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

Siebold Viburnum Makes Wonderful Small Tree

Posted by Hugh on May 3rd, 2015

Viburnum sieboldii ripening red (later black) fruits in late August

Newly Opened Flower Cluster

The genus Viburnum is no stranger to U.S. gardens. Many species and cultivars of viburnums are popular. Siebold viburnum (V. sieboldii) is a large spring flowering species from eastern Asia (USDA hardiness zones 5-7), but is under-planted in today’s gardens. This multi-trunk large shrub to 12 to 15 feet high or 25 to 30 feet tall as a small tree.

This large, coarsely-textured shrub is covered with clusters of creamy white flowers in mid-spring (late May into June). Clusters of edible berry-like fruits (drupes) follow, each 1/3 inches in diameter; drupes eventually turn pinkish red starting in late August. Birds and other wildlife snap up the ripened black fruits fall into winter. The smooth light gray bark is a winter asset.

Dark green prominently veined leaves hang on long into autumn, eventually turning yellowish green before abscising. This naturally large multi-branched shrub is easily trained into a small tree and is a good choice for planting under power lines. Fashioning a young shrub into a small tree via pruning is not difficult.

Siebold viburnum grows and blooms more abundantly in full sun on a well-drained, moist, moderately acid soil. Two-year established shrubs are moderately shade and drought tolerant. It is rarely troubled by diseases and pests.

Plant enmasse to develop a tall hedge or thicket to shelter wildlife and provide them a feeding station.

Two cultivars of note:

Ironclad™ (‘KLMfour’) grow 15 feet tall and 12 feet wide with rugged foliage which gives striking coarse textured look

‘Seneca’ (U.S. National Arboretum introduction) is exceptionally hardy (zone 4) with lustrous dark green leaves that often hold on until late November.

Good News About Garden Impatiens

Posted by Hugh on May 1st, 2015

Impatiens Bounce Pink Flame at Univ. of Georgia Trial Gardens (photo by Meg Green)

Gardeners no longer have to give up growing garden impatiens (Impatiens walleriana). No, the worldwide disease outbreak of downy mildew on garden impatiens is not over. But new disease resistant cultivars of impatiens are arriving at garden centers this spring.

Two of the newest are: SunPatiens® Spreading Shell Pink and Bounce® Pink Flame (‘Balboufink’). Sunpatiens thrives in half-day to full sun. Bounce impatiens are New Guinea types and grow either in modest shade to half-day morning sunlight (zones 6-8).

Spreading Shell Pink, the newest addition in the series, is covered with lovely soft pink flowers from late spring to first fall frost. After transplanting a strong rootsystem takes hold quickly and these impatiens thrive in summer’s heat, rain and humidity. Plants have a vigorous spreading habit and plants maintain excellent plant form through the summer in full sun to light shade.

Bounce impatiens are interspecific hybrids with New Guinea impatiens (I. x hawkeri); they look like old-fashioned garden impatiens in plant habit, flower form and count, but are completely downy mildew resistant. One of four new cultivars in the Bounce series for 2015, Pink Flame boasts massive numbers of stunning, bright pink bicolor blooms on plants that are 12 to 18 inches high and spread.

Bounce and Sunpatiens are low-maintenance flowering annuals to grace your garden this year and many more. Both new impatiens are highly disease and pest resistant. Feed plants monthly with a water soluble fertilizer such as Miracle-Gro™, Daniels™ or Schultz™. Mulch at transplanting time and irrigate during moderate dry spells through the season.

All-America Selections (AAS) has picked out these two impatiens for their exceptional performance in the AAS container trials.

Sooty Mold Is Symptom Of Aphid Feeding

Posted by Hugh on April 29th, 2015

Sooty mildew on hackberry leaves (Photo courtesy of Dr. Alan Windham, UT Ext. Plant Pathologist, Nashville, TN

Wooly Asian hackberry aphids (A. S. Windham photo)

Aphids are small (1 to 10 mm long) and pear shape. Infestations are often worse during wet cool days of spring; they are frequently feed on new growing shoots and leaves. Actively growing weeds also harbor aphids and may migrate over to favorite garden plants. Summer feeding aphids should never be counted out. Feeding aphids may spread a number of bacterial and virus diseases from sickly to healthy plants.

Color varies by aphid species and are capable of changing their color. Common colors include green, dark pink, yellow, and black. Many are smooth and shiny, and a few are wooly or covered with fluff. Most aphids are wingless, but some may form wings a new aphid colony to find a new food source when plants they’re feeding on are in poor shape.

Aphids do not possess chewing mouthparts. They don’t nip chunks out of leaves or stems. Instead they have piercing or “stylet” mouthparts to draw out the sap from sugary phloem tissues. Plant damage shows up as leaf curling, stunted growth, yellowing (chlorotic), or any combination thereof.

