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

Hardy or Not– Grow Agapanthus

Posted by Hugh on April 8th, 2013

Lily of the Nile (Agapanthus)

Lily-of-the-Nile (Agapanthus praecox orientalis) is native to South Africa (USDA Zones 8–11), and is not reliably hardy in the Southern Appalachian region (USDA zone 6 and 7). However, many gardeners are successfully growing it as a “tender perennial”. Agapanthus grows in an outdoor flower bed or in a container.

The ball shaped light blue or white tubular shaped flower clusters first appear in late spring and early summer. By promptly deadheading spent flowers, agapanthus may produce another 1-2 flushes in summer and early fall.

Agapanthus grows 2-3 feet in height and 1 ½ -2 feet in spread with dense tuft of 1 inch wide strap-like dark green leaves which measure a foot or more in length. It prefers a compost rich soil (media), constant moisture and partial sunlight. Weekly watering promotes a deep, extensive root system.

During the winter months lay a thick 3 inches of organic mulch over the crown to protect the roots from frost. Remove the mulch once warm spring weather returns.

Container-grown plants should be cut back and brought indoors by early November and nurtured as house plants through the winter. Divide crowded root clumps every 2 to 3 years in early spring.

If you garden further north (USDA zone 5) tender agapanthus should be dug up and stored inside for the winter. Allow plant(s) to thoroughly dry out and trim back the foliage. Keep the dormant crown in a cool, dark location for the winter between 35 – 40ºF. In late winter move the dormant corms into a warm area and moisten the soil to force new growth. Bring plants back outdoors in mid-May to enjoy another summer in the garden.

Mealy bug and red spider mite can be major pest problems.

Silverbell Tree Are Great Additions To Your Garden

Posted by Hugh on April 6th, 2013

Carolina silverbell (Halesia diptera) in Conlon Garden

Carolina silverbells (Halesia spp.) bloom as the last bracts of flowering dogwood (Cornus florida) have fallen. Clusters of white or pale pink bell-shaped flowers open along the branches. Flowers appear first and medium green leaves emerge a few days later. Silverbells vary tremendously in the wild. Some grow large shrub-like, or as small multi-trunked trees to 20-25 feet in height, or as medium 30 to 50 feet high and 20 to 35 feet wide.

Over the past decade botanists have reclassified Halesia. Two-winged silverbell (H. diptera) grows a small 20-30 feet tall and wide, and fruits are 2-winged drupe seed capsules. Carolina silverbell (H. tetraptera, formerly H. carolina) is the taller species at 30-40 feet high and 25-30 feet wide, and fruits are 4-winged drupe seed capsules.

Young multi-stemmed shrubs are easily trained into single trunk trees. Fall leaf color is variable, in most years turning pale yellow in the Southern Appalachian region (USDA hardiness zones 6 and 7). Dry brownish seed capsules persist through most of the winter. In the winter months the dark gray-furrowed bark, marked with thin black vertical lines, is more noticeable.

Silverbell is primarily an understory tree, preferring partial sun (full morning sun, afternoon shade). Ideally, it prefers a slightly acidic, compost- rich, moist, well-drained soil. summer foliage often yellows (turns chlorotic) in high pH soils. Irrigate a newly planted tree in years 1 and 2 until it adapts to moderately dry summers. Fertilize lightly in late winter or before the tree blooms.

Leading cultivars: H. tetraptera ‘Rosea’ opens rose-pink and fade to pale pink. H. diptera ‘Magniflora’ bears 25% larger blooms than the species. ‘Wedding Bells’ is a new multi-branched shrub form from Dr. Mark Brand at the University of Connecticut.

Silverbells are disease and pest free if properly sited. This wonderful native provides food and shelter for birds and pollinating insects.

Coastal Azalea Copes With Heavy Clay Soils

Posted by Hugh on April 4th, 2013

Rhododendron atlanticum at Duke Gardens in Durham, NC

Coastal Azalea (Rhododendron atlanticum) is a deciduous native azalea that grows along coastal plains of the Mid-Atlantic and Southeast U. S. Their white 1 to 1 ½ inch tubular flowers appear about the time that lilac petals are beginning to fading. Flowers are snowy white with a pinkish blush, and emit a distinctly clove fragrance. Blooms open a few days before the new spring foliage.

