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

‘Mojito’ Elephant Ear Is A Tropical Joy

Posted by Hugh on April 24th, 2016

Colocasia esculenta ‘Mojito’ at Biltmore Estates, Asheville, NC

Colorful Foliage of ‘Mojito’

‘Mojito’ elephant ear (Colocasia esculenta), aka taro plant, has become a new favorite in the Conlon garden where it is not dependably winter hardy (Zone 6b). According to Tony Avent at Plant Delights Nursery in Raleigh, NC, tubers are dependably winter hardy in zones 7b -10. ‘Mojito’ (pronounced “Mo-he-toe”) is a sport of Colocasia ‘Burgundy Stem’ x ‘Black Marble’. Its fancy leaves are medium green splashed with dark purple flecks. ‘Mojito’ is a thick-leaved, strong stemmed plant that stands up in summer downpours.

Elephant ears are easy to grow. Your garden or container soil (media) should be well-drained, mildly acidic, organically rich. Soil pH should range between 5.6 and 7.0. Locate in direct or partial sunlight and keep soil moderately moist. Keep garden plants adequately mulched and away from prevailing winds.

Elephant ears are constant feeders and love a steady diet of water plus water-soluble fertilizer such as Miracle-Gro®, Jack’s Classic®, or Peters® every 2-3 weeks from planting time (mid-May here in zone 6b) to late August at the one-half strength rate. By late summer expect Mojito to reach 2-3 feet high and wide, less so on drier sites.

Disease and pest problems are rare if plant(s) are properly sited and cared for. Potential crown or stem rot problems are best avoided by growing in a well-drained soil (media) and by not overwatering.

In areas with moderate winters (zone 7) elephant ears should be heavily mulched during winter to protect the central tuber which will likely perish in temps in the lower teens. Spread 2-3 inches of loose non-packing mulch such as straw or oak leaves.

In zones 5 and 6 container plants or tubers should be dug up, bagged, and stored in a cool (unheated) attached home garage where winter temps should not drop below 40 ºF. Remove all leaves and stems and hold in a semi-dormant state. At the start of spring, repot and gradually reintroduce elephant ears and other sensitive semi-tropicals to rising outdoor temperatures.

Where to purchase: independent garden centers and mail-order nurseries like Plant Delights Nursery, Raleigh, NC.

Monitor And Manage Two-Spotted Spider Mites

Posted by Hugh on April 21st, 2016

Two spotted mite on henbit (magnified) (photo courtesy of Dr. Frank Hale, Univ. of TN)

Phlox -2-spotted mite damage (credit: Mt. Cuba Center)

Two-spotted spider mites are destructive pests that ravage a wide host of shrubs and garden plants, including certain house plants, annuals, perennials, herbs and vegetables. Many evergreens are also susceptible.

Two-spotted spider mites are warm season arachnids, not insects, and are exceptionally troublesome over a hot dry summer. They have a short lifecycle, from egg to adult can be completed in about seven days. High numbers can build up and get out of hand in less than a month.

Two-spotted spider mites have sucking mouth parts and most frequently feed on the underside of leaves, sucking out green sap which results in a mottled or flecking appearance. Severe infestations can cause leaves to drop off and massive webbing over plant foliage.

Monitor periodically to see if they are present and in what quantities. Take a clipboard with a piece of white or yellow paper. Briskly shake the flowers or foliage over the paper and inspect for mites. Adult mites are easy to spot; they will be moving and have 8 legs (insects have 6 legs). They’ll have two black spots on both sides of the abdomen. Also use a 20x hand lens for accurate identification.

A number of miticides are available but they must be applied correctly. Thorough coverage of all plant parts is essential. Many miticides are contact only, but some are translaminar, e.g. penetrate through the leaf tissue and remain active in the leaf.

Horticultural oil sprays can be used. Spray once every 7-10 days(no more) to maintain mite populations at low levels. Insecticidal soaps can also be applied. Professional miticides, not necessarily available to home gardeners, include abamectin (Avid 0.15 EC), acequinocyl (Shuttle O), bifenazate (Floramite 50 WP), etoxazole (TetraSan 5 WDG), spiromesifen (Forbid), and hexythiazox (Hexygon).

