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

Mussaenda: A Stunning Tropical For Summer Gardens

Posted by Hugh on August 27th, 2017

Mussaenda red hybrid at Biltmore Estates in Asheville, NC

Mussaenda ‘Queen Sirikit’

Mussaenda (Mussaenda spp.) is a small tropical tree or large shrub. It’s a spectacular bloomer that grows to 10-15 feet tall in tropical zones (USDA zones 10-12). It is sometimes called “tropical dogwood” or “Buddah’s lamp”. In large containers it will reach 1-3 feet tall. Mussaenda blooms from late spring to mid-fall in mild-winter areas. Bloom colors range from yellow, red or creamy white with red, white or pink bracts or sepals surrounding the flowers. The spectacular blooms attract butterflies, bees and birds.

Plant into a well-drained potting mix or humus-rich, mildly acidic soil and keep media moderately moist. Mussaenda grows robustly in direct sunlight, preferably 6 hours or more daily in cool regions of the U.S. Further south (zones 7b -11), expose to morning or late afternoon sun only and keep mostly shaded during the hot midday period for best summer flowering. The plant establishes quickly, within 6 weeks after initial planting. Prime flowering season is from late spring to very early fall (in zones 6 and 7).

Feed with a slow-release fertilizer granules such as Osmocote® or Nutrikote® at package directions. Cuttings should be collected in late summer. Flowering and growth slows down or stops once temps fall into the low 50°Fs. Overwinter in a greenhouse or a sun room. Prune back plant(s) hard before bring it indoors for overwintering. Mussaendas are relatively insect and disease free, although scale, mealybugs and mites are sometimes problems.

Swallowtail on flowers

Cultivars:

Five different species are in cultivation and along with hybrid cultivars, ranging in height from 2 feet to 15 feet tall.

M. erythrophylla ‘Queen Sirikit’ grows very shrub-like with pale yellow to white flowers with red centers and peach colored bracts. Their pendant flowers often appear floppy ‘flowers’ and in urgent need of water.

Tropical Beauty Of African Rose Mallow

Posted by Hugh on August 24th, 2017

Hibiscus acetosella ‘Cranberry’ in Baltimore, MD

Hibiscus ‘Red Shield’

African Rose Mallow (Hibiscus acetosella), aka Red-leaf Hibiscus and false Roselle, is grown in most of the U.S. as a colorful annual, although it is rated as a perennial shrub for USDA Zones 9-11. It is native to Africa and, as expected, thrives in hot tropical environment such as in the deep South or Southern California and Arizona where the growing season is a lot longer. Many U.S. gardeners grow rose mallow for their tropical foliage in summer and not for their flowers.

Rose mallow starts blooming in very late summer when daylength becomes shorter. Bloom continues through the winter until frost, or in tropical climates until daylength increases. Individual blooms measure 3.75 inches (9.5 cm.) and last one day.

If grown under full sun and adequate soil moisture, plants become deeply rooted and do not require staking. Foliage color is more intense and blooms fully in open sunny sites. Leaf hues are not as intense in partial sun and plants may need staking. They’re fast growing, up to 5 to 7 feet, along with a narrow single main stem. To promote a better branched, shrubbier habit, pinch off the apical growing tip several times during the summer to develop a stocky 3- to 6-foot tall plant.

Plant it in any well-drained garden soil or in a rapidly draining potting mix when grown in large containers. To repeat this tropical hibiscus flourishes in areas with high summer heat and humidity. Leaves also tolerate salty air along coastal areas.

‘Red Shield’, ‘Cranbury’, and ‘Maple Sugar’ are popular cultivars (possibly the same variety?). Their glossy purplish-red multi-lobed foliage looks similar to Japanese maples.

The brightly colored flowers attract numerous insect pollinators and birds and hummingbirds. Usually deer stay away. Leaves are edible, the crunch of leaf lettuce, but with a slightly bitter taste (in my opinion). Please pass the salad dressing.