Coastal azalea forms a low compact deciduous shrub. It rarely grows taller than 4 feet in height and 4 to 6 feet wide. It should be grown in full sun (in zone 5b -6) and in partial shade (zones 7-8). Coastal azalea grows best in a well- drained acidic soil. It should be watered during prolonged summer dry spells. Its bluish-green foliage remains disease and pest free if plants are not environmentally stressed.

Coastal azaleas are highly stoloniferous, spreading by underground stems and forming small plant colonies around themselves. They tend to sucker a lot less in clay soils. The cultivar R. atlanticum ‘Winterthur’ has an outstanding compact growth habit and tends not to sucker.

R. atlanticum is parent to a number of hybrid deciduous azaleas:

‘Fragrant Star’ (R. canescens x R. atlanticum) – fragrant white flowers (slightly larger than ‘Snowbird’); 4 by 4 foot compact shrub with blue green foliage, introduced by Briggs Nursery in Olympia, WA.

‘Snowbird’ (R. atlanticum x R. canescens) – 4 by 4 foot compact shrub with blue green, mildew resistant foliage; introduced by Biltmore Estates in Asheville, NC.

‘Marydel’ (R. atlanticum x R. periclymenoides)- abundant pinkish-white, fragrant flowers from late April into May; introduced by the late Polly Hill.

‘My Mary’ [R. atlanticum x R. periclymenoides] x R. austrinum – very fragrant yellow flowers in late April.

‘Appalachian Spring’ Dogwood Highly Disease Resistant

Posted by Hugh on April 1st, 2013

Flowering dogwood (Cornus florida)

This may be old news, but definitely worth repeating. Twenty five years ago a dreaded dogwood disease threatened to eliminate our beautiful spring flowering tree from our gardens. Appalachian Spring flowering dogwood (Cornus florida ‘Appalachian Spring’) was found at the Camp David Presidential Retreat atop Catoctin Mountain in Maryland.

Currently, Appalachian Spring is the only dogwood cultivar resistant to dreaded anthracnose (Discula destructiva) disease. It was introduced in 1990 by plant scientists at the University of Tennessee in Knoxville. These same scientists have also released four additional dogwood cultivars which are resistant to powdery mildew. Appalachian Spring is not resistant to powdery mildew disease.

Flowering dogwood is a small understory tree, preferring partial sunlight (morning and early afternoon hours are best). The white bracted flowers open in early spring in the Southern Appalachian region (USDA hardiness zones 6 and 7). Dogwood blooms heaviest in full day sun, but the tree’s life span is generally shorter. Two-year old established dogwoods exhibit good drought tolerant, but do benefit from irrigation during long dry spells. Mulching conserves soil moisture and cools the soil. Possible infestations of dogwood borer are also reduced.

Flowering dogwood grows in average garden soil that is well drained. Adding generous amounts of compost spread over the planting site (not the hole) is recommended. Young trees grow vigorously, often reaching 15 to 20 feet in height in 10 years. Feed dogwood(s) in late winter with 10-10-10 or equivalent fertilizer. In the fall green drupe fruit turn bright red, usually 2-3 weeks before the dogwood foliage turns bright red. Birds and other wildlife are dependent on dogwood mast over the fall and winter months.

Golden Hakone Grass Is Worth The Extra Care

Posted by Hugh on March 29th, 2013

Hakonechloa 'Aureola' Awakens Shady Garden Spot

Awaken dark zones in your shade garden with this wonderful golden treasure from Japan. Golden hakonegrass (Hakonechloa macra ‘Aureola’) grows 12-18 inches tall and 18-24 inches wide in a cascading mound form.

Very thin green stripes (veins) line the mid-rib of the ½ inch wide golden leaf blades. Tiny, relatively ininsignificant, floral spikes (inflorescences) appear for a short time in late summer. The grass blades take on a pink to reddish tinge in the cool fall air before all vegetation withers away for a long winter’s nap.

Golden hakone prospers in moist, humus-rich, well-drained soil. Contrarily, it grows poorly in compact heavy clay soils. Hakone prefers a partially shaded garden spot. Feed with a water soluble fertilizer (Miracle -Gro®, Schultz®, or Hollytone®) at package directions every 4-6 weeks from early spring thru mid-summer.

In its first year golden hakone starts off very slowly, and spreads from underground stolons. Soil moisture is in maximum need the first two years to successfully establish hakone grass. This extra attention will be worth your patience. Hakone grass will rarely trespass on spaces occupied by neighboring hosta, astilbe, heuchera, and others in the shade garden.

