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

Alexandrian Laurel For Deep Shade

Posted by Hugh on May 17th, 2018

Danae racemosa at Knoxville Botanical Gardens

Red fruits and glossy foliage in late fall

Alexandrian Laurel or Poet’s Laurel (Danae racemosa) is a wonderful evergreen shrub that is rarely planted in U.S. gardens. Danae is indigenous to Iran and Syria. This evergreen shrub needs partial to full shade and the warm climes of southeast or Pacific northwest states (USDA hardiness zones 6 – 9). If winters are exceptionally cold in zone 6 (parts of Tennessee, Virginia and North Carolina), plants may freeze to the ground and re-sprout from underground rhizomes in late spring.

Danae grows 3 feet in height (4 to 5 feet wide) with lovely arching shoots. Its glossy green leaves are 3 to 4 inches long and 1.5-inch wide, arranged alternately along the branch. Small, inconspicuous yellow-green flowers appear in late spring from the leaf axils. In the fall orange-red berries in clusters. The brightly colored fruits (berries) are the truly outstanding asset of the plant. They persist through much of the winter.

Danae is a great woodland evergreen plant, growing in the deepest shade. It is demands a well-drained, moist, mildly acidic loamy soils. Danae is slow to establish and it should be watered if the dry periods last longer than 3 or 4 weeks. It is slow growing. The foliage will yellow and burn if exposed to direct sunlight. Shoots (canes) last 3 years; older gangly shrubs should be renovated every 3-4 years.

Plants may be propagated by division in early spring or from seeds collected in late fall and sown directly in a bed. You may have to wait two springs for most seedlings to emerge. The cut foliage is ideal for flower arrangements.

Historical perspective: Its common name is from Greek mythology – the foliage was used to adorn heroes scholars, poets and athletes. Statues depict honorees wearing a garland of leaves from the stems of this plant.

Berggarten Salvia Favors Both Gardeners And Culinary Afficiendos

Posted by Hugh on May 13th, 2018

Salvia officinalis ‘Berggarten’ at Univ. of Tennessee Gardens, Knoxville

New Planting at Dallas Arboretum

Common sage (Salvia officinalis), a member of the mint family (Lamiaceae), is the culinary sage familiar to most cooks (USDA hardiness zones 5 to 8). The species grow 1.5 – 3 feet high and wide. Multitudes of showy two-lipped, 1-inch long, violet-blue flowers arise on short, upright spikes in late spring. Flowers attracts numerous bees and butterflies.

The cultivar ‘Berggarten’ is a compact perennial form that typically grows 1-2 feet tall. Its grayish green 2-4 inch long leaves are wider than the species and strongly aromatic. Its large oval leaves are unlike that of your typical garden sages.

Berggarten salvia is a culinary delight. In southern climes (zones 8-9), foodies and gardeners alike will treasure this evergreen perennial. In early spring trim back to newly emerging growth or strong stems. Spikes of violet-blue flowers appear in early summer. Medical curative properties are also attributed to some species of the Salvia genus.

Salvias grow in average, dry to medium moisture, well-drained soil and in full sun. Leaves develop a purplish cast in full sun. They tolerate very light shade, but plants tend to grow weakly and need staking if not grown in full day sun. It tolerates alkaline soils. Poorly drained soils leads to fatal root rots.

Few serious insect or disease problems trouble Berggarten salvia if planted in the right location. The plant is tolerant of deer. Monitor the plant for powdery mildew, rust, stem rot, fungal leaf spots, whiteflies, aphids, mealybugs, spider mites. Plant and flowers attract butterflies.

Berggarten is an excellent addition to an herb or vegetable garden. Grow it also in mixed containers, in borders, or in rock gardens. Over time, plants develop a woody shrub base and is best cut back in the spring to 4 – 6 inches.