Prairie Dropseed (Sporobolus) – A Durable Ornamental Grass

Posted by Hugh on August 20th, 2017

Sporobolus at NC Arboretum

Prairie Dropseed at NC Arboretum in Asheville

Prairie dropseed (Sporobolus heterolepsis) is one of the finest warm season grasses native to the Western U.S. (USDA hardiness zones 3 to 9). Initially, this clump-forming perennial grass grows at a slow to medium rate. By early summer its fine textured deep green leaves form an arching fountain habit. Prairie dropseed inhabits prairies, meadows, open ground, and along railroads.

Clump develops into a mound an average of 2-3 feet tall and wide. By late summer, loose, airy, tan colored inflorescences emerge on 2-3 feet tall spikes along with its unique fragrance. Some report that it smells like coriander, cilantro, or popcorn. By late October the foliage turns russet color and in winter to light bronze.

Prairie dropseed excels in hot, dry conditions where it can really soak up the sun. This grass is exceptionally drought tolerant and is tolerant of soils with low fertility. Initially slow to establish, new plants may be started from seed, although it does not freely self-seed in a garden.

No serious insect or disease problems trouble this native grass. Deer generally leave it alone. Its deep fibrous rootsystem provides exceptional soil erosion control and it resistant to air pollution.

‘Tara’ is a dwarf selection from Roy Diblik. Tara grows slower than the species and has a more upright v-shape habit; leaf blades take on a golden to pumpkin orange color in fall. Utilize it to edge front of beds and borders and in rock gardens. It is beautiful in mass plantings such as meadows. In fall, foliage turns a rust-red color, and seeds provide food for birds.

Landscape use: grow it for its architectural form or as a tall groundcover, or in rock, prairie, meadow, and rain gardens. Annual maintenance is minimal. Cut back old clumps and you may opt to fertilize lightly with 10-10-10 or equivalent in early spring.

Blonde Ambition® Blue Grama Grass

Posted by Hugh on August 17th, 2017

‘Blonde Ambition’ Blue Grama Grass near Fort Collins, Colorado

Seed heads

Looking for something a little different, plant Blonde Ambition® blue grama grass (Bouteloua gracilis ‘Blonde Ambition’). It was discovered and introduced by David Salman of High Country Gardens. This prairie species is native from Manitoba Canada, south through the Rocky Mountains, Great Plains, and Midwestern states, to Mexico. It is exceptionally heat and cold hardy and recovers rapidly following a heavy snow cover (USDA hardiness zones 3 – 9).

The fine-textured gray-green leaf blades (to 1/4 inch wide) typically form a dense clump growing 18 to 24 inches tall. Foliage turns golden brown in late autumn, at times taking on an orange and reddish hues.

Blonde Ambition is unlike any other ornamental grass in cultivation. In early summer its unique eyelash-like chartreuse flowers stand like tiny horizontal flags on stems that rise a foot or more above the foliage. The chartreuse flower color ages to blond, so different compared to the dark purplish flowers of the species. The long lasting blonde seed heads stay fastened to wiry blue-green stems and poke through after a heavy snow.

Plant in full sun in most any soil, acidic or alkaline, as long as it is well-drained. Initially, irrigate a new plants so it fills in faster. It tolerates poor soil and is highly drought resistant. Lightly fertilize with 10-10-10 or equivalent in early spring, although this tough grass will cope with low fertility. Start off by mowing off the planting in the early days of spring. Diseases or pests are non-existent and deer and most other four-legged browsers of vegetation stay away.

Blonde Ambition was a 2011 Plant Select winner. It is primarily available from e-commerce native plant nurseries.

Avoid Dreaded Tulip Fire Disease

Posted by Hugh on August 14th, 2017

Tulip Fire (Photo by Chuck Gleaves, Horticultural Director at Kingwood Center in Mansfield, Ohio)

Tulip mix

For over a one-half century Kingwood Center in Mansfield, Ohio has been widely known for their fabulous tulip displays every spring. Over the past few years Kingwood’s garden staff had noted a decline in bloom because of a disease identified as “Tulip Fire” (Botrytis tulipae).