Golden hakone is rarely bothered by disease or insect pests and is not troubled by deer. ‘Aureola’ hakone grass was selected the Perennial Plant of the Year in 2009.

Shredded Umbrella Plant Handles Dry Shade

Posted by Hugh on March 27th, 2013

Syneilesis aconitifolia at Kingwood Center, Mansfield, Ohio

Shredded umbrella plant (Syneilesis aconitifolia) is a non-aggressive woodland ground cover which is native to dry hillsides in China, Japan, and Korea (USDA hardiness zones 4 thru 8). It has a medium green lacy foliage which you will treasure in the shade garden.

While its flowers may be tiny and inconspicuous, the circular umbrella foliage canopy is nothing short of WOW! In early spring the new foliage emerges through the decaying leafy garden debris which carpets the ground. Each leaf is completely clothed with white hairs, exhibiting a soft gray color and fine texture. As the plant matures, a green umbrella leaf canopy dominates and the gray hairs slough off.

While shredded umbrella plant gets by in a moderately dry woodland habitat, it thrives in a compost-rich, well-drained, moist, heavily mulched soil. The rhizomes slowly spread (2 feet wide in 5-7 years) to form a small plant colony.

Stout 16-18 inch high sturdy stems support the circular leaves. On multi-year old plants, individual leaves may average a small dinner plate in size and are dissected as some Japanese maple varieties.

Shredded umbrella plant mixes well with other woodland favorites such as dwarf Solomon seal (Polygonatum humile), brunnera, and ferns. Munchkin Nursery on-line is one of several sources of shredded umbrella plant.

Tiger Eyes® Sumac Far Less Aggressive

Posted by Hugh on March 25th, 2013

Rhus typhina 'Tiger Eyes' in late summer

I’m uneasy to recommend our native invasive sumac in a home landscape, but Tiger Eyes sumac (Rhus typhina ‘Bailtiger’), known as Tiger Eyes®, is far less aggressive (USDA hardiness zones 4-8). Its brightly colored cut-leaf foliage will definitely catch your attention in the summer. Leaves turn maroon-red in the autumn.

This small deciduous tree or medium tall shrub grows 6 by 6 feet high and wide (eventually to 10-12 feet high after 10 or more years). Short-growing Tiger Eyes is also a treasure planted in wide-based garden containers, perhaps mixed with low growing annuals, perennials, and/or vines. Lush tropical-like summer foliage and fall color blast ends with coarse hairy dark stems over winter.

As landscape plants sumac exhibits tremendous adaptability. This sun-lover thrives on neglect, at home in damp, nutrient poor soils. Seasonal foliage colors are more dynamic when planted in full sun. One-year established plants survive long dry spells, although leaves take on a haggard appearance.

Tiger Eyes is a sterile form and will not seed in and spread all over the neighborhood. Flowers are not significant. Tiger Eyes is less aggressive regarding suckering, but it does forms small plant colonies over time. It is not difficult to confine to a space. Prune it mercilessly to the ground whenever you feel the urge.

Something New to Grow – Esperanza, Yellow Bells

Posted by Hugh on March 22nd, 2013

'Gold Star' Esperanza -photos by Susan C. Morgan, Dallas Arboretum, Dallas TX

'Gold Star' closeup

Esperanza or Yellow Bells (Tecoma stans) is a 6 foot tall perennial shrub that grows in South Texas and Mexico (USDA zones 8-10). Esperanza means “hope” and it is destine to become a popular flowering annual in more U.S. Southeastern gardens. It demands a well drained soil and full sunlight.

In the Southern Appalachian region (USDA hardiness zones 6 and 7), plant esperanza as a bedding annual or large container plant. Large trumpet-shaped yellow flowers bloom from May to October. The 2 1/2-inch bright yellow flowers are highlighted byattractive shiny green foliage. The flowers have an odd but pleasing fragrance and attract bees.

Its growth rate is exceptionally fast if provided lots of irrigation and fertilizer. Place esperanza near the back or edge of a border. If grown as an annual, it will grow 3 to 4 feet high x 2 to 3 feet wide in average garden soil with a neutral to alkaline pH. Water and fertilize when first planted and into late spring. Once established, it can tolerate long summer dry periods as is frequent in Texas.

