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

Mimosa Tree – Love It Or Not

Posted by Hugh on July 21st, 2022

Over the hot spring and summer months, weedy Mimosa trees (Albizia julibrissin) stand beautiful along U.S roadsides. During the rest of the year, people pay very little attention to this arboreal Asian beauty that inhabit a vast area from Iran to China (USDA hardiness zones 6-9).

From late spring through summer, mimosa struts an attractive fine textured green foliage and lovely flowering. It leaves out as late as mid-May in its northern range. Wild seedlings produce pale pink to dark pink feathery blooms from late June thru July. The showy fragrant flowers attract numerous bees and hummingbirds. Fall leaf color changes is non-existent.

Mimosa grows 20-25 feet tall of equal and broader widths. Under cultivation, it may achieve 35-40 feet high. It grows best under full sun and in almost any adequately drained soil. It copes with subpar sites, often overpowering an abandoned urban lot or a roadside fencerow. Its seeds take flight from miles away.

The cultivar ‘Summer Chocolate’ exhibits fern-like dark purple foliage. The cultivar is rated hardy in USDA zones 7-10. Chocolate mimosa grows rapidly to 20 feet tall and wide; that is nearly half the size of a mature green leaf specimen.

Chocolate Fountain™ is a recently released weeping purple leaf cultivar from Dr. Tom Ranney at North Carolina State University (zones 7-10). Dramatic, deep purple, fern-like foliage graces the pendulous, weeping habit, enhanced by delicate pink flowers in summer. An elegant accent for smaller spaces or containers.

In general, mimosa trees tend to be short-lived, around 15- 20 years. However, trees tend to colonize, depositing loads of seeds that beget lots of seedlings. They improve the soil’s tilth and nutrition, so that one day, an opportunist native species may take over in its place.

Late winter thru early summer (February-July) is the ideal planting time. Remove unwanted and dead branches at any time. Over the first two years, water deeply during extreme heat and dry periods and the entire growing season those growing in containers. Fertilizing a mimosa tree is unnecessary as roots manufacture their own nitrogen.

Rose of Sharon – A Summer Delight

Posted by Hugh on July 16th, 2022

Rose of Sharon (Hibiscus syriacus), aka althea, is a vigorous, upright, vase-shaped, multi-stemmed, deciduous shrub that typically grows 8-12 feet tall with some exceptions. Altheas may also be trained as small trees or espalier. Showy 5-petaled flowers appear over a long summer period and sometimes into early fall. The center of each flower has prominent single staminal column (except where noted). The palmately-veined, coarsely toothed leaves are medium green leaves measure 2-4 inches in length but fall color is non-existent.

Hibiscus Pollypetite® (photo courtesy of PW)

Altheas are highly dependable landscape shrubs and among the easiest to maintain. They grow in average, medium moisture, well-drained soils and in full sun to part shade. Flowering is best in full sun and in moist, humus-rich soils. Established shrubs exhibit good summer drought tolerance. Prune to shape in spring. Old altheas may be cut back to the ground in late winter. Altheas are easily propagated by stem cuttings.

Disease and insect problems cause little overall injury to altheas and new aftergrowth covers up most damage. Feeding of Japanese beetles in June may injure foliage; Neem Oil or Sevin® dust will destroy beetles, Do not use insecticides when altheas are starting to bloom to protect bee pollinators. Altheas are rated deer resistant, meaning deer rather prefer other shrubs.

Altheas may be planted in groups for hedging or singly used as a specimen. Utilize them for foundations and shrub borders.

Chiffon® Series is an outstanding series from Proven Winners. Flowers are mostly sterile, meaning they may produce only a small amount of seed. Shrubs grow 8-12 feet tall and 6-10 feet wide. Currently, there are 5 color choices in the series: Blue Chiffon®, Dark Lavender Chiffon®, Magenta Chiffon, Pink Chiffon®, and White Chiffon®.

Pillar™ Series are planted as space-saving shrubs that grow 10-16 feet high and 2-3 feet wide. Now available in three color choices: Purple Pillar®, White Pillar®, and Red Pillar®.

Pollypetite® (H. paramutablis x H. syriacus) is a dwarf hybrid form. This rounded shrub grows 3-4 feet tall and wide with large rounded pure lavender purple flowers with soft ruffled edges and no center eye. Leaves are very dark green.

Paraplu Adorned® (NEW) has leaves that flush bright yellow in spring and are everchanging thru the season. It grows 10 feet tall and 4 feet wide with an upright, vase-shaped, spreading habit that can be trained as a small specimen tree or group several into a privacy screen.