Their reproduction rates are very rapid. Aphids can reproduce without mating. Aphids also molt 4 times before maturing as adults. The old flakey skins are frequently seen over leaf surfaces. A wet or sticky honeydew deposit builds up over leaves and stems; later, black mold fungus colonizes over leaf surfaces. The sooty appearance looks unattractive. The sooty mold may be partially hosed off.

Several pesticides are effective against aphids in a garden. Insecticidal soaps and oils kill aphids on contact. Systemic pesticides like neonicotinoids provide longer activity, but may harm many beneficial insects such as bees and butterflies. Products containing Beauveria bassiana, Azadirachtin (neem oil) and Endeavor (pymetrozine) control aphids without harming most beneficial insects.

The soft bodied aphids have numerous natural enemies including ladybugs, lacewings, fly larva, wasps, true bugs. Parasitic wasps may be purchased and released to reduce aphid populations.

American Fringetree – A Spring Flowering Treasure

Posted by Hugh on April 28th, 2015

American fringetree

American fringetree (Chionanthus virginicus) is one of the finest spring flowering trees (USDA hardiness zones 4-9). Individual flower heads are large and billowy, snowy white, and very fragrant in the early evening hours. Flower panicles peak through the large leaves, and are large and showy compared to Chinese fringetree (which I also like).

Leaf sizes range from 3 to 10 inches in length and exhibit a high-gloss upper surface. Fringetrees rate above average disease and insect resistance. Seedling forms are quite variable in summer leaf colors (medium to dark green) and in fall leaf color (pale green, yellow, and brown). On occasion, individual fringetrees surprise with sensational autumn color.

In its early years plants start off slowly. Shoot growth may be wild and require pruning attention. Shrubs can be trained into 1 to 3 trunk trees through judicious annual pruning. Remove most, if not all basal suckers during the first 3-4 years. Staking may be required the first 1-2 years to develop a strong leader(s).

American fringetree is dioecious; male flowers are non-fruiting, while female flowers bear ½ inch long egg-shaped blue-black fruits (drupes). Seeds collected and sown in the fall germinate 2-3 years later. ‘Emerald Knight’, a male form, exhibits slightly upright branching and dark green leaves. Reportedly, ‘Emerald Knight’ may be propagated vegetatively.

American fringetree prefers full sun but grows okay in light shade with less flowers. Plant in a wide range of soils that are well-drained and lightly acidic. A 3 to 5 gallon plant will grow to 25 to 30 feet tall and wide in 20 years. Keep newly planted shrubs lightly mulched and irrigated. Two-year established plants demonstrate good drought tolerance. In southern climes fringetree performs better sited under light afternoon shade.

Caveat: People often confuse the name “fringetree” (Chionanthus) with “fringe flower” (Loropetalum)

New ‘Pam’s Mountain Bouquet’ Kousa Dogwood

Posted by Hugh on April 25th, 2015

Fused Bracts of ‘Pam’s Mountain Bouquet’ Chinese Dogwood (photo by Dr. Alan Windham, UT Plant Pathologist, Nashville, TN)

‘Pam’s Mountain Bouquet’ is a new Chinese dogwood (Cornus kousa) cultivar from the plant scientists from the University of Tennessee Dogwood Working Team (USDA hardiness zones 5-8). Mountain Bouquet is a near-white flowering form whose petal-like bracts fuse into near perfect squares. The cultivar blooms slightly later than other flowering dogwoods, helping to extend dogwood’s spring flowering season.

Mountain Bouquet tends to bloom heavily annually. Its unique fused bracts should become the point of conversation in your garden. About 82% of all bracts display some degree of fusion among the yellow-green colored bracts. UT plant scientists report that 80% of bracts were partially attached; 50% had all four bracts fused together. Mountain Bouquet is also highly resistant to powdery mildew and dogwood anthracnose foliar diseases.

The cultivar was discovered among a planting of seedlings at the University of Tennessee (UT) Arboretum in Oak Ridge, TN from seed gifted to UT by Ms. Polly Hill. ‘Pam’s Mountain Bouquet’ is a selection from the original seedlings.

Mountain Bouquet is expected to become available to homeowners in the next 3-4 years as nurseries build up their inventory. You may ask: “who is Pam?”. She is the wife of Dr. Robert (Bob) Trigiano who developed this amazing new dogwood.

Japanese Kerria Beautiful Old-fashioned Shrub

Posted by Hugh on April 23rd, 2015

Japanese kerria (Kerria japonica)

Kerria’s Winter Green Branches (Biltmore Estates, Asheville, NC)

Japanese Kerria (Kerria japonica) is an old fashioned shrub that never seems to go out of style (USDA hardiness zones 5-9). Some call it the “Yellow Rose of Texas”, although kerria originates from eastern Asia. Its showy yellow buttercup-like flowers bloom in spring, after the forsythias have finished. In winter you’ll fall in love with kerria’s graceful arching bright green stems.