Our Native Bigleaf Magnolias

Posted by Hugh on May 9th, 2018

Magnolia macrophylla in flower

M. ashei on East TN State Univ. campus in Johnson City, TN

Bigleaf magnolias are represented by four species: (M. macrophylla), umbrella magnolia (M. tripetala), Fraser magnolia (M. fraseri), and Ashe magnolia (M. ashei). All are medium-size trees with huge leaves and large flowers that appear after the leaves unfurl. All are native to the southeastern United States as far north to West Virginia and Ohio (USDA hardiness zones 5-8). A mature tree attains heights of 30 to 40 feet and matures into an irregular pyramidal tree habit. In the northern areas the tree is deciduous and semi-evergreen in the southeastern U.S.

Its enormous size foliage makes it a true horticultural oddity. Leaves are alternate, simple, 12 to 36 inches long and 7 to 12 inches wide. They’re bright green above and silvery gray below. Petioles are 2 to 4 inches long. Its yellow fall color rarely stands out.

Their large leaves decompose slowly and do create a litter headache. Their enormous leaf size relegates their plantings primarily to large properties and private woodlands where weak branches and unusual leaves are sheltered from ice and wind storms. Leaves are intolerant of most urban pollutants.

Here in Tennessee and North Carolina, all species grow in moist, humus-rich, well-drained mountain soils, and in full sun to partial shade. Established plants are only marginally drought tolerant. In the mountains, trees closely associate their roots nearby a small creek or stream. Foliage is not tolerant of most urban pollutants. A tree may take 10 or more years before first blooms form. Goblet-shaped flowers are creamy white, rose-purple at the petal base, and measure a foot or more across. Flowers appear in late spring, high in the tree, and mostly hidden within the dense foliage. Up close, flowers are pleasantly fragrant.

Fruits (called “cones”) are round (cone-like), rose-colored, and nearly 3-inches long. Cones are unique, persistent, and attract numerous bird species. Cones open to reveal the red coated seeds, each one attached by a thin silk-like thread.

Large-leaved magnolias are primarily sold by a small number of native plant nurseries.

Fall color of M. macrophylla at Biltmore Estates in Asheville, NC.

The Next Generation of Weigelas

Posted by Hugh on May 5th, 2018

‘Wine and Roses’ Weigela

‘Variegata’ weigela

Weigela (Weigela florida) is old-fashioned shrub with rose colored blooms and arching branching habit in mid-spring. This shrub is native from Japan, Korea, and China (USDA hardiness zones 5-8). New hybrids of weigelas are arriving at garden centers this spring. Compared to previous cultivars that were 6-9 feet tall, new introductions grow only 2-5 feet high. Some new weigelas flaunt flashy variegated foliage. Flower color choices include red, lavender, pink, and white and open in mid-spring. Blooms attract bees, butterflies, and an occasional hummingbird.

Weigelas can be planted anytime from spring thru early fall in full to partially sunny sites. Foliage of dwarf varieties tend to burn in full sunlight in southern climes. Shrubs bloom heavier in high light. Plants grow in any average soil, but do prefer a compost-rich well-drained site. During their first year or two after planting, irrigate during dry periods when weekly rainfall amounts are less than one inch. Feed weigelas in early spring with a slow-release shrub fertilizer such as Osmocote™ or Nutrikote™.

Prune away winter dieback before or immediately following spring bloom. All other pruning should be done soon after flowers fade. Summer or fall pruning reduces bloom next spring. Weigelas have very few disease and insect problems.

Utilize weigelas with purple foliage as accent plants with green and white variegated leaf cultivars. Dwarf forms, some only 1-2 feet tall, My Monet™ or Fine Wine™) are wonderful mixed together with perennials or annuals in large containers or in garden beds.

Some Cultivars to try:

Crimson Kisses™ – 3 foot tall rounded shape covered with dark, lipstick-red flowers kissed with a white eye.

‘Minuet’ – 2 to 3 foot tall and wide with purplish-green foliage and red and lavender blooms flowers.

My Monet (‘Verweig’) – cream, pink and green variegation on a dwarf (18 inches tall and 2 feet wide) plant; pink blooms open in late spring; partial sun preferred.

Midnight Wine (‘Elvera’) – purple foliage and pink flowers, a uniquely dwarf 8-10 inch tall and almost 1 ½ feet wide shrub in a mound.

‘Polka’ – a compact, 3-5 feet plant with thick dark green foliage. Its flowers are a rich velvety two-toned pink with a yellow throat.

