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

‘Slender Silhouette’ Sweetgum…Very Few Gumballs!

Posted by Hugh on September 4th, 2011

'Slender Silhouette' sweetgum

Sweetgum (Liquidambar styraciflua) is a medium to large landscape tree, which matures to 65-70 feet in height and 35 feet in spread. To many people it’s called the cursed “gumball” or “ankle twister” tree, not be confused with the fruit balls of the American sycamore or London plane tree (Platanus spp.).

Gumball detractors should look at ‘Slender Silhouette’ sweetgum which produces very few, if any, fruit. ‘Slender Silhouette’ matures to 45-50 feet in height and 12-15 feet in width. Growth rate is rapid at 2-3 feet per year. The cultivar imposes a decidedly vertical architecture to the landscape. The tree’s narrow form makes it a good fit for smaller properties either utilized as a specimen tree or as a tall hedge (green privacy fence).

Foliage is glossy dark green through the spring and summer months. Fall color, which is varies by location and soil pH, ranges from yellow, orange, red, and burgundy. Leaves are 3-5 inches broad with 5, sometimes 7, star-shaped pointed lobes.

Sweetgum is native to USDA zones 5-8, and thrives in the Southern Appalachian region (USDA zones 6 and 7). Bark is light brown and young twigs and branches often form scaly ridges similar to burning bush (Euonymus alata ‘Compacta’).

Landscapers often prefer planting sweetgum over maples (Acer spp.) and ashes (Fraxinus spp.) for its forgiving nature regarding soil type, including on marginally drained clay sites. Sweetgum is not dependable as a street tree where roots may be restricted.

‘Autumn Bride’ Started A Heuchera Evolution

Posted by Hugh on September 1st, 2011

Heuchera villosa 'Autumn Bride'

Autumn Bride heuchera (Heuchera villosa ‘Autumn Bride’) is blooming now. This native ground cover, aka “hairy alumroot”, displays wide lime-green foliage which is not as colorful as many new H. villosa hybrids introduced in recent years. However, the white flowers on Autumn Bride are showier and more numerous.

Heucheras prefer a moist, well-drained, compost-rich soil. Plants are heat and humidity tolerant in the Southern Appalachian region (USDA zones 6 and 7). Grow either in direct morning sunlight in z-6 or in partial shade in z-7. Autumn Bride languishes in deep shade and dry soils and is best grown in a mulched bed.

Autumn Bride and the newer cultivars are not your grandmother’s puny heucheras. Plants are long-lived and vigorous. Leavesappear fairly battered by late autumn and are best cutback along with spent flowers. Feed a handful of 10-10-10 granular fertilizer per plant before growth starts in the early spring. Water soluble fertilizers such as Miracle Gro™, Schultz®, and Espoma® are also good choices. Follow package directions.

Autumn Bride started a heuchera evolution. Planting tips: ‘Autumn Bride’ makes a terrific 1½ to 2 feet tall bedding plant (see photo) when planted en masse. Space plants 2-3 feet apart.

Heuchera villosa are deer resistant.

Gaillardia Survival Depends On Winter Soil Drainage

Posted by Hugh on August 29th, 2011

'Mesa Yellow' gaillardia

In recent years several hybrid cultivars of blanket flowers (Gaillardia x grandflora) have been introduced. Some are annuals and others perennials. This North American prairie native is hardy in USDA zone 5 hardy. Gaillardias should thrive in the Southern Appalachian region (USDA zones 6 and 7), but they don’t! Soggy winter clay soil is their Achilees’ heel.

Gaillardias grow in average well-drained soil under full sunlight. Two-year established gaillardias are heat and drought tolerant. Blanket flowers have a compact mounding habit. Perennial cultivars excel in garden beds or in containers.

Flower colors range from reds, oranges, yellows, and multi-blends, with average bloom sizes between 3 to 4 inches across. Their long flowering period continues from early June through September. Deadheading increases flower numbers.

The cultivar ‘Fanfare’ produces flowers with a dark burgundy center surrounded by red fluted ray petals and flared yellow edges. ‘Fanfare’ is a vigorous grower at 16-24″ in height and 24-28″ in width.

The cultivar ‘Mesa Yellow’ grows 16-18 inches tall and 20-22 inches wide. Their bright yellow flowers form 2-3 weeks earlier than ‘Fanfare’.

Whether the perennial crown survives through the winter is determined by the soil’s drainage capacity. Seedlings from past year’s seed may come back. Plants are deer and rabbit proof, and flowers attract numerous butterflies.

Sunpatiens Worth The Hype

Posted by Hugh on August 26th, 2011

Sunpatiens ‘Compact White’ at Dallas Arboretum

Sunpatiens™ live up to all their hype, with a caveat. They are still impatiens, which means they love (and can’t go without) water. In the Southern Appalachian region (USDA zones 6 and 7), Sunpatiens prosper in direct full day sun to part shade, but can’t go without weekly watering. The flower bed should be mulched and irrigated immediately following planting to shade roots and get transplants off to a vigorous start.

