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

Three Native Landscape Grasses To Try

Posted by Hugh on June 7th, 2016

Leymus grass at Atlantic Botanical Gardens

Blue Lyme Grass at the Atlanta Botanical Garden

Nassellia tenuissima in UT Gardens, Knoxville, Tennessee

Nassella tenuissima in UT Gardens, Knoxville, Tennessee

These three native grasses are easy to establish in average, dry to medium moist, well-drained soils and in full sun. They tolerate a wide range of soils including dry rocky sites, and are exceptionally drought tolerant. Figure on 1 to 2 years for each to become fully established.

Blue Lyme Grass (Leymus arenarus ‘Blue Dune’) is a vigorous spreading cool season grass, 24-30 inches tall, with steel blue foliage and arching growth habit. Blue Lyme is a vigorous grower in warm areas of the U.S. (USDA Hardiness zones 4-10).

Tall flower spikes appear in mid-summer. It grows in a wide range of soils, wet to dry, and in either full sun to partial shade. It grows less aggressive in dry, clay soils. Foliage remains evergreen in zone 8-10; otherwise, blades take on a beige tint in early fall.

Prairie dropseed (Sporobolus heterolepsis) is a clump-forming, warm season, perennial grass found in prairies, glades, and open land areas native to the Midwest U.S. (USDA hardiness zones 3-9). Light airy inflorescences (flower panicles) rise several inches above the fine textured, deep green foliage in September and October.

Prairie dropseed forms mounds of arching foliage, each 1 ½ feet tall and 3 feet wide. Leaf blades turn a golden fall color with orange hues and later to light bronze over winter. Flower panicles have pink and brown tints, and emits a hint of coriander or popcorn fragrance. Tiny rounded mature seeds drop to the ground from their hulls in autumn and serve up a morsel for seed feeding birds. It generally does not self-seed in the garden.

Mexican feather grass or silky thread grass (Naasella tenuissima) is a light airy ornamental grass that flutters in the slightest of breezes (USDA hardiness zones 5-10). Plant in groups of 5 or more to create waves of fine foliage. In the first year irrigate over the first 2-3 months until established and is highly drought tolerant from this point on.

Their green silky inflorescences will soften landscape areas from late spring into late summer, the plumes swaying in the slightest breeze. Plumes turn brown in late summer. Remove winter dead growth at the start of spring.

Prairie dropseed (Sporobolus heterolepsis)

Recommendations On Hardy Crape Myrtles

Posted by Hugh on June 4th, 2016

Lovely bark on ‘Tonto’ crape myrtle at Chanticleer

‘Acoma’ crape myrtle

Crape myrtles are dependable trees and shrubs in zones 7 – 10. In northern areas of USDA zone 6, a number of crape myrtle varieties (cultivars) are rated as winter hardy perennials but not develop into a full sized woody tree or shrub described on the plant tag. In northeastern U.S. cities such as Philadelphia, Wilmington or Baltimore, crape myrtles are rated as hardy perennials.

In record breaking cold winters main branches and trunks frequently dieback near the ground and need to be cut back near the ground. Dieback may occur 1-2 years every decade. By mid-spring new shoots should vigorously sucker back from the ground. From several new shoots, select 1, 3, or 5 strong shoots to develop a new single or multi-trunk tree or shrub. Fertilize when you see emerging shoots. It will likely bloom on the new shoots by late summer.

In the northeastern U.S. select varieties, some public gardens have found to be hardy. Andrew Bunting, plant curator at the Scott Arboretum (campus of Swarthmore College in Swarthmore, PA) reported the following cultivars survived the frigid winter 2013-4 with virtually no damage:

fauriei ‘Fantasy’ (35 ft. tree form, small white flowers)

fauriei ‘Townhouse’ (30 ft. tree, small white flowers)

indica ‘Carolina Beauty’ (tree form, small deep pink flowers)

indica ‘Pink Velour’ (10 12 ft. shrub, small bright pink)

x ‘Acoma’ (10-12 ft. shrub, large pure white)

x ‘Lipan’ (26-28 ft. tree, large lavender flowers)

x ‘Muskogee’ (26-28 ft. tree, large pink flowers)

x ‘Natchez’ (28-30 ft. tree, large white flowers)

x ‘Osage’ (15-18 ft. tree, large clear pink)

x Tuscarora’ (28-30 ft. tree, large dark pink)

x Tuskegee’ (28 ft. tree, large dark pink)

Many of the hardiest cultivars, now numbering 33 originated from the U.S. National Arboretum breeding program. If you wish to start out with just 3 or 4 varieties, select ‘Natchez’ and ‘Muskogee’ (tree forms) and ‘Acoma’ and ‘Osage’ (shrub forms).