Esperanza plant(s) must be dug moved indoors in zone7 and further north in the fall for freeze protection. Cut back plants severely to force new growth indoors.

Long 4- to 6-inch long capsule fruits (beans) set on after the flowers. Quick removal of the beans increases flower numbers. Collect the ripen seeds for starting new esperanza plants in the spring.

In times past Indians made bows from esperanza wood. In Mexico a beer was prepared from its roots and for a variety of medicines.

Fall Color Calendar For Red Maple

Posted by Hugh on March 20th, 2013

'October Glory' red maple in East Tennessee

Red maple (Acer rubrum) is commonly planted as a 40-60 feet tall street or shade tree (USDA hardiness zones 3-9). Tiny red flowers burst open early, often in early March throughout the Southern Appalachian region (USDA hardiness zones 6 and 7). Flowers give way to reddish double winged samaras. Its glossy dark green 3-5 lobed leaves are 3-6 inches across and with deep red petioles. Red Maple’s most identifiable trait is its vibrant autumn leaf colors, which can vary by a month or more depending on cultivar.

Red maple is native to moist well drained soils, preferably in full to partial sunlight. It tolerates wet soils and is unswayed by temporary flooding, such as in rain gardens. In some Midwest states it has earned the nickname “swamp maple”. It is resistant to urban air pollutants.

Red maple may be troubled by insect or disease problems, often when tree is planted on a poor landscape site. Leaf aphids, wood borers and scale insects can be occasional pests. Verticillium wilt disease attacks the vascular system, frequently the result of unusually long dry spells lasting three or more years.

Red maple is sometimes called “soft maple” because high winds and ice storms may break branches. Its notoriously shallow root system may raise adjacent sidewalks or driveways. Pruning is best postponed until the spring and summer months when sap pressure in low. Sap from this species can be used to make maple syrup.

Five popular cultivars (rated by fall leaf color date) in the southeast and mid-Atlantic states include:
Autumn Blaze® (A. x freemanii) – 50 ft. x 40 ft. – earliest deep burgundy red leaf color
Red Sunset® (A. rubrum) – 45 ft. x 35 ft. – early bright red leaf color
‘Autumn Flame’ (A. rubrum) – 35 ft. x 15 ft. – better red color in southeast U.S.
‘Armstrong’ (A. rubrum) – 45 ft x 15 ft. – columnar habit for narrow street plantings and variable fall color
October Glory® (A. rubrum) – 40 ft. x 35 ft. – one of the latest for red fall color

Little Girl Magnolias Avoid Early Spring Frosts

Posted by Hugh on March 17th, 2013

'Susan' Magnolia

The early flowering deciduous magnolias, namely star (Magnolia stellata) and tulip (M. soulangeana) magnolias, are often susceptible to late winter-early spring frosts. In the 1980’s the U.S. National Arboretum released the series of 8 shrub-type cultivars called the “Little Girl Magnolias”. They were crosses between M. liliiflora and M. stellata. Over ten years these deciduous shrubs will grow 10- 20 feet tall and wide.

Little Girl magnolias represent a great leap forward in developing a later flowering forms. Each cultivar blooms 7-10 days later in spring. The large goblet-shaped flowers are long tepals (petals and sepals) which measure 6 to 9 inches in length. ‘Ann’, ‘Betty’, ‘Susan’, and ‘Jane’ have been the popular choices among the eight introduced cultivars.

Flower colors vary by cultivar in pink to purple shades. Little Girl magnolias often surprise with occasional blooms through the spring and summer months. They are commonly large multi-stemmed shrubs, which can be easily trained into small trees. The deciduous leaves are thick and leathery and cope with summer’s heat and dry spells. With proper care and on the right planting site, magnolias are generally long-lived and disease and pest free.

Little Girl magnolias grow in moist, well-drained soils, preferably with a slightly acidic pH, and in full to partial sun (3 – 4 hours minimum sunlight). They do not tolerate flooding or wet feet. Prune spring flowering magnolias soon after the spring flowering flush is over. Prune to remove basal suckers and to maintain the desired shrub or tree form.

Magnolias can be easily started by layering a branch to the ground in the spring. Bend the flexible shoot to the ground and hold down with a heavy rock. By autumn a rooted shoot may be cut away from the main branch, dug up, and moved to its new garden location or gifted to a garden friend.