Sunpatiens are best planted immediately after the last spring frost date. This gives them enough time to establish in the landscape before the dog days of summer. Again, the goal is for the foliage to shade roots over the summer. Late plantings in June do not perform as well as late April and May settings.

Plant Sunpatiens in a well-drained, compost-rich soil and feed them with a 5-6 month rated slow release fertilizer at label rates. Established plants grow 36-48 inches tall and 36 inches wide. Setting on 14” to 20” centers will provide an impressive floral display in front of your home or business.

Once planted, it’s critical that Sunpatiens are plugged into a regular irrigation schedule. Extra watering in mid-summer may be necessary when natural rainfall is exceptionally low. Sunpatiens flourish under hot summer heat and tolerate light frost in the autumn. Their thicker flower petals and foliage seem less prone to disease.

Sunpatiens mimic New Guinea impatiens in appearance, but are alot more heat tolerant. At this time color choices for Sunpatiens are limited, with more coming every year.

Kousa Dogwood Not Summer Heat Tolerant

Posted by Hugh on August 23rd, 2011

Kousa dogwood summer foliage

Chinese (Kousa) dogwood (Cornus kousa) rates four stars (out of four) as a beautiful small flowering landscape tree. Since the 1970’s, a deadly anthracnose (Discula spp.) fungus disease has threatened to eradicate our native flowering dogwood (C. florida). Kousa dogwood rates as a highly disease resistant alternative. Its Achilees’ heel is its less than stellar foliar heat tolerance.

In the Southern Appalachian region (USDA zones 6 and 7) most kousa seed-produced cultivars do not handle summer heat issues well. Leaves curl up and reduces photosynthesis. Leaf tips and edges may also scorch. Many of the 100 + kousa cultivars listed in Cappiello and Shadow’s book on dogwoods* are not heat tolerant in the mid-South.

Newly-planted trees are both heat and drought susceptible and should be irrigated the first two years after planting. Cooling the soil by watering helps. Irrigate weekly from mid-June thru early September when summer temps are consistently in the 90’s and natural rainfall is deficient. Drip irrigation keeps kousa foliage dry and disease free while conserving water usage.

A number of U.S. nurseries are currently evaluating several, still unnamed, seedling selections which may be more heat and drought tolerant in the Southeast U.S. landscapes. Expect to see a few at local garden centers in the next 4 – 5 years.

* Cappiello, Paul E. and Don Shadow. 2005. Dogwoods. Timber Press. Portland, OR

‘Gateway’ Joe-Pye Fits Most Gardens

Posted by Hugh on August 22nd, 2011

'Gateway' Joe-Pye

On hot clammy August days, towering 6-8 feet in height, there is Joe-Pye* weed (Eupatorium purpureum) to enjoy. It is visually hard to miss when driving along rural roads in the Southern Appalachian region (USDA zones 6 and 7). Joe-Pye’s flowering sends me a timely message that autumn is only six weeks away.

For gardens the cultivar ‘Gateway” (E. purpureum spp. maculatum ‘Gateway’) is a better fit, more compact at 4-5 feet tall and 3-4 feet wide. Its enormous compound inflorescences measures 12-18 inches in diameter. From late summer into fall the dusky pink flowers invite numerous butterflies and other insects into your garden and make great cut flowers.

Gateway’s upright form and stout branches require no staking. The large narrow dark green leaves are 5-8 inches long and coarsely-serrated, arranged in whorls around the purple and white splotched stems. The mighty architectural seed heads persist well through the winter months.

Joe-Pye, aka “Queen of the Meadow”, demands full to partial (6-hours minimum) sunlight. Joe-Pye is a wetland native and thrives in moist, compost-rich garden soil. Fertilizing this long-lived perennial is not necessary. Plants emerge in late spring and grow very rapidly. Situate in the rear of flower borders due to its plant size and coarse foliage texture. Joe-Pye has no serious diseases or insects and is deer resistant.

* According to forklore, the plant is named for Joe Pye (or Jopi), who was a traveling Native American medicine man. He lived in New England around the late 1700s and sold various herbal remedies to the colonists to treat kidney and urinary problems and typhoid fever. Leaves were also dried and burned as incense to repel flies.

Summer Leaf Drop From Trees

Posted by Hugh on August 20th, 2011

Leaf shedding from tulip poplar

It’s late summer in the Southern Appalachian region (USDA zones 6 and 7). Outdoor temperatures continue to hit 90°F almost daily, and weekly precipitation is low. Over the past 3-4 weeks leaves have been dropping prematurely from landscape trees.

Tulip poplar (Liriodendron tulipifera), river birch (Betula nigra), willow (Salix spp.), sycamore (Platanus x acerifolia), elm (Ulmus spp.), hackberry (Celtis spp.) and redbud (Cercis canadensis) appear the worse offenders.

