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

Evergreen Kousa Dogwood? – Depends on Where You Garden

Posted by Hugh on March 28th, 2012

Chinese dogwood in flower

Chinese (kousa) dogwood (Cornus kousa) is a small spring flowering dogwood. Kousa blooms about 2 – 3 weeks after our native flowering dogwood (C. florida) has finished. Lustrous dark green leaves begin to emerge a week or two before the lovely pointed 3- inch white bracted flowers. Fall leaf color is purplish red and not quite as vibrant as C. florida. Its patchy exfoliating bark is a winter asset which gets better as the tree ages. The fleshy raspberry fruits are not a popular food source with birds and four legged critters in the fall.

Evergreen kousa dogwood (Cornus kousa var. angustata) is a variant also listed as Cornus angustata. Angustata forms a shorter tree with narrow pale green evergreen foliage is reliably evergreen in USDA zones 7-b and 8, and takes-on a purple wintry tint in zones 6-b and 7-a. The tree is deciduous in zone 6-a and further north. Protection from winter winds may retain the autumn foliage longer. Angustata mature tree height averages 20-25% smaller than the species.

Plant in part shade and in well-drained compost rich soil in southerly climes of zones 7-b and 8 and in full sun further north. Angustata is only moderately tolerant of summer heat and humidity and should be irrigated during periods of extreme drought.

Two evergreen cultivars are:

Empress of China®, introduced by John Elsley, flowers abundantly in mid to late May.
‘First Choice’, a selection from JC Raulston Arboretum in Raleigh, NC. has good flowering and growth rate.

Very Tall Stake For A Weeping Blue Atlas Cedar

Posted by Hugh on March 26th, 2012

Weeping Blue Atlas on Poor Site

Weeping Blue Atlas Cedar (Cedrus atlantica ‘Glauca Pendula’) is “gravity prone”. This strongly weeping tree just doesn’t happen without staking in its formative years. At planting position a sturdy 12-16 foot metal or plastic stake or rod close to the trunk at planting time.

The staking and tying procedure is neither complicated nor time consuming. When the spring growth flush has finished and while the leader is still soft enough (flexible), bend the leader upward and tie to the stake or trellis. Use soft jute or cotton twine, and not wire twist-ems® or plastic ties. After 6-8 months, loosen the ties so they won’t girdle the tender main shoot (leader).

The new shoots emerge in mid to late April. The needles have fully elongated by late May. Staking is best performed anytime from late June thru mid July in the Southern Appalachian region (USDA hardiness zones 6 and 7). The shoots should be slightly hardened but still flexible. If too stiff, the main shoot (leader) may not bend to straighten up vertically and leave a crook.

How many years you continue to stake ‘Pendula’ depends on the mature height desired. Most gardeners train to 5-8 feet, but I encourage you to set a higher goal between 12-16 feet.

Another idea is to train Blue Atlas cedar to an arbor or trellis at a garden entry (see photo below).

Staking when young provides an early foundation for a well-shaped mature tree. Plants can be alot like people. Youngsters left to their own devices become unruly adults.

Cedrus atlantica 'Pendula' on Trellis

Contorted Filbert Offers Great Fall And Winter Interest

Posted by Hugh on March 23rd, 2012

Catkins of Harry Lauder's Walking Stick

Contorted filbert (Corylus avellana ‘Contorta’), aka Harry Lauder’s walking stick, is an 8-10 foot tall shrub. It grows in average well-drained acidic or mildly alkaline soil and thrives either in full or partial (6 hours) sunlight. Contorted filbert is usually sold in a grafted form.

It is also called corkscrew hazelnut because most branches, twigs and leaves display a twisting or spiraling nature. Showy yellowish brown male catkin flowers grow to 2-3 inches in length in late winter and early spring. Tiny female catkins are barely visible. Contorted filbert does not bear fruits (nuts).

The light green almost circular leaves (2-3 inches in diameter) are double-toothed along the leaf margin. The foliage turns a drab yellow in the fall. Following leaf abscission, the curlicue branching provides considerable autumn and winter interest.

Contorted filbert has no serious insect or disease problems. Susceptibility to crown gall is often associated with a poorly drained site. Occasional scale insect infestations may be eradicated with 1-2 applications of dormant oil in the winter months before new leaves emerge. Root suckering may become a maintenance nuisance. These straight growing (not twisted) suckers tend to eventually dominate the entire shrub and should be removed.

‘Red Majestic’ is a new contorted filbert. The new spring growth emerges with burgundy red tint which bleaches out to a dark green foliage by late May.

Evaluating The Weeping Redbuds

Posted by Hugh on March 21st, 2012

Weeping Redbud (Cercis)

There are so many fine redbuds (Cercis spp.) which are hardy in the Southern Appalachian region (USDA zones 6 and 7) and elsewhere. Through research and breeding efforts at the JC Raulston Arboretum in Raleigh, NC, Southeast U.S. gardeners can grow several more cultivars of our native Eastern redbud (C. canadensis and subspecies texensis) and chinese redbud (C. chinensis). There are two popular and one new weeping form.

