolerates a wide range of light and soil conditions. It copes summer heat, humidity and drought. Foliage is evergreen in warm southern climates (zones 7-10). Purple blooms (white variety also available) arise above the strap-like evergreen leaves in early autumn. (zones 5-10).

Rhododendrons You Should Be Growing

Posted by Hugh on March 1st, 2020

“A healthy plant in the right place with proper maintenance” is a rhododendron that has few problems. Rhododendrons and azaleas are acid loving plants meaning plants should be planted in humus-rich slightly acidic soil (pH 5.2 -6.5).

If the soil is not well amended, rhododendrons will have trouble surviving long term. Once planted, water during dry periods, feed lightly in the spring with a fertilizer for acid loving plants, and stand back and enjoy. Most varieties are hardy from USDA hardiness zones (4)5 through 7(8). Rhododendrons are potentially troubled by several disease and insect problems. Choose only the most dependable cultivars, many of which are listed here.

R. maximum (Rosebay rhododendron), 15’ x 20’ & larger Midsummer White to rose; shallow rooted; best in partial shade; var. roseum 4’ – 6’ x 6′ -10’ Pink to red; best in partial shade.

R. catawbiense ‘Roseum Elegans’ or ’English Roseum’ 4-6’ x 6-8’ Mid-summer large pink, almost impossible to tell apart.

R. catawbiense ‘Grandiflorum’ 6’ x 8’ Mid-summer; pinker form than Roseum Elegans.

R. catawbiense ‘Purpureum Elegans’ 3.5’ x 5’ Mid-summer; large, purple blooms.

R. catawbiense ‘Album’ 5’ x 7’ Midsummer White with green or brown margins.

R. catawbiense Boursault’ 6’ x 8’ Mid to late summer Darker Pink Vase shaped as gets larger.’

R. catawbiense ‘Lee’s Dark Purple’ 6-7′ x 7′-8′; deep purple with green-yellow blotch on petals.

R. catawbiense ‘Nova Zembla’ 3-6’ x 3-6’ Midsummer; deep red flowers, especially in shade.

R. x ‘Janet Blair’ (Dexter hybrid) 4′ x 4 – 5′ pinkish mauve with golden bronze blotch.

R. x ‘Chionoides’ (R.ponticum hybrid) 5’x 5’ Late spring to early summer; pure white with yellow blotch on petals; dark green, narrow leaves.

R. catawbiense ‘Cunningham’s White’ 7’ x 7’ Mid to late summer; White, rays of purple or brown; Foliage turns purple in the winter.

R. catawbiense ‘Scintillation’ 6’x 6’ Midseason; Pink, brown throat Fragrant, dense, glossy leaves. Foliage turns purple in the winter.

PJM Rhodendrons (Rhododendron x carolinianum) 4 to 6’ x 4 to 6’ very early spring March; ‘Olga’ (Pink), ‘PJM Elite’ (reddish purple), to original ‘PJM (Lavender); ‘Aglo’ (Pink) are leading varieties; purple winter foliage, loose open form as it matures.

‘Alleghany’ Viburnum – A Versatile Spring Flowering Shrub

Posted by Hugh on February 26th, 2020

Alleghany viburnum (Viburnum x rhytidophylloides ‘Alleghany’) is a hybrid cross between V. rhytidophyllum and V. lantana ‘Mohican’ (USDA hardiness zones 5-8). ‘Alleghany’ viburnum is rated a four season landscape shrub, with multiple year-round appeal including a durable semi-evergreen leathery foliage, dependable spring flowering, and showy fruits in fall and winter.

This lovely spring flowering shrub grows 10-12 feet tall and 12 -15 feet wide. Its dark green semi-evergreen leaves are resistant to bacterial leaf spot. Branch wood is coated with tiny gray-brown woolly hairs on stems and on the undersides of leaves. This medium sized flowering shrub is an excellent choice for privacy screening.

In most years leaves turn purplish in winter and persist through ice and snow into mid-February. In mid-April, showy creamy white flat-top flowers open at the ends of branches. Up close, flowers emit a faint unpleasant stale odor; otherwise observe from 6 or more feet away. Glorious clusters of dark red fruits fill the branch tips from late summer to early fall. The combination of fruits along with coarse green foliage are major autumnal assets. Red fruits ripen to black and numerous birds flock to this shrub for food and winter protection.

