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

Working With Poorly Drained Soils

Posted by Hugh on September 8th, 2018

Soil Amending

Inkberry holly

As a rule, yews (Taxus spp.), Japanese hollies (Ilex crenata), azaleas (Rhododendron spp.), blueberries (Vaccinium spp.), and roses (Rosa spp.) are common examples of landscape plants that fail in poorly drained soils.

Holly cultivars like ‘Hoogendorn’ and ‘Soft Touch’ fair better in clay soils that most other Japanese hollies in the Southern Appalachian region (USDA hardiness zones 6 and 7). A better alternative is to substitute inkberry holly (Ilex glabra) in any planting bed where soil quality is suspect. A number of perennial plants die or are setback after spending their winter in waterlogged soils.

You can improve soil drainage by adding generous amounts of organic matter and coarse gravel such as sand, pea gravel, and perlite. It is difficult to estimate the exact amount to incorporate

Constructing and planting in raised bed is another option.

Not New –Still Top Landscape Performers

Posted by Hugh on September 6th, 2018

Abelia ‘Rose Creek’ in mid-fall at Biltmore Estates in Asheville, NC

‘Arctic Fire’ dogwood at Univ. of TN Gardens Knoxville

A senior gardener knows that many new plant cultivars (varieties) are often no better than what had come before. Many “superstar” shrubs, some released a decade or more ago, are still topnotch performers in many parts of the U.S. Here are six which I continue to recommend highly.

‘Low &Behold® Blue Chip Jr.’ Butterfly Bush is a super compact 18-30 inch tall shrub (or perennial) with deep indigo blue flowers above silvery blue foliage. For peak performance, plant in a full sun and in moist well-drained soil. Blue Chip Jr. is the smaller version of ‘Blue Chip’, another outstanding performer. (USDA hardiness zones 5-9).

Arctic Fire® Red Twig Dogwood (Cornus sanguinea) receives lots of notice for its brilliant red stems through the winter season. Bright green spring foliage turns gold-yellow in the fall. This compact 4-5 foot tall shrub grows well in either full to partial sun. (USDA hardiness zones 2-7).

‘Purple Pillar’ althea

Purple Pillar® Rose of Sharon (Hibiscus syriacus) flaunts a narrow columnar habit that’s a perfect fit in a small urban garden or large container. In mid-summer it produces showy 4- inch wide, semi-double, purple blooms. A mature shrub may be grow 16 feet tall and only 3 feet wide. Utilize as an accent specimen, narrow screen or hedge. (USDA hardiness zones 5-9)

‘Rose Creek’ Flowering Abelia (Abelia x grandiflora) is a compact version of a large old-fashioned shrub. Cultivar grows only 2-3 feet tall and 3-4 feet wide. New leaves emerge with a pinkish tone and matures bright green. White slightly fragrant flowers are produced from late spring to fall. In fall the flowers take on a copper-rose hue. (USDA hardiness zones 6-9).

Bobo® Panicle Hydrangea (Hydrangea paniculata) is a much smaller version of Limelight ® hydrangea. Compact growing Bobo grows 4 – 5 feet high and 3-4 feet wide. The white flowers are held upright on sturdy stems; Bobo has a long bloom period from late July into fall. (USDA hardiness zones 3-8).

Spirea thunbergii ‘Ogon’

Goldthread® Spirea (Spiraea thunbergii ‘Ogon’) is a compact growing (3-5 feet tall and wide) deciduous shrub with wiry arching branching. Clusters of tiny white flowers (each to 1/3” diameter) appear in early spring before its awesome foliage emerges. Goldthread spirea is a showy accent plant with narrow willow-like chartreuse colored leaves (to 1.5” long and to 1/4” wide). In most years, fall leaf color is average. (USDA hardiness zones 4-8)

‘Henry Eilers’ Coneflower (Rudbeckia)

Posted by Hugh on September 1st, 2018

R. subtomentosum ‘Henry Eilers’

quilled flowers

Called “sweet coneflower” (Rudbeckia subtomentosum), this U.S. Midwest prairie species is a long-lived perennial that grows in a variety of soils (USDA hardiness zones 4-8). Sweet coneflower prefers full or partial sun (6 hours minimum) and a moist well-drained loamy soils. It is highly drought tolerant after its first year in the garden.

