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

Fountain Grasses Are Summer Sizzlers

Posted by Hugh on April 21st, 2012

: Purple Pennisetum Grass in Hot Parking Lot

Fountain grass (Pennisetum setaceum ) is a warm season grass native to Northern Africa (USDA zones 8-10). It is a dense clump-forming grass with several topnotch cultivars. Most popular are purple fountain grasses (varieties ‘Purpureum’ and ‘Rubrum’) for their heat resistant dark reddish purple foliage. The pink to purplish pink foxtail plumes (flowers) rise above the dark colored foliage starting in mid-summer into early fall. Fountain grass averages 3-4 feet in height and 2-3 feet in spread. Some cultivars grow taller and wider.

Fountain grass is the most popular annual grass planted in the Southern Appalachian gardens (USDA zones 6 and 7). It flourishes in full to partial sunlight (6-hours minimum) in average well-drained soils. Foliage and plume colors are more intense in full sun. P. setaceum is more drought tolerant than the “other” fountain grass (P. alopecuriodes), native from eastern Asia and west Australia.

Spring planted fountain grasses establish rapidly and tolerate short dry spells in summer. Weekly irrigation is your best bet. Fertilize at planting time with a 5-6 month rated slow release fertilizer or feed monthly with water soluble Miracle-Gro™, Schultz®, or a comparable product according to package rates.

Warm season grasses turn shades of brown as the weather turns colder in late fall. Snow or ice encrusted ornamental grasses can be quite beautiful. You may opt to shear them back in early fall, as old floral heads (plumes) tend to self-seed.

Fountain grasses stand out mixed with other perennials, by themselves in enmass, or in planted in containers. They’re mostly disease and pest free as well as deer resistant.

Pest Alert_ Downy Mildew on Annual Impatiens

Posted by Hugh on April 19th, 2012

Disease on Underside of Leaf (photo courtesy of Dr. Alan Windham)

In 2011 across Europe, seventy percent (70%) of the garden impatiens (Impatiens walleriana) were hit with downy mildew. Disease outbreaks were also reported in a few U.S. coastal cities last year. U.S. growers have been preparing for the possible outbreak in summer 2012. The potential for this disease can be catastrophic as the fungus can overwinter in the soil.

Gardeners should purchase disease-free plants at garden shops this spring. They should inspect plants closely, and don’t buy those with yellowed or misformed leaves. They should not plant where impatiens were growing last summer. If other annuals, say snapdragons or zinnias, were infected last year, this form of downy mildew will not effect impatiens.

At this time downy mildew appears to be limited to seed-produced impatiens. Vegetatively-produced impatiens (from cuttings or tissue culture) appear to be clean. Some kinds of impatiens are not susceptible to downy mildew, such as SunPatiens and New Guinea impatiens.

Downy mildew is a systemic pathogen. Symptoms include a downy white coating on the underside of the leaves. Defoliation soon follows. Other clues include leaf stippling, chlorosis (yellowing), and downward curling of leaf margins. If plants become infected, there is no pesticide spray option available. Dig up and discard all contaminated impatiens immediately and never compost the diseased plants.

Permit me to offer a calming statement. If you are planning to or have already planted impatiens this year, enjoy the colorful array which impatiens do provide. U.S. greenhouse growers have been aware of the problem for almost a year and plants for sale should be disease-free. Stay informed about this disease.

Peruvian Lilies – A Gift Which Keeps On Giving

Posted by Hugh on April 16th, 2012

Peruvian lilies (Alstroemeria)

Peruvian lilies (Alstroemeria spp.), also called Lilies of the Nile), are not true lilies (Lilium spp.). Likely, you have purchased a bouquet of alstroemerias from the florist section of your local supermarket. In addition, many potted hybrid varieties have been introduced from Holland and elsewhere over the past decade.

Turns out that some Peruvian lilies are perennials, winter hardy in the Southern Appalachian Region (USDA hardiness zones 6 and 7). Perennial types are best suited for an east front border of the flower garden, exposed to mostly morning sunlight. In the deep South (zones 8 and 9), they prefer filtered (not direct) sunlight through nearby trees.

Afternoon sunlight is harsh in the summer on the leaves and reduces flower life. Mulch around plants in late fall in colder zones 5-b to 6-a climates or transplant back into a container and grow them in a cool garden room over the winter.

Peruvian lilies require little care after planting. Fertilize established plants in late winter with a handful of granular 10-10-10 around each plant. Irrigate Peruvian lilies weekly, particularly during summer dry spells.

Peruvian lilies comes in several flower colors including in white, yellow, salmon, pink and red. Perennial varieties average 18-36 inches in height in garden beds and in deck or patio containers. Cut flowers may last for 7 to 10 days.

Turk’s Cap Lily for Your Summer Enjoyment

Posted by Hugh on April 12th, 2012

Turk's Cap Lily in Tennessee Garden (photo by Joy Stewart, Bristol, TN)

Turk’s cap lily (Lilium superbum) is native perennial started from bulbs. The strong single stem grows up to 6 feet tall. Leaves generally form in whorls of 3-9 along the stem. The lanceolate leaves are individually upwards of 7 inches longand 1 inch wide, and rather stiff to the touch.

