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

‘Silberlocke’ Korean fir Gets Lots of Favorable Comments

Posted by Hugh on June 16th, 2013

Abies koreana 'Silberlocke' in Oak Ridge, TN Garden

In any season visitors to your garden should immediately take notice of ‘Silberlocke’ korean fir. Korean fir (Abies koreana) is a densely branched pyramidal evergreen tree. Growth is slow in the beginning, eventually reaching 50 feet or more in mature height. The wide 3/4 inch long needles are dark green and glossy above and silvery on the underside. Upright purple 3-inch cones are a distinctive feature of this fir.

‘Silberlocke’, aka ‘Horstmann’s Silberlocke’, typically grows as a compact pyramidal shrub form, 8 to 10 feet tall in its first 10 years, eventually maturing to 18 to 20 feet tall and 12 to 18 feet wide. The needles are uniquely recurved and silvery-white beneath. Silberlocke was introduced in 1986 by German plantsman Gunter Horstmann.

When properly sited in full sun (minimum of 6 hours) and a compost-rich, well-drained soil. It prefers a cool well-drained site (USDA hardiness zones 5 to 7) and often fails in summer heat and humidity further south. If you garden in USDA zone 7 and/or the soil is a heavy clay loam, grow ‘Silberlocke’ korean fir grafted onto Japanese Momi fir Abies firma rootstock.

Silberlocke has few serious disease or pest problems. Stem cankers and Phytophthora root rot often kill most firs (Abies spp.). Generally, firs languish, if not die, in hot droughty soils and urban pollution. Maintain a 2-3 inch thick mulch layer around Silberlocke to conserve soil moisture and moderate root temperatures.

Feed once yearly with 10-10-10 granular fertilizer in late winter or apply an acidic water-soluble product such as Miracle Gro™, Jacks™, or Hollytone™ in spring and early summer.

Silberlocke’s silvery needle foliage and erect standing purple cones provide 4-seasons of interest. Plant availability is usually limited to specialty conifer nurseries from e-commerce. Again, specify grafted stock if you garden in zone 7.

Summer Chocolate™ Mimosa Tree Worth A Try

Posted by Hugh on June 12th, 2013

Summer Chocolate Mimosa at Dallas Arboretum

Mimosa tree (Albizia julibrissin) is treasured as a four month landscape tree for its tropical-like foliage and flowering. This small deciduous tree grows 20 to 25 feet tall and its horizontal branching reaches out widely.

Mimosa leafs out in late May with lush green, tropical-looking pinnately compound foliage and growth is very rapid. From mid-June thru early July, the fragrant lovely flowers appear above the foliage and attract numerous hummingbirds. Its autumnal leaf color is forgettable.

New mimosa cultivar Summer Chocolate™ makes a wonderful garden accent plant, prized for its dark purple foliage and pink feathery blooms. In late winter you may opt to cut back last year’s plant to the ground and re-grow it only for the colorful textural foliage, thereby eliminating flowers and seed pods.

Mimosa is not long-lived, perhaps surviving 15-20 years before a soil disease or other maladies destroy it. It is a pioneering species on abandoned sunny urban sites and poor highway soils. A 2-year old established tree is exceptionally drought tolerant; its roots improves soil tilth and nutrition. Mimosa fixes its own nitrogen.

Many gardeners in the Southern Appalachian region classify mimosa as an “exotic invasive” (USDA hardiness zones 6 and 7).

Give Lots of Space To Bottlebrush Buckeye

Posted by Hugh on June 4th, 2013

Aesculus parviflora in Louisville, KY

If you have lots of planting space, aggressive bottlebrush buckeye (Aesculus parvifolia) is what you want. This deciduous, multi-stemmed shrub grows 8 to 12 feet tall and 8 to 15 feet wide.A Southeastern U.S. native, bottlebrush buckeye is a late spring flowering shrub and requires little extra attention other than pruning. Plant in full sun in zones 5 and 6 and in partial shade in zones 7 and 8. It becomes very drought tolerant after two years establishment.

Older unkempt shrubs can become aggressive spreaders and grow taller and wider. Roots develop a strong suckering propensity. Suckers are easily checked by closely mowing around the shrub. Otherwise, a three gallon (#3 size container) shrub may eventually swallow up 300-400 square feet of ground in 20 years.