Established plants emerge in mid-spring as a rosette of leaves and grow rapidly to 4-5 feet in height. Basal foliage is toothed, gray-green leaves (lower leaves are 3-lobed). The green stems and leaf undersides have a downy texture, a covering of many fine hairs.

Flowers of ‘Henry Eilers’ are uniquely different — the yellow petals (rays) are rolled instead of flat, giving the flower a quilled appearance. The ray petals surround the purplish-brown dome center. The 3-inches wide flowers bloom in clusters atop sturdy upright branched stems from very late July thru September.

The unique flowers attract numerous bees, butterflies, and seed feeding birds such as cardinals, finches, and jays. Snip flower stems to add to indoor decoration. Deadhead spent flowers to encourage additional bloom. Dark gray-green 3-6 inch long leaves, some 3-lobed, are found around the plant base along with smaller unlobed ones. Leaves emit a mild sweet vanilla or anise smell when crushed.

Fertilize at planting time and annually in the spring with a slow release product such as Osmocote™ or Nutricote™. No serious insect or disease problems trouble this coneflower species. Do not crowd plants as powdery mildew may occur. Taller plants may need some support, particularly if grown in partial shade.

Plants should be propagated by crown divisions in early spring. If grown from seed, only 20% may display the quilled flower trait.

Editor’s note: some species of Rudbeckia spp. are also called “Coneflowers”. In general, coneflowers are in the genus Echinacea spp.

Growing Morning Glories

Posted by Hugh on August 28th, 2018

Mornng glory vine

Field bindweed (invasive)

Morning glory vines (Ipomoea tricolor) add a dash of old fashion charm to today’s gardens. YES! these aggressive vines demand a high degree of attention. Their funnel or tubular-shaped flowers open in the morning and close late in the afternoon. In a single growing season, vines may grow 6 to 12 feet and more (depending on variety). Morning glories will also aggressively self-seed.

Vines bloom non-stop from June to October. Flower colors are available in purple, blue, red, white, pink and bi-colors. Many gardeners opt to grow morning glory vines to cover trellises, pergolas, arches and fences. Grow some in hanging baskets and train vines to drape over the sides.

Morning glories are usually grown from seed and may be started indoors 4 – 6 weeks before the last spring frost. Where the growing season is long, direct seed into the garden or a large container after all threat of frost has passed. Select a site that gets plenty of sun. Morning glories prefer moderately fertile, well-drained soil that needs to be kept consistently moist until the vine(s) are well established. Morning glories bloom their best in full sun.

Soak the seeds for 24 hours prior to sowing to spur higher numbers and faster germination. Distribute the seeds and cover lightly with soil and water thoroughly. Irrigate every few days if rainfall is light. Some gardeners will pre-start the seeds in peat pots and transplant them after 4-6 weeks.

Fertilizing is usually not necessary. Feeding liquid fertilizer, such as Miracle-Gro or Jack’s monthly, will spur increased growth and flowering. Be careful… do not overfertilize as this can produce more foliage than flowers. To prevent unwanted self-seeding, old flowers should be completely removed before they form seed pods, an almost impossible task.

Morning glory vines are generally not troubled by diseases or pests. When not properly sited, they may be infected with fungal leaf spot, rust, and wilt diseases. Aphids, leaf miner, spider mites and caterpillars may also pop up. Deer will browse on the leaves and vines. The seeds are poisonous.

Morning glories are often mistaken for their weedy white blooming cousin, field bindweed (Convolvulus arvensis), also called Creeping Jenny. Field bindweed, a hardy perennial vine, spreads by deep roots and is nearly impossible to get rid of. Its deep winter hardy roots allow bindweed to overwinter in colder climates to return again and again. Field bindweed blooms either white or pink flowers; the flowers and leaves are smaller than morning glory.