Addendum: For many years Chanticleer Gardens in Wayne, PA has grown ‘Tonto’ in a partially protected area (see photo). 8-10 ft. shrub, red flowers, light tan bark

Three Native Flowering Shrubs For Your Summer Landscape

Posted by Hugh on June 1st, 2016

Itea virginica ‘Henry Garnet’

Plumleaf azalea bloom in July

Virginia sweetspire (Itea virginica) flowers in late spring with dark green, pest-free summer foliage that turns brilliant red in fall (USDA hardiness zones 5-9). It thrives in full sun to partial shade, and in moist mildly acidic soils. It is also highly drought tolerant once established. Fertilize with slow release fertilizer in early spring such as Osmocote or Nutrikote.

Virginia sweetspire grows 3 to 6 feet tall and wide, depending on the cultivar planted. Leaves turn ruby red in fall. Pruning is rarely needed except to remove unwanted suckers after flowering has finished. Recommended cultivars include: ‘Henry’s Garnet’ @ 5-6 feet, ‘Little Henry’ @ 4 – 5 feet; or ‘Merlot’ @ 3 – 3 ½ feet

Summersweet (Clethra alnifolia) is a deciduous shrub native to wet areas, such as low spots, stream banks, ponds, etc . (USDA hardiness zones 4-9). This densely-branched, round canopy deciduous shrub typically grows to 3-8 feet high (depending on cultivar) and bears highly fragrant white (or pink) flower panicles in mid to late summer. Flowers give way to dark brown seed capsules in autumn and persist through winter. Dark green, obovate, 3-4 inch long leaves develop fall in color shades ranging from yellow to golden brown; fall hues are highly variable from one year to the next. Flowers attract abundant butterflies and bees.

Fertilize with slow release fertilizer in early spring. Summersweet is trouble-free with little disease and pest problems. Roots tend to sucker and plants form small colonies. Leading cultivars are ‘Ruby Spice’@ rose-pink, 8 feet tall; ‘Hummingbird’ @ white, 3-4 feet tall; and ‘Sixteen Candles’ @ white, 4-5 feet tall.

Plumleaf azalea (Rhododendron prunifolium) is an Alabama/southwest Georgia native (USDA hardiness zones 5-9) that blooms in mid-late July. Bright orange-red flowers will light up any garden spot whether in full sun or partial shade. A dark red flower form is available. Flowers are not fragrant but still attract numerous butterflies and bees.

It grows in average well-drained soil and asks for little nutrition. Irrigate during summer dry spells. It appears to be soil pH insensitive, but likely prefers an acidic range between 5.5 to 6.5. Plumleaf azalea grows 8-10 feet tall, but may be maintained to a 5-6 feet height and width. No diseases and insects pests trouble it. Pruning is rarely needed except for shaping the shrub.

Note: Cultivars of Virginia sweetspire and summersweet shrubs are readily available for sale. Plumleaf azaleas are rarely sold at local garden centers but you can purchase them from e-commerce nurseries on-line.

Tips On Growing Delphiniums

Posted by Hugh on May 30th, 2016

Double-flowered delphinium

Modern day delphiniums (Delphinium spp.), also called larkspurs, are the result of 2 centuries of complex breeding efforts in Europe and U.S. Delphiniums are short-lived perennials, at their best for 2-3 years. They’re most attuned to the cool temperate climes of the northern U.S. Delphiniums belong in the Buttercup (Ranunculaceae) family (USDA hardiness zones 4–7).

Most tall flowering hybrids are derived from D. elatum. Pacific Giant hybrids typically grow 4-5 feet tall on long stems. New Millennium™ hybrids from New Zealand, reportedly are better performers in warm humid zones. Taller varieties are best staked or caged to support their weak hollow stems. Flower colors range from blue, pink, lilac, and white.

Plant delphinums in full sun and in mildly acidic, well-drained, compost-rich soil. Light midday shade is recommended in southerly zones. Soil pH between 6.0 and 7.0 is ideal. Soil drainage is key! Do not allow soil to become overly dry nor stay forever soggy. Delphiniums respond to a steady diet of fertilizer in spring and summer. Apply granular 10-10-10 fertilizer in early spring (or at planting), and follow up with a second and third monthly feeding starting in late June using water soluble products such as Miracle-Gro®, Daniels®, or Peter®.

