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

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.

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.