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

Hibiscus Sawfly Devastates Plant Foliage

Posted by Hugh on August 3rd, 2011

Hibiscus Sawfly Damage

The hibiscus (mallow) sawfly is a devastating pest of hibiscus (Hibiscus moscheutos) and hollyhock (Alcea rosea). The adult sawflies are small, barely a quarter inch long. They are mostly black, except for a yellowish brown spot on their thorax, and their smoky wings. The pale green larvae mature to 1/2 inch in length.

The larvae turn hibiscus foliage into lacy skeletons. The adult females lay eggs in the upper surfaces of leaves and, at first, produce blister-like bumps. The larvae hatch, move to the underside of the leaf, and begin to feed voraciously. Mature larvae pupate at the base of the plant. Hibiscus sawfly develops up to six generations from mid-spring until frost.

Select one of two control strategies:

foliar sprays of any one of the following insecticides: acephate, pyrethrins, synthetic pyrethroids (such as bifenthrin, permethrin, and cyfluthrin), and spinosad; spray every 7 -10 days or when leaf damage is observed.
soil drench with any insecticide product containing imidacloprid; only one application offers season long control.

Sawfly resistant cultivars may be in the future. Currently, there is no resistance in H. moscheutos, but some in swamp rose mallow (H. grandiflora), and in scarlet rose mallow (H. coccineus).

Related: Blog on ‘Fireball’ hibiscus published June 18, 2011

To Grow Crocosmia Or Not?

Posted by Hugh on July 19th, 2011

'Lucifer' Crocosmia at Kingwood Center, Mansfield, Ohio

This South African native, also called ‘montbretia”, thrives in full sun in well-drained average garden soil. A richly composted soil tends to boost foliage size and bloom count, but often weakens bloom stems, requiring some staking. Crocosmia may struggle in a wet soggy wintry soil. Established plants are exceptionally summer heat and drought tolerant.

Brightly colored flowers rise on wiry stems above the sword-like leaves in early July in the Southern Appalachian region (USDA zones 6 and 7). The foliage closely resembles gladiolus. Most cultivars are hybrids and vary in flower color, height and plant vigor.

Flower stalks arise from fast-multiplying underground bulbs (they’re really corms) in red, orange, yellow and mixed colors. The most popular cultivar is ‘Lucifer’, a Blooms of Bressingham introduction. ‘Lucifer’ produces vivid red flowers on 4-5 foot arching wiry stems. Crocosmias make excellent cut flowers.

Corms are planted 3 to 4 inches deep in fall or early spring. In northerly zone 5, either plant corms 6 inches deep or lift and store them by late fall. Container-grown plants are also sold at most garden shops.

Many low growing forms (not ‘Lucifer’) tend to start slow their first year, but wind up as long-lived perennials. Over the years crocosmia may become a nuisance (perhaps invasive?) as corms spread to other garden areas. Mites may draw sap (stipple) leaves in a dry summer.

Panicled Raintree Promises Showy Lantern Pods

Posted by Hugh on July 15th, 2011

Chinese Flametree With Autumn Lantern Seed Pods

Chinese flametree (Koelreuteria bipinnata) is also called bougainvillea raintree. This rare tree, available primarily from internet nursery commerce, deserves to be planted more. It has performed well in the Southern Appalachian region (USDA zones 6-b and 7) and is questionably hardy further north.

Flametree is less popular in Southeastern landscapes than goldenrain tree (K.paniculata). Low branching and broad canopy limits its landscape use to a small 25-30 foot tall specimen tree. Very showy dense terminal panicles of small fragrant yellow flowers appear in mid- to late summer, nearly 3-4 weeks after goldenrain tree (K.paniculata).

Large clusters of two-inch-long showy rose-colored “Chinese lanterns” form quickly after flowering which persist to mid-October. The papery thin seed husks retain their pink color indoors in dry flower arrangements. The bark on Chinese Flame-Tree is smooth and light brown when young, becoming more ridged or furrowed as the tree matures.

Flametree’s dark green summer compound leaves, each 1-2 feet long, turn yellow for a short autumn interlude before falling. Later, numerous fertile seeds drop, which potentially, may raise invasive issues for this species.

(See also blog on Goldenrain tree (K. paniculata) published 7-1 -11)

Summer Blooming Oyama Magnolia

Posted by Hugh on July 10th, 2011

A friend on vacation sent me the attached photo from Wooster, Ohio. When I told him that it was Oyama magnolia (Magnolia sieboldii), he asked why gardeners are not growing it. Good question!

Oyama magnolia is a 10-15 feet tall (and equal spread) deciduous tree or large shrub from eastern Asia. It prefers to grow in partial sunlight and in moist, well drained loamy soil (USDA zones 6 -8). Oyama is an ideal tree/shrub magnolia for a small garden. Spring bloom is in May, avoiding the threat of frost injuring the flower buds of this later blooming magnolia.

The 3-6 inch long medium green foliage is first to appear in April, coated with a silvery pubescence. White nodding egg-shaped flower buds appear in late June, and blooms appear intermittently thru most of the summer. The 1-3 inch wide saucer shaped flowers are white, centered by crimson stamens within. Oyama begins to flower at an early age.