After the spring flush of flowers is over, cut back plants by at least one-half to spur a brief secondary bloom cycle later in summer; flowers will form on shorter stems. In northerly areas, particularly those devoid of snow cover, protect plant crowns with loose straw or non-packing leaves; do not pile too much mulch as it might smother the crowns.

Delphiniums have few issues with disease and pest issues. High humidity and poor air circulation can cause powdery mildew. Do not irrigate delphiniums overhead or do so early in the day so foliage can dry off. Snails and slugs may be occasional pests.

Hybrids of D. elatum produce 5 to 6 feet tall floral spikes; site tall varieties in back of garden border. The Belladonna group (Zones 3–7), crosses between D. elatum and D. grandiflorum, produce loose, multi-branched spikes of white, blue, or lilac colored flowers. They grow 2 to 4 feet tall, easier to grow, and are longer lived.

Magic Fountain™ and Blue Fountains™ series are seed produced and grow 2-3 feet tall.

“Neo-Nicotinoid Free” — What Does This Means”

Posted by Hugh on May 27th, 2016

Pesticides on Store Shelf

Earlier this year several big box store and regional independent garden center chains announced that the plants they sell in 2016 will be “neonicotinoid-free”. Large regional nurseries and greenhouse operations are also jumping on-board the anti-neonic bandwagon. This means that pesticides containing the ingredient acetamiprid and imidacloprid are members of the neonicotinoid class, and are forbidden to be sprayed on plants sold at these stores.

Neonic insecticides are thought to be harmful to bees. Studies have shown that small amounts of neonics can harm bees feeding on the pollen and the nectar of treated plants and larger doses can kill. More and more gardeners are making it a point to stop using insecticides that contain neonics and to buy only plants not treated with these pesticides.

Terms like “bee-friendly” and “use of beneficial insects” carry greater value. Plant growers are learning that the term “bee-friendly” delivers a more positive message with buyers.

Neonic pesticides include: imidacloprid, acetamiprid, clothianidin, dinotefuran, nithiazine, thiacloprid and thiamethoxam. A short list of popular brand names pesticides that contain the ingredient Imidaclopyrid include: several Bayer Advanced™ Products, Ferti-lome 2-N-1 Systemic, Hi-Yield Systemic Insect Spray, Marathon, Merit, Ortho Bug B Gon® Year-Long Tree & Shrub Insect Control.

Neonics, imidacloprid in particular, are commonly applied to plants as foliar sprays and soil drenches. Because these pesticides are systemic, they’re taken up by the entire plant and can even spread into the surrounding soil. Depending on the type of neonic and amounts used, one application of a foliar spray can last up to 4 – 5 months in herbaceous plants and a year or more in woody plants. Soil drenches, which are commonly used on roses and trees, can last two or more years in the plant leaves (needles), twigs, and root system. Treated seeds will carry through the pesticide inside the developing plant.

Be aware: Imidaclopyrid is still sold by most of these garden centers.

Six Summer Annuals Your Grandma Did Not Know About

Posted by Hugh on May 24th, 2016

Pentas attract butterflies

‘Dragon Wave’ Begonias in Container

Angelonia (“summer snapdragon”)… are outstanding performers in the summer flower garden, yet so many gardeners have never heard of them. Angelonias demonstrate outstanding heat and humidity tolerances. Serenita™ (12-14 inches high), Serena™ (15-18 inches high), and Archangel™ (12-14 inches tall high) series, are available in purple, lavender, pink, and white colors.

Dragon wing® Begonias…Since their introduction in the late 80’s, these angel wing types of begonias have gained a following, particularly with landscapers and gardeners who need to plant large flower beds. Individual plants cover three times the space of a wax begonia (fewer plants means less cost). They are non-stop bloomers over 5-6 months. One caveat: plants usually grow quickly after planting, but are not floriferous their first month in the ground, but are the last to stop flowering in fall.

Euphorbia Frost® series… Mr. James Newburn, assistant director – curator at the University of Tennessee Gardens in Knoxville, calls euphorbias “the baby’s breath of the landscape world”. Euphorbias have dark green (bronze leaf also available) foliage and pure white flowers on delicate stems that create airy clouds. It is a heat tolerant, drought resistant plant, truly a “plant it and forget it” addition to containers, hanging baskets or landscape beds.