Alleghany viburnum prefers either full or 6- hours minimum daily sunlight for heaviest flowering. Moist, slightly acidic, well-drained soil is essential. A 2-year old established shrub exhibits above average drought tolerance. Fertilize in early spring with a slow release fertilizer such as Osmocote or Nutricote.

This large viburnum is available either as a large landscape size balled and burlapped (b&b) or smaller size container-grown plant. In early spring rake away old fallen leaves and mulch viburnums for a clean appearance.

This viburnum has no serious insect or disease problems. Prune, if necessary, after spring flowering and before July 15.

Best fruit numbers occur with cross pollination from Viburnum spp. parents or clones within the hybrid.

‘Alleghany’ Viburnum – A Versatile Spring Flowering Shrub

Dependable Conifer Trees For Southeast U.S. Landscapes

Posted by Hugh on February 21st, 2020

Arizona cypress (Cupressus arizonica var. glabra) is a southwestern U.S. conifer tree that is often underplanted. Soil drainage is an absolute must! Growth rate is moderate (15 feet high after 10 years) and eventually will reach 30-50 feet at maturity. (zones 7-9). I have seen multi-year specimens thriving in zone 6b.

‘Crater Blue’ deodar is a highly desirable shrub form

Deodar cedar (Cedrus deodara) is a medium-growing tree that typically grows to 40-50 feet high within its first 25 years. Shrub forms are also available. In its native Central Asia habitat, these cedars reportedly grow much taller. Young deodars start out pyramidal, maturing to flat-topped trees with broad-spreading horizontal branching. Deodar cedars prefer locations that are warm and humid in summers and protected from harsh drying winter winds (zones 6b -8).

Atlas cedar (C. atlantica) grow exceptionally well in the Southeast. Blue needle forms (var. ‘Glauca’) are most popular. Give trees lots of room as young cedars start out pyramidal, but develop wide-spreading horizontal branches as the age (zones 6-9).

Weeping Blue Atlas Cedar (*Cedrus atlantica* ‘Glauca Pendula’)

Few pines (Pinus spp.) perform well in the southern U.S. Notable exceptions are loblolly pine (P. taeda), longleaf pine (P. palustris), and Eastern white pine (P. strobus) (Zones 3-8). Site selection and spacing are of key importance. Pines are susceptible to numerous pests including bark beetles, shoot borers, Zimmerman moth larvae, pine sawfly, scale, among others.

Two deciduous conifers thrive in the Southeastern U.S. Bald cypress (Taxodium distchum) is native to the swamps of Georgia and South Carolina (USDA hardiness zones 4-9), yet is hardy from Florida north to central Michigan. Dawn redwood (Metasequoia glyptostroboides), native to China, also performs equally well (USDA hardiness zones 4-8). Both mature into large 60-80 foot landscape trees, but several dwarf tree and shrub forms are available.

Japanese cedar (Cryptomeria japonica) excels in the southeastern U.S. with few disease or insect problems are available (USDA hardiness zones 5-9). Tree cultivars grow 40-50 feet tall; dwarf tree and shrub forms are also available.

Additional conifers that have been proven reliable include false cypress (Chamaecyparis pisifera), hinoki cypress (Chamaecyparis obtusa), Alaskan cedar (Xanthocyparis nootkatensis), Korean fir (Abies koreana), Western arborvitae (Thuja plicata), Golden larch (Pseudolarix amabilis), and China fir (Cunninghamia lanceolata).

Some Conifers Don’t Like Summer Heat And Clay Soils

Posted by Hugh on February 16th, 2020

Most conifers are best grown in deep, moist, well-drained, acidic loamy soils and in full sun. In the deep South evergreen conifers are challenged by warm soils, poor soil drainage, and humidity. Humidity increases their susceptibility to diseases. Once established they are drought tolerant, but most fail in poorly drained wet soils.

White fir (*Abies concolor*) prefers cooler summers

Many pine species melt in regions where summers are hot and humid. Notable examples include: Scot’s pine (Pinus sylvestris), Austrian pine (P. nigra). Their natural range in the northern U.S. is from Illinois to New Jersey These pines and others are susceptible to a number of fungal needle disease and insect problems. Contrarily, Loblolly Pines (P. taeda), shortleaf pine (P. echinata), and long leaf pine (P. palustris) grow well in many Southeastern states.