This fungal botrytis disease tends to accumulate in the soil in wait of an ideal environmental weather pattern. In previous years the staff had treated tulip beds with appropriate fungicides, but spring 2017 was the year of “the perfect storm”. Most of the tulips in six large beds were lost to this botrytis disease. Combined with an unprecedented attack from rodents, garden staff had to pull out the tulips and posted signs of the “crop failure”.

“The problem has been accumulating for 62 years”, says Chuck Gleaves, garden director, “and no immediate solution is expected”. Most gardeners have learned to adopt principles of crop rotation. Pesticide applications will not work here. All the tulips were removed from the six affected beds. This fall garden staff plan to plant hyacinths. No tulips will be planted in the affected beds for a minimum of two years. Planting costs will increase because hyacinths are considerably more expensive over tulips.

Gleaves promises that Kingwood will continue to grow lots of tulips, but in different areas and rotate hyacinths with tulips in selected beds. Over time, they hope to reduce the accumulated inoculum of Botrytis.

Additional Notes:

Non-chemical control

Check bulbs carefully and discard any with signs of the small black sclerotia in the outer scales, or with any signs of decay
Remove infected bulbs promptly to avoid contaminating the soil with sclerotia
Do not plant tulips for at least 3 years in sites where tulip fire has occurred
If a contaminated site must be replanted, dig the ground deeply to try and bury the contaminated upper layers deep enough to be below planting depth
Rotate tulips to new garden areas each year to avoid fungal scerotia buildup in soil.
Treat tulips as annuals and remove them after flowering.

Chemical control: Integrate chemical tactics with cultural controls. Alternate or tank-mix fungicides (not use same fungicide all the time):

Chipco 26019
Daconil
Cleary’s 3336 EG or OHP 6672 (Thiophanate methyl).

Sun Or Shade –These Six Shrubs Don’t Care

Posted by Hugh on August 10th, 2017

Mountain laurel at I-26 Rest Area, Asheville, NC

Daphne odora ‘Aureomarginata’ at Biltmore Estates, Asheville, NC

A surprising number of flowering shrubs perform beautifully in either sun or shade, making them quite versatile where planning a landscape. All can be utilize around outdoor living areas such as decks and patios. Several good candidates are these six:

Japanese pieris, aka lily of the valley shrub (Pieris japonica) is a versatile shrub for sun to part shade (USDA hardiness zones 5 to 8). This broadleaf evergreen shrub grows to 8-12 feet tall and up to 8 to 10 feet wide; most cultivated cultivars are generally smaller in size. New spring foliage emerges with a bright, rich orangey or bronze tint, which matures to dark, glossy green in summer. Leaf size ranges from 1 to 3.5 inches long.
Winter daphne (Daphne odora) is a broadleaf evergreen best grown in warmer climates (zones 7 to 9). It blooms from late-winter into early spring;. Soft pink to white flowers are sweetly fragrant. Leaves may scorch in full sun. Winter Daphne grows 3 to 4 feet tall with a spread of 2 to 4 feet.. Foliage is glossy and leathery; each obovate, 4-inch-long leaf is a rich, deep green. Several cultivars are available with ‘Aureomarginata’ (creamy or golden leaf edges are popular.
Oakleaf hydrangea (Hydrangea quercifolia) is among the largest of the six shrubs, reaching 6 to 8 feet tall and wide provided you select the correct cultivars. Species oakleafs easily grow 2-3 times larger. Shrub blooms on old wood; if pruning is necessary, wait until after flowering (zones 5 to 9).
Japanese kerria (Kerria japonica) is frequently mistaken for forsythia as both bear bright yellow flowers in spring and display a low-growing, arching shrub habit. Its flowers are single, five-petaled, yellow to golden yellow, rose-like blooms. Kerria grows to 3-6 feet tall and to 6-8 feet wide on slender, green stems that retain their color in winter. It is both deer and drought tolerant (zones 4 to 9).
Mountain laurel (Kalmia latifolia), related to Japanese Pieris, are at home in 1-2 hours of dappled or filtered sunlight. This evergreen shrub grows 5-7 feet tall and wide with glossy green 4-5 inch long leaves. Select from over 40 colorful cultivars, ranging from white, pink, pink-rose flowers which open in May (zones 5-9).
Leatherleaf mahonia (Mahonia bealei) is native to the forested areas of the far western U.S., reliably hardy in zones 5 to 8 and copes with considerable shade. It’s a broadleaf evergreen with a spreading to upright habit, usually reaching 4 – 6 feet tall by 4 – 5 feet wide, although if sited close to a wall or fence, it can be trained to grow taller.

