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

Select List Of The Better Kousa Dogwood Varieties

Posted by Hugh on April 10th, 2019

Cornus kousa ‘Wolfeyes’ at UT Arboretum, Oak Ridge, TN

C. kousa ‘Lustgarten Weeping’ at Rutgers University, NJ

There are over 100 named varieties (cultivars) of kousa (Chinese) dogwoods (Cornus kousa) in nursery trade (USDA hardiness zone 5-8). Most cultivars grow 20-30 feet high with some exceptions. Kousa dogwood blooms 2-3 weeks after U.S. native flowering dogwood (C. florida). Most grow shrub-like and tree forms require extensive training at the nursery.

Flowers are 2-4 inches wide with either white or pink tapered bracts. Flowers appear after the leaves emerge. Fleshy pinkish-red to red fruits ripen in late summer. Flowers and foliage are highly resistant to anthracnose disease and deer tend to stay away.

Several cultivars are very new and others are not well known. Dogwood researchers, such as at the University of Tennessee, continue to evaluate the best cultivars for the Southeastern U.S. Key characteristics they search for include drought tolerance, heat resistance and better tree forms.

Some cultivars that show great promise include:

‘Blue Shadow’– exceptional dark green foliage; blooms at an early age.

‘Gold Cup’ – dark green foliage marked with a prominent golden yellow streak in the leaf center and small white blooms

‘Gold Star’ – slow growing tree; green leaves with butter-yellow center blotch.

Heart Throb® (’Schmred’) – red-colored bracts do not fade out in southeast U.S. heat as do many red flowering varieties.

Fruits of C. kousa

‘Lustgarten Weeping’ – strong weeping form but is reportedly disease prone.

‘Milky Way’ – popular “generic” variety that flowers early and prolifically; flowering tends to be biennial, heavy one year and light the next.

‘National’ – vigorous, vase-shaped tree and dark green foliage

‘Scarlet Fire’ Kousa dogwood

Scarlet Fire® -new! 2018 introduction from Rutgers University with fade-proof red (dark pink) bracts.

‘Summer Stars’ – heavy-blooming; good drought tolerance.

‘Wolf Eyes’ – slow growing compact (10-12 feet) shrub form; creamy white variegated foliage is scorch-resistant; small white flowers fade into foliage.

Spring Ephemerals

Posted by Hugh on April 6th, 2019

The cold dreary days of March have waned and many of our great Appalachian wildflowers have awakened. These plants are often referred to as “ephemerals” because they come up, bloom, and fade away in 6-9 weeks. They bloom in a shady woodland or garden environment before the deciduous tree canopy has completely leafed out.

Trout lilies and mayapples

Their appearance tells gardeners that spring is nearly here. We are heartened to see them popping their heads up. Virginia bluebells (Mertensia virginica), trout lilies (Erythronium americanum),
celandine poppies (Stylophorum diphyllum), spring beauties (Claytonia virginica), bloodroot (Sanguinaria canadensis), twin leaf (Jeffersonia diphylla), and toothwort (Dentaria diphylla) are blanketing woodland areas. By late spring or early summer, most will have died back to the ground preparing for the next year’s display.

In designing your own wildflower garden, these favorites associate with each other: foamflowers (Tiarella spp.), coral bells (Heuchera spp.), several ferns, yellowroot (Xanthorhiza simplicissima), woodland phlox (Phlox divaricata), and Jack in the pulpit (Arisaema triphyllum). They prosper well under deciduous trees and where the soil does not get bone dry.

Spring wildflowers do not demand moist, fertile soil. They gather nourishment from the soil organic matter. The chances of spring wildflowers to seed-in and naturalize in your landscape are greater in humus-rich ground. If their soil, light and water needs are met, these spring beauties tend to form small colonies.

Some young wildflowers may be difficult to identify from seed. For example, Virginia bluebells may take 5-6 years to reach full flowering-sized size. Be careful not to mistakenly weed out young bluebells that look like tiny clumps of bibb lettuce.