Never rely on the same miticide in the garden. Select two miticides for spider mite spray program that are different chemical classes.

Credit: Pesticide recommendations supplied by Dr. Frank Hale, University of Tennessee Entomologist, Nashville.

Mite Webbing on Marigolds in Late Summer

Japanese Holly Fern

Posted by Hugh on April 18th, 2016

Japanese holly fern (Cyrtomium) In Woodland Area at Biltmore Estate in Early February

Japanese Holly Fern (Cyrtomium falcatum ‘Rochfordianum’) is a handsome, evergreen fern for gardens in USDA hardiness zones 6-11. It earns its name from its stiffly erect holly-like fronds. Individual fronds are vase-shaped, 1 to 2 ½ feet long with glossy, leathery, serrated, holly-like compound leaflets (pinnae). The slender, arching fronds arise from erect, scaly rhizomes just above the soil surface.

Spore masses are light green when young and dark at maturity; they cling to the backs of leafy fronds. Japanese holly fern is evergreen in frost-free growing areas, but tends to lose its fronds in colder climates. It also tolerates more sun than many other woodland ferns.

It is best grown in compost-rich, well-drained soil with medium moisture and in part shade to full shade. Annual mulching around holly fern is beneficial; it does not ask for much feeding. It tolerates dry air, low light and gas fumes in the home better than most ferns. Extreme summer dry spells or too much sun will singe pinnae.

Holly fern develops into an effective groundcover and can be grouped to edge a woodland or shady border. It performs well in containers either planted by itself or mixed with other woodsy perennials. Holly fern also makes a great indoor plant in the colder parts of the U.S. Holly fern is not troubled by disease or pest problems. Problems with root rots or leaf spotting may indicate a poor site. Deer and rabbits usually stay away from the sharp needle foliage.

‘Palibin’ Lilac A Good Choice For Small Landscapes

Posted by Hugh on April 15th, 2016

Tree form of Syringa meyeri ‘Palibin’

Dwarf Korean lilac (Syringa x meyeri ‘Palibin’) forms a dense multi-stemmed deciduous shrub, 4 to 5 feet high and 5 to 6 feet wide, with rounded top or canopy (USDA hardiness zones 3-7). It branches low to the ground.

Flower buds form which are distinctively violet in color. In mid-spring this diminutive lilac is covered by billowy panicles of fragrant purple flowers. Trusse are excellent for cutting and enjoying inside the home for their color and fragrance. Spring foliage first arises burgundy and becomes dark green all summer long.

Palibin lilac maintains its neat and tidy compact form. Plant in full sun and a well-drained soil for best flowering annually. Initial growth rate is slow and under proper care, specifically annual feeding and pruning, will prosper for 25 to 30 years. It then may need to be renovated by pruning.

Compared to other lilac species (Syringa spp.), Palibin leaves are smaller and the overall shrub offers a fine texture appearance. The small pointed leaves do not develop an appreciable fall color. Smooth gray bark and fruits (seed capsules) offer no ornamental value.

This low maintenance shrub should be grown primarily in full sun. It is very adaptable to both dry and moist sites, but not in standing water. It is not sensitive to soil type or pH and leaves tolerate urban inner city conditions. Wait to prune a month after spring flowering to avoid removing spring flowers. Palibin is a good choice for attracting butterflies.

Dwarf Korean lilac can be utilized as a single specimen shrub or group as short hedges or privacy screens. It also may be nurtured in a large container for several years. Foliage is highly powdery mildew resistant on landscape sites with good air movement. As the above photo depicts, nurseries are now training Palibin lilacs into small compact trees.