All shrubs prefer moist, rich, well-drained soils and some amounts of morning sunlight. They are moderately drought tolerant after the first year. Flowers attract bees; fruit attracts birds deer resistant, birds love the berries. Prune within 4-6 weeks after spring bloom has ended.

Flowering Shrubs of Summer

Posted by Hugh on August 7th, 2017

Rose of Sharon (Althea)

Plumleaf azalea (close-up)

In several areas of the U.S. (USDA hardiness zones 6-9), summer landscapes along the east and west coast and Southern U.S. are filled with these botanical beauties:

Panicle hydrangeas (Hydrangea paniculata) – so many great choices of these hydrangeas, mostly with lime white flowers starting in July into August. Most popular cultivars are ‘Limelight’, ‘Little Lime, ‘Quickfire’, ‘Vanilla Strawberry’, ‘Diamond Rouge’, ‘Bobo’.

Bigleaf hydrangeas (Hydrangea macrophylla) – Bloomstruck® series, Endless Summer® series, LA Dreamin®, ‘Nikko Blue’, Lets Dance® Diva collection are among the winter hardiest to date

Chastetree (Vitex agnus-castus) -10-15 feet shrub in color choices ranging from purple (also lavender, pink and white) blooming; new dwarf 5-8 feet cultivars are coming to garden centers in near future. The current popular forms are ‘Shoals Creek’, ‘Montrose Purple’ and ‘Woodlander’s White’.

Summer sweetshrub (Clethra alnifolia), aka sweet pepperidge is an absolute bee favorite in my garden. Popular cultivars include ‘Sixteen Candles’, ‘Rosea’, and ‘Hummingbird’.

Flowering abelia (Abelia x grandifolia) – choose old-fashioned shrubs @ 12-15 feet;, modern compact cultivars at 4-6 feet such as Rose Creek®, ‘Mardi Gras’, Canyon Creek®,and ‘Ed Goucher’; low growing types 2-3 feet bsuch as Kaleidoscope®, ‘Confettii’, ‘Sherwood’ .

Altheas or Rose of Sharon (Hibiscus syriacus) -choose from Chiffon® series, ‘Blue Bird’, Roman Goddess series from U.S. National Arboretum (Aphrodite’, ‘Minerva’, ‘Diana’, and ‘Helene’).

Crape myrtles (Lagerstroemia x) – white, pink, rosy-pink, lavender, and red crape myrtles; available to four size catergories: tree (26-30 feet), intermediate (13 -20 feet), semi-dwarf (5-12 feet), and dwarf (3-5 feet).

Bluebeard shrubs (Carypteris x clandonensis) – small 2-3 feet high compact shrub that bloom from mid-summer into fall . Select cultivars ‘Dark Knight’, Longwood Blue®, Beyond Midnight®, Grand Bleu®, and Petite Bleu®; also gold leaf ‘Worcester Gold’.

Blue Mist shrubs (Caryopteris divaricata) – taller growing @ 4-6 feet and also bloom from late summer into fall; select from Snow Fairy® and ‘Blue Butterflies’.

Caryopteris divaricata ‘Snow Fairy’ at Biltmore Estates in Asheville, NC

Additional choices available from specialty nurseries include plumleaf azalea (Rhododendron prunifolium) and butterfly bush (Buddleia davidii) that bloom through most of the summer into autumn.