Numerous native plant nurseries sell these beloved late winter-spring wildflowers or ephermerals. A few favorites include Sunlight Gardens (www.sunlightgardens.com) in Andersonville, TN and Sunshine Farms (www.sunfarm.com) in Renick, WV.

Virginia bluebells
Bloodroot

Hybrid Wax Begonia Revolution

Posted by Hugh on April 1st, 2019

Whopper Rose with Green Leaf at Chicago Bot. Garden

Big begonias with coleus and lantana

Wax begonias (Begonia x semperflorens) are popular summer annuals in public and private gardens. Begonias are excellent for mass bedding, in mixed borders, and in large containers. Plants hold up to summer heat, humidity, and moderate dry spells. The foliage stays mostly pest and disease free.

A few years back, two series of interspecific hybrids (Begonia benariensis), were introduced by the Benary Seed Co. and trademarked as Big™ and Whopper™ begonias. These hybrids boast larger showier flowers than traditional wax begonias. Color choices in the Big series are red, rose and pink. Whopper series come in red and rose only. Whopper plants grow 20-25% larger than Big. This means fewer plants to plant for good garden coverage which will save you money.

Big™ begonias bloom non-stop for almost six months (mid-May thru October (USDA hardiness zones 6 thru 9). Big begonias are available in bronze-leaf (full sun) and green leaf (part sun) forms. Bronze-leaf types perform at their best (leaf color) in full sun, and green leaf cultivars prefer partial shade. Begonias need well-drained soils amended with lots of well-rotted compost.

In 2017 Pan American Seed released the Megawatt™ series. Current varieties include ‘Red Green Leaf’, ‘Pink Bronze Leaf’, ‘Rose Green Leaf’, ‘Red Bronze Leaf’ and ‘Rose Bronze Leaf’. Proven Winners (PW) has recently introduced Surefire™ Series with a red and a rose variety. Expect new color choices to be added over time.

All hybrid wax begonias grow robustly, 18 to 24 inches tall and 16-18 inches in spread, by the end of summer. Plants grow compact and are well-branched. Flower size varies from 2 to 3 inches across. The brightly colored blooms are visited by many kinds of butterflies over the long bloom season. Flowers are self-cleaning and require no deadheading. Space plants 15-18 inches apart depending on which series that you plant.

Begonias perform best with moderate fertility. At spring planting, feed with a slow-release fertilizer such as Osmocote™ 14-14-14 or Nutricote™ 13-13-13. One to two additional feedings in mid-summer with a water-soluble fertilizer (such as Miracle-Gro®, Schultz®, or Jacks®) are often needed in southern climates (zones 7-9). Add 2 to 3 inches of mulch to prevent weeds and to conserve soil moisture. Irrigate during extreme dry spells to maintain plant vigor and flowering.

Temperamental Big Leaf Hydrangeas

Posted by Hugh on March 25th, 2019

Hydrangea macrophylla

H. macrophylla ‘Summer Crush’

Get use to it… big leaf hydrangeas (Hydrangea macrophylla), also called hortensia hydrangeas, are temperamental (USDA hardiness zones 6-9). After a long winter of sub-freezing temperatures, these blue (or pink) flowering shrubs should be stunningly beautiful in spring. However, if the late winter- early spring temps flucuate wildly, grab your pruning shears.

Too most gardeners, myself included, find growing these hydrangeas totally frustrating. Bloom buds on the old wood are predictably injured two out of three springs in zone 6 eastern TN, Southwestern VA, and western NC (southern Appalachian region). Flower buds and stems are most susceptible to injury as the plants start to break dormancy in late winter, then get smacked by a sudden cold snap.

To protect against winter freeze damage: 1. site big leaf hydrangeas close to your house or a heated structure; 2. do not feed plants in the fall; 3. select better cold tolerant cultivars (varieties).

In northern climes, such as Midwest or New England states, cover big leaf hydrangeas with mulch or leaves. In late winter inspect the lower buds as the plants start to awaken. You don’t want to trap excessive moisture around the growing buds and invite diseases to the plant.