Update: Prevention / Treatment Options For Rose Rosette Disease

Posted by Hugh on April 13th, 2016

Rose Rosette Symptoms (photo by Dr. Alan Windham, Plant Pathologist, Univ. of Tennessee, Nashville

Rose rosette is a devastating disease of most species of garden roses, including hybrid and shrub roses. Rose rosette disease has spread from the Rocky Mountains to the East Coast over several decades and is poised to obliterate the rose industry. To date, there is no known effective treatment.

Rose rosette is caused by an Eriophyid mite called Phyllocoptes fructiphilus, which transmits the virus. Symptoms of the virus include: (1) excessive thorn production, (2) leaf distortion, and (3) excessive branch development, known as “witches broom” that will eventually kill the plant.

U.S. plant scientists have joined a multi-state comprehensive project to develop a management plan. USDA has extended a $3.3 million research grant to a 17-member group headed by David Byrne of Texas A&M University to fight rose rosette. “We are anxious for us to develop options for managing this virus”, says Dr. Gary Knox, Professor of Environmental Horticulture and Extension Specialist at the UF/IFAS North Florida Research and Education Center. Rose production is a $400 million annual business in the U.S.

A nursery might not know it has the disease and sell rose plants to unsuspecting customers. Months later the disease shows up. The major issue is being able to detect the virus before it shows up. A Florida team is developing techniques to detect low levels of the virus in the plant. The goal is to detect the virus in non-symptomatic plants utilizing a rapid field-based assay. They are trying to develop a field-based detection system to find the virus early.

Scientists are looking at new compounds for preventing or managing the disease. The team is treating plants with compounds that would potentially help plants better defend themselves against the virus and are trying to reduce the severity of the symptoms.

Finally, plant breeders are attempting to develop a new generation of roses that are highly resistant to the rose rosette virus.

Information credit: Edited article from Greenhouse Grower Magazine, March 2016

New Coreopsis Cultivars All The Rage

Posted by Hugh on April 12th, 2016

Coreopsis verticillata at Kingwood Center, Mansfield, Ohio

Coreopsis ‘Jethro Tull’ (photo from ItSaul Plants, Inc.)

Threadleaf coreopsis (Coreopsis verticillata), also called tickseed, is a popular summer flowering perennial. Coreopsis are native to the U.S. and produces hundreds of pale-yellow blooms. Depending on cultivar, plant grows 12 to 18 inches tall and 2 feet wide. Some gardeners even plant old-time favorites like ‘Zagreb’ and ‘Moonbeam’ as annuals (USDA hardiness zones 4 – 9).

Big flower tickseed (C. grandiflora) produces larger flowers on taller plants, up to 3 feet high. Flowers are bright yellow and daisy-like. Many cultivars re-bloom a second and even third time if mowed back after a bloom cycle has finished. They tolerate hot, humid summers, but garden soil should not be allowed to dry out. Height and spread vary by cultivar and level of care (irrigation + fertilizer).

Coreopsis are one of the easiest perennials to grow. For best show plant 3 or more of one cultivar for a sea of color in a sunny front garden border or in containers. Set out plants anytime from late April through September. Plant 12 to 18 inches apart in a sunny spot and in well-drained soil. Plant the crown just at or above the soil surface.

Removing spent flowers encourage re-blooming, prevents reseeding, and gives the flower bed a neater look. Yellow to gold flowers attract numerous nectar seeking bees and butterflies. Leaving the seedpods on plants will attract large numbers of goldfinches.

Divide clumps every 3 years for optimum plant performance. Aphids may be occasionally pests. Powdery and downy mildew on foliage in garden areas with poor air circulation; some cultivars are rated better for mildew resistance.

Recent Coreopsis Introductions:
‘Cosmic Eye’- daisy blooms with wine-red petals, tipped in soft yellow and surrounding an orangey yellow button eye; grows 18 inch high by 24 inch wide. Introduced by Darrell Probst and is reliably hardy in zones 4 – 9 with winter snow cover.

‘Jethro Tull’ – compact grower, 18 inches high by 24 inches wide with dark-green leaves and blanketed with single golden-yellow daisies with a ring of tubular petals; hybrid introduced by ItSaul Plants in Georgia.