The white bottlebrush flowers in late spring-summer are spectacular. Reddish floral anthers add extra appeal. The white bottlebrush flower clusters are 12-18 inches long and stand tall above the foliage. Bottlebrush flowers for 2-3 weeks and attract numerous butterflies and other pollinators. A. parvifolia var serotina ‘Rogers’ blooms 3-4 weeks later than species.

Bottlebrush buckeye has bold dark green palmately compound (5-7 leaflets) foliage. This shrub belongs to nature’s “bold and beautiful” class. The compound foliage turns bright yellow for a short time in autumn before dropping.

Few diseases or insects mar the foliage compared to other buckeyes and horsechestnuts. Bottlebrush appears resistant to deer and rabbits, perhaps because of its aggressive growth habit.

The pear-shaped nuts (buckeyes), encased in husks, ripen in early fall. Collect early before critters swipe them. Fresh nuts should be planted immediately before they shrivel. Sow 2 inches deep in moist compost rich soil and several will germinate late next spring.

Bottlebrush buckeye is commonly available from e-commerce nursery sources on-line and from wholesale nurseries.

Why Some Vines Do Not Bloom

Posted by Hugh on June 1st, 2013

Closeup of Wisteria frutescens 'Amethyst Falls'

Why doesn’t my wisteria (Wisteria spp.) or climbing hydrangea (Hydrangea anomala subsp. petiolaris) vine bloom? There are primarily four (4) reasons why these vines have not flowered. In order of importance they include:

1. The flower buds, which usually formed on the previous summer’s wood, may have been pruned off. Do not prune vine after July 1st as it initiates next spring’s floral buds at this time.

2. Vine may have been over-fertilized, particularly too much nitrogen. Japanese (W. floribunda) and Chinese (W. sinensis) wisterias, as well as our less aggressive U.S. native species (W. frutescens), rarely require feeding. Wisterias gather all they need from any ordinary well-drained soil. Fertilized wisterias, particularly overfed vines, produce lush stems and foliage at the expense of flower production.

3. In some years flower buds are killed by low winter temperatures or late spring frosts.

4. Age matters. Your vine may not have reached “puberty”, is not mature enough to set flower buds. Hydrangea vines grown from cuttings often take 5 or more years to reach blooming age. Grafted vines bloom sooner.

To correct a long flowerless wisteria, vertically cut the surface roots within 12 inches of the vine with a sharp spade. Do this in May or June before flower bud initiation begins in July. This will unduly stress the vine by damaging the roots and likely cause the wisteria to induce flower buds for next spring.

Determinate Vs Indeterminate Tomato Varieties

Posted by Hugh on May 26th, 2013

Luscious Vine Ripen Tomatoes

There are many tomato varieties from which to select. You may find 100 or more varieties listed in garden catalogs. Depending on your garden space and needs, the two categories of tomato varieties to grow are determinate or indeterminate types.

Short bush type growers are called determinate tomatoes. They require no support and you can grow them on the ground or planted in wire cages. Determinate tomato plants grow well in containers. No pruning is required, as plants grow 3 to 4 feet tall. Determinates bear most of their fruit in a short time span, and most are harvested over a few weeks. Many have a short growing season and early harvest. You may plant the same variety weeks apart to stagger harvest dates through summer into fall. Most determinates are hybrid varieties, but a few are non-hybrid heirlooms.

Taller indeterminate tomatoes need to be supported on a trellis or a large tomato cage. They’re often pruned to keep the plant in bounds. Indeterminates easily grow 6 feet or more in height and take up lots of garden space. Flowers develop all summer into the autumn until frost kills plants. Indeterminates are better for those gardeners who just want a few fresh tomatoes every few days over 3-4 months. Indeterminates grow and yield poorly in a container.

Most heirloom tomatoes are indeterminate. Heirloom varieties have become very popular over the past decade. In the Southern Appalachian region (East Tennessee, Southwest Virginia, and Western North Carolina), varieties such as ‘Brandywine’, ‘Mortgage Lifter’, ‘German Johnson’, ‘Mr. Stripey’, and ‘Cherokee Purple’ show up at the annual Tomato Fest in Kingsport, Tennessee every year and win lots of blue ribbons.