Leaves turn pale yellow before abscising in mid-autumn. Small pink fruits appear in late summer, and split open to reveal orange-red seeds in late September. Branch bark wood is light gray.

Feed magnolias with a slow release fertilizer in early spring. They benefit from annual mulching. Pruning shrub to desired shape and size, and to remove dead or broken branches.

Oyama magnolia is available from a few on-line specialty nurseries.

Tough And Reliable Chinese Astilbes

Posted by Hugh on July 4th, 2011

Astilbe chinensis at Kingwood Center, Mansfield, Ohio

Astilbes (also called “false spireas”) are favorite late spring flowering perennials. The Astilbe x arendsii hybrids from Germany are most popular and available at local garden centers. Astilbes are very hardy in the Southern Appalachian region (USDA zones 6 and 7).

If low maintenance is your goal, try Chinese astilbe (Astilbe chinensis var tacquetii). Their care is less demanding than the Arendsii hybrids. Chinese astilbes bloom nearly two weeks later. Group many together for mass effect of plume flowers and dense compound foliage.

The ‘Visions’ series are personal favorites. The original ‘Visions’ bears raspberry plume flowers. Later cultivars, ‘Visions in Red’ and ‘Visions in Pink’, are also nice. Plants form a 9- inch tall mound with bronze-green leaves and dense panicles of raspberry colored flowers on 12-15” tall stems.

‘Pumila’ forms a thick ground cover with 8-12 inch tall lavender purple flowers in mid- summer. ‘Superba’ is a taller flowering form and more available in nursery commerce.

Chinese astilbes grow in moist, well drained soils and partial sunlight. Two –year old established plants are exceptionally drought tolerant, have no serious disease or pest problems, and are generally not a favorite of deer.

Goldenrain Tree – A Golden Shower of Bloom

Posted by Hugh on July 1st, 2011

Golden Raintree in Urban Parking Lot

Goldenrain tree (Koelreuteria paniculata) is a medium sized landscape tree maturing to 30-40 feet in height and spread with rounded canopy. A native of China, Japan, and Korea, the tree is winter hardy in the Southern Appalachian region (USDA zones 6 and 7). Large panicles of dark yellow flowers set off a golden fireworks for your 4th of July celebration.

Individual flowers barely measure a 1/2″ wide, but the multi-branched floral panicles measure 10-15 ” across. The bipinnately compound leaves are also large at 8 to 14 inches in spread. The medium green colored spring/summer foliage turns pale green in autumn before dropping.

Yellow-green triangular 1 to 2 inches long seed capsules soon follow after flowering. The papery seed capsules are often called “Chinese lanterns” and are a significant ornamental feature. Each lantern may contain 1-3 hard black globular seeds. By early fall the capsules have turned dark brown. Bark of old trees is ridged with shallow reddish brown furrows.

Goldenrain tree grows in a wide range of soils, including high pH soils. It’s rarely bothered by pests and demonstrates exceptional heat and drought tolerances. It excels as a specimen yard tree, or utilize planted along wide avenues or in parking lots with their lower branches limbed high.

Seed viability may potentially be an invasive plant issue in some Southeastern states.

Looking ahead: see also blog on Chinese flametree to be published 7-15-11

Biltmore Estate and Gardens

Posted by Hugh on June 30th, 2011

Biltmore House

I have visited the Biltmore Estate on several occasions, but my May visit this year was special. I had the opportunity to interview Parker Andes, Biltmore’s Director of Horticulture, and Bill Alexander, Landscape and Forest Historian.

Few properties match the overall grandeur of Biltmore Estate and Gardens in Asheville, North Carolina. Biltmore is a historical perspective of America over a century ago. The property was designed by Fredrick Law Olmstead, Sr., deigned the father of American Landscape Architecture. Famed botanist and horticulturist Chauncey Beadle maintained the grounds nearly 60 years.

Olmstead took on over 1000 acres, an area some 50 times larger than another of his grand projects – New York’s Central Park. The 3- mile entry driveway winds through dense woodlands to the estate home and gardens of tycoon George Vanderbilt. Along the drive are native rhododendrons and azaleas (Rhododendron spp.), mountain laurels (Kalmia spp.), hemlocks (Tsuga spp.), pines (Pinus spp.) and thick stands of bamboo (Bambusa spp.).

Espanade of Replanted Tulip Poplars

A double lined esplanade of 2^nd generation tulip poplars (Liriodendron tulipifera) frame the entrance to Biltmore House. The four-acre Walled Garden and the 16th-century Italian garden are adjacent to the house.

The Spring Gardens Festival had just ended, and newly-planted summer annuals replaced thousands of tulips, hyacinths, etal. The adjacent rose garden was fully in bloom. According to Bill Alexander, the garden staff is launching a multi-year rose trial of varieties gathered worldwide.

Rose Garden at Biltmore

Many mature specimen trees and shrubs are found on the property: one of the first dawn redwoods (Metasequoia glyptostroboides) brought to the U.S. from China in the early 1940’s; a century-old Persian ironwood (Parrotia persica) with its mosaic patterned bark, and a mature Katsura tree (Cercidophyllum japonicum). The enormous size and majesty of the Olmstead- planted beeches and oaks is always breathtaking.

