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

Cosmos For Sunny Gardens

Posted by Hugh on May 15th, 2015

Cosmos Flowering in September

Reliable Cosmos

Cosmos, indigenous to Mexico and South America, are one of the easiest-to-grow flowering annuals. They start blooming in early summer and are at their best in late summer and early autumn. Two most popular species are Cosmos sulphureus and C. bipinnatus. Flower heads are composed of disc and ray flowers.

Cosmos is a member of the aster family. Today’s hybrids are brightly colored (red, pink, orange or white) that bloom freely like wildflowers. They attract birds and butterflies, particularly Monarchs. Blooms make terrific floral bouquets that will last for 7 – 10 days. Cosmos light green foliage is very fern-like.

Be aware that cosmos self-seeds freely. You may self-seed directly into the spring garden after the last spring-frost date or purchase plants at garden centers. Space plants approximately 1-2 feet apart; with tall varieties, space plants closer and let them support one another.

Cosmos thrive in average to subpar soils at neutral or slightly alkaline pH and that are well-drained. Plant heights vary from 1 to 5 feet depending on soils, cultivars, moisture, and fertilization. Excess soil nutrition will cause plants to grow luxuriantly at the expense of flower numbers. Plants tend to flop over in rich soil and may require staking to prevent stem breakage in high winds.

Pinch off spent flowers to encourage continuous bloom. Pinching stem tips reduces plant height and encourages branching, although is rarely necessary. Cosmos are mostly free of disease and pest troubles.

Fill Flower Gardens & Containers With Sweet Alyssums

Posted by Hugh on May 12th, 2015

White Alyssum (border) & angelonia (in back)

Sweet alyssum (Lobularia maritima) is one of the easiest annuals to grow. A member of the mustard family (Brassicaeae), it is native in the Mediterranean region and the Canary and Azores Islands (AHS heat zones 3-8). Modern day cultivars possess exceptional heat, humidity, and drought tolerance in summer months once fully established. Alyssums may be utilized in mixed containers and hanging baskets; they are used to edge garden beds and borders.

Low growing alyssums lay down a fragrant spreading carpet of floral color. Medium green leaves are barely 1-inch in length. Alyssums grow 4-9 inches high and 18- 36 inches wide depending on variety. Flowers are self-cleaning and available in numerous color choices, including pink, rose, lavender, purple and apricot.

Dense clusters of sweetly fragrant white 4-petaled flowers cover the foliage mounds from spring to early summer. Individual flower clusters measure 2-3 inches in diameter, and they bloom from planting time up to hard frost. Alyssums are frequently planted as a winter annual in zone 9 and further south. In regions with long hot summers, alyssums tend to decline in summer’s heat unless planted sited under partial afternoon shade.

Plant alyssums in sun to partial sun and apply slow release fertilizer at planting time. Plants are shallow-rooted and do benefit from mulching and moderate irrigation in the summer heat. In mid-August alyssums may look tired, leggy or seedy; if so, clip back a few inches, irrigate, and re-fertilize. Plants will return to their glorious best within 1-2 weeks. Alyssums are not troubled with serious disease or pest problems.

Alyssum varieties:

‘Rosie O’Day’ – All-American Selection (AAS) winner with rose pink flowers.

Snow Princess® – AAS winner with outstanding performance and is very heat tolerant.

White Knight® – new in 2014 with dark green foliage and covered with fragrant white blossoms

Stream®series – Lavender Stream and White Stream are real performers.

Caution: Gardeners with sensitive skin should wear gloves when working with alyssums

Chinese Fringetree Gains In Popularity And Availability

Posted by Hugh on May 9th, 2015

Chinese fringetree (Chionanthus retusus)

When in bloom in mid-spring (May), the fringetrees (Chionanthus spp.) definitely will catch your eye. Chinese fringetree (C. retusus), is one of the finest small to medium sized flowering trees, not to be confused with the U.S. native fringetree (C. virginicus) (USDA hardiness zones 5-9). Both produce spectacular white lacy flowers in late spring. Flower panicles are larger and showier on American fringetree, and its growth form is often wild without some annual pruning.

Over the past quarter century the Chinese form has developed a growing “fan base” among American gardeners. Its high gloss, dark green foliage holds its sheen through the spring and summer months and are disease and pest free. Fall color is non-distinct yellow and is rarely spectacular. The aged furrowed bark on Chinese fringetree is very attractive.