Upwards of 1-12 flowers nod downward from 4-8″ long stalks branched along the main stem. Each orange trumpet-shaped flower is 3-4 inches across, with 6 tepals (petals) which flare outward and reflex backward toward the base of the flower. Tepal colors range from orange to dark orange and are marked with numerous brownish purple dots in the throat of the flower. Long reddish brown stamens extend from the flower, tipped by reddish brown pollen sacs.

Turk’s cap lily blooms in early to mid-summer for approximately one month. Flowers emit a slight fragrance. Pollinated flowers form seedpods filled with thin papery winged seeds. Below ground bulbs also develop a few offsets which can be dug up and replanted.

Turk’s caps thrive in moist meadows and open forest lands in the U.S. They prefer full or partial sunlight (6-hours minimum) and an organically rich loamy garden soil. Established plants can cope with modest dry spells. Starting Turk’s caps from seed is slow, taking four years or more to attain flowering bulb size. This limits their availability in the marketplace.

The large showy flowers attract hummingbirds, butterflies, and moths. Deer consume aboveground vegetation and bulbous roots are relished by voles.

Botrytis Disease in Marigolds Can Be Avoided

Posted by Hugh on April 10th, 2012

: Botrytis Disease in Marigolds

Marigolds (Tagetes spp.) have been long time favorite summer annuals in Southern Appalachian gardens (USDA zones 6 and 7). Marigolds come in three sizes: 18-36 inch tall “African” marigolds, 12-18 inch medians and 8 -12 inch “French” border types and in two color choices- orange and yellow. Begin planting in April or May after frost danger has passed. Figure in a six week period for establishment and marigolds possess exceptional drought and heat tolerance over the summer months.

Botrytis, also called “gray mold”, is a serious fungus disease. Flower petals turn brown and are often covered with gray, fuzzy masses. Brown target-like spots may also appear on the foliage.

Botrytis is most troublesome during periods of extended cloudy, humid, and wet weather conditions. Flowers may capture and hold water from rainfall and irrigation. Irrigation should be scheduled in the early morning hours. You should select marigold cultivars with flowers that shed and do not retain water droplets.

Sanitation or removing old (spent) and diseases flowers is key to reducing the spread of botrytis through the garden bed. Avoid wetting the flowers when watering and adequately space plants to promote good air circulation.

An alternative is to apply fungicide sprays as soon as disease symptoms appear. Among the pesticides registered for use are Chipco 26019® (iprodione), Daconil® (chlorothalonil), and either Cleary’s 3336® or Domain FL® (thiophanate-methyl).

Bloomerang™ Lilac For Non-Stop Flowering

Posted by Hugh on April 8th, 2012

Young 'Boomerang' Lilac in mid-April Garden

In most Northeast and Midwestern states, lilacs (Syringa spp.) are the classic spring-flowering shrub, treasured for their beautiful and fragrant flowers. Lilacs are vigorously growing shrubs and are utilized in the landscape as single specimens or as multiple hedging shrubs for privacy. Further south, in the warmer Southern Appalachian region (USDA zones 6 and 7), most lilac cultivars tend to disappoint because of low flower numbers and their susceptibility to foliar powdery mildew in late summer.

Bloomerang™ is a hybrid cross of four lilac species (Syringa patula x S. macrophylla x S. meyeri x S. juliana). It grows bushy and compact at 5 feet tall and 6 feet wide. Boomerang grows vigorously, fits into small garden spaces, and forms a lovely low growing hedge.

Clusters of sweet-scented flowers open deep purple that densely cover the branches in April and bloom off and on until October frost. Flower clusters fade to pink and fall without any need for deadheading. Although the long re-blooming trait is never showy, you and your gardening friends will likely take notice.

Boomerang is best pruned immediately following spring bloom, to form a dense shrub with more branches and flowers. This lilac is deer resistant and its small dark green leafy foliage is moderately resistant to powdery mildew.

Lilacs grow in full to partial sunny locations and in a low acidic to slightly alkaline soil pH. Lilacs benefit from annual feeding containing minor nutrients such as Miracle-Gro™, Miracid™, Hollytone™ or Schultz® fertilizers. Follow package label directions.

Re-blooming Iris For Twice (and More) Flowering

Posted by Hugh on April 6th, 2012

Re-bloomer Iris germanica 'Sugar Blues'

Gardeners who desire more flowering from garden iris (Iris spp.) should be planting re-blooming types. Some cultivars may re-bloom up to three times in one growing season. The re-blooming trait is found both in bearded and beardless irises (I. germanica).

Re-bloomers need to be well established for one year, sometimes two, to bloom multi-seasonly. Some re-bloomers are sporadic, and a short list of dependable varieties is included below.

Information on growing tall bearded iris is found in an earlier blog (April 1, 2012). Re-bloomers multiply faster than one-time bloomers, and need to be divided every two to three years to avoid overcrowding. Some cultivars need to be well established before they re-bloom; lift and divide only part of the clump and leave the remaining portion undisturbed to re-bloom. Also, clipping off the foliage too early in late summer reduces re-bloom potential.