Texas Elephant Ears Study*

Posted by Hugh on August 23rd, 2018

‘Gecko’ (left) ‘Madiera’ (right)

Dr. Jared Barnes and colleagues at Stephen F. Austin University in Nacogdoches, Texas, trialed 46 Colocasia species/cultivars over two years to determine what performed best over a two-year growing period. First of all, Nacogdoches is in east Texas (Zone 8-b) and typifies the upper coastal plain, stretching from there east to South Carolina. Cultivars were grown in full sun and ratings were taken every two weeks during the growing season on a 1 (poor) to 5 (perfect) scale.

Only two cultivars earned a ranking above 3.5 in both of the trial years: Colocasia esculenta Madiera is commonly referred to as elephant ears, however, it has two traits that set it apart from the green giants you may be thinking of. First of all, Madiera about a third to half the size of the green forms of C. esculenta. Secondly, the foliage is a deep purple, making it a very striking garden plant. Listed as Zone 7 hardy, gardeners farther north can grow it, harvest tubers in the fall, store the tubers in a cool, dry location in a paper bag, and replant the following year.

The second outstanding performer is C. esculenta Red-Eyed Gecko (a Plants Nouveau introduction). It grows about 4-feet tall and wide boasts chartreuse foliage with a red spot in the upper side of foliage where the petiole is attached on the underside of the leaf. Variety listed as hardy to Zone 8.

*Information and photos reprinted with permission from Dr. Michael Chappell published 8/10/2018 edition of Ball Publishing, Nursery & Landscape Insider e-newsletter editor.

Ligularias For Moist Sites

Posted by Hugh on August 20th, 2018

Dark foliage of Ligularia ‘Marie Britt Crawford’

L. stenocephala ‘The Rocket’

Ligularias (ligs) are big leafy perennials whose roots must be kept constantly moist so that plants don’t wilt or “faint”. An established plant may tolerate several days in dry soil, yet the droopy foliage will recover from the water loss each night. Several species are tropical (under the genus Farfugium). Bigleaf ligs (L. dentata) and narrow-spiked ligularias (L. stenocephala), aka “golden ray”, grow well in temperate climes (USDA hardiness zones 6 and 7).

Leaves of some varieties may size up to 15-20 inches across. Ligs often suffer from bouts of fainting in the mid-afternoon due to summer heat and water loss from transpiration. Plant may wilt even if the soil is moist. By early evening the leaves mostly recover.

Lig’s showy bright yellow or orange flowers arise above the foliage in early summer. You may opt is cut-off the flower spikes in favor of lustrous 20-inches wide, coarsely tooth round foliage. Ligularia ‘Marie Britt Crawford’ is one such variety. Narrow-spiked ligs produce bright yellow or orange flower spikes, 2-5 inch flowers and 18-24 inch racemes and triangular, deeply toothed leaf margins.

Good site preparation and minimal annual maintenance will give ligularias a long life in a perennial garden. Set these perennials in moist, even soggy soil under partial sunlight, preferably morning sunlight. Ligs can be sited in boggy ground near a pond or a water garden; however, never submerge ligs in water. Provide lots of organic matter to the soil, a boggy location and this shade giant is luxurious.

Pest control is simply a matter of controlling slugs and snails from devouring the leaves, which create a “shot-hole” appearance in the foliage. Ligularias are propagated by division, generally in the spring or late in the summer. Clumps should be divided every 4-5 years.

Special Planting instructions: dig a hole large enough to accommodate a 3-5 gallon size container. Line the bottom of the hole with a plastic liner to retain moisture around the roots and to reduce the need of irrigation. Fill the hole with rich potting soil or a soil mix containing high amounts of humus or compost.

Leading Temperate Varieties:

L. stenocephala ‘The Rocket’ – tall 4-6 feet high narrow spikes of bright-yellow daisy flowers on purplish black stems and jagged-edged green leaves.

L. stenocephala ‘Baby Rocket’ – compact 2 1/2 – 3 foot selection above with large, serrated, dark green leaves and a bouquet of mustard-yellow floral spikelets on multiple chocolate stems.

L. dentata ‘Desdemona’ – rounded dark-green leaves with a purple backside; tall stems bear clusters of bright golden orange 3-3½ inches daisy flowers.

L. dentata ‘Orthello’ – large, rounded dark-green leaves with a purple underside; tall 3-4 feet tall floral stems bearing clusters of bright golden orange 3-3½ inches wide daisy flowers.