Hydrangea breeders (Bailey’s , Proven Winner’s and Spring Meadow Nurseries to list three) continue to introduce hardier bigleaf hydrangeas that bloom on both new and old wood. Old wood flowers are set on last year’s shoots and new flowers are made on current season’s growth. Do not prune hydrangeas late in the summer, as you may be removing flower buds the following spring.

Over a quarter century, Proven Winners Colorchoice™ and Bailey’s Nurseries (Endless Summer™, Bloomstruck™, and Summer Crush™ brands) have introduced new hydrangea genetics. Try short growing Let’s Dance™ series in small gardens. Also, grow a different hydrangea species such as mountain hydrangea (H. serrata). New from PW Colorchoice is the Tuff Stuff® series of mountain hydrangeas which display superior bud hardiness and re-bloom. Tuff Stuff Ah-Ha® re-blooms heavily and has large lacecap blooms with double sepals,that are either pink or blue depending on soil (media) pH.

Spike Winterhazels

Posted by Hugh on March 20th, 2019

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Winterhazels (Corylopsis spp.), native to China and Japan, is a wonderful genus comprised of winter flowering shrubs of varying heights and widths (USDA hardiness zones 5 to 8). Few U.S. gardeners know of them. Their bright yellow flowers are a lot bigger and showier than the witchhazels (Hamamelis spp.) which are close botanical relatives. In my early March garden the winterhazels start blooming as the witchhazels are finishing up.

The winterhazels occupy partially shaded shrub borders or woodland areas. Eight species, sometimes more, are available from on-line nurseries. Spike winterhazel (C. spicata) and buttercup winterhazel (C. pauciflora) are low spreading forms that fit into smaller urban and suburban gardens. Their slightly fragrant flowers are lemony yellow with red-purple anthers.

Spike winterhazel grows to 4-8 feet tall and to 6-10 feet wide. Individual flowers, only 3/8 inches long, comprise small drooping clusters (racemes to 2 inches long); clusters hold 6-12 flowers. After bloom, 4-inch long circular (ovate to obovate) leaves unfold with a bronze-purple tint; within 2-3 weeks leaves take on a bluish-green color. Tiny hairs on the leaf surface give the leaves a dusty look by late summer. Fall leaf color is an yellowish-green. Fall seed capsules swell and hold two small seeds.

Winterhazels prefer a compost-rich, well-drained, acidic soil in full sun to part shade. They tolerate most garden soils except heavy clays. Plants favor shading from direct afternoon sun in southerly climate zones 7-8 as well as shelter from high winds. Flower buds/flowers are susceptible to cold injury if winter temperatures are severe.

After flowering or by late spring, prune winterhazels as needed to hold shrubs in check. Feed with 10-10-10 or equivalent granular fertilizer. No serious insect or disease problems trouble these low maintenance shrubs.

Significant cultivar: With its circular golden foliage, C. spicata ‘Aurea’ is an attention grabber from March through October. New spring foliage opens rosy-pink, turns golden yellow, and to bluish green by early summer. Nodding racemes of small, bell-shaped pale yellow flowers open in the late days of winter and last 2-3 weeks. Frigid nights in the mid- 20’s rarely trouble the blooms. Flower fragrance does not overwhelm.

The Fragrant Viburnums

Posted by Hugh on March 15th, 2019

Korean Spice viburnum

Judd viburnum

Fragrance is a wonderful trait to include in your landscape. Although most viburnum species are not odorous, these 7 stand out for their spring floral fragrance. Bloom dates mentioned here are for zones 6-7 (TN, VA, NC and KY).

Burkwood Viburnum (V. x burkwoodii) is semi-evergreen, 7 to 8 feet tall and wide, with glossy dark green leaves that turn burgundy red in winter. The 2 to 3-inch flower clusters open spicy-fragrant white flowers in March or April. Red to black fruit appear in July to August. ‘Mohawk’ is an outstanding selection that is bacterial leaf spot resistant. Zones 4-8.