Sugar Tip® is a double-flower seedless form that grows 6-8 feet high and 4-6 feet wide, bright cream and bluish-green variegated foliage and large clear pink double blooms.

Several other varieties are available at garden centers. The varieties listed above are among the best.

Beware: altheas can self-seed aggressively and become a weedy nightmare. Seedless forms are becoming more available.

A Late Season Blooming Tree

Posted by Hugh on July 10th, 2022

Seven Son Flower (Heptacodium miconioides) is a large, multi-stemmed, deciduous shrub that grows 15-20 feet tall and 10-12 feet wide at maturity. This rare unique specimen is catching on in the U.S. because of its year-round appeal (USDA hardiness zones 5-9). It is an excellent choice for a lawn specimen or plant several in a row to create a tall shrub border. It may also be trained as a single- or multi- trunk deciduous tree.

Starting in late summer into early autumn, terminal panicles of fragrant, creamy-white jasmine-like flowers arise. Flowers are flattened clusters of stalkless blooms (six in number). Flowers are followed in fall by small, purplish-red fruits (½” long drupes) crowned by very showy, rose-pink calyces which elongate after bloom and last into late fall. Floral display of white-petalled flowers last several weeks. Petals fall and ruby red sepals expand, giving the appearance of twice blooming from August to October.

Of winter interest the tan-brown bark exfoliates to reveal its attractive brown inner bark. The medium green leaves are narrow, shiny, and ovate-oblong in shape. A nursery-grown container plant transplants easily. This tree/shrub is becoming more available at on-line nurseries but is still difficult to find at independent garden centers.

This moderately fast-growing tree performs best in full sun and in good landscape soils that exhibit good drainage and retain enough moisture to survive dry periods. Light spring pruning is needed following harsh wintry weather.

Butterflies, other pollinating insects, and hummingbirds frequent the nectar-filled blooms late in the season. Serious insect or diseases are rare with this plant if the plant is properly sited and maintained. Seven son is the recipient of a number of Regional Plant Awards in the U.S. and Great Britain.

Cultivars:
Tianshan® is new selection for smaller gardens, grows 8-12 feet high by 5-7 feet wide.

Temple Of Bloom®, introduced in 2019 by Proven Winners (PW), grows 10 feet tall and wide.

Rhizomatous Alliums

Posted by Hugh on July 1st, 2022

Alliums are a members of the lily family, containing 1100 species, including the edible kinds that you add to your burgers and salads. In the ornamental flower world include spring- blooming bulbs, culinary herbs and durable foliage and bountiful summer flowers.

Whether your summer garden is located in a challenging part of the U.S. such as Texas or Oklahoma or a moist humus-rich ground in New York or Virginia, take a peek at the perennial gems in the onion family (genus Allium). Recently, Richard Hawke, Director of Ornamental Plant Research at the Chicago Botanical Gardens CBG), published the top-rated rhizomatous alliums in the Midwest region (see below).

Rhizomatous alliums just ask for sun and well-drained soil. All are all drought resistant and thrive on dry sites. They are all highly drought tolerant, especially after plants have established themselves their first season. Pest and disease issues are usually rare. Watch for occasional leaf spots, molds, thrips, and onion flies. Allium plantings are busy with beneficial insect life, covered by numerous bees and butterfly species. And deer don’t dig onions or chives.

I have a number of favorites, many of them on the “CBG’s Best Of” listing which appears in the August ‘22 Fine Gardening Issue. Let me start with A. ‘Millenium’, Perennial Plant of the Year winner in 2018. It produces masses of 2.5″ rosy-purple flowers above the dark green foliage in midsummer.

A. ‘Windy City’- thin dark-green leaves provide a dramatic backdrop for 2″ lavender-purple flower clusters on strong, dark stems. Spent flowers persist for winter interest, and are near-sterile, meaning very little seed. This compact variety is perfect for small spaces such as in a rock garden.

A. tanguticum ‘Summer Beauty’ – long-blooming ornamental onion that produces showy, globe-shape 2” lavender-pink blooms in mid-summer and shiny deep green throughout the season.

In the CBG evaluation, three rhizomatous alliums were highly mentioned but not rated:

A. ‘Serendipity’ – sport of ‘Millenium’ great stuts attractive blue green foliage. Globe-like, 2.5” rosy-purple blooms that flower abundantly in mid to late summer.