Kerria is easy to grow and is highly adaptable to almost any garden locale. Depending on cultivar, it grows 3-8 feet tall and 6 -10 feet wide. You may opt to grow it in full or partial sunlight and it tolerates moderate shade. It develops into an excellent woodland plant, although flowering is less. Kerria adapts to almost any soil type, preferring a moist well-drained site.

Provide lots of room as this shrub tends to sucker freely; holding plant colonies in check may become a chore. Foliage may burn in full afternoon sun, particularly white edged variegated forms. Container grown nursery-grown plants may be set almost anytime from late winter to mid-autumn.

Keep the soil moist until the shrub becomes established after its first year. It suffers during long dry spells resulting in stem dieback. No fertilizing is necessary as nitrogen stimulates suckering and less flowering. Fall leaf color is insignificant.

Kerria should be pruned following spring bloom to maintain a desired size and to remove dead branches and twigs. Every few years kerria should be completely renovated following spring flowering; cut back the entire shrub to within 12 inches from the ground. Diseases and pests are rarely a problem.

Selected Cultivars:

‘Geisha’ – attractive yellow and white speckled variegated leaves.

‘Golden Guinea’- large single flowers and 4-5 feet tall shrub (commonly sold in U.S. garden centers).

‘Picta’ – white edged leaves; protect from afternoon sun in southerly areas; prune off reverted green leaf shoots.

‘Pleniflora’ (‘Flora Pleno’) – double flowered form with wicked suckering habit.

‘Shannon’ – produces larger single blossoms on 5 to 6 feet tall shrub.

Many New Beebalm Cultivars Continue to Roll Out

Posted by Hugh on April 21st, 2015

Monarda didyma at Kingwood Center, Mansfield, Ohio

Bee balms, aka bergamots or Oswego tea (Monarda spp.) are native to eastern North America (USDA hardiness zones 4-9). Plants are easy to grow, bloom beautifully, and multiply rapidly. They are treasured for their raging colored flowers and medicinal properties. Numerous bee pollinators as well as butterflies and hummingbirds favor the summer blooms.

The native M. didyma produces scarlet red flowers on stems up to six feet tall. New hybrid cultivars are crosses with the shorter M. fistulosa and/or early blooming lavender to pink flowers ofM. bradburiana. The resulting hybrids come in red, violet, purple, pink, and white.

Classic selections such as ‘Gardenview Scarlet’ and ‘Jacob Cline’ continue as standard bearers in the red beebalms. ‘Purple Rooster,’ ‘Raspberry Wine,’ and Grand Parade are rated the best in the purple category. ‘Marshall’s Delight’ (3 ½ feet height) and ‘Pardon My Pink’ (10-12 inch height) are two of the better pinks.

A new Sugar Buzz™ series includes ‘Bubblegum Blast’(hot pink), ‘Cherry Pops’ (cherry red), ‘Grape Gumball’ (vibrant magenta), and ‘Lilac Lollipop’ (lilac). All four cultivars are similar in size, mid-summer bloom time, and vigor. Their 12-15 inch size range fits perfectly into the middle of a flower border. The solid dome flowers sit atop strong, well-branched stems and all display above average resistance to powdery mildew.

Beebalms grow naturally in moist meadows, along rivers and streams, and in forest clearings. Surprisingly, they do grow near black walnut trees. Full sun is best, although plants do thrive in partial sunlight if air movement is adequate. Cutting plant(s) to the ground in late summer will stimulate fresh new growth.

Beebalms should be grown in a well-drained, compost-rich, moderately acidic (pH of 5.5-6.5) soil. They also prosper in containers filled with a porous peat/bark soil-less media mix. Plants are moderate feeders; three bi-monthly feedings of water-soluble fertilizers such as Miracle-Gro™, Nature’s Source™, and Daniels™ is adequate.

Deadhead old flowers for re-bloom a month or so later. Maintain moderate soil moisture levels. Irrigate plants in early morning so as not to encourage, powdery mildew. Aphids, spider mites, thrips, and whiteflies are a few common pests. None are fatal.

Wonderful Bellworts For Woodland Gardens

Posted by Hugh on April 18th, 2015

Late May foliage

Bellwort (Uvularia grandiflora)

The soft yellow bell-shaped flowers of bellworts (Uvularia spp.), aka merrybells, contribute to spring’s awakening in U.S. woodlands and shade gardens (USDA hardiness zones 3-9). On both U. grandiflora and U. perfoliata, flower stems pierce (pass through) the center of the leaves. A third species, (U. sessilifolia), nicknamed Wild Oats, grows in northern woodlands; leaves of latter are sessile (without a peduncle) and are not pierced by floral stem.

