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

Winter Storage of Non-Hardy Tropicals*

Posted by Hugh on October 16th, 2011

Musa 'Siam Ruby' at Kingwood Center, Mansfield, Ohio

There is frost on your pumpkin. By late October, northern U.S. gardeners (USDA zones 3 thru 6) must protect non-hardy tropicals such as cannas (Canna spp.), bananas (Musa spp. and Ensete spp.), elephant ears (Colocasia spp. and Alocasia spp.) and angel trumpets (Brugmansia spp.). Most gardeners living in zone 7-b and further south have little difficulty overwintering most cold sensitive tropicals outdoors.

Cannas (rhizomes) and elephant ears (tuberous roots) should be lifted from garden beds and stored in dry peat moss above freezing over winter. Container plants require winter storage as well. Stems should be cut back to the soil line and soil is shaken away from the root mass. Rhizomes and tuberous roots are stored in dry soil or sphagnum peat moss between 35-45° F.

For angel trumpets and non-hardy bananas, gardeners have two options. Option one is to cutback and bareroot angel trumpets and Musa spp. bananas. Do not cutback single-trunk bananas (Ensete spp.) as you must leave the growing point intact. To induce dormancy, store them in a cool location such as in an unheated garage or cellar (35° F minimum for cannas and 45° F for bananas). Reduce watering to once monthly and stop fertilizing, causing leaves to drop.

Option two for angel trumpets and bananas is to grow them. Angel trumpets and Musa spp. bananas are cutback to 5-6 inch stubs (for space saving) and cared for in a sunroom or greenhouse. Feed them with half-strength house plant brand fertilizer (such as Schultz™, Miracle Gro™ or Hyponex™) at every third watering.

‘Diabolo’ Ninebark Has More Than 9 Lives

Posted by Hugh on October 7th, 2011

'Diabolo' ninebark tree form

The cultivar Diabolo ninebark (Physocarpus opulifolius ‘Diabolo’) is an aggressive grower. A knowledgeable gardener with a sharp pair of pruners may quickly and easily train Diabolo ninebark into a small tree. Plant a ninebark tree in a large container for multi-seasonal color around your deck or patio.

Its common plant name “ninebark” says a lot. The outer bark peels off, exposing a lovely dark cinnamon inner bark. Narrow gray-brown outer strips peel off as thin opaque tissue, many more than nine times.

In tree form, Diabolo grows more than 12 feet in height and 8-10 feet in width. When left unpruned, vigorous Diabolo can overwhelm its landscape space. Ninebark grows in any type of soil including marginal clay. To maintain a single or multi- stem tree shape demands bi-monthly pruning attention during the growing season to remove unwanted stem and root suckers. Tidy-up pruning takes less than 5 minutes.

Plant a ninebark tree in a large 25-30 gallon container or in the ground where you may enjoy its year-round beauty. Its root system is winter hardy in the Southern Appalachian region (USDA zones 6 and 7). Numerous ¼-inch wide white flowers appear in May which contrast beautifully against the reddish burgundy Diabolo foliage. By early August, the burgundy tinted leaves have faded to medium green. Autumn foliage finishes greenish yellow before dropping.

I recommend using the following hand pruners: Corona™ #3160 or Fiskars® Powergear Bypass Pruner.

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.