A. ‘Big Beauty’- soft pink 3” flowers with gray-green foliage in early to mid-summer.

A. ‘Lavander Bubbles’ – blooms a month later than ‘Millenium’ with darker shade of 3″ purple floral globes above attractive glaucous blue-green foliage.

Read the full CBG report in Fine Gardening magazine (August 2022 issue).

New Annual Vincas ‘Kawaii Soiree’ Series

Posted by Hugh on June 26th, 2022

Sun-loving vincas (Catharanthus) are annual periwinkles. This may confuse gardeners who also grow perennial periwinkles (Vinca spp.) that are grow in shady groundcovers.

New from Proven Winners (PW)!! Soiree Kawaii® series of vincas (C. roseus) are bred by Suntory and entered the market around three years ago. I highly recommend that you include them to your list of summer flowering bedding plant.

The name Soiree Ka·wa·i·i means “cute” in Japanese to describe the adorable flower size and shape. Compared to most vincas, petals are dissected and offer a finer floral texture in garden beds and containers. Their bright, attractive flower petals are irresistible to pollinators, especially hummingbirds and butterflies. These micro-blooming vincas grow compact and spreading, and are exceptionally floriferous.

Look for plants to arrive in mid-South garden centers in late April. Plant them into your garden after garden soil temps have risen above 55 °F and the frost danger has passed. Enjoy continuous bloom thru the early non-killing frosts in autumn. Don’t wait a day. Plant them in garden beds and landscape containers and watch flower numbers explode almost within the first week.

Soiree Kawaii vincas perform best in well-drained, humus-rich garden soils and in containers. One caveat: vinca plants despise soggy wet cool soils. Fertilize plantings every 4-6 weeks with a water-soluble product like Miracle Gro® or Peters®. Mulch beds and irrigate over long dry spells. Plants bloom non-stop during the hot humid days of summer.

Soiree Kawaii vincas are valued for their neat mound-like form (6-10 inches tall / 12-18 inches wide). Their glossy dark green leaves make flower colors pop. Even more impressive is how nicely the plants fill out beds and containers, including window boxes and hanging baskets. Pinching is rarely needed.

Currently, six colorful varieties in these compact growing vincas are available. Soiree Kawaii come in white, pink, coral, lavender, peppermint, and red shades. My personal favorites so far are Peppermint® and Blueberry Kiss®.

Modern day vincas exhibit improved disease resistance compared to olden varieties that your mother once grew.

Growing Healthy Blackberries in Your Garden

Posted by Hugh on June 19th, 2022

T-Trellis blackberry planting

Yummy blackberries from the garden excel in flavor compared to store-bought. To get the most out of a blackberry planting, select a full sun location with well-drained organically rich loamy soils. The site should be close to a water supply to get the planting off to a good start and to maximize berry size and numbers.

Ground preparation for perennial blackberries should begin a full year before planting to be weed-free with shallow cultivation and hand pulling as necessary. Mulch with wood chips, bark, pine needles, or composted leaves to prevent weeds, conserve soil moisture, and add organic matter. Disease and insect problems are rare if the patch is properly cared for. Inspect for cane borers (look for sawdust) every few weeks. A weedy blackberry patch attracts serious disease and pest problems over the life of the planting.

The crowns and roots of blackberry plants are perennial. Above ground shoots (canes) live only two years. Each spring blackberry plants produce more suckers from the crown and roots. In the first season vegetative canes (called “primocanes”) grow and go dormant during the winter. Beginning in year two last year’s primocanes, now called the “floracanes”, bloom and produce fruits; new vegetative primocanes emerge that will crop the next year.

For ease of care, blackberries (crowns) are typically grown in a hedgerow or trellis. Crowns should be planted a minimum of 3 – 4 feet apart in rows which are 6 to 8 feet or more apart. Thornless varieties are highly favored when harvesting and pruning off the last year’s bearing flora-canes in late winter. Blackberries start bearing in the second year and fully in the summer of year three.

One year-old canes are sold at local garden shops or from mail order nurseries on-line. Dormant blackberry canes are planted in late winter, usually in mid-April, when injury from damaging frost have diminished (USDA hardiness zones 5-9). Plants should be set at or near the same depth that they grew at the nursery. Firm soil around the roots and water. After planting prune canes back to 4-6 inches in height above the ground.

Blackberries are fertilized annually in mid-April with 1 pound of 10-10-10 or equivalent per 100 square feet of ground area. Apply half of the fertilizer in late March and a second equal amount 6-8 weeks later.

Cultivars: consult the land grant University in your state or the local Extension office. Recommended here in the mid-South (TN-VA): thornless varieties: ‘Triple Crown’, ‘Navaho’, ‘Arapaho’, ‘Black Satin’, and ‘Chester’.