‘Mercury Rising’ – another Darryl Probst introduction large velvety-wine daisy flowers with contrasting gold-orange button center, appearing in succession from mid summer to mid autumn. Some flowers may appear frosted in creamy-white. Cut plants by half in mid-July if plants begin to flop. (hardy in zones 4 – 9 with winter snow cover).

‘Route 66’ – threadleaf coreopsis discovered in 2005 in a Pennsylvania garden; plants grow 24-28 inches tall with bright yellow petals with large red eye; long blooming period from late June until mid October.

Summer Blooming ‘Little Lemon’ Goldenrod

Posted by Hugh on April 10th, 2016

Newly Set ‘Little Lemon’ Goldenrod in August

Goldenrods are members of the aster family (Asteraceae); approximately 100 species of goldenrods are native to North America. Across most of the Eastern and Midwestern U.S., goldenrods are frequently spotted growing in moist soils in open farm fields, in ditches, and along edges of streams. The golden yellow blooms attract countless bees, butterflies and other pollinators.

A new addition to my garden is ‘Little Lemon’ goldenrod (Solidago Little Lemon (‘Dansolitlem’ PP17297)]. Little Lemon is an exceptionally compact goldenrod with bright lemony yellow flowers that bloom from late July into August (USDA hardiness zones 5-8). Soft yellow is a sharp departure from the mustard yellow color of most goldenrods. Deadheading will induce secondary flowering into September.

Wild goldenrod species grow tall, much too big for most urban gardens. Compact growing Little Lemon should please city gardeners with limited growing space. Newly set plants should be mulched and watered regularly the first season until established. Established goldenrods are among the most drought tolerant perennials.

Fertilize at planting time and in late winter in successive years with 10-10-10 or equivalent. Few diseases and pests trouble goldenrods. Rust seems to be the biggest culprit, particularly if summer weather is unusually wet. Rust rarely kills goldenrod.

Little Lemon goldenrod combines well with other late summer blooming perennials and annuals such as Japanese asters (Kalimeris), ‘Short and Sassy’ heleniums, blanket flowers (Gaillardia), stone crop (Sedum), and stokes asters (Stokesia) in garden beds and mixed in containers. Their bright yellow flowers are great additions to fresh or dried flower arrangements.

Goldenrods hold their form through most of winter. On a brisk cold winter morning a hoarfrost over the skeletal remains of goldenrods is an inspiring view.

Utilize Sweet Flag For Garden Accent

Posted by Hugh on April 7th, 2016

Acorus gramineus ‘Ogon’

Sweet flag cultivar (Acorus gramineus) is an iris-like perennial usually planted for its wavy drifts of golden yellow foliage. This dwarf ground cover, indigenous to China, Korea and Japan, grows 6-12 inches tall. Sweet flag is a member of the acorus family (Acoraceae) (USDA hardiness zones 6-9 and should be winter protected in zone 5).

Green variegated leaf cultivars with striped yellow or green blades are also available. The narrow leaf blades barely measure ¼ inches across. A bright patch of sweet flag spread slowly by creeping roots (rhizomes). Foliage gives off a citrusy scent when pinched or stepped upon. Sweet flag copes with only light foot traffic. In June or July tiny greenish yellow sedge-like flowers appear followed by tiny fleshy berries; flowers and fruits offer little in ornamental value.

Growing requirements for sweet flag are similar to that of most sedges (Carex spp.). Sweet flag grows in average garden soil and in full sun to partial shade (depending on location). It can tolerate heavy shade but its rich golden hue is lost. To succeed, sweet flag wants above average soil moisture; it thrives in shallow boggy conditions such as around a water garden. Scorched leaf tips arise when the soil becomes parched. In southern climes, plant sweet flag in afternoon shade or full day filtered sunlight. Foliage stays evergreen in warmer zones.

Sweet flag has no serious disease or insect problems. In early spring a single application of slow-release organic base fertilizer is adequate.