White or Concolor firs (Abies concolor) enjoy the cool climes and gravelly soils of the Rocky Mountains. Frazer fir (Abies fraseri) grows well at 4000 to 6000 feet elevations of Tennessee, Virginia and North Carolina.

Norway spruce (Picea abies) and Colorado spruce (Picea pungens) struggle summer heat and humidity in zones 7 and points south.

Umbrella Pine (Sciadopitys verticillata), not a true pine, do not perform well in heavy clay soils.

Umbrella Pine at NC Arboretum in Asheville, NC

Oriental arborvitae (Platycladus orientalis) is highly susceptible to Berckmann’s canker (aka arborvitae blight. American arborvitae (Thuja occidentalis) is resistant (Zones 6-9).

Italian cypress (Cupressus sempervirens) is native to southern Europe and western Asia. tree and shrub forms take on the familiar narrow-columnar or fastigiate form and grows 40-60 feet (less frequently to 80 feet) tall. Some selections develop a spreading, open-horizontal form (var. horizontalis) (Zones 7-10).

European Larch (Larix spp.), a deciduous conifer, is highly susceptible to pest and disease issues in the Southern U.S. (USDA zones 2-6) . Japanese larch (L. kaempferi) is slightly more dependable in the mid-South in sandy loam soils (Zones 4-7).

Rocky Mtn junipers (Juniperus scopulorum) prefer well-drained soils and the cooler climes of the Midwestern U.S. (Zones 3-7) .

Hemlock (Tsuga spp.) struggle with wooly adelgid, is significant insect pest (Zones 3-7). Effective pesticide and biological controls are currently available. New promising resistant varieties are entering the testing stage.

Zone 6 Hardy Camellias

Posted by Hugh on February 11th, 2020

Once upon a time, across the Southern U.S., camellias were highly prized for their showy flowers in the fall-winter landscape. What has changed is that gardeners in the Middle Atlantic and mid-Southern states can now grow them equally well.

Camellias are evergreen woody shrubs native to Asia. Currently, after decades of inter-breeding with species from South Korea and Japan, hardier varieties bloom reliably well from New York City south through Virginia, Tennessee, and North Carolina. Blooms of some cultivars measure 5 inches across.

According to the American Camellia Society, over 30,000 cultivars of camellia have been named. Depending upon the cultivar, bloom period is in the fall, winter or spring. The bloom cycle of a variety lasts 4 to 6 weeks. A hard cold snap can burn the open blooms, but tight budded flowers are unharmed. Floral colors include shades of pink, red, lavender, white, and multi-colored. Plants vary in size from 5 to 15 feet tall with a spread between 6 to 12 feet in width.

Camellias like an acidic soil (5.5 -6.8 is the ideal range), along with good soil drainage and moisture. Water shrubs as needed during summer dry spells. Camellias benefit from spring feeding with a fertilizer labeled for acid-loving shrubs. A partially sunny spot or a location with morning sun and afternoon shade is perfect. Prune camellias as needed in spring after blooming has finished.

Today’s camellias, in part, are the result of plant breeders Drs. William Ackerman (USDA- retired) and Clifford Park (Camellia Forest Nursery). They introduced a series of interspecific crosses between C. oleifera and C. sasanqua, C. hiemalis, or C. vernalis selections. Many, not all, are identified under the “Winter” and “April” series logo. They bloom in the fall or spring respectively.

Over fifty zone 6 hardy camellias are currently available. In addition, plants of several zone 7 hardy varieties will survive in zone 6 (minus 10 °F) unharmed. The open and partially closed blooms will be injured during cold snaps, but tight budded varieties often are not damaged.

Changing Garden Soil pH

Posted by Hugh on February 6th, 2020

In general, the garden soil pH fluctuates only slightly unless you accidentally spilled fertilizer or limestone. Soil pH is also affected by rainfall patterns, decomposing organic matter, and bacterial activity in the ground. In the eastern U.S. rain water is slightly acidic.

