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

Pinxterbloom Azalea

Posted by Hugh on May 1st, 2012

Pinxterbloom Azalea at Jenkins Arboretum in Philadelphia, PA

Pinxterbloom (Rhododendron periclymenoides), formerly R. nudiflorum, is a hardy deciduous azalea native to a large geographic area of the eastern United States. Pinxterbloom naturally grows nearby streams in a light woodland setting, but appears to tolerate dry rocky sites equally well after 2 years established. Shrub heights vary from 4-8 feet. Pinxterbloom spreads by underground stolons and shrubs may become quite dense.

Flowers open in mid to late spring and are often mistaken for honeysuckle blooms. Flower clusters (called “trusses”) appear just before the leaves emerge and bear 6 – 12 blooms each, which open 1½ – 2 inches wide. Flower colors vary among species populations from white to dark pink, most pale to pastel pink. The open petals curve back to show off the long extended stamens and styles. Flower fragrance also varies among plant populations.

Pinxterbloom azalea prefers an acidic, organically rich, moist, well-drained soil. Root rot and plant death often occur on poorly drained sites; planting on raised beds may be a good option on a heavy clay site. Partly shaded or dappled sun exposure is best.

Disease and insect problems are infrequent when pinxterbloom azalea is sited correctly. Soil moisture and acidity are key factors for successfully growing U.S. native azaleas.

Sapsucker Feeding May Blacken Maple Trunks

Posted by Hugh on April 29th, 2012

Sapsucker Holes Create Sappy Trunk

You see or hear a sapsucker tapping in a yard tree and pay little attention to it. The bird perforates the tree or shrub trunk and main branches with numerous shallow holes, similar to a riveter working with sheet metal. A sapsucker feeds on the cambium sap and on insects under the bark.

The holes are deep enough to cause sap leakage, particularly in the winter months when sap pressure in maples (also dogwoods, elms, birches and yellowwoods) is the highest. The sugary sap coats the trunk, and sooty mold fungi grow over the sap secretions. The result is a yucky black stain similar to pitch!

What to do? Nothing!! The sapsucker is at work, doing his/her natural thing. Sapsuckers are members of the woodpecker family. They serve an important function: listening and removing damaging insect borers which may be feeding on the tree sapwood.

Unfortunately, sapsucker feeding does not always indicate that the bird has found insects inside the tree. Yes, the numerous holes are unsightly, but are not injurious to the life of the tree. The black sooty appearance on the trunk should wash off in the months ahead.

According to University of Arkansas Extension horticulturist Dr. James Robbins, favorite tree species for sapsuckers include maple (Acer spp.), pecan (Carya), birch (Betula spp.), pine (Pinus spp.), elm (Ulmus spp.) and some oaks (Quercus spp.). Sapsuckers are attracted to old holes and other bark injury and may return to the same tree(s) for several years.

Pest Alert- Boxwood Blight

Posted by Hugh on April 27th, 2012

Leaf Spotting and Black Stem Canker Symptoms (Photo credit: Craig Adkins, NC State Extension)

Boxwood blight is a disease caused by a fungus (Cylindrocladium pseudonaviculatum) which is a serious threat to most boxwood (Buxus) and related species such as sweetbox (Sarcococca spp.). To date there is no evidence of resistance to boxwood blight in any Buxus species.

Plant pathologists in England first identified the disease in the mid-1990’s. It was first detected in the United States in North Carolina and Ohio in late 2011. The disease is now confirmed in 8 additional states (CT, MA, MD, NY, OR, PA, RI, VA) and in British Columbia.

Initial symptoms of boxwood blight include leaf spotting, rapid leaf drop, blackened stem cankers, and severe dieback. Most boxwoods are not immediately killed by the disease, but the plant(s) will become badly defoliated and unsightly.

Boxwood blight is spread primarily by water (rain splash, irrigation, runoff, etc.), by sale or exchange of plants in the nursery/garden center trade, and through contaminated tools, equipment, boots, etc. The sticky spores infect pruners and other tools, clothing, tires, and, of course, boxwood leaves.