Comparing Encore™ and Bloom-A-Thon™ Azaleas

Posted by Hugh on August 4th, 2017

Rhododendron ‘Encore Autumn Rouge’ in late August

‘Bloom-a-thon Lavender’ at Biltmore Estates

Hey gardeners, how about azaleas that bloom nearly 5 months a year. Flowering lasts for 4-6 weeks in spring and another 12-16 weeks in summer and fall. Check out Encore™ and Bloom-A-Thon™ series of azaleas (USDA hardiness zones 6-10).

The main differences between these two azaleas is the Bloom-A-Thon series tend to bloom more abundantly in shaded sites and foliage and flowers will burn in full direct sunlight in hot parts of southern U.S. (zones 7b-10). The Encore series are bred to bloom in full sun and bloom less in shaded areas. The Bloom-A-Thon series tends to be more cold hardy for zones 6-9. Encore is hardy in zones 7-9 with nine or more cultivars winter hardy in zone 6 as well. Encore azalea come in lots more color choices.

To repeat, the Encore™ azaleas tolerate more direct sunlight and prefers 4 to 6 hours of direct sun; give them some afternoon shade in warmer climes. Bloom-A-Thon™ prefers part sun to dappled shade; too much direct sunlight may scorch flowers, particularly in the summer sun.

Bloom-A-Thon at this time only are available in four cultivars (red, white, lavender, and double pink). Growth height and width vary with the white cultivar (smallest) at 24 to 36 inches tall and wide and the lavender cultivar (tallest) at 60 to 72 inches tall and wide. Encore azalea series now includes 31 varieties with many different single and double flowers with many color choices.

General care: Water azaleas deeply at planting and keep garden and container soils moist into late fall. Established 1 year and older plants are generally moderately drought tolerant unless summer weather is unusually droughty. Fertilize according to recommended package directions for azaleas of popular brands of water soluble products such as Miracle-Gro™, Peters™ or Espoma™. Do not fertilize after early September. Pruning, if needed, in early spring is usually light, primarily to remove any dead or damaged wood and to shape and size the shrub.

Hard Working Perennials For Your Late Summer Garden

Posted by Hugh on August 1st, 2017

Mexican sage (Salvia leucantha)

New England aster

Add several fall-flowering perennials to your garden that will add late season color and pizzazz . These are reliable tough perennials, and beneficial pollinators love them. Visit garden centers in August to make your purchases.

However, for these great plants to return next year and subsequent years, plants need to get their root systems established. Have plants in their permanent garden spots by mid-August if you garden in northern climes. Most are hardy in zones 5-9.

Check out these hardworking perennials for a great autumn floral finish.

Tame goldenrods (Solidago x spp.) such as (S. rugosa) ‘Fireworks’ or (S. sphacelata) ‘Golden Fleece’ are garden-winning classics.

Fall blooming asters like New England (Symphyotrichum. novae-angliae) and aromatic asters (S. oblongifolius). There are lots of great cultivars.

Fall sunflowers (Helianthus spp.) – these are the perennial kinds like (H. angustifolius ‘Lemon Queen’), willowleaf (H. salicifolius), H. x multiflorus ‘Sunshine Daydream’ or hybrid cultivars like Helianthus x ’Lemon Queen’.

Hardy Plumbago (Ceratostigma plumbaginoides) is a low growing (ground cover) that starts blooming in August into autumn those blue flowers provide an unexpected pop of color as the rest of the landscape fizzles.

Pitcher Sage (Salvia azurea) is a Central U.S. native that grows in a variety of soil types. Russian Sage (Perovskia atriplicifolia) is mostly bloomed out by late summer unless properly deadheaded(zones 5-9). Blooming in late summer and early fall, pitcher sage is admired for its sky blue flowers and high drought tolerance. This salvia grows to 30 to 36 inches in height, but may be pinched back for bushier growth.

Mexican sage (Salvia leucantha), zone 7 hardy, is a fall-flowering perennial often at full-tilt as cooler temperatures set in.

