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

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.

February Blooming Hybrid Witchhazels

Posted by Hugh on January 26th, 2020

Witchhazels (Hamamelis spp.) are somewhat coarse, loosely-branched, medium to large, deciduous shrubs that typically grow 12-20 feet tall. (USDA hardiness zones 5-8). They are particularly noted for their strapped shape, often fragrant, mid- to late winter flowers which appear before the spring leaves emerge. Five cultivars were selected by Mr. Tim Brotzman, an Ohio nurseryman who has been growing witchhazels for over than a half century.

Witchhazels generally grow 12-15 feet tall with an upright, vase-shaped, ascending branches and a spreading habit. The sweetly fragrant long-lasting flowers appear in February and last into March. The bright green 5-6 inch circular leaves appear weeks later in spring. Yellow-orange to yellow fall color can be quite attractive in some years. The first three winter-flowering witchhazel are Chinese hybrid witchhazel (H. x intermedia):

1. ‘Jelene’– clusters of bright coppery orange flowers

2. ‘Diana’ – sweetly fragrant copper-red flowers

3. ‘Primavera’ – bright yellow, spider-like flowers with narrow 3/8 to 5/8 inch long petals

4. Chinese witchhazel H. mollis ‘Wisley Supreme’ – fragrant golden-yellow flowers

5. Japanese witchhazel ‘H. japonica ‘Shibamichi Red’ – is a relatively recent introduction of Japanese witch-hazel named after the well-respected Japanese nurseryman, Akira Shibamichi. Flowers open a bit on the late side of the February/March period to reveal unusually showy cherry red, strap-shaped petals which are highly scented. This variety grows more slowly and the blooms are a bit smaller than hybrid witch-hazels. The shrub attains a height and spread of 8 feet.

Witchhazels are best planted in a shrub border or woodland garden that receives at least one-half day sunlight. They’re valued for fragrant late winter flowers and good fall color. Clip and bring in an attractive winter bouquet that will add fragrance to your home.

No serious insect or disease problems trouble witchhazels. Occasionally, caterpillars and Japanese beetles may chew on the summer foliage. Witchhazels are deer resistant.

Ten Stars Of The Winter Landscape

Posted by Hugh on January 21st, 2020

Here are 10 reliable plants that shine in my Tennessee garden (Zone 6-b) during the winter season:

Witchhazels (Hamamelis spp.) –two species bloom in winter: (a). Vernal witchhazel (H. vernalis) blooms in mid- to late- January (zones 4-8). (b). Chinese witchhazel hybrids (H. x intermedia) dominate the month of February into March. – deciduous, large multi-stemmed shrub or small tree that grow 12 to 15 feet tall with wide spreading branching; select hybrid forms including ‘Jelena’ (coppery-orange flowers), ‘Diane’ (copper-red to red flowers), ‘Gingerbread’ (orange flowers), ‘Westerstede’ (yellow flowers), and ‘Pallida’ (yellow flowers). (zones 5-8).
Chinese Paperbush (Edgeworthia chrysantha) – their showy nodding flowers appear in late February into early March (zones (6)7-9).
Carolina Jessamine (Gelsemine sempervirens) – puts on a spectacular display of fragrant, bright yellow flowers starting in late February (depending on weather) and lasting 4-6 weeks, Sports semi- to evergreen foliage (zones 6 to 9).
Lenten Rose (Helleborus x hybridus) – modern day varieties have some gardeners ripping out those they planted 25 years ago. (zones 4-9).
Christmas Rose (Helleborus niger) – also noted for their long bloom period in some years starting in late January, most in February through mid-April. (zones 3-9).
Fragrant Honeysuckle (Lonicera fragrantissima) – Extremely fragrant (lemony), short-tubed, creamy white flowers often appear in mid-winter before the leaves emerge. Flowers are followed by small, somewhat inconspicuous, red berries. (zones 4-8).
Japanese Cornel (Cornus officinalis) (zones 5-8) and Chinese cornel (C. mas) (zones 4-8) – bloom the latter days of February or early March as prolific open about a week or so later.
‘Pink Dawn Viburnum (Viburnum x bodnantense) – puts on a late winter spring show of pink flower clusters followed by thick, lustrous, rich green foliage and cinnamon-colored branches. (zones 5-8).
Chinese wintersweet (Chimonanthus praecox) – yellow 1 ½ inch wide flowers with a purplish-brown center open with fragrant flowers (to 1” across) typically bloom in winter (December to January) on leafless branches. (zones (6)7-9)
Daphne (Daphne odora) – highly fragrant creamy-white, pink, or yellow blooms open in late winter and persist well into spring. (zones 3 to 10).