L. dentata ‘Britt-Marie Crawford’ – large, glossy, purple-black leaves and bold daisy-like orange-yellow flowers.

Favorites Among The Rose Of Sharon (Althea) Shrubs

Posted by Hugh on August 15th, 2018

‘White Chiffon’ hibiscus (scene in a shopping mall)

‘Sugar Tip’ hibiscus

Rose of Sharon, aka shrub althea, (Hibiscus syriacus) is a woody hibiscus shrub that is hardy in temperate northern areas of the U.S. (USDA hardiness zones 5-9). This summer flowering shrub is exceptionally easy to grow. At one time, it was a great pass-along shrub that fell out of favor. However, old fashioned varieties frequently reseeded around the garden. New cultivars strut variegated foliage, double flowers, and infertile (sterile) blooms that produce little or no seed.

Rose of Sharons are available in a wide range of flower colors including pink, purple, blue, white, and almost red. Blooms may be single, semi-double, and double and range in size from 2-5 inches across. They grow in average to good garden soils with moderate drainage. For maximum flowering, site plants where they receive 6 or more hours of direct sun and feed annually with a slow-release fertilizer such as Osmocote™ or Nutricote™. Blooms attract numerous bees and butterflies. Japanese beetles may mar the flowers for a few weeks in early summer, but shrubs generally rapidly recover.

After their first year, Rose of Sharons are highly drought tolerant. Shrubs respond well to annual pruning and to severe “rejuvenating” by pruning to a few inches above the ground. Some gardeners opt to grow them as perennials by cutting he plant back every year or two. In late spring the “shortened” plant(s) emerge and only grow a few feet tall with many stems and flowers.

‘Lavender Chiffon’

Top Picks Among Rose of Sharon Cultivars:

Chiffon® series feature anemone-like double blooms for low seed set and long-blooming; color choices: Lavender (purple), Blue, and White; 8-12 feet x 6-10 feet wide.

Sugar Tip® – pure pink double blooms (no seed) and variegated creamy-white / bluish-green foliage; 8-12 feet x 6-8 feet.

Purple Pillar® – slender columnar growth habit (16 feet tall x 3 feet wide), ideal fit for small urban gardens; 4-inch vibrant purple single to semi-double flowers with red centers.

Utilize Rose of Sharon as a specimen shrub or small tree, as a shrub border, or set into a large container.

Growing Castor Bean Plant

Posted by Hugh on August 10th, 2018

Castor Bean (Ricinus communis)

Over the years castor bean (Ricinus communis) plants have been a common sight in public gardens. These tall ornamental annuals are cherished for both their colorful flowers and seed capsules, and bold foliage. The species, a botanical member of the spurge family (Euphorbiaceae), is indigenous to the southeastern Mediterranean region, Eastern Africa, and India. Unlike many spurges, the sap is watery and not milky.

Castor bean is known by a number of colloquial names including mole killer plant and castor oil plant. Each fruit is a spiny capsule containing large, bean-like seeds, with a brownish mottling shells. Despite its name, castor bean is not a true “bean”. Plant stems and spiny seed pods vary in color and are showier than the actual blooms. The male flowers are yellowish-green with creamy white stamens. The female flowers hide within the spiny seed pods, have red stigmas, and are produced in less numbers than the male.

Modern day landscape varieties are selected for leaf and flower color as well as oil production. Growth rate is very rapid and can easily grow 10 feet and more in a single growing season. Its enormous, glossy palmate star-like leaves measure anywhere from 6 to 30 inches across, and leaf lobes, numbering 5 to 11, are deeply cut. Each leaf is attached by a long slender petiole to the main stalk. With some varieties the leaves start off reddish purple, bronze or green, gradually developing darker tones as they mature.

Planting into your landscape, sow the seeds or transplant starts in full day sun and in deep humus-rich soil. In northern areas, where the growing season may be short, start plants from seeds indoors. Shelter plants from strong winds that can damage the large, glossy leaves. Water and fertilize generously for super- sized plants.

In the 16th century, castor oil was utilized as an alternative to lamp oil. In the U.S., castor bean plants were grown for its oil, used in making soaps, linoleum, nylon, paints, et al. In the first half of the 20th century it was also used as a laxative and in skin and hair cosmetic products. Plant roots repel gophers and moles.