Fringetrees are 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 will germinate 2-3 years later.

Chinese fringetree prefers a full sun location. It tolerates a wide range of soils provided they’re well-drained. A 3 to 5 gallon plant will grow to 25 to 30 feet tall and wide in 20 years. Two-year established plants demonstrate good drought tolerance. It performs better sited in light afternoon shade in southern climes.

‘Tokyo Tower’ is a columnar form that matures to 15 to 18 feet height and only 6 to 8 feet in width. ‘China Snow’ is a slow-growing shrub form from Tennessee nurseryman Don Shadow; it grows 8 feet tall and 5 feet wide in ten years with snowy white fringed blooms.

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

Cardinal Flower Attracts Hummingbirds and Butterflies

Posted by Hugh on May 6th, 2015

Cardinal flowers at Biltmore Estate, Asheville, NC

With their vibrant red colored blooms in July and August and a strong vertical growth habit, you visually can’t miss with our native cardinal flowers (Lobelia cardinalis) (USDA hardiness zones 3-9). Hummingbirds and butterflies won’t pass them by either.

Cardinal flowers are also called scarlet lobelias. Their vibrant red single raceme flowers single them out from other summer-flowering perennials. The non-branching flower stalks are covered from top to bottom with small flowers. In the garden blooms can be present from early to late summer, particularly if you keep them deadheaded. In the wild, they tend to bloom 3-4 weeks later if moisture is adequate.

Cardinal flowers prefer a compost-rich moist site in full sun. Mulching is highly recommended for even soil moisture. Set plants 2 to 3 feet apart. You may also opt to submerge pots of cardinal flower in a water garden, plant them in a rain garden, or on the edge of a stream or lake. Periodic flooding makes it look better; again, roots crave soil moist.

This clump-forming perennial has no serious pest or disease problems. Deer seem to leave it alone. It is best divided after three years in early spring. There are several cultivars available including the popular red, pink and white. Some of them include ‘Alba’ (white blooms), ‘Heather Pink’ (pink) and a ‘Black Truffle’ (dark chocolaty-purple foliage and bold red flowers). Black Truffle’s dark foliage holds throughout the spring and summer months.

L. cardinalis serves a parent in the breeding of new hybrid lobelias. Some of the hybrid forms may not be as hardy as cardinal flower itself.

Pampas Grass – Have We Learned A Lesson?

Posted by Hugh on May 4th, 2015

Dwarf Pampas Grass

Many areas in the mid-South and northeast U.S. (USDA hardiness zones 6 and 7a) learned a hard lesson in the harsh cold winter of 2013-14. Over the past decade gardeners had been lulled into zone bending, insisting on planting species from a warmer zone. One of them was pampas grass (Cortaderia selloana). Very few clumps survived here in the Southern Appalachian region (USDA hardiness 6 and 7).

Pampas grass, depending on cultivar, grows 5 to 10 feet tall and 3 to 6 feet wide. It is a clump growing grass that thrives in full sun and medium soil moisture. A one year old clump displays exceptional drought tolerance. Showy plume flowers appear in mid-summer. Pink or white plumes (inflorescences) cultivars are available at most garden centers in the Southeastern U.S.

One of the most cold-hardy pampas grass varieties is dwarf pampas grass (C. selloana ‘Pumila’). Hardy to zone 6, winter snow plus a 2-3 inch layer of loose leaves provides a protective mulch covering before the start of winter.

Referring to ‘Pumilo’ as “dwarf” is misleading as some varieties of pampas grass are even shorter. Its showy silvery-cream plumes can be used in dried flower arrangements. Vegetative green grass portion grow 3 feet tall and wide. Add another 18-36 inches for the silvery white plumes to rise above the green mound.

Pampas grass establishes quickly, usually in one season. Feed and irrigate the first year after planting. One year old plants are very drought tolerant and require little care other than once a year pruning. Wait until late winter or early spring before cutting pampas grass back. Wear protective clothes as the leaves are razor-sharp!

Usually its enormous size, attractiveness, and architecture are good reasons to consider pampas grass. It is often planted as a stand-alone ornamental grass. Placement in front of tall evergreens helps to make it a statuesque landscape focal point.

Point of reference: at some garden centers you will find Hardy Pampas Grass. This grass is a different genus (Eranthus) and is cold hardy in zones 4b and 5.

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.