Many kinds of stonecrop sedums come in a variety of sizes such as ‘Autumn Joy’, Dazzleberry® series, and ‘Matrona’.

Fall anemones (Anemone x) come in shades of white, lavender, and pink in full sun to partial shade.

The Ornamental Grasses:

Maiden hair grasses (Miscanthus sinensis) are beautiful in the early autumn landscape. Cultivars such as ‘Adagio’, ‘Rigoletto’ and ‘Morning Light’ are rated as less invasive types.

‘Northwind’ switch grass (Panicum spp.) offer long panicles of feathery flowers. Pink or white muhly grass (Muhlenbergia capillaries) display colorful billowy inflorescenses.

Little blue stem (Schizachyrium scoparium) are popular native warm season grasses; many varieties tend to lodge (fall apart) late in the season. ‘Standing Ovation’, a new variety, doesn’t fade or flop as temperatures drop off into winter.

Pest Alert – Crape Myrtle Bark Scale

Posted by Hugh on July 28th, 2017

Crape myrtle bark scale (Photo by Dr. Frank Hale, UT Entomologist, Nashville, TN)

Crape myrtle bark scale (photo by Dr. Frank Hale, Univ of Tenn. Extension Entomologist)

A new scale has been observed infesting crape myrtles (Lagerstroemia x indica) in north Louisiana and Texas cities. In the summer of 2016 it was found threatening crape myrtles in the Piedmont area of North Carolina and in west Tennessee (Memphis). Crape myrtle bark scale is a felt scale related to azalea bark scale and oak eriococcin scale. (Eriococcus lagerostroemia). It feeds on plants in Japan and China.

Female scales produce fluffy white filaments that cover their bodies. In spring they produce eggs beneath their body then die. Tiny crawlers hatch from the eggs, settle in their new spot, and begin producing white filaments. They have at least 2 overlapping generations. At low density, crape myrtle bark scale feeds in rough areas around branch collars but as the population increases all the bark may be covered. These scales are most often noticed because trees become covered in black sooty mold. At first many people assume this is from crape myrtle aphids and the scales may go undetected. If you notice unusually heavy honeydew and sooty mold on crape myrtles take a closer look at the bark.

This pest excretes honeydew that coats leaves and limbs, resulting in a sticky coating from the excess sugars excreted from the insects’ feeding. Sooty mold grows on the honeydew. This results in a black (sooty mold) coating that appears on the bark of the branches and trunks of crape myrtles. Additionally, white cases are visible, and they enclose the adult female scales.

Insects appear as white, waxy encrustations likely to occur anywhere on the plant but often near pruning wounds or in branch crotches. Up close, the bark scale insect is white to gray in color. Larger female scales “bleed” a pink liquid when crushed. Crape myrtle scale appears pink in color inside the case. Careful examination may reveal dozens of pink eggs under some of the larger white scale covers.

Recommendations for managing the scale are still being developed; however, current management suggestions for this scale include:

Wash the trunk and reachable limbs of heavily infested plants with a soft brush and mild solution of dishwashing soap. The egg masses and female scales will be washed off, resulting in improved effectiveness of insecticides. Also, the black mold building up on the bark of infested trees will be removed by washing. The scales and sooty mold may be removed by using water pressure. Removing the loose bark is important because the protected areas where the scales hide are removed. This removes the areas that the scales may use for protection from unfavorable weather in winter.
First application should be made between May and July with follow-up applications every 3-4 weeks as needed. Systemic insecticides include dinotefuran (Safari™) and imidacloprid (Merit™ or Bayer Advanced Garden Tree and Shrub Insect Control™). Drench applications of neonicotinoids are typically effective against phloem feeders. Read the labels for restrictions on using neonicotinoid pesticide as crape myrtle flowers attract multitudes of beneficial pollinators. Horticultural oil, especially the heavier dormant rate, can also reduce scale numbers.

If you find this scale on your crape myrtles, take a sample to the local Extension office for identification.

Credit: information for this blog supplied by the Extension Services of Louisiana State University in Baton Rouge and University of Tennessee in Knoxville.