Warning: the colorful castor bean “beans” are highly ornamental and highly poisonous. if ingested. If you wish to save the seed from one year to the next, wear rubber gloves to carefully cut apart the seed stalk. Allow the seed pods to dry in a cool dry room; crack open and remove the seeds carefully. Place the seeds in a paper envelope and store inside your refrigerator. Be certain to label “highly poisonous”.

Recommended Varieties:

‘New Zealand Purple’

‘Carmencita Bright Red’, ‘Pink’, ‘Rose’

‘Gibsonii’

‘Red Spire’

Korean Sweetheart Tree

Posted by Hugh on August 1st, 2018

Fruit capsules fill the tree in August

Unique Striated Bark

The late Dr. J. C. Raulston, N.C. State University horticulture professor emeritus, discovered Korean sweetheart tree (Euscaphis japonica) in 1985 on the Korean Peninsula while participating in a U.S. National Arboretum collection expedition (USDA hardiness zones 6-8). Dr. Raulston brought seeds back to the N.C. State Arboretum for assessment and evaluation. The species common name “sweetheart tree” was coined by Tennessee nurseryman Mr. Don Shadow.

Small 9-inch long terminal panicles of yellow flowers appear in late spring, most hidden within the dense foliage and go mostly unseen. Opposite pinnately compound leaves are 6-10 inches long. The compound leaves are comprised of dark green, 2-4 inch long leaflets. The tree’s greatest asset is the showy bountiful clusters of heart-shaped fruit capsules. They gradually ripen from green to pink to finally red in late summer. In early to mid-October the fruit capsules split apart to reveal a tiny, shiny, black seed within. The grayish colored bark has white striations which provide some winter interest.

Sweetheart tree prefers a good loamy well-drained soil and planted in full sun to partial shade. Feed annually with a slow-release fertilizer such as Osmocote® or Nutricote®. Although an older established tree is highly drought tolerant, provide supplemental irrigation to a new 1-3 year old tree if summer rainfall is sparse.

No serious disease and insect problems trouble this small 2o-25 feet tall tree. In the early years corrective pruning is recommended for shaping the young tree. Availability is primarily from on-line plant nurseries.

Native Plumleaf Azalea Blooms In Late July

Posted by Hugh on July 28th, 2018

July-blooming Plumleaf Azalea

Rare Yellow Flowering Form

Plumleaf azalea (Rhododendron prunifolium) is a native deciduous azalea that grows in the Chattahoochee River Valley on the Georgia-Alabama line (USDA hardiness zones 6-9). It is one of the signature plants of Callaway Gardens in Pine Mountain, Georgia.

Their bright orange-red flowers surprise in late July into early Augusta and blooms may last for 2 weeks or more. Spring and summer foliage is medium-green and remains mostly blemish-free. Compared to many other spring blooming native azaleas, flowers are not fragrant. Fall leaf color is also uneventful. Insect and disease problems are rare if the plant is properly sited.

This 5-8 feet tall and wide shrub performs best in morning sunlight and shaded from the harsh afternoon summer sun. It grows in well-drained, compost amended soil. Plumleaf azalea prospers in the calcareous clay soils found in the Appalachian region without pH correction. Plant in full-day light shade in zones 7-9. Set the shrub into a shallow wide dug hole that has been generously amended with compost and/or peat.

Feed in early spring with a slow-release fertilizer such as Osmocote™ or Nutricote™. An alternative nutrition program is to use a water soluble product such as Miracle-Gro™ or Jack’s™ in early spring and again in early summer. Maintain 2-3 inches of a pine-based mulch around the base of the shrub. Irrigate plant(s) the first 2 years of establishment and you will be rewarded for many summers to come.

Plumleaf azaleas are usually available from mail order companies on-line. It is best to purchase and plant them before late spring so that their fine shallow rootsystem can adapt to their new site before winter arrives.

Plumleaf azaleas bloom on new current season’s wood. Prune deciduous azaleas anytime after bloom to maintain a desired height and spread. Plumleaf azalea is primarily available at local native plant nurseries or is offered online.