‘Dawn’ Bodnant Viburnum (V. x bodnantense) is an open branched shrub that grows to 10 feet or more high. This March-blooming specie opens with small open clusters of fragrant pink flowers that may be injured by freezes. ‘Dawn’ is the most popular cultivar. Zones 5-7

‘Cayuga’ snowball viburnum is a hybrid (V. x carlcephalum x V. carlesii) that grows 6 to 10 feet tall and wide. The mildly fragrant snowball flowers are white 4- to 5-inch clusters that open in April to early May. Fruits matures to black in early fall. Leaves are highly resistant of bacterial leaf spot and powdery mildew. Leaves turn dull purplish to dull red in fall. Zones 5-8.

Korean Spice Viburnum (V. carlesii) grows 4 to 8 feet tall and wide, with a dense, rounded habit. The leaves are similar to those of fragrant snowball, turning burgundy to purple in fall. Flowers are clove-scented, white, 2- to 3- inch clusters, opening in March to April. Fruit are red to black and mature in late summer. Zones 4-8.

Judd viburnum (V. carlesii x V. bitchiuense) is a deciduous shrub that typically matures to 6-8 feet tall and 6-10 feet wide. Very fragrant white flowers in spring and dark green foliage, black fruit in fall and purple fall color. Ovate to ovate-oblong or elliptic, dark green leaves (to 2.5 inches long) turn burgundy purple to red in fall. Zones 5-8.

Prague Viburnum (V. x pragense), a hybrid between Viburnum rhytidophyllum and V. utile, produces pink floral buds open to 3-to 6-inch wide, creamy white, lightly fragrant flower clusters in April into May. The 2-4 inch long semi-evergreen leaves are highly glossy. It is a fast growing upright shrub, 10 feet or more high. It is an excellent choice for a rapid growing screen or hedge. Green fruits first turn red and mature glossy black. Zones 5-8.

Japanese Viburnum (V. japonicum) is an underutilized evergreen species that grows 6 to 8 feet tall and wide. Habit is dense and rounded with leathery, glossy green leaves. Flowers are fragrant and white, and fall berries are red. It forms a good screening plant. Zones 7-9.

Bleeding Hearts Delight In The Spring Garden

Posted by Hugh on March 10th, 2019

Dicentra spectabilis (pink flowering form)

‘Alba’- white flowering form

Bleeding hearts (Dicentra spp.) are truly one of nature’s glorious delights in the spring garden (USDA hardiness zones 3-9). Old fashion bleeding hearts (D. spectabilis), indigenous to Asia, grow taller and wider compared to their North American counterparts – wild bleeding heart (D. exima) and Dutchman’s breeches (D. cucullaria).

Old fashioned bleeding bear larger (and showier) flowers and their foliage is slightly coarser (less dissected) than their U.S. relatives. All green vegetation generally disappears into summer dormancy unless the planting spot is moist and moderately shady.

The bright red, pink or white, heart-shaped, pendant flowers are supported on arching stems. Old-fashioned bleeding hearts grow 24 inches tall and to 36 inches wide. D. exima plants grow about half the size. Prompt cutting back of the foliage to 4-6 inches immediately following bloom often encourages secondary flowering.

Some cultivars: ‘Alba’ – white-flowering forms of both species; ‘Gold Heart’ – bright chartreuse foliage and pink and white flowers; ‘Valentine’ – a vigorous hybrid form with showy cherry red/white tipped flowers; ‘Luxuriant’ (probably a hybrid between D. eximia (eastern U.S. native) and D. formosa (western U.S. native) – deeply-cut, grayish-green foliage and cherry red blooms.

Good soil drainage is essential for their long term survival. Plant in full to partial shade in a humus-rich, mildly acidic to slightly alkaline (pH range 6.0 to 7.5) soil. In late winter feed a slow-release fertilizer at the low label rate. Bleeding hearts linger in clay-based soils that stays too wet in winter.

Garden centers sell either packaged dormant roots or container-grown plants. Space plants or roots 18-24 inches apart in shade or part shade. Lightly mulch around plants in a woodland garden. Bleeding hearts may self-sow in the garden. In southerly regions plants may die back and become dormant by mid-summer.