Ten Stars Of The Winter Landscape

Plant Disease Warning: Phytophthora ramorum

Posted by Hugh on January 16th, 2020

Rhododendron infected with
*Phytophthora ramorum* (Pr) (photo by Dr. Alan S. Windham)

Known as “sudden oak death”, this serious plant disease (Phytophthora ramorum) (Pr) from the West Coast kills oak and other species of trees. It has caused devastating effects on the oak populations in California, Oregon, and Washington, and is also present in Europe. Symptoms include bleeding cankers on the tree’s trunk and dieback of foliage.

Pr causes foliar blight/leaf spots over 80 susceptible landscape plants including: maple (Acer), Camellia, witchhazels (Hamamelis), mountain laurels (Kalmia), honeysuckle (Lonicera), magnolias (Magnolia), Japanese andromeda (Pieris), Douglas fir (Pseudotsuga), azaleas and rhododendrons (Rhododendron), lilac (Syringa), and viburnums (Viburnum).

All nursery plants from the West Coast are strictly inspected by the USDA for Pr. However, mistakes do happen. In the spring 2019 rhododendrons infected with Pr were shipped to some stores in Tennessee. Fortunately, the plants were quarantined and quickly destroyed.

Pr is a water mold fungus disease known as ramorum leaf blight, ramorum dieback, and sudden oak death (SOD). In certain areas of California and Oregon, Pr causes bark cankers on several oak (Quercus) and tan oak (Lithocarpus densiflorus). The bark cankers are fatal to oak and tan oak if the lesions girdle the trunk. Otherwise, trees that develop foliar blights and leaf spots do not die, but may serve as “reservoir” hosts for the pathogen.

Pr produces “bleeding” cankers on the trunks and branches. The formation of droplets of dark reddish brown liquid on the bark is not usually associated with bark cracks or insect holes. If the outer bark is scraped away, black zone lines surround dead areas in the inner bark. Once a bark canker girdles a branch or stem, the portion of the plant beyond that point dies. Tree death may occur within several months to several years after initial infection. Infected trees are attractive to opportunistic ambrosia and bark beetles, as well as secondary colonization by the sapwood decay fungus (Hypoxylon).

West coast nurseries are forbidden to ship susceptible host plants. All plants must pass inspection “free of Pr” can be shipped to other states. No chemical control measures are currently available.

Zone 6 Hardy Camellias

Posted by Hugh on January 11th, 2020

In the Southern U.S., camellias are treasured for their showy flowers in the fall-winter landscape. Their glossy evergreen foliage looks great all year long. Hardy varieties are now available for zone 6 northern gardens (-10 to 0 °F). This means that gardeners in Tennessee, Kentucky, Virginia and most coastal cities in Eastern U.S. can grow camellias. Blooms measure 3-5 inches across with yellow stamens centers.

Depending on variety, flowering may last 4 to 6 weeks. Short periods of freezing temperatures can burn the blooms currently opened and those scheduled to open within a few days, but buds tightly closed may survive, swell, and open. Color choices include shades of red, pink, lavender, white and multi-colored flowers. Varieties vary in size, from 8 feet to 15 feet in height and 6 feet to 10 feet in spread. Annual spring pruning can alter plant dimensions.

Camellias like well-drained, mildly acidic soils along with adequate soil moisture. In northern areas grow shrubs in a partially sunny site or one with full morning sun and afternoon shade. Established camellias are moderately drought tolerant; irrigate during prolong dry spells in summer and fall. Fertilize camellias in early spring with a product labeled for acid-loving shrubs.

Modern day hardy camellias are interspecific crosses between C. oleifera, C. sasanqua, C. hiemalis, C. japonica, and C. vernalis. Camellias start blooming in early fall into very early winter and a second flowering period in March and April. Petals are shed and require no dead-heading. In northerly climes, zone 6 hardy camellias are planted and mulched anytime from early spring up to Labor Day (and no later).

Reward yourself by planting two or more camellias in your garden to flower during the transition periods in early fall and in late winter when temperatures are seasonally mild. Here are some favorites:

Fall Bloomers: ‘Snow Flurry’ (white), ‘Autumn Pink Icicle’ (clear pink), ‘Sweet October’ (white/pink tinge), ‘Winter’s Joy’ (pink double), and ‘Long Island Pink’ (light pink).

Mid-March/April Bloomers: ‘Pink Icicle’ (shell pink), ‘April Tryst’ (deep red), ‘April Remembered’ (4.5 in. wide (11 cm), semi-double pale pink-large flower), ‘April Rose’ (deep rose pink).

‘Snow Flurry’ Camellia at NC Arboretum in Asheville, NC

12 Woody Trees And Shrubs Perfect For Containers

Posted by Hugh on January 6th, 2020

Japanese maples, hydrangeas, hollies, boxwoods, camellias, and dwarf conifers are popular favorites to grow in pots. Often, they’re part of mixed plantings coordinated with colorful annual and perennial flowers.