Growing Berries at Antler Hill Farm

I concluded the delightfully full day with a trek through the new Antler Hill area, where the Winery and Creamery (not the original) are situated. Close by is the Historical Farm, which includes the livery, coppersmith, and woodworking shops. Visitors have the opportunity to play games popular in the 19^th and early 20th centuries. An antique farm equipment museum was recently added near the fruit, vegetable and herb gardens.

Magnificent Mountain Laurels (Kalmia)

Bringing Biltmore Gardens home to your garden is no longer wishful thinking. The horticultural team has partnered with several nurseries around the world to reproduce many of the fabulous plants which have grown on the grounds for over a century. Periodically, I plan to feature these horticultural treasures in my blog: whatgrowsthere

July Lawn Care

Posted by Hugh on June 28th, 2011

Beautiful Home Lawn in mid-June

Around July 4th it’s time for a second (and last) application of crabgrass preventative. The herbicide which you applied in late winter is likely worn off. The basic herbicide preventative product tradenames (and active ingredients) are: Barricade® (prodiamine), Dimension® (dithiopyr), Echelon® (prodiamine + sulfentrazone), Pendulum® (pendimethalin), and Ronstar® (oxadiazon). Irrigate (1/2 inch water or 1 1/2 hours watering with an oscillating sprinkler) within a few days after application to activate the herbicide.

Cutting (mowing) of cool season grasses (tall fescue, bluegrass, red fescue, ryegrass) needs to be raised to 3- inch height over the summer months. Fertilizing a cool season lawn is not recommended unless it is kept irrigated over the summer months. Warm season lawns (burmuda, zoysia, centipede) likely need additional nitrogen applied.

July is Japanese beetle assessment time. What is the level of beetle feeding activity on shrub flowers and foliage? This will determine grub levels in the soil feeding on lawn roots this fall. Will you need to begin an insecticide program this fall?

Looking ahead: Has bad weather, diseases, insects, and/or weeds devastated your lawn? You should assess the need for fall renovation in late summer (early September thru mid-October). Tackling this task now in the middle of summer rarely works out. Allow the cooler autumn weather to work in your favor.

Flaming ‘Fireball’ Hibiscus Quite A Summer Show

Posted by Hugh on June 18th, 2011

Hibiscus 'Fireball' photo by North Creek Nurseries

‘Fireball’ hibiscus (Hibiscus x moscheutos ‘Fireball’) is a vigorous hardy perennial with burgundy tinted cutleaf foliage and huge 10-12 inch clear red flowers from mid-summer to late summer.

Plant height is 4 – 5 feet and 2 – 3 feet in width. A strikingly beautiful plant, ‘Fireball’ thrives on heat and humidity. It wants full sun and a moist well drained soil to reach its full flowering potential. Expect hundreds of blooms on 3-4 years old established plants grown in a richly amended composted soil and kept irrigated.

Flowers are both huge and showy. Blooms are the size of dinner plates. A prominent pistil and stamen is in the center of each flower. Each bloom lasts but one day, but ‘Fireball’ blooms almost nonstop from July to early September.

Hardy hibiscus demands heat, moisture and long days. They are late to emerge from the soil, many years after May 15th in the Southern Appalachian region (USDA zones 6 and 7). Feed them regularly with a water soluble 20-10-20 fertilizer (or equivalent). Hibiscus sawfly, mites, and aphids may be serious nemeses.

This late flowering habit makes hardy hibiscus ideal companion plants to interplant with spring blooming bulbs like daffodils and tulips.

Fireball™ is one of several hardy hibiscus bred by the Fleming Brothers in Lincoln, Nebraska. It was their favorite perennial.

Bagworms Can Devastate Evergreens

Posted by Hugh on June 8th, 2011

Bagworm on conifer- photo by Alan Windham

Bagworms feed on more than 128 species of plants, including junipers, cedars, arborvitae and white pine. More than one year of severe defoliation will kill a formerly healthy specimen. Bagworms have one generation per year. Eggs usually hatch in mid to late May across the Southern Appalachian region (USDA zones 6 and 7).

Upon hatching, the young larvae crawl out of the bottom of the bag and begin eating plant foliage. Maturing larvae can do considerable defoliation during early summer. As the worms age, they construct a silken shelter over their body and are more difficult they are to kill.

Bagworms’ carrot-shaped bag is constructed of bits of material from the plant upon which it’s feeding and expands as the bagworm grows. The bag is carried wherever the worm goes. When disturbed, the bagworm merely pulls its head back into its bag for protection.

Insecticides should be applied when the bagworms are small, but after all have hatched by early June. After mid-June pesticide control is too late. Complete spray coverage is essential. Carbaryl (Sevin), Bt (Dipel), Malathion, acephate (Orthene), and pyrethroids like bifenthrin (Talstar), cyfluthrin, and permethrin), and spinosad (Conserve SC) are highly recommended. Spinosad controls the hard to kill older bagworms.