What these trees have in common, other than yellow fall color, is that growth is continuous from early spring thru late summer. Trees produce new leaves as long as air temperatures and soil moisture are favorable. Such trees abort excess foliage when environmental conditions become stressful.

Another way of stating: these species tend to overachieve, producing more leaves than they can support as environmental conditions turn negative. Under typical hot dry summer weather, they conserve through a dry patch by shedding leaves. The older interior foliage is typically the first to abort. Most summers all seven listed species lose leaves prematurely.

Bottom line: prematurely shedding leaves is very normal for these and some other landscape trees. Deep irrigating of trees reduces leaf loss, but is generally unnecessary. Leaf loss is a natural phenomena and is not detrimental.

The Challenge and Reward of Harlequin Glorybower

Posted by Hugh on August 17th, 2011

Harlequin glorybower in mid-August

Harlequin Glorybower (Clerodendron trichotomum) is a rambling 15 foot tall shrub, and can be easily shaped into a multi-stemmed 10-12 foot small tree. Glorybower shines in the late summer and early fall landscape. Its sweetly scented, very showy flowers attract the attention of gardeners as well as hummingbirds and butterflies.

Glorybower reaches its northern- most hardiness limit here in the Southern Appalachian region (USDA zones 6-b and 7). Some winters do not treat glorybower kindly. Significant reconstruction is needed. Moderate pruning in late winter repairs most ills with fast growing glorybower looking great by summer.

Flowers are arranged in wide 6 – 9 inch clusters, comprised of individual white 1 ½ inch blooms and are borne on current season’s wood. Next up in mid-September are the metallic looking topaz colored fruits with beet red calyxes which give quite a show.

Foliage texture is bold with broad 4 to 9 inch long dark green leaves providing cooling shade to a nearby deck or patio. Its pale yellow autumnal leaf color contributes little. Glorybower is relatively disease and insect free.

Glorybower grows in a moist well-drained average soil and in full to partial (minimum 6- hours) sunlight. A 2-year old established tree is only moderately drought tolerance and requires irrigation during long dry spells.

This under-utilized native of Japan and China is sold principally by internet nursery vendors.

Old-Timey ‘Royal Standard’ Hosta Still Rules

Posted by Hugh on August 14th, 2011

Hosta 'Royal Standard' at Kingwood Center

Kingwood Center is a wonderful public garden in Mansfield, Ohio with several top notch beds of hostas. One glorious bed of ‘Royal Standard’ hosta blooms their heads off from mid-August into September. With over 35,000 registered hostas available, why look back at this vintage variety.

Royal Standard was patented and introduced in 1965 by Wayside Gardens and still remains popular. Its 4 – 5 inch long green leaves are ordinary compared to modern day hosta cultivars. A multi-division clump develops foliage around 18 inches tall and spreading to 4 feet across. White trumpet shaped flowers rise 24 inches tall on leafy scapes in August and are pleasantly fragrant.

Royal Standard grows in a wide array of garden soils, yet it excels in compost rich soils. Two-year established Royal Standard demonstrates good summer heat and drought tolerance in the Southern Appalachian region (USDA zones 6 and 7).

Morning sunlight followed by light afternoon shade is preferred, but I have seen a terrific bed planted in a gas station island under full day sun, assumedly with regular irrigation.

Plant foliage dies down in the winter. Clumps are easy to divide either in early fall or late spring. Slugs are the principal major pest problem of many hosta cultivar, including ‘Royal Standard’.

‘Kim’s Knee High’ Coneflower For Small Gardens

Posted by Hugh on August 11th, 2011

'Kim's Knee High' coneflower

We are in the midst of an Echinacea revolution. Purple coneflower (Echinacea purpurea) is a popular 5-6 foot tall native perennial commonly planted in meadow and butterfly gardens. Kim Hawkes, former owner of Niche Gardens Nursery in Chapel Hill, N.C. introduced compact growing ‘Kim’s Knee High’ a decade ago. It is still one of the finest cultivars.

‘Kim’s Knee High’ fits into most small gardens at 2-3 feet in height and 1-2 feet in spread. Coneflower grows in average well-drained soil and in full to partial (minimum of 6 hours) sunlight.

‘Kim’s Knee High’ is low maintenance. It exhibits moderate heat and drought tolerance after one year’s establishment in the garden. Coneflower thrives on late winter feeding. Clumps should be divided every 3-4 years.

The 3 ½ inch rose pink ray petalled flowers are slightly reflexed, and surround a russet-orange cone center. Coneflower blooms from late June through late August in the Southern Appalachian region (USDA zones 6 and7). Deadheading old spent blooms extends flowering time through first October frost.

Coneflowers attract numerous butterflies and bees, and seeds are a major winter food source for many species of birds, particularly finches and hummingbirds. Seeds self-sow and become nuisance weeds. Remove all old growth in the early fall to avoid the seed load or wait until late winter in order to feed the birds.

Pest problems are minimal if plants are not overcrowded. Coneflowers are deer resistant.