Wine & Roses (‘Alexandra’) – burgundy foliage and rose-pink flowers in late spring; grows 4-5 feet tall.

‘Red Prince’ – red flowers, dark green foliage and arching stems; 5-6 feet tall and 4-5 feet wide; occasional secondary bloom in late summer.

‘Variegata’ – 6 feet tall, deep pink flowers, green leaves with a creamy white edge.

Princess Flower Excels Where Summers Are Hot

Posted by Hugh on May 1st, 2018

Princess Flower in container

Closeup of flower

Princess Flower or Glory Bush (Tibouchina spp.) is a tropical shrub (from Brazil) that produces beautiful showy purple flowers. It blooms over a long time span (USDA hardiness zones 9-12). The most popular species in cultivation is T. urvilleana. A well-tended plant can be trained into a miniature tree in a large container for patios and decks.

This fast growing tropical needs an organic-rich, moist, well-drained soil. Sunlight and proper soil moisture are key components for nurturing a strong healthy plant. Under partial shade, shoot growth tends to be leggy and flower numbers are a lot less. Plant requires frequent (bi-weekly) pinching to increase branching.

Plant should be fed every 3 weeks with a water soluble fertilizer such as Miracle-Gro™ or Jacks™. An alternative nutrition program is to feed a controlled-release fertilizer such as Osmocote™ or Nutrikote™ to soil or container media.

Princess Flower produces 3-inch wide violet or purple flowers, particularly all summer long in southern climes. With proper care a plant in soil may reach 10- 15 feet tall and 6-10 feet wide. In a large container, expect less than half that size. Heaviest blooming happens in summer and falls of as air temps cool in the fall. In zones 8 (winter low temps around 20-25°F), Princess Flower may flourish through the Thanksgiving holiday. Further north move plant(s) into a greenhouse or sun room. Holdover plants should be cutback hard, repotted, and fed every 4-5 weeks from December thru February.

Popular cultivar is ‘Athens Blue’ with deep purple flowers. Scale, nematodes, and geranium budworm are occasional problems.

Warning: if you live in a warm region where Princess Flower is hardy, remove seed pods to prevent Tibouchina from becoming invasive.

Erosion Control – Try Weeping Lovegrass

Posted by Hugh on April 28th, 2018

Weeping Lovegrass (Eragrostis curvula) at Biltmore Estate in Asheville, NC

Weeping Lovegrass (Eragrostis curvula) is a warm season, perennial bunchgrass. It grows to a height of 2-4 feet and the long narrow 1/4 inch wide leaves (10 to 20 inches in length) suggest the grass is “weeping”. Seed heads may be erect or drooping and produce small very numerous seeds (1.5 million per lb.). Weeping Lovegrass is easily established by seeds and spreads by tillering. Over a years time a single plant can colonize an area 12-15 inches in diameter. Lovegrass was first imported into the U.S. from South Africa in the late 1920’s.

Weeping Lovegrass grows best in the dryland agriculture of Texas, Oklahoma, Arizona, New Mexico, Nevada and California (east of mountains). Weeping lovegrass is also used along roadsides and for hillside stabilization in the Mid-Atlantic States. The species establishes rapidly, produces a deep rootsystem, a key feature for erosion control. Unlike its native cousin, purple lovegrass, weeping lovegrass is commercially available at reasonable cost.

Weeping lovegrass can be an aggressive competitor in ecosystems and is considered an invasive species in some states. It thrives on soils of low fertility. Fertilizer applications should be made in April for first seed crop and in August for second. Weeping lovegrass produces taller plants than purple lovegrass (E. spectabilis), but can still be considered a low-maintenance grass. The root system of weeping lovegrass is fibrous as well as deep and is utilized on steep embankments for erosion control.

It grows on almost any well-drained soil, but prefers the sandy loams. Lovegrass responds well to fertilization. Used for pasture (early spring / fall), hay, erosion control, and for steep bank areas throughout Western Plains and also used in transition zone of Eastern USA primarily for forage and erosion control.