Egyptian Star Flower (Pentas)… large clusters of starry blooms that attract lots of butterflies and hummingbirds to the summer garden. Pentas grow well in containers and in garden beds in full sun and moist, well-drained soil. Kaleidoscope®, Butterfly®, and Graffiti® are rated the best series. Varieties grow 2 to 3 feet tall and 15 inches wide and flower colors from deep red, red, pink and white.

Scaevola (fanflower)… this Australian native thrives in hanging baskets, containers or as garden beds in full sun to part shade. It is easily to grow in average, medium, well-drained soils. Bombay® and Surdiva® series, in a choice of white, pink, or blue flower colors, are the leading ones to try.

Torenia (“wishbone flower”)… an alternative bedding plant instead of garden impatiens (Impatiens walleriana). Summer Wave® is a new trailing series that thrive in summer heat and humidity. Mounding series include Kauai® and Moon®. Torenias bloom all season in hanging baskets, containers, garden beds with a vigorous growth trailing habit. They also perform in partially shady beds and ask for very little maintenance. Plant them 10-12 inches apart in a well-drained soil.

Japanese Crape Myrtle Flaunts Stunning Bark

Posted by Hugh on May 21st, 2016

‘Fantasy’ crape myrtle at JC Raulston Arboretum in Raleigh

‘Townhouse’ crape myrtle

Most crape myrtle cultivars marketed through garden centers are hybrids that combine the large colorful flowers of Common Crape myrtle (Lagerstroemia indica) with the mildew-resistant foliage and cold hardiness of Japanese Crapemyrtle (L. faurei). Japanese Crape myrtle are cold hardy (USDA hardiness zones 6-b to 9) and are heat tolerant. They are rated hardy to winter minus 10 ºF.

Japanese Crape myrtle is a multi-stemmed, medium 40 foot tree deciduous tree. At the JC Raulston Arboretum (JCRA) in Raleigh, NC, the cultivar ‘Fantasy’ is 50 feet tall after 30+years. It flaunts a stunning flaking cinnamon brown bark. In my opinion, it’s the showiest of all crape myrtles. A close second is a 40 foot tall ‘Townhouse’ with a dark chocolate bark. Fantasy is rated less cold hardy than Townhouse.

Japanese Crape myrtle produces abundant pure white flower clusters averaging 4 inches in diameter. Compared to most other crape myrtles, flower clusters are looser than those of L. indica that do not droop as much following heavy rains. Tree blooms only once, usually in early summer in Tennessee, Virginia, and North Carolina.

Main multi-stemmed trunk grows upright with tips of branches slightly nodding, and rounded crown. It grows best in full sun and in moist fertile soil. It tolerates dry soils once established after 1 year. Do not plant on public lands, particularly non-irrigated sites such as highway medians, urban streets, and parking lots. Feed in early spring with a slow release fertilizer. Annual mulching around trees is highly recommended.

After flowering, Japanese crape myrtle grows through the summer and, in some years has trouble hardening off before winter. To prevent early frost injury, do not fertilize after mid-summer. Flowers are smaller compared to hybrid cultivars.

Compared with hybrid cultivars, Japanese crape myrtle is susceptible to aphids, scale, and powdery mildew. Its leaves are highly mildew resistant.

Hold In Confinement

Posted by Hugh on May 18th, 2016

Purple form of Ruellia at UT Gardens in Knoxville, TN

Purple flowering form of Ruellia at UT Gardens in Knoxville, TN

Oenothera speciosa held in check at gas station island

Some plants are incredibly aggressive. Herbicides like Roundup™ won’t phase them. They often escape and take over other areas of your garden or neighborhood.

Four notorious examples are ditch lilies (Hemerocallus fulva), swamp milkweed (Asclepias incarnata), Mexican petunia (Ruellia brittoniana), and pink evening primrose (Oenothera speciosa). You can grow these four weedy offenders in confinement. All will survive on totally inhospitable sites and their spectacular flower show lasts a month or more.

Ditch lilies grow in absolute worst conditions. They bloom for 2-3 weeks starting in late June (USDA zones 6 -8). Each bloom lasts one day, but the large floral scape holds many flowers. Orange is the common color, although other colors are found. Flowers are mostly sterile, but their rootsystems are aggressive.