Special Thank You to Mr. Ben Hunter in Kingsport, TN for information on growing blackberries

Ten Native Flowering Vines

Posted by Hugh on June 13th, 2022

Trees and shrubs are not the only woody landscape plants to invite into your landscape. Check out these ten native vines. But first do some homework. Some of these vines grow aggressively which can mean more maintenance work for you.

Vines are a part of the vertical landscaping trend. They are also space-savers. Native flowering vines are being added to pollinator gardens to attract butterflies, moths, and hummingbirds. Vines may grow intertwined over limbs of trees and shrubs; trained on fences, trellises, walls, and arbors; or a third option, allowed to roam freely as ground covers.

Ten Popular Native Vines:

Pipevine (Aristolochia macrophylla) grows 20-30 feet long and produce Dutchman pipe-shaped bronze flowers in summer. Butterflies, particularly the Pipevine Swallowtail, flock to the fragrant flowers.

Crossvine (Bignonia capreolata) is fast growing evergreen vine that grows up to 20 feet long. Fragrant, tubular, orange-red flowers appear in late spring. It has tendril branches that terminate in adhesive disks that easily attach to walls. ‘Tangerine Beauty’ is a popular cultivar.

Trumpet Creeper (Campsis radicans) is an extremely vigorous fast-growing woody vine up to 40 feet long with trumpet-shaped flowers that should be supported on sturdy arbors or fences. Choose from yellow, orange, or red blooms. Warning: this vine suckers profusely and grows too aggressively.

Texas or Scarlet Clematis (Clematis texensis) blooms from mid-summer to fall and tops out at 6-10 feet length. This sparsely leafed vine is often trained to intertwine through nearby shrubs. Cultivars: ‘Gravetye Beauty’ (red flowers) and ‘Duchess of Albany’ (pink flowered).

Leatherleaf clematis (Clematis glaucophylla) produces lavender to purple urn-shaped flowers with curling white tips. Vines grow 6-10 feet long is native to portions of Tennessee. Treat this vine as a deciduous perennial and allow it to ramble over small to mid-sized shrubs.

Carolina Jessamine (Gelsemium sempervirens) is a vigorous vine, up to 20 feet that add a dash of yellow blooms to walls and sturdy arbors in very early spring. Train it as a 3-5 feet tall mound shrub or attach one on your mailbox post. Favorite cultivar: ‘Margarita’.

Coral Honeysuckle, Trumpet Honeysuckle (Lonicera sempervirens) is a 12-15 foot in sun or partial shade. Red or yellow trumpet like flowers appear early spring into mid-summer. Evergreen leaves are circular. Favorite cultivars: ‘Major Wheeler’ (orange-red flowers) and ‘John Clayton’ (yellow flowers).

Virginia Creeper (Parthenocissus quinquefolia) grows 6-8 feet long and is frequently seen growing up trees. Its deciduous foliage turn beet red in the fall. Blue-black berries form in late summer and quickly consumed by birds. Warning: aggressive grower and seeds freely.

American Wisteria (Wisteria frutescens) grows a lot less aggressive compared to its Asian counterparts in in sun or partial shade. Train it up a 15-20 foot pole or tree trunk; blooms are blue or purple in mid-spring. Favorite cultivar: ‘Amethyst Falls’ (lavender purple).

Passion Flower (Passiflora incarnata) is a hardy fast grower vine, up 12 feet in length that climbs by tendrils. Its unique 2-3 inch wide flowers are white with purple filaments. Grows in full sun to partial shade, dies back in winter, and restarts in spring. Warning: roots may spread aggressively and become weedy.

Passionflower Vine

Posted by Hugh on June 7th, 2022

Passionflower (Passiflora incarnata) is a fast-growing, trailing vine that climbs via axillary tendrils. It is woody where winter climes are warm. In zone 5, the foliage dies back to the ground in cold winters. This summer-flowering vine is native to the southeastern U.S. where you see it growing habitat in sandy soils along stream banks, roadsides, woodland edges, meadows, and pastures. It thrives in moist loamy soil in partial to full sun.

Maypop is a common name for this vine, relating to the loud popping sound made when the ripened tan colored fruits are stepped on. Under optimum growing conditions the vine spreads from root suckers and may cover large ground areas. The vine does not have to climb in order to produce flowers. If a bushy growth habit is desired, pinch the vines monthly.