Re-bloomers are heavy feeders and benefit from two feedings, once in the spring, nearing the end of the regular flowering period, and a second time in mid- August, the start of the 2nd or 3 rd re-blooming period. Fertilize with a low nitrogen analysis, such as 5-10-5. Re-blooming cultivars need frequent irrigation during dry summer periods compared to standard irises.

A baker’s dozen cultivars include: Best Bet, Bountiful Harvest, Clarence, Hemstiched, Immortality, Jennifer Rebecca, Mother Earth, Pagan Goddess, Pagan Dance, Autumn Tryst, Champagne Elegance, Orange Harvest, Rosalie Figge.

Complete Care of Tall Bearded Iris

Posted by Hugh on April 4th, 2012

Tall bearded Iris-- Queen of the Perennial Garden

Most gardeners plant tall bearded iris from late August through October to insure good root development before winter sets in. Spring planting is another option as iris may be purchased in containers. Bare root rhizomes need to soak overnight in water before planting. Bearded irises prefer a sunny location and a slightly acidic well-drained soil. Work in plenty of compost into the garden soil prior to planting and lightly mulch iris 1-2 inches after planting. Irrigate the bed every 5-7 days if natural precipitation is light; once the first new center leaves appear, iris rhizome(s) have rooted.

Remove the bloom stalks after flowering and cut the foliage down to 3-4 inches in late fall. Irises need dividing every 3-4 years to prevent overcrowding. Right after Labor Day is a fine time to divide and/or transplant in the Southern Appalachian region (USDA zones 6 and 7). Avoid the stressful hot days of summer. Plant each rhizome shallow, barely beneath the surface of the soil.

Irises grow best in raised beds, particularly if the garden soil is heavy clay. Add superphosphate (0-45-0) to the soil before planting. A good low-nitrogen fertilizer such as 6-12-12 can be used early in the spring. Do not mulch or overwater.

Tall bearded rises are susceptible to a number of disease and pest issues. Remove and discard (do not compost) all dead leaves and bloom stalks by late fall so not to overwinter various diseases and pests.

In the spring treat leaf spot diseases with Daconil™ fungicide. To manage iris borers, aphids and beetle grubs, choose a systemic insecticide like Merit™ (imidacloprid).

Katsura Tree Comes Home To America

Posted by Hugh on April 1st, 2012

Katsura Tree at Chanticleer Garden near Philadelphia, PA

Katsura tree (Cercidophyllum japonicum) is a large 50-60 feet tall tree from Japan and China. Katsura became extinct in North America during the Pleistocene Age and was re-introduced in 1862 by botanist Thomas Hogg. It is truly a beautiful tree, yet is still rarely planted.

Katsura is hardy in zones 4-8. It prefers a moist well-drained, compost-rich soil in a full sun to partial shade setting. Katsura’s annual growth rate is medium to fast, and develops either single or multi-trunked.

Spring foliage is unique, 2-4 inch wide circular leaves edged with tiny round -edged teeth. New leaves emerge reddish purple, quickly turns matted green, then to blue green in summer, and muted yellow-orange in autumn. On a cool late September morn the maturing Katsura foliage fills the autumn air with a cinnamon-like fragrance. Katsura is dioecious, an individual tree either male or female. The latter forms tubular seed capsules which disperse thin circular winged seeds on a windy October day.

Nursery stock is predominantly balled and burlapped (b&b), but container grown trees are becoming more available. Most full service garden centers can order it for you or purchase one on-line.

Katsura requires ample space such as in large residential lots, public parks, golf courses, and commercial properties. Foliage stays pest free.

Katsura cultivars abound starting with ‘Amazing Grace’, an exquisite weeping form with exceptional blue-green foliage.

Piedmont Azalea

Posted by Hugh on March 30th, 2012

: Piedmont Azalea (R. canescens) at Callaway Gardens

Early flowering Piedmont azalea (Rhododendron canescens) is one of the most common native deciduous azaleas in the southeastern U.S. It is frequently confused for pinxterbloom azalea (R. periclymenoides) which blooms 3-4 weeks later. Piedmont azalea is hardy in USDA hardiness zones 6 to 9.

Piedmont azalea reaches a mature height between 6 to 15 feet, about one-third higher than wide. There is great variability within this species. Flower colors may vary from white to deep pink, depending on the seed parentage in the geographic area. The fragrant blossoms appear in early spring before the leaves emerge. Floral stamens protrude outward two to three times beyond the length of the tubular petals. The lightly fragrant flowers invite numerous butterflies, hummingbirds, and bees into the early spring garden.

It is found in deciduous woodlands where it receives ample sunlight in early spring, and stays mostly shaded through the summer months. It prefers a moist, organically rich, well-drained, and acidic soil. Fertilize shrub(s) lightly and add pine straw or pine bark mulch to conserve soil moisture.

Piedmont azalea has a shallow stoloniferous rootsystem, and a shrub may form plant colonies around itself. Prune upright growing Piedmont azalea immediately after flowering to increase shrub density and width. Piedmont azalea is susceptible to a number of eating or chewing pests.