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

Fall Color in U.S. Native Azaleas

Posted by Hugh on October 4th, 2011

R. vaseyi fall color

Finally, Americans are paying closer attention to our wonderful native plants. In the Southern Appalachian region, there are 16 and more species of deciduous azaleas which may be grown here. In addition, there are numerous natural hybrids growing in the mountains.

I asked Jay Jackson, owner of Appalchian Native Plants, Inc. in Laurel Bloomery, TN which deciduous azaleas offer the best fall color. He rated these six as the best:

Pinkshell azalea (R. vaseyi)
Sweet or smooth azalea (R.arborescens)
Swamp azalea (R.viscosum)
Natural hybrids of (R. arborescens) x (R. cumberlandense)
Cumberland or bakeri (R. cumberlandense)
Flame azalea (R. calendulaceum)

The species rating order may change from year to year with the weather conditions prior to fall foliage color-up.

October Starts Out With Fall Sunflowers

Posted by Hugh on September 26th, 2011

Helianthus spp. at Knoxville, TN Garden Center

I thank the person who gave me a native swamp sunflower (Helianthus angustifolia). This long-lived perennial appears to have its own internal clock for blooming around the first day of October. Its long narrow rough-textured leaves average 6 inches in length. The 2-3 inch wide flowers appear first on top of the tall 6 to 7 foot plants, and numerous floral side branches soon follow.

Fall sunflowers are best grown in full sun to insure shorter sturdier plants which need no staking. Plants growing in partially shaded sites do not branch well and produce fewer flowers. If you have no room for 6-10 foot plants, cut them back by half once or twice before the mid- August. Pruning improves branching.

Swamp sunflowers are abit hoggish when it comes to soil moisture. Established plants possess moderate drought and great heat tolerances. Do not fertilize fall sunflowers as they are voracious feeders and tend to need staking, a chore I like to avoid.

In ten years plants have never become invasive in my garden. I suspect the late flowers have not enough time to mature viable seeds. Two other fall sunflowers to select for your fall garden are 18- inch tall ‘Lowdown’ willowleaf (H. salicifolius ‘Lowdown’) and 6-8 foot tall Helianthus x ‘Lemon Lady’.

Helianthus spp. are winter hardy in the Southern Appalachian region (USDA zones 6 and 7). Plant fall sunflowers from March thru July so that plant roots have adequate time to become well anchored and survive the winter cold.

Franklinia Will Survive If…

Posted by Hugh on September 22nd, 2011

Franklinia at NC Arboretum in Asheville

Franklinia (Franklinia altamaha) is admittedly a very finicky large shrub or small tree. Pure white, five-petal, 2 ½ – 3 inch camellia-like flowers bloom sporadically from August thru mid-October. Flowers are slightly fragrant. In the fall glossy green leaves gradually transition to blends of red, orange and burgundy hues.

Franklinia grows best on an eastern exposure site with full morning sunlight and sheltered from strong afternoon sun. Franklinia has a fibrous root system, preferring soil conditions similar to azaleas and rhododendrons. If growing rhododendrons are a challenge, stay away from franklinia. Soil must be compost-rich, excellently drained, and moderately acidic.

Franklinia was named to honor Benjamin Franklin. Originally discovered growing in southeastern Georgia (USDA zone 8), franklinia grows surprisingly well in our cooler Southern Appalachian region (USDA zones 6 and 7). The species is extinct in the wild, but readily available from internet nursery commerce.

Fertilize in early spring with an acidic based soluble fertilizer such as Miracle Gro®, Miracid®, or Hollytone®. Franklinia also favors an annual feeding of Epsom salts (magnesium sulfate) @ 1 Tablespoon per gallon of water per tree. Applying limestone or gypsum anywhere around the feeder roots of franklinia is highly discouraged.

Fall Is For Planting

Posted by Hugh on September 15th, 2011

Gardening is part of Outdoor Living

Does your garden need a refresh? Summer’s heat and drought, devastating storms, and disease and pest problems combine to place a pall over your outdoor living space. Perhaps, you desire an entirely new look. Maybe you’re tired of the same old beds of roses, daylilies and other perennials. Maybe your garden saps too much of your time and you seek some low maintenance ideas.

Autumn is a good time to visit a full-service garden center where year- end plant bargains abound. Your first visit should primarily be fact-finding. Do not load up on new plants, but seek out new ideas and solutions. Check out patio furnishings, grills, stonework, or maybe exterior lighting in key areas of your garden.

Shade trees and shrubbery are on sale at 30-50% off, although selection, compared to their spring inventory, is more limited. Spring flowering bulbs are on sale. Bulbs like daffodils, camassias, and crocuses offer many years of floral spring beauty. Tulips and hyacinths are not long-lasting, although 3-4 years is not bad. Mix in bulbs with winter/spring blooming pansies and violas for almost 7-8 months of floral color.

Pinks (Dianthus spp.) are planted in late summer and early fall to take advantage of soil warmth. Plants grow out their rootsystems before winter sets in.

Reminder: guaranteed success with winter blooming pansies and violas sets October 15^thas the key planting deadline. If planted later in the fall, these cold tolerant annuals survive, but their winter flowering is alot less.

Re-Bloomers Need Your Help

Posted by Hugh on September 10th, 2011

Encore 'Autumn Carnation' Late Summer Bloom

Re-blooming is an unusual plant trait. Selected cultivars return this time of year for a repeat floral show. In my garden Encore™ azaleas (Rhododendron spp.), re-blooming irises (Iris spp.), and re-blooming daylilies (Hemerocallis spp.) are back for second round of flowering in late summer and early fall.

The gardener/landscaper must supply needed soil moisture and nutrition (primarily nitrogen) so that plants don’t struggle through a stressful summer season. Plants become recharged by frequent irrigation and adequate feeding. In certain situations you may need to monitor and treat a disease and insect problem.

As plants finish blooming in their prime season, remove all spent flower heads to avoid seed formation. For iris prune off old flowers in late May, for daylilies in late June or early July. Encore azaleas bloom in mid-April thru early May and require no deadheading. Timing may vary according to where you garden in the Southern Appalachian region (USDA zones 6 and 7).

In addition, many perennials re-bloom a second and third time after spent flowers are removed and plants are re-nourished. Some easy to grow re-bloomers include: blanket flowers (Gaillardia x grandiflora), perennial salvia (Salvia x nemorosa), tickseed (Coreopsis verticillata), summer phlox (Phlox paniculata), Shasta daisy (Leucanthemum x superbum) and veronica (Veronica spp.).

‘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.

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

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.