Acid rain is the result of these pollutants (mostly sulfate and nitrate) from
power plant smokestacks and automobile exhausts. When acid rain falls upon land, it acidifies the soil, lowering its pH. Soils at high elevations such as mountain peaks are especially prone to acidification, as more rainfall is received compared to soils in valleys or other low areas.

The activity of beneficial microorganisms can also influence plant growth. Natural bacteria aids if decomposing soil organic matter. The accumulation of organic matter may tie up of nutrients, particularly nitrogen. Minor nutrients such as iron, manganese, and molybdenum

Acidic loving plants such as azaleas, rhododendrons, mountain laurels (Kalmia), blueberries (Vaccinium), specific oaks (Quercus spp.), birches (Betula nigra), lenten roses (Helleborus spp.) and many bog plants prefer acidic soils within a pH range between 5.0 – 5.5. The summer foliage of some shade trees such as willow oak, pin oak, and river birch turn chlorotic (yellow) if soil pH rises above 7.0. Leaf chlorosis is often common on urban street trees that are surrounded by concrete sidewalks and building foundations which raises soil pH (acidity declines).

Some species of hydrangeas are also pH sensitive. Flower color of mophead hydrangeas (H. macrophylla) are pH sensitive. Expect blue flowers if soil pH is 6.6 or below; hydrangea blooms turn pink if pH is 6.6 or above. Leaves of oakleaf hydrangeas become chlorotic above a neutral pH (7.0).

Limestone will raise soil pH. It also supplies calcium and magnesium, two key elements important for plant growth. Lime also makes phosphorus more available for the plant growth and increases nitrogen availability. Common liming materials include: (1) ground limestone; (2) dolomitic limestone (dolomite); and (3) hydrated lime. Dolomite is high in magnesium.

Sulfur will lower the soil pH (make the ground more acidic). Most independent garden centers will supply elemental sulfur (called “flowers of sulfur”). Most gardeners spread sulfur and lime in late fall so that winter rain or snowfall will breakdown the products into the soil.

The amount of lime to apply depends on current soil pH, soil type (sand, silt, or clay), and amount of organic matter. Also, what kind of plant(s) are you growing. You are limited on how much to apply the soil per year. Consult your county Extension agent. He or she will likely recommend conducting a soil test; the agent can help interpret the results of the soil test.

Care Of Rhododendrons

Posted by Hugh on January 31st, 2020

*Rhododendron catawbiense* on top of Roan Mountain, TN

In the U.S., two species of rhododendrons, Catawa (Rhododendron catawbiensis) and Rosebay (R. maximum), are plentiful in the Appalachian Mountain region. Their roots feed in part on the rich humus material in the rocky mountain soils. Over time fallen leaves, twigs, and flower parts decay into additional humus. Humus improves soil aeration and drainage, yet aids in retaining some moisture.

Rainfall in the mountains is more plentiful than at lower elevations where most urban gardeners reside. In the mountains the ground is moist and cooler. Thus, the two basic growing requirements of rhododendrons – abundant moisture and good soil drainage- must be satisfied in warm urban gardens. This is also the secret for growing azaleas and their botanical cousins Mountain laurels (Kalmia latifolia).

Early Summer blooming Rosebay Rhododendron

Rhododendrons will flourish in urban gardens through proper siting (sun/shade), choosing the best varieties (cultivars), and special care. In warmer urban climes, rhodies prefer exposure to morning sunlight and mostly afternoon shade. You may opt to remove some lower tree branches to allow more light to filter through the canopy. Protect from drying winter winds by planting a hedge or windbreak. Drying winds most often come from a southwesterly direction. Therefore, plant rhododendrons on a northeast slope or the northeast corner of your house.

Soil drainage: If your garden contains heavy clay, construct a raised bed and fill it with fertile garden soil along with lots of compost and/or peat moss, and coarse sand or perlite. Typical bed size may be 5 feet in width and whatever length you have space for.

At the start, fill the bottom of the trench with 6 inches of coarse pebbles or small rocks for improved drainage. Test the soil in the bed to make certain that the soil pH is 6.2 or lower. After planting, if you garden in an urban area, you may want to install drip irrigation, particularly over the dry summer period(s).

Each spring, spread 3-4 inches of an organic mulch such as pine needles or pine bark around the base of each rhododendron. Over time, the decaying mulch will add more humus to the ground to keep shallow-rooted rhodies cool and moist.