All are U.S. natives and bloom in April, May or June depending on regional location. Bellworts are members of the Liliaceae family, and are among the easiest of wildflowers to grow. Their nodding bell-shaped flowers are a springtime delight. Bellworts appear delicate looking, but are hardy and enduring. Over the years individual clumps colonize among themselves from thick fleshy white underground stolons.

Bellwort leaves are elliptic, glaucous (blue-green), and entire on 6-18 inch tall plants. Each solitary flower is just over an inch long composed of six soft yellow tepals (three petals and three sepals). Fruits (three-angled seed pods) form in the fall.

Plant bellworts in partial to full shade in compost-rich, moist, well-drained woodsy soil. Leaves turn clear yellow in early fall; it’s not unusual to observe some leaf burn on edges after a dry summer. Bellworts tolerate dry calcareous (limestone) sites after settling in for 2 years. No insect or disease problems are rare, but young emerging shoots may be damaged by slugs.

“Wort” is a name formerly given to plants used for food or medicine. Bellwort was sometimes used to cure throat problems.

Gomphrena (Globe Amaranth) For Summer Easy Color

Posted by Hugh on April 15th, 2015

Late summer display of Gomphrenas at UT Gardens in Knoxville, TN

Gomphrena at UT Gardens in Knoxville, TN

Gomphrena, aka Globe amaranth, is an annual bedding plant that blooms profusely in the summer heat and sun. Small ball-shaped flowers are clove-like in appearance. Many gardeners tend to ignore them at the garden center for showier flowering annuals. By mid-summer, a peek into your neighbor’s yard may cause to rethink that decision. Gomphrenas root down deeply and bloom way into the autumn, often without additional care. Dried gomphrena flowers are favorites of florists.

Depending on the choice of variety, plants grow 10 to 24 inches high and 12 to 16 inches spread. Their color palette includes purple, pink, orange-salmon, and red. Gomphrena’s small flowers are magnets for attracting butterflies and other nectar feeders to garden beds and containers.

Gomphrenas prosper in full sun and in average well-drained soil. Space plants a foot or so apart. Add a slow-release fertilizer to each planting hole. If summer leaves look chlorotic, 1-2 applications of a water-soluble fertilizer such as Miracle-Gro, Nature’s Source and Daniels will green them back up. Once plants are well established, water needs become minimal.

Gomphrenas attract very few insect pests and no diseases. Spider mites may be troublesome when weather is exceptionally dry. A blast of water to the underside of leaves reduces their populations without resorting to pesticides.

‘Fireworks’ is one of the new generation of gomphrena cultivars; one inch flowers appear as explosions of pink with yellow stamens. ‘Audray Bicolor Rose’ has two-toned flowers, rose colored at the base and white on top. The Las Vegas series (white, pink, purple) have been outstanding performers.

‘Audray Bicolor Rose’ gomphrena, Kingwood Center, Mansfield Ohio

Less Invasive Rose Of Sharons (Altheas)

Posted by Hugh on April 12th, 2015

‘Purple Chiffon’ Althea

‘Diane’ althea

In several states rose of Sharon or altheas (Hibiscus syriacus) are classified as exotic (non-native) invasive shrubs (USDA hardiness zones 5-8). Their seedlings are invading U.S. woodlands. Plant breeders are now developing less invasive cultivars.

The double-flowered altheas produce far fewer fertile seeds; stamens and pollen sacs are mostly embedded within the flower petals. Azurri Blue Satin® is a new seedless form with celestial blue blooms. Sugar Tip® althea is covered with light pink and white double frilly petal blooms; Sugar Tip’s variegated foliage is green with creamy white edges. Both cultivars grow 8-12 feet tall and 4-6 feet wide.

Most double-flowered altheas produce some fertile flowers and are much preferred over open single invasive forms. Among the best are Blue Bird (dark blue double), Blushing Bride (multi-pink shades double), Freedom (purplish-pink), and four cultivars in the Chiffon series (Blue, Lavender, Pink and White).

Over a quarter century ago, the U.S. National Arboretum released four tetraploid cultivars, called the Roman Goddess series. Diana (white), Aphrodite (rose), Helene (white/purple), and Minerva (lavender) are seedless forms.

Altheas grow best in full sun and in average, well-drained, pH neutral soil. Altheas are utilized as single specimen shrubs, or grouped together for hedging, privacy screening or border plantings. They attract butterflies and hummingbirds, plus deer generally leave altheas alone. Prune as needed to size and shape from late fall thru winter. Altheas bloom on current season growth. Apply a slow release fertilizer such as Osmocote™ and Nutrikote™ in early spring as new growth begins to emerge.