Traveller Weeping Redbud (C. canadensis ssp. texensis ‘Traveller’) produces deep rose pink flowers in early spring. Leaves are dark green with high gloss over its upper surface. Traveller has graceful arching branches. The tree’s overall form is mound-like and grows taller and wider over time. Its rootsystem is strong and vigorous.

Lavender Twist redbud (C. canadensis Lavender Twist™ or ‘Covey’) is more winter hardy (USDA zones zones 5-9) than Traveller (USDA zones 6-9). It demands staking to straighten up (for height) the main leader. Without staking, Lavender Twist’s strong weeping nature will turn it into a low trailing shrub. Staking also helps to better anchor the tree’s less vigorous root system.

Lastly, there is the new Ruby Falls™, described as a 4-6 feet tall and 6-8 feet wide weeping Lavender Twist with purple ‘Forest Pansy’ redbud foliage. Ruby Falls is a 2010 introduction from NC State University and is available in very low numbers worldwide. It is rated as winter hardy in USDA zone 6

All three weeping redbuds fit in a small garden, and all should be utilized as a small accent tree in ready view from the garden patio deck and from inside the home.

Protect Fruit Trees and Bee Population

Posted by Hugh on March 19th, 2012

: Cedar rust infection spot

Warm weather in early spring means scab, cedar apple rust and powdery mildew diseases are upon the new leaves as they start to emerge. Preventative spraying for leaf diseases will result in management of additional fungi diseases through the growing season.

Fungicides are protectants and not cure-alls. A light rain shower (as little as ¼ inch of precipitation) will wash off the “water soluble” spray and it must be re-applied as soon as possible. Timely spraying helps to break the disease cycle.

Beginning in late March, across most areas of the Southern Appalachian region (USDA zones 6 and 7), spray only fungicides in early spring as not to injure our fragile bee populations which are pollinating flowers. Most insect pest problems on fruit trees do not start until after petal fall.

Cedar-apple rust and powdery mildew are primarily threats in the wet cool spring period. Cedar apple rust infections decline by late May. Keep in mind that some apple varieties are more susceptible than others to disease pressures.

Begin spraying when flower buds are in the tight cluster to pink stages. Several products are labeled including Mancozeb (also sold as Dithane), metiram (Polyram), Captan and Ziram. Consult your state/county Extension agent for specific rcommendations where you garden.

Don’t Let’em Sucker

Posted by Hugh on March 18th, 2012

Crabapple suckering

Some grafted and budded shrubs and trees develop a bad habit to sending up shoots (suckering) from its rootsystem. This creates an untidy appearance around the base of shrubs and trees. Far worse, the root suckers may compete for domination over the cultivar graft. They may rob photosynthate, water and nutrients from the grafted plant. Eventually, the grafted portion may die.

Gardeners select grafted plants for a number of reasons. The grafted cultivar may exhibit more attractive foliage (e.g. Japanese maples, European beech, or purple leaf plum) or better disease resistance (e.g. crabapples, callery pears).

Rootsystems also may have desirable features. Dwarf rootstocks reduce the size of apple trees. Hybrid tea roses are mostly grafted on a rootsystem capable of growing in most soil types.

Sucker growth above ground may be susceptible to fire blight disease, a serious bacterial pathogen which is difficult to control. Aphids, lacebugs, leafhoppers and borers may contaminate wood with serious virus pathogens.

Don’t attempt to spray the sucker growth with a translocated contact herbicide such as Glyphosate ( Roundup™ and other trade names) or Phenoxy herbicides such as 2,4-D, dicamba and MCPP). These chemicals likely will move to the rootsystem to injure or kill the tree.

Powis Castle Artemisia Is Exceptional

Posted by Hugh on March 16th, 2012

'Powis Castle' Artemisia

Most artemisias (aka “wormwood”) can not cope with the summer heat and humidity in the mid-South. Their silvery foliage tends to burn out (some say “melt out”) in mid to late summer. ‘Powis Castle’ artemisia is truly the exception. Powis Castle is likely a hybrid (Artemisia arborescens x A. absinthium

Powis Castle is a bushy, woody-based perennial or subshrub which forms a 2-3 foot high and wide mound. Powis Castle rarely flowers. Its finely divided foliage is evergreen in most gardens in the Southern Appalachian region (USDA hardiness zones 6 and 7). The silvery foliage creates an excellent contrast with green and other colorful leafy plants in the garden.

Artemisias are best planted in well drained soil and in full sun. They tend to grow poorly in soggy winter soils. No soil fertilizing is generally necessary. Diseases and insect problems are of little consequence.

Older plants tend to run randomly because of their rhizomatous root system. Do not cutback artemisias in the fall. Instead, treat them as hardy mums or asters and wait until new spring growth appears before pruning back. Tidy up the garden bed to recapture a fresh new foliage look.