Crowded clumps should be divided in spring or fall. Cut pieces of the rhizome with two to four buds (or eyes) each and replant. Divide clumps just after flowering or in very early spring, as growth starts to emerge.

Spring flowers attract butterflies and hummingbirds. Aphids, slugs and snails occasionally feed on the leaves. Plants are deer and rabbit resistant.

Bleeding hearts make great companions with other woodland favorites as ferns, lungworts (Pulmonaria spp.), brunneras, coral bells (Heuchera), and foam flowers (Tiarella).

Note: in recent times the genus Dicentra has been changed to Lamprocapnos.

Easy To Care Siberian Iris

Posted by Hugh on March 6th, 2019

Iris sibirica ‘Caesar’s Brother’

‘Humors Of Whiskey’ (past AIS Award Winner)

Siberian iris (called beadless iris) are favorites of gardeners and landscapers. Why? – ease of maintenance, plant longevity, and trouble free. Their flowers are smaller than the bearded iris blooms, but their grass-like foliage stays attractive all season long. They are more cold hardier.

Siberian irises are mostly hybrids of two southwest Asian species, I. sibirica and I. sanguinea (USDA hardiness zones 3-9). The narrow, grass-like foliage forms a vase-shaped clump to 2 feet high. Autumn foliage turns rusty brown in late fall. Flowering stems rise above the foliage to 3 feet height in May-June.

Siberians perform well in most garden soils, but perform best in a humus-rich, mildly acidic soil. In spring feed with 10-10-10 or equivalent granular fertilizer. In early summer apply a booster feeding using a water soluble product such as Miracle-Gro™, Jack’s™, or Espoma™. Mulch iris in spring to conserve soil moisture and prevent weed infestation. Remove spent bloom stalks, and brown and withered leaves to keep planting looking attractive. In late fall cut back all leaves 1-2 inches above the ground.

In Northern states (zones 3-6), Siberians perform best in full day sun (or 6-hours minimum). In Southern areas, shelter from the mid-day sun.

Cultivars: Over 200 varieties are available, principally from online iris nurseries. (American Iris Society descriptions)

‘Butter and Sugar’ – white standards, yellow falls, 28 inches tall.

‘Caesar’s Brother’ – dark purple flowers, 36 inches.

‘Dreaming Yellow’ – cream standards, pale yellow falls, 30 inches.

‘Humors of Whiskey’ -pink-white standards and golden brown falls, 29 inches.

‘King of Kings’ – crisp white self with yellow shading in center; 33 inches tall.

‘Miss Apple’ – two-toned red flowers with yellow highlights, 30 inches tall

Siberian irises are generally pest-free, with very little susceptibility to the two main problems of bearded iris, namely iris borer and bacterial soft rot. Voles and mice may munch on rhizomes. Plants tolerate deer and rabbits.

Divide big healthy clumps into 2-4 fans in late summer or fall, depending where you live. In southern climes, early fall is a better time. Clumps can grow undisturbed for several years, unless they become crowded, plant vigor declines, or bloom size falls off.

Growing Nasturtiums

Posted by Hugh on March 1st, 2019

Nasturtium ‘Double Delight Cream’

Nasturtium mix

Old-fashioned nasturtiums never lose their appeal, whether in the garden or as a garnish on a salad, or added to stir-fries, or favorite pasta dishes. Depending on the variety, some may be grown as climbers on fences and trellises or as bushy plants in a window boxes and containers.

Around the world there are several species of nasturtiums, also called Indian cress. The two most common species grown in U.S. gardens are: Tropaeolum majus , a trailing (climbing) type, and T. minus, a bush (compact) type. Nasturtiums are considered annuals, although they can be herbaceous perennials in southerly climes (zones 8-11).

Nasturtiums flower best in full sun, but prosper in partly shaded locations, particularly where summers are torrid. They love cool, damp, well-drained soil. If plants begin to flag in the heat of summer, cut them back and they’ll regrow and flower again when cooler weather returns in fall.