Sweet flags are utilized as textural and color accent plants around water gardens, streams, ponds, or in moist open woodland gardens. It is also planted in rock gardens or border fronts. Sweet flag can be used to edge decorative containers.

Leading cultivars:

‘Ogon’ – the most popular form with golden-colored foliage.

‘Minimus Aureus’ – 3-4 inch tall miniature ground cover that forms a golden mat; plant some between stepping stones (emits light citrus fragrance).

‘Variegatus’ – grows 6-9 inches tall with white-and-green striped grassy foliage.

War On Aphids

Posted by Hugh on April 4th, 2016

Aphids on spiraea (picture by Dr. Frank Hale, University of Tennessee Entomologist)

Oleander aphid on Milk Weed (Asclepias)

Aphids are pests that feed on many kinds of garden plants. These tiny insects wreak massive destruction in multiple ways. There are many different kinds (and colors) of aphids. They’re small, 1/16 inch more or less, and feed on plant sap to obtain nutrients. In greenhouses they reproduce without mating; one aphid can start a new colony. Aphids can arrive with plant material, move from one crop to another, or from nearby garden weeds to favorite host plants.

Damage is caused in several ways. Large numbers can lead to reduced growth and vigor. As aphids develop, they deposit a sticky ‘honeydew’ substance on plants on which sooty molds grow – which can spoil the appearance and marketability. Feeding by some kinds causes severe plant distortion. Aphids can transmit disease viruses to healthy plants from sickly ones.

Aphids infest many greenhouse crops, garden vegetables and fruit plants, and landscape trees, shrubs and vines. Common favorites include roses, salvia, impatiens, pansy; vegetables such as pepper, cabbage and kale, tomato; tree fruits such as apple, peach and cherry; and cane fruits such as raspberries and blackberries. A complete list would run many pages long.

Their reproduction rates are incredibly fast and quickly get out of hand inside a home greenhouse where the environmental conditions are perfect. Numbers grow from a few to many thousands in a few weeks. Tiny aphids are often difficult to see and their body colors make them well-camouflaged. Numbers increase when environmental conditions are warm and moist, and plants are well-fertilized.

Don’t invite aphids into your greenhouse and garden. Inspect new plants before purchasing, particularly those bargain plants at flea markets or give-away by other gardeners. Aphid outbreaks can be managed with many effective biological agents and chemical pesticides.

What To Know About Flowering Vines

Posted by Hugh on April 1st, 2016

Hyacinth Bean Vine (Lablab purpureus)

Spanish Flag Vine (Mina lobata)

For some gardeners planting vines is not for the faint of heart. Vines need space, support, training, and for some – lots of pruning. Some vines don’t demand lots of room while others chew up lots of space. Small vines like clematis or annual morning glories (Ipomoea) may be grown in a large patio container for many years on heavy duty cord, wire or wood lattice trellis. Some woody vines become massive and need support on a solidly built pergola. To select the best vine for your space, consider the following tips.

Is the vine an annual or tender perennial or a long-lived woody vine like trumpet (Campsis), climbing hydrangeas (H. petiolaris anomalis), crossvine (Bignonia capreolata), and wisteria (Wisteria spp.)? Long–lived woody vines need to be cut back hard from time to time; the vine’s trunk and main branches may become enormous and need space to grow and a structure sturdy enough to support it.

Annual vines are great for tucking into small garden spaces, including on patios and decks. Instead of building a trellis, you might allow annual morning glories to weave through nearby shrubs and trees for support. Plant the annual vines in decorative containers and climb onto a nearby shrub or tree via tendrils.

Some examples of annual vines include hyacinth bean (Lablab purpureus), climbing black-eyed Susan (Thunbergia alata), Spanish flag (Ipomoea lobata), and morning glory vines. They usually do not hurt adjacent trees for support and die off in fall. Beware – some vines will disperse a large number of seeds.

Vine’s Level Of Annual Maintenance: Woody vines like trumpet vine and wisteria can become pruning nightmares and quickly become unmanageable. These vines grow tall, ramble, and often require working from ladders.