If and when these outdoor trees and shrubs outgrow their pots, you have one of three options available: 1.) move plants into a bigger pot, 2.) repot the plant in the same pot after pruning back roots and shoot growth, or 3.) plant them in the ground.

Here are 12 plants (trees and shrubs) that are perfect for pot culture in residential landscapes. Note the USDA hardiness zones for each selection.

1. Cutleaf weeping Japanese maple (Acer palmatum)- lacy green or purple foliage in spring and summer and colorful fall color. Tree form is umbrella-like. Recommended compact varieties are ‘Tamukeyama’, ‘Crimson Queen’, ‘Garnet’, ‘Shaina’, among others (zones 6-9).

*Nandina domestica* in planters at Biltmore Estates, ASheville, NC

2. Hinoki false cypress (Chamaecyparis obtusa) – some favorites include ‘Crippsii’ (6-8 feet high) and ‘Verdonii (3-4 feet high). (zones 4-8).

3. Nandina or heavenly bamboo (Nandina domestica) – many varieties available from 2 – 6 feet. In southern climes, avoid invasiveness be selecting male only varieties. (zones 6-9)

4. Japanese yews (Taxus x media ‘Hicksii’) grows 9 feet tall and 6 feet wide in containers (zones 4-7).

5. Deodar cedar (Cedrus deodara) offer several shrub forms which are ideal for pot culture; recommend ‘Crater Blue’, ‘Feelin Blue’. (zones 6-9)

6. Dwarf Dawn Redwood (Metasequoia glyptostroboides ‘Schirrmann’s Nordlicht’) – this deciduous conifer grows 4-6 feet tall over 10 years. zones 5-8)

7. Japanese plum yew (Cephalotaxus harringtonia) – ‘Fastigiata’, dark-green, tight columnar evergreen; ‘Duke Gardens’ (4-5 feet high and wide); ‘Korean Gold’ (3-4 feet) (deer-resistant). (zones 6-9)

8. Dwarf camellias (Camellia sasanqua) – compact growing dark evergreen foliage; ‘Shishi Gashira’; ‘Yuletide’ (6 feet tall and high) (zones 7-9).

9. Panicle Hydrangeas (Hydrangea paniculata) – select smaller forms at 3-6 feet height such as ‘Little Quickfire’, ‘Little Lime’, ‘Bobo’ with showy cone-shaped flowers from mid-summer to early fall. (zones 3-8)

10. Tiger Eye® Sumac (Rhus typhina ‘Bailtiger’) -5-6 foot tall deciduous shrub or small tree with fine textured dissected chartreuse seasonal foliage. (zones 4-8)

11. Boxwood (Buxus sempervirens) – hardy hydrid forms are available including variegated form like Wedding Rings® and ‘Variegata’ (zone 5 -8)

12. Inkberry holly (Ilex glabra) – native evergreen hollies like
Strongbox® and miniature Gem Box® are highly dependable for pot culture. (zones 4-9)R

‘Sun King’ Aralia Named 2020 Perennial Plant Of The Year

Posted by Hugh on January 1st, 2020

Plants with golden foliage can brighten up almost any drab garden patch. Sun King golden aralia (Aralia cordata ‘Sun King’) is no exception, hardy in USDA hardiness zones 3-9. It is also known as Japanese spikenard and mountain asparagus. Under ideal conditions this thornless, rhizomatous, herbaceous perennial grows rapidly to 3-5 feet tall and as wide in a single season.

The golden compound foliage emerges in mid-spring and retains its bright color throughout the summer. Growth rate is rapid and dies back to the ground in late autumn. In mid-summer numerous small clusters of tiny white flowers shoot up, borne on 2 feet tall racemes. Lustrous purplish-black berries follow in the fall.

Sun King makes a bold almost tropical statement in a semi-shade garden. Grow it in a compost-rich moist soil and in ½-day sunlight (morning hours preferred). It is adaptable to a wide soil pH range. The foliage may burn in full day sun. In USDA zones 8 and 9, grow only in dappled sunlight to avoid foliage burn. Golden aralia should be kept mulched and irrigated over long summer dry spells.

Sun King aralia mixes well in large containers planted with green and other brightly colored foliage plants. It combines with variegated Solomon seal, hostas, brunnera (Brunnera macrophylla), lungworts (Pulmonaria spp.), coral bells (Heuchera spp.), and astilbes. Golden aralia is deer resistant and its tiny white flowers attract numerous honeybees.

A native of Japan, Korea, and China, ‘Sun King’ aralia was introduced to the U.S. by Barry Yinger.

Caution: Birds love the tiny berries, but they’re NOT edible for humans).