Disease spread is rapid, often in less than a week if weather is warm and humid. The disease is carried by splashing or wind driven rain. At this time there is no cure for boxwood blight. Here are some key steps for gardeners and landscapers to follow:

Know the primary symptoms of boxwood blight and check boxwoods in the garden regularly
Before purchasing inspect boxwoods at garden centers, and reject any with yellow spotted leaves and black stem cankers
During pruning, dip clippers into a 1-to-10 ratio of bleach to water or 70 percent ethanol solution for 1-2 minutes before moving on to a new plant.
Properly dispose of all diseased plants or clippings; do not compost them
Limit buying of new boxwoods and avoid combining new with existing plants
Take suspect boxwood plants and clippings to a county Extension office or to a full service retail garden center for proper diagnosis.

Exceptional Describes ‘Major Wheeler’ Climbing Honeysuckle

Posted by Hugh on April 25th, 2012

'Major Wheeler' Climbing Honeysuckle (photo courtesy of North Creek Nurseries)

Climbing or coral honeysuckle (Lonicera sempervirens) is a native vine. It can be spotted growing on fence rows along roadsides and in woodlands from Connecticut to Nebraska, and south to Texas and Florida. ‘Major Wheeler’ is one of the better climbing honeysuckles noted for its non-stop production of bright red trumpet flowers and green mildew resistant foliage.

Red tubular flowers cover the vine in mid- to late spring, and it continues to scatter blooms all summer long. Major Wheeler becomes a major hummingbird and butterfly magnet from miles around. Flowers form on both previous year’s and current season’s wood.

Climbing honeysuckle grows in full sun to partial shade and in average soils. Flower numbers are heaviest in full sun. Fertilizing is generally not needed unless growth and flowering are not prolific in infertile soils. Once established, Major Wheeler is very drought tolerant.

Rate of growth is fast, estimated at 8-12 feet per year. Prune annually to tidy up the enormous mass of growth. Ideal pruning time is immediately after the major spring bloom flush. Pruning will spur re-growth and new flowering. Expect removal of 50-80% of the old growth after pruning is completed.

Train on a sturdy fence, trellis or arbor from the beginning. Major Wheeler will quickly cover over any old fence that may be an eyesore. Its mildew resistance is outstanding compared to other varieties. Occasionally, aphids and scale insects may infest climbing vines, necessitating spraying with Bayer Advanced Garden Insecticide™, Malathion, or acephate (Orthene™).

‘Major Wheeler’ climbing honeysuckle was found by Charles Wheeler, the former president of the NC Botanical Gardens and is winter hardy to USDA zone 4.

‘Fireworks’ Pennisetum

Posted by Hugh on April 23rd, 2012

'Fireworks' Pennisetum in late August at Dallas Arboretum

Fountain grasses are popular annual grasses that thrive in Southern Appalachian gardens (USDA zones 6 and 7). The new cultivar ‘Fireworks’ is totally spectacular. The mid-vein of the grass blade is burgundy red and edged in hot pink.

Fireworks displays three seasons of awesome foliage color before dying off in the fall. Red plume foxtail flowers bloom from mid-summer to early fall. Fireworks grows as a thick clump that is 3-6 feet tall and 1-3 feet wide. Utilize Fireworks as an accent plant in landscape beds and containers.

Fireworks flourishes in full to partial sunlight (6-hours minimum) in average well-drained, low acidic soils (pH 6.0 to 7.0. Weekly irrigation is a plus. It establishes rapidly and tolerates short summer dry spells.

The vibrant tri-colored grass blades intensify in the early autumn cooler temperatures. In the deep South (USDA zones 7-b to 9), foliage colors often fade under extreme sunlight and heat (see photo above).

Fireworks should be fertilized at planting time with a 5-6 month rated slow release fertilizer. Another alternative is to feed monthly with water soluble Miracle-Gro™, Schultz®, or a similar product according to package rates.

Grass blades turn brown in the first hard autumn freeze. Snow or ice embedded ornamental grasses can be quite beautiful. You may opt to shear them back in early fall as the old floral heads (plumes) often self-seed. Fireworks fountain grass is relatively disease and pest free and is deer resistant.

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).