Pest Alert – Gardeners Should Avoid Planting Garden Impatiens

Posted by Hugh on May 23rd, 2013

Bed of New Guinea Impatiens (in foreground)

Downy mildew in impatiens (Plasmopara obducens) infects garden impatiens, double impatiens and balsam. However, New Guinea impatiens, SunPatiens™, and most annual summer flowering plants are not susceptible. Impatiens are the favorite flowering annual used in shady garden areas. Double impatiens and balsam are favorites in hanging pots and other types of containers.

U.S. greenhouse growers continue to be vigilant when outbreaks of downy mildew are spotted. All diseased plants are disposed immediately and not sold to consumers. Mistakenly, healthy looking impatiens may be shipped that have been contaminated with the microscopic “oospores” which cause the disease. The plants do not show visible symptoms at time of shipping. Contamination of the garden soil with the long-lived downy mildew oospores may become a serious problem in the years ahead.

Early symptoms of diseased impatiens may appear as yellowed or off-colored leaves with a white mildew coating the foliage underside. Eventually, most leaves turn yellow and fall off, leaving only the stems.

Infected plants in the garden can not be saved by spraying a fungicide. Greenhouse growers and professional landscapers have downy mildew fungicides available to them, but these products are not available to home gardeners. Your best planting alternatives in shady garden areas are New Guinea impatiens, SunPatiens, shade coleus, and torenias.

A remedy for impatiens downy mildew disease will be found. Right now, do your part by not spreading this problem.

Garden Impatiens in shade garden

• Special thanks to Dr. Alan Windham, Extension Plant pathologist, University of Tennessee Plant and Soil Diagnostic Lab, Nashville, TN.

Pest Alert- Protect Young Trees and Shrubs From Cicadas

Posted by Hugh on May 20th, 2013

Adult cicada (photo courtesy of Dr. Frank Hale, Univ. of Tennessee Entomologist, Nashville, TN)

No insect creates more newspaper headlines than the periodical cicada (Magicicada spp.). Their sudden emergence, every 13 or 17 years reads like a chapter from a science fiction novel. Their high-pitched noise or “mating call” fills the late spring air.

Both the 13-year and 17-year cicadas are uniquely common in the eastern U.S., found no other place on Earth. The two populations, called “broods”, emerge at different times, that is, 13- or 17-year intervals depending on the locale.

Early American colonists thought they were a “locust plague”. People often confuse cicadas and locusts. A locust is actually a species of grasshoppers and feeds on foliage. An adult cicada does not feed on foliage, but feeds on twig sap. The female cicada makes injurious slits in twigs and limbs of trees to deposit eggs.

The adult periodical cicada is 1 to 1½ inches long (photo). The body is black, while the legs, eyes and wing veins which are reddish-orange. Large numbers of adults emerge in May or June when the soil temperature 4 inches deep reaches 67° F. Four or five days after emergence, the males start their high-pitched mating call to attract females. Mating occurs and females begin laying eggs.

The female cicada has a knife-like ovipositor that she uses to slit twigs of woody plants. Apple, pear, dogwood, oak and hickory are among their favorite host plants. In each slit, the female lays 24 to 28 eggs. Each female can lay a total of 400 to 600 eggs. Pencil thickness wood is the main target. Young trees are very susceptible to severe injury.

Preventative measures should be in place to protect young trees and shrubs. Pruning should be delayed until after cicada emergence so damaged branches can be removed. Cover small woody landscape and fruit trees with cheesecloth or spun row cover for protection while cicadas are present. Insecticide spraying are not an effective option.

* Special thank you to Dr. Frank Hale, Univ. of Tennessee Entomologist for providing information on cicada life cycle.

‘Florida Sunshine’ Anise Tree

Posted by Hugh on May 18th, 2013

Florida Sunshine anise tree (Illicium parviflorum

Illicium 'Florida Sunshine' at Milliken Arboretum in Spartanburg, SC in October

‘Florida Sunshine’), aka Ocala yellow star, is a southeast U.S. native which grows well on moderately shaded sites. Its evergreen, chartreuse colored, spring-summer foliage turns golden yellow in the fall. As its common name hints, the evergreen foliage emits a licorice scent.