Seeding Lovegrass: Weeping lovegrass is easy to establish from seed between May 1 and June 15. Seed are planted with small seed drill. At this time weed competition is less, seedling emergence is more uniform Rainfall is a lot less compared to early spring. Seed alone at a rate of 3 to 5 pounds per acre, or 1 to 2 pounds per acre in mixtures with other species. Fertilizer containing nitrogen (N), phosphorus (P), and Potassium (K) should be applied prior to seeding. A second N feeding may be applied in mid-summer.

‘Alleghany’ Viburnum Is A Four Season Gem

Posted by Hugh on April 25th, 2018

Viburnum ‘Alleghany’

Large shrub

Alleghany viburnum (Viburnum x rhytidophylloides ‘Alleghany’) aka lantanaphyllum viburnum, is a large easy to grow semi-evergreen (USDA hardiness zones 5-8). It will grow to about 10-12 feet tall and a spread of 12 feet at maturity. This low maintenance shrub is a hybrid cross between V. rhytidophyllum and V. lantana ‘Mohican’. The cross was made in the Netherlands in 1925 and released by U.S. National Arboretum in 1966.

Its leathery dark green leaves are resistant to bacterial leaf spot. Its stiff upright branches are coated with woolly gray-brown hairs on stems and on the undersides of leaves. Its semi-evergreen foliage makes it an excellent choice for privacy screening. Foliage is evergreen in the South.

In most years leaves turn purplish in winter and persist through ice and snow through late February. In mid-spring, showy creamy white flat-top flowers open at the ends of branches. Upclose, flowers emit an unpleasant stale fragrance. When adequately pollinated from other viburnum species planted nearby, spectacular clusters of dark red fruits are produced from late summer to early fall that look great against the coarse green foliage. Red fruits ripen to black and attract numerous birds.

Alleghany viburnum grows well in any soil as long as it is drains adequately. Sun to part shade sites are preferred. Flowers are more plentiful in full sun. Feed with a slow release fertilizer such as Osmocote™ or Nutrikote™ in early spring as leaves emerge.

Alleghany viburnum is rated a four-star landscape shrub, with multiple season assets including beautiful semi-evergreen leathery foliage, dependable flowering, and showy fruits in fall and winter. Established shrubs are highly drought tolerant. In early spring rake away old leaves and mulch viburnums for a clean appearance. This viburnum has no serious insect or disease problems.

Prune as needed immediately after flowering because next year’s flower buds form in summer. Best fruit set occurs with cross pollination from parents or clones of the within hybrid.

Benefits Of Mulching

Posted by Hugh on April 22nd, 2018

Trunk filled with compost

Mulching benefits garden soil and enhances the landscape appearance.

Here is how:

Pine needle mulch at Biltmore Estates in Asheville, NC

Prevents weed seeds from germinating, thereby reducing hand weeding.
Mulching keeps plant roots moist and cool in summer.
Fall mulching acts like a thermal blanket and aids newly set plants to establish their roots quickly.
Reduces the need to water the garden as often.
Conservation measure via soil runoff protection.
Reduces soil compaction which permits rainfall and irrigation water to penetrate the soil surface.
Encourages beneficial insects and microorganisms.
Mulch decomposes and improves the organic level of the soil.
Offers a tidy appearance to the garden.
Certain kinds of mulch increase or decrease soil pH over time. Decomposition of oak leaves, holly leaves, and pine needles will lower pH over time. Mulch derived from hardwood bark tends to raise soil pH slightly over time.

Acid-loving plants such as blueberries, rhododendrons, azaleas, mountain laurels (Kalmia), and many evergreen shrubs benefit from low pH soils. To raise soil pH, apply hydrated lime (contains calcium) or dolomitic limestone (contains magnesium). Mulches derived from fresh sawdust or wood chips may tie up available soil nitrogen and plant foliage turns yellow (chlorotic). Do not over apply uncomposted mulches around landscape plants.

Typically, spring mulching entails adding 3-4 inches of composted mulch which may be purchased from garden centers or big box stores. Your city may sell or giveaway partially decomposed yard waste, a mix of cut tree/shrub prunings plus lawn clippings and leaves which have been ground up and composed for 3-6 months.