The uniquely pretty flowers and edible fruits should attract curious children to an arbor, pergola, trellis, fence, or wall where the vines can be enjoyed.
Vines are moderately resistant to damage from deer.

Passionflower vine features three-lobed, dark green leaves and showy, 2.5″ diameter, fringed flowers having white petals and sepals and a central crown of pinkish-purple filaments. In fall, ripened maypops can be eaten off the vine or made into jelly.

No serious insect or disease problems trouble this native vine. Bumblebees, selected butterflies and moths, and hummingbirds are attracted to blooms.
Established vines are drought tolerant, but an organic mulch keeps roots cool and moist. Roots can spread aggressively and in poorly drained soils root rot can occur, especially in the winter. Heavy fertilizing leads to vigorous growth. Prune back vines back in late winter before leaf out.

Fire Risk: This plant has an extreme flammability rating and should not be planted on a trellis or pergola close to your home.

Summer Blooming Golden Raintree

Posted by Hugh on June 1st, 2022

Golden raintree (Koelreuteria paniculata)is a medium sized deciduous tree that grows 30 to 45 feet tall and 25-35 feet wide, a horizontally branched tree Zones 5-9). This tree has a medium to fast growth rate, blooms at an early age with upright twigs with yellow flowers, a rare color among flowering trees whenever the time of year. The bright star-like flowers sparkle for almost two-weeks long in early July (Tennessee/Virginia).

The tightly closed papery fruits are highly decorative and often included in dried floral arrangements. Its papery lantern-like fruits contain viable seeds that dehisce (explode) from the husks in late autumn.

Golden raintree tolerates a range of soil types but prefers moist, well-drained soil that is neutral to slightly alkaline. Raintree transplants easy and prefers full sun. The wide spreading branched tree is commonly planted in lawns and patios or as park, shade or street trees.

Identification features: Leaves are pinnate or bipinnate, feathery, compound leaves (to 18″ long), each leaf having 7-17 irregularly deeply lobed leaflets. Leaves emerge pinkish bronze to purplish in spring, mature to a bright green in summer and turn yellow (quality variable) in fall. Bright yellow flowers (1/2″ wide) appear in early summer in long, terminal, panicles (12-15″). Falling blossoms from several raintrees may lay down an attractive golden carpet around the trees. Stems also have prominent, shield-shaped leaf scars.

This great summer flowering tree tolerates summer heat and drought as well as urban air pollution. It is mildly resistant to deer injury and is pest and disease free. Sometimes suffers from coral spot fungus, root rot, and cankers. Branches are rated as brittle wood and may be damaged in seasonal storms. Golden raintree reseeds easily and can become weedy; listed as an invasive species in some states.

Cultivars: ‘Fastigiata’ has a narrow upright habit, 30 feet tall and 6 feet wide framework. ‘September’ blooms later in August-September and is not rated as cold hardy as species.

Cinnamon Clethra

Posted by Hugh on May 27th, 2022

*Clethra barbinervis* growing at the High Line in NYC

Japanese clethra (Clethra barbinervis) is a large, upright, deciduous shrub or small tree (USDA 5-8). As a small tree it generally grows 10-20 feet tall and features horizontally drooping, terminal racemes (4-6 inches long); the white flowers are pleasantly fragrant. Its bloom period continues over several weeks from mid to late summer. In autumn, its blemish-free, glossy, dark green foliage turns brightly yellow, sometimes taking on reddish tones.

This Asian clethra is larger in all respects than our native sweet pepperbush (Clethra alnifolia). As a multi-branched shrub, it typically grows 8 to 12 feet tall. In early summer, the small ivory flowers appear and later give way to peppercorn-shaped seed capsules borne on the branch tips in fall. The dark brown seed capsules persist through winter.

By mid-autumn the bark begins peeling off in small, irregular patches to expose a cinnamon inner-bark. It is often nicknamed “cinnamon clethra”. It is the plant’s most striking feature. As the tree ages, its polished exfoliating cinnamon bark stands out against newly fallen snow.

Clethras grow in average, medium to wet, well-drained soil in full sun to part shade. Shrubs prefer partial shade and moist, humus-rich, slightly acidic soils. In northerly climes (zone 5), the Asian form should be grown in locations protected from harsh wintry winds and where it may not be reliably hardy.

Cinnamon clethra is a good choice for a woodland garden. Flower spikes are less fragrant than those of C. alnifolia, but attract butterflies and bees. No serious insect or disease problems trouble this tough multi-branched shrub or small tree.

Japanese clethra is rarely sold by local garden centers but is available from on-line specialty nurseries.