Its aromatic foliage is cut and utilized in creating fresh herbal wreaths and in potpourri. During medieval times wormwood was a popular remedy for whatever ailed you from gout, kidney stones, scurvy and liver problems.

‘Goshiki’ Osmanthus Brightens Up Any Garden Spot

Posted by Hugh on March 13th, 2012

Holly-like foliage of 'Goshiki' Osmanthus

Holly Tea Olive (Osmanthus spp.) comprises a number of evergreen shrubs from Japan which are winter hardy in USDA zone 7- 9. ‘Goshiki’ (O. heterophyllus ‘Goshiki’) is a hardier compact evergreen shrub, which grows very slowly at 3-4 inches per year. It is long-lived, maturing to 5- 6 feet in height and 5 to 7 feet in width after many years.

The Japanese name “Goshiki” translates to “five colors”. Its spiny juvenile foliage mimics American holly (Ilex opaca). New leaves start out with a rosy pink tint, shortly becoming pale yellow and gold flecked over a dark green background. Tiny white flowers in late October are mostly inconspicuous, hidden within the leaf axils. Flower fragrance is very pleasant from several feet away. Tiny bluish black fruit are rarely seen in most years.

Goshiki prefers a moist, well drained and acidic soil. It grows in almost any garden spot from full sun to light shade. Utilize Goshiki in a low front or medium border, a low screen, and a short hedge. Its spiny foliage forms a sharp barrier deterrent.

Goshiki is winter hardy in the Southern Appalachian region (USDA Zones 6 and 7). Osmanthus is mostly pest-free and deer resistant.

Efforts To Solve Japanese Barberry Invasive Problem

Posted by Hugh on March 11th, 2012

'Crimson Pygmy' Japanese Barberry

Japanese barberry (Berberis thunbergii) is a very popular landscape shrub. Japanese barberry is indigenous to Eastern Europe and Asia and is commonly planted in USDA hardiness zones 4-8.

There is justified concern over the invasive nature of Japanese barberry. A number of states have declared most barberry species (Berberis spp.) to be invasive and have banned its future use. Invasive plants may displace and overtake native species, thereby reducing biological diversity. Native fauna populations, which depend on native species for food and shelter, also suffer.

Cultivar selections are very numerous. Shrub sizes may vary from 5 to 8 feet in height and 6 to 9 feet in spread. Foliage colors range from green, yellow, gold, purple, red and variegated types. Dark yellow flowers bloom in early spring, and many set few to large crops of small bright red berries which may persist into the winter.

Japanese barberry thrives in full sun and in any soil that is well-drained. It tolerates urban air pollution, moderate shade, and drought. Japanese barberry is effective as a living fence or hedge in yards and parking areas. It also makes a thorny deterrent against deer.

Current research on Japanese barberry centers on evaluating the seed viability of current cultivars and to breed new sterile (seedless) cultivars. ‘Aurea Nana’, ‘Aurea’, ‘Bagatelle’, ‘Golden Devine’, and Mentor barberry (B. x mentorensis) have a low seed count. ‘Aurea Nana’, ‘Aurea’, and ‘Golden Devine’ sport vibrant yellow leaves, while Bagatelle has red leaves and Mentor has green leaves.

All About Crabgrass

Posted by Hugh on March 8th, 2012

Young crabgrass seedling

Crabgrass is an annual grassy weed which dies out around the first autumn frost. Seeds dropped last summer germinate when the soil warms up from early spring through summer. When spring soil temperatures reach 55-60 degrees (the forsythia shrub is blooming), apply a pre-emergent crabgrass preventative. These herbicides are very effective applied in late winter and again in early July in the Southern Appalachian region (USDA zones 6 and 7).

Some additional lawn care tips to reduce crabgrass infestations:

1.) Spring lawn fertilizing. A thick lawn keeps out crabgrass by making it harder for the crabgrass seeds to sprout. Split apply a slow release lawn fertilizer in late winter and again in mid-spring at the equivalent rate of 2 lbs of actual nitrogen per 1000 sq. ft.

2.) Mow high. A thick, tall lawn grass keeps the soil temperatures cooler and prevents sunlight from lighting the soil. Short mowing weakens the grass, and warms up the soil, making crabgrass seed easy to germinate. Seeds don’t germinate well over shaded ground.

3.) Delay lawn renovation (reseeding bare spots) until fall. In the spring lawn seed germinates in a few weeks, but crabgrass seed comes up faster. Fall seeding is better because crabgrass is dying and new lawn seeding germinates and grows rapidly without crabgrass competition.

4.) Dethatch and aerify lawns in early fall. Crabgrass loves compacted soils. Soil aerification, if needed, is best delayed until fall because you are opening the ground, favoring crabgrass seed germination.

5.) Lime, if needed, in the late fall. Lime raises the soil pH. The proper soil pH allows more nutrient uptake to the lawn grass which means a healthier growing turf.