When not to mulch: do not mulch fall-planted fruit trees and shrubs the first year. Vole and other critters make their winter homes in the mulch and gnaw on the sweet soft bark of these plants. After the winter is over, fruiting plants may be permanently mulched.

Uniquely Different Spider Azalea

Posted by Hugh on April 19th, 2018

R. stenopetalum ‘Linearfolium’ at Biltmore Estates in Asheville, NC

Although rarely seen, spider azalea (Rhododendron stenopetalum ‘Linearfolium’) will be a pleasing addition to your woodland garden (USDA hardiness zones 6-8). Few people would ever guess that it is an azalea. This airy shrub grows 3-4 feet tall and a whole lot wider. It is slow growing, but is worth the wait. This unique semi- evergreen azalea hails from Japan.

April blooming spider azalea.

The very narrow (ribbon-like) leaves of spider azalea are mostly deciduous, nearly 3 inches long, and crinkly textured. The pink April/May flowers are very spider-like and appear in terminal clusters of three. Flowering may last 4-6 weeks in a dappled shade garden locale and are lightly fragrant up close.

Flowers are unique in that the 1 1/4 inch-long pink sepals tend to be slightly larger than the pink petals. Flowers are borne on tips of branches. The overall shrub is finely textured and will catch the attention of friends and visitors to your garden.

Spider azalea thrives in cool shade, best in partial day sun, preferably in the morning. Roots demand a moist, humus-rich, well drained, acidic soil and high shade that permits filtered sunlight. Do not plant in deep shade. The foliage is easily harmed by dry winds.

Feed spider azalea at the same time as you fertilize other azaleas and rhododendrons — once annually in late winter or early spring. Use a slow release fertilizer such as Osmocote™ or Nutrikote™. Maintain a 2-3 inch layer of an acidic based mulch comprised of pine needles or pine bark chips. Pruning is rarely needed and performed to shape the plant or to remove a dead or broken small branch. Irrigate as needed the first year to establish new shrub. Disease or pest troubles are rarely seen.

A number of sources, including Niche Gardens in Chapel Hill in North Carolina and Woodlanders Nursery in South Carolina, NC, list the variety ‘Seigai’.

Growing Celosia In The Summer Garden

Posted by Hugh on April 16th, 2018

Celosia ‘Arrabona Red’

Cutflower celosias sold at a Brooklyn, NY market

Celosias (Celosia argentea), aka cockscomb, feather, and plume amaranths, are summer flowering annuals in most of the U.S. (USDA hardiness zones 10-11). Mature plant height varies by cultivars, generally between 6 inches and 3 feet in height, taller types grown for the florist market. Celosia plants are classified into three groups: a crested type (C. cristata), plume type (C. plumosa), and spike or wheat type (C. spicata).

Celosias prefer full-day sun, although a minimum of 6 hours of direct sunlight is adequate. A compost rich, mildly acidic, well-drained garden soil is ideal. Plants are set outdoors in the garden when spring daytime temperatures stay above 60 °F. Add 2-3 inches of an organic mulch after planting and deeply water newly set plants. Mulching aids to suppress weed infestation and in soil water loss from evaporation. Celosias are not water hogs, but need irrigation during long summer dry spells.

At planting time apply a slow release granulated fertilizer such as Osmocote™ or Nutrikote™ according to package directions. Over the summer months, if plants need additional feeding, use a water-soluble fertilizer such as Miracle-Gro™ or Jacks™ every 2-3 weeks through mid-September. With taller cockscomb varieties, tie flower stalks to stakes to keep them from falling over; or simply pinch back shoots by one-half to develop a bushier plant. In addition, remove spent flowers to promote new blooms.

Celosia is rarely troubled by disease and insect problems. Inspect plants for mites over a hot dry summer. Good soil drainage is absolutelyessential to avoid root rot problems. Leading plumosa varieties: ‘Arrabona’, ‘Fresh Look’, ‘Dragon’s Breath’, ‘Prestige Scarlet’. ‘Intenz’, Century® series, and ‘Flamingo Feathers’ are spike type celosia. Cristata types include Bombay® and Kimono® series. Floral color range is purple, deep red, wine red, gold, and yellow gold.