Leaves of swamp milkweeds are favorite food source of monarch butterfly caterpillars (larvae). Their rootsystem spreads aggressively and they also seed in. Plants form clumps that survive over many years in wetland areas. Swamp milkweeds grow 3-5 feet tall on erect branched stems. Small, fragrant, pink to mauve flowers (1/4 inches wide) are common and a white flowering form is occasionally seen. Orange butterfly milkweed (A. tuberosa), also native, is far less aggressive.

Mexican petunia, aka Texas ruellia, is three-foot-tall evergreen shrub that bears many tubular, blue or purple, petunia-like flowers on dark stems through the summer. This fast grower may self-seed and roots are prolific. It is grown as an annual in cooler zones and will perennialize in zones 6-b where I live.

Pink evening primrose is another nightmarish perennial that blooms almost one month. It spreads aggressively by rhizomes. Plants die back after flowering in the summer heat.

All four are great choices for planting in confined spaces such as in parking lot islands or median strips along busy highways. Plant them in containers and keep blooms deadheaded to prevent seed formation.

Tulip Poplar And Cultivars

Posted by Hugh on May 15th, 2016

Most flowers are hidden among foliage

Mature Liriodendron tulipifera on East TN State University Campus in Johnson City.

Tulip poplar (Liriodendron tulipifera), aka yellow poplar and tulip tree, is a large stately deciduous tree of eastern North America (USDA hardiness zones 4-9). This fast growing native typically grows 60-90 feet tall. It is also an important timber tree.

A member of the magnolia family, flowers attract large numbers of bees. Ornate 2-inch-wide goblet-shaped flowers are yellow with an orange band at the base of each petal. Most flowers go unnoticed, hidden among the 8- inch-wide leaves that have emerged a week or two prior. Dry, scaly, cone-shaped brown fruits follow, each bearing numerous winged seeds. In some years (not all), bright green tulip shaped foliage turns golden yellow in fall.

The size of this native tree will become menacing to homeowners. Young tulip poplars grow with a pyramidal form and mature with a broad rounded canopy. Trunks of mature trees may reach 4-6 feet in diameter, usually rising column-like and devoid of lower branches. Tulip poplars grow rapidly and become too big for an average residential property. Branches are not weak wooded in the early years, but weighty branches on older trees tend to snap off branches in wind and ice storms. Shallow rootsystem grow in lawns and will likely uplift sidewalks in urban areas.

Although not prone to serious disease and insect problems, leaves may be plagued by sap feeding aphids which exude sticky sap over decks, patios and cars beneath. Over a dry summer tulip tree may shed up to one-third of their leaves, perhaps abit messy for some homeowners. Shallow root systems do limit the types of plants that may be grown within the drip line. During hot, dry weather the leaves tend to turn yellow and drop off.

Leading cultivars:

‘Arnold’ – columnar 50 feet tall and 20-25 feet wide

‘Aureomarginatum’ – green with gold leaf edge

‘Little Volunteer’ – compact 35-40 feet tall and 30-35 feet wide

‘Sun King’ Golden Aralia Glows In Summer Garden

Posted by Hugh on May 12th, 2016

‘Sun King’ Golden aralia

'Sun KIng' Aralia in Baltimore, MD Garden

‘Sun King’ Aralia in Baltimore, Maryland Garden

Plants with golden foliage brighten up a dark area in the garden. Sun King golden aralia (Aralia cordata ‘Sun King’) is no exception, hardy in USDA hardiness zones 3-9. Bright golden compound leaves emerge in mid-spring and Sun King aralia retains its bright color through the summer months.

This long-lived perennial grows 4 to 6 feet high and 3 to 4 feet wide. New growth emerges in mid-spring and growth rate is rapid; foliage dies back in late autumn. Many small clusters of tiny white flowers emerge, borne on 2 feet tall racemes in mid-summer. Lustrous purplish-black berries follow in early fall.

Sun King makes a bold almost tropical statement in a shade garden. Grow it in a compost-rich moist soil and in ½ day sunlight (morning sun preferred). It adapts to a wide soil pH range. The foliage will likely burn in full day sun. In zones 8 and 9, grow in dappled sunlight all day long to escape foliage burn. Aralia should be irrigated during long summer dry spells.

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

A native of Japan, Korea, and China, ‘Sun King’ aralia was introduced to the U.S. by Barry Yinger. Tony Avent at Plant Delights Nursery in Raleigh, NC says: “Aralia ‘Sun King’ is one of the most amazing new perennial introductions in the last decade”.