The overall fall-winter show is nothing short of spectacular in a dull winter landscape. Leaf petioles and stems turn scarlet-red in the fall. Its ½ inch diameter creamy white flowers are easily missed in late spring.

Florida Sunshine grows vigorously into a dense shrub, 6 to 8 feet tall and slightly less in spread. Winter shade is advised to prevent leaf burning. Moist soils hasten annual growth rate. One year-established shrubs demonstrate better than average drought tolerance. Disease and pest problems and resistance to deer feeding have been reported, although additional reports need to be gathered.

Foliage may scorch in direct sun on exposed wintry sites in zone 6 areas. At the Milliken Arboretum in Spartanburg, SC (zone 7), Florida Sunshine is planted out on an open site with irrigation.

Make Florida Sunshine a bright focal point in your garden. It is a good choice for partly shaded woodland settings or in foundation plantings, or as a low – growing evergreen hedge. In containers its golden accent should be mixed with other colored foliage plants. Tender roots in containers should be protected over the frigid winter months.

Florida Sunshine was introduced by Tony Avent, owner of Plant Delights Nursery in Raleigh, N.C.

‘Bikini-tini’ Colocasia Creates Movement in The Garden

Posted by Hugh on May 15th, 2013

Cupped Leaves of Bikini-Tini Colocasia

Colocasia (Colocasia esculenta), aka taro, ape plant, and elephant ear, among other names, is marginally hardy in the Southern Appalachian region (USDA hardiness zones 6 and 7). The 2011 colocasia introduction ‘Bikini-tini’ has garnered high praise from neighbors and friends visiting my garden in the summer.

Bikini-tini is a strong stemmed thick-leaved plant that grows 4 to 5 feet in height. Its bluish-gray leaves cup upward, supported by dark purple petioles and prominent veins beneath. Its cupped leaves capture and pour out rainwater, creating motion in the garden.

Elephant ears are easy to grow. Your garden or container soil should be well drained and compost rich. Soil pH should range between 5.6 and 7.0. Site in direct sunlight, and keep the soil moderately moist. Elephant ears are heavy feeders and thrive on a steady diet of water plus fertilizer. Use a water soluble product such as Miracle-Gro®, Jack’s Classic®, or Daniels® every 2-3 weeks from mid-May (planting time) to late August at the one-half strength rate. An alternative is to feed once with an organic slow release fertilizer in early spring.

Disease and pest problems are rare when plant(s) are properly sited and cared for. Potential crown or stem rot problems are best avoided by growing in a well drained soil (media) and by not overwatering.

Bikini-tini is rated winter hardy to USDA zone 6 with some protection. Protect the crown over the winter with 2-3 inches of a loose leafy mulch such as straw or oak leaves.

Australian Fanflower A Hot Choice in U.S. Southern Gardens

Posted by Hugh on May 12th, 2013

Scaevola (pink variety)

Fanflower (Scaevola aemula) is a relatively new annual bedding plant choice. This Australian native thrives in tough environmental conditions, including the hot, humid summers in the Southern U.S.

Fanflower grows well in hanging baskets, containers or garden beds. It grows in average, moderately acidic, well-drained soil and prefers full or partial sunny areas in the garden.

Non-stop powder blue flowers arise in the leaf axils on trailing stems. Once established, tough hardy fanflowers are only stopped by a heavy frost in late fall in the Southern Appalachian region (USDA hardiness zones 6 and 7). The medium green, oval-shaped toothed leaves average 2-inches in length.

Exhibiting a trailing growth habit, fanflowers grow vigorously, 6 to 9 inches tall and spreading up to 24 inches wide along with adequate summer moisture and nutrition. Some taller forms are available. Fanflower has no serious insect or disease problems.

Typical blue fan-shaped summer flowers give the plant its name. The Surdiva® series features 3 colors: blue, light blue, and white. They make ideal edging plants in containers or garden beds mixed with other annuals and perennials. The Bombay® series includes a pink flowering form, ‘Bombay Pink’.