Nasturtiums thrive on neglect and don’t require rich soil. In fact, if you amend soil with too much nitrogen-rich fertilizer or manure, lots of dark green foliage and few flowers will result. In plain soils, amend the site by mixing in a 1-inch layer of compost. Plants ordinarily don’t need fertilizing during the growing season. Mulching is an added plus.

Nasturtium flowers range from pastels, yellows, oranges, and red shades, in either single or double flowers. Colorful seed mixes are also available. Flowers of most modern day varieties stand above the foliage.

Some of the best selections include:

Apricot Twist’ (trailing variety) – 3 to 4 feet long and double apricot-orange splashed with raspberry red flowers.
‘Empress of India’ (semi-bush variety) – 1 – 2-foot vines and features large, bright scarlet flowers and blue-green foliage.
‘Jewel of Africa’ mix (trailing variety) – 4 – 6 foot long in yellow, red, cream, and pink flowers and unique variegated leaves.
‘Moonlight’ (trailing variety) – up to 7 feet long and produce unusual, pale yellow flowers.
‘Peach Melba’ (heirloom bush variety) – creamy yellow blooms with maroon markings near centers.
‘Tip Top’ series – compact ‘Alaska’ series with mottled leaves and bright flowers in yellow, red and orange.
‘Tom Thumb’ series – shorter (6-9”) type with large, vivid blooms in bright yellow, red and orange; excellent for small gardens.
‘Vesuvius’ – compact plant habit and brilliant deep salmon flowers and deep blue foliage.
‘Whirlybird’ series (bush type) – a mix of flower colors, or in separate colors, including cream, salmon, gold, and cherry rose. The flowers are semi-double.

After sowing, keep the bed well-watered and weed-free. Nasturtiums are relatively trouble-free. Aphids may feed on the new leaves and flowers; washed bugs off with frequent sprays of water or use insecticidal soap.

Nasturtiums are high in vitamins A, C (10 times as much as lettuce), and D. Harvest nasturtium young leaves, flower buds and open blooms in early morning; those collected later in the day are more pungent. Wash and dry the flowers and leaves and store in a plastic bag in the refrigerator. Unripe seed pods have a peppery flavor somewhat like watercress and may also be used in salads.

Saucer Magnolias

Posted by Hugh on February 25th, 2019

Saucer magnolia

Multi-trunked Saucer Magnolia

Saucer magnolias (M. x soulangeana) are deciduous hybrid magnolias (M. denudata x M. liliiflora) as broad shrubs or small trees. They typically grow 20-30 feet in height and width. Saucer magnolias are often called tulip magnolias because of the shape of the colorful blooms. Flower colors range from white, pink, rose, purple, magenta, and burgundy. Flowers are pink with white interiors.

There are hundreds of hybrid cultivars available in nursery commerce. Be aware that the early blooms are prone to spring frost injury. Saucer magnolias do not tolerate heavy wind or salt spray.

Large fragrant flowers (to 10 inches across) open before the leaves emerge. Sparse numbers of additional flowers may bloom sporadically later in spring on new growth, but the later flowers are usually less vigorous and less colorful than those of the primary bloom.

Saucer magnolias date back to the 1820’s and are widely planted across the U.S. and Europe. In the early spring garden, saucer magnolia is a landscape show-stopper. Lush summertime leaves are dark green and leathery—adding nice contrast to silvery-gray bark. The husky gray branches and big, fuzzy flower buds stand out in the winter landscape.

Saucer magnolias thrive in a moist, humus-rich, mildly acidic, well-drained soil and in full to partial sunlight. For optimum flowering, mature trees should have more sunlight. The tree’s shallow competitive roots are best maintained in a grass-free mulched area. Trees tolerate short periods in wet soggy soils without injury. Once established, generally after 1-2 year span, saucer magnolias are highly tolerant of summer dry spells. Summer leaves may turn yellow (chlorotic) in iron deficient alkaline soils. Disease and pest problems are rare.

Balled-and-burlapped (b&b) or container-grown plants are best planted from late winter up to the early days of autumn. Prevent soil compaction around root zone by limiting foot traffic over the root system. Magnolias seldom have serious pest or disease problems; inspect for magnolia scale. Deer generally stay away from magnolias.