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

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.

Adding Compact Summer Flowering Shrubs

Posted by Hugh on May 24th, 2022

Yes, to reduce annual garden maintenance some gardeners are switching to space-saving flowering shrubs. Patio gardeners are popping compact shrubs into containers such as spireas, hydrangeas, crape myrtles, chaste tree, weigelias, and buddleias. They’re looking to add color and reduce their maintenance workload.

Numerous new [rose] varieties have been created that are relatively resistant to the defoliating fungus disease black spot that allows them to grow and flower non-stop for several months. They’re indeed easy to care for and highly fragrant.

Roses have changed so much over the past quarter century. More buyers are opting for the easy growing species roses such as Brindabella™, Oso Easy® and Flower Carpet® series, ‘Ringo’, ‘At Last’, and lots more. Many are very fragrant.

Many panicle hydrangeas (Hydrangea paniculata) bloom in July and, color-wise, the blossoms age gracefully, beautiful over two plus months. Best in the group are: ‘Bobo’, ‘Little Quickfire’, and reblooming H. serrata ‘Tuff Stuff’ and hybrid ‘Arriba’.

Dwarf chaste tree (Vitex agnus-castus) are now available in shorter forms. Breeders are just starting to work on these plants. Blue Diddley® and Blue Puffball™ are currently available and more are coming. Both varieties grow only 3-4 feet tall and 4-5 feet wide, a mound-shaped plant with deep blue, fragrant flowers from June to August. Flowers form on new growth. In colder climates dwarf forms can be used as a perennial or dieback shrub and emerge with new fresh growth in the spring.

Butterfly bush (Buddleia) have changed so much. I am in love with the Lo and Behold® and Pugster® series from PW and Walters Gardens’ Cascade series. The flower panicles are enormous at 12-14″ long and 4″ thick. The flower panicles continue to sprout new shoots until the cool fall weather arrives.

Vitex ‘ Blue Diddley’ (Photo courtesy of PW)

Whale’s Tongue Agave

Posted by Hugh on May 21st, 2022

Whale’s Tongue Agave

Over the past 10-15 years, interest in growing agaves has really caught fire, whale’s tongue agave (Agave ovatifolia) in particular. It grows to 3 to 4 feet tall and 4 to 6 feet wide in 5 to 8 years, especially with summer water. Like many agaves, whale’s tongue blooms after 15-20 years, and the main crown dies after blooming.

Whale’s tongue agave has distinguishing blue leaves, arranged in a spiral rosette. Leaves are cupped and can vary from long and narrow (24 inches x 8 inches) to short and broad (18 inches x 10 inches). The grand undulating leaves are lined with dark brown curved teeth measuring one-quarter to one-half inch in depth and end in a terminal 1- to 2-inch spine.

Whale’s tongue blooms only once. Sometime between 10 to 20 years, Whales’s tongue ends its life with a spectacular floral show. A multi-branched flower stalk arises 10 to 15 feet high with densely clustered chartreuse flowers. The resulting seed pods develop and mature before frost. Thereafter, the entire plant dies. Unlike most agaves, whale’s tongue does not produce offsets (pups).

Flowering Stage: whale’s tongue agave at Dallas Arboretum

Site selection is highly important. Agaves are exceptionally drought tolerant and suitable for xeric gardens. Whale’s tongue agave looks awesome in mass plantings. Agaves possess a large tap root and do not transplant well. The majority of the roots are surface roots and do not require a deep hole at planting.

Never overwater agaves! In fact, agaves perform best in high porosity soil. Agaves are highly drought tolerant and soil drainage, either in the ground or a container. They grow happily in soil with average to low fertility and in full sun to dappled shade. In a ground bed plant on a slope in soil generously amend to soil with crushed gravel, gritty sand or chit.

Agave hardiness is the most important concern (USDA hardiness zones 7-11) and in a protected area of zone 6b. When planting in clay soils, deeply amend bed or container soil with coarse sand or pea gravel in a 50:50 ratio. In early spring apply a slow-release fertilizer.

Two clones are available from tissue culture: ‘Frosty Blue’ (gray to powdery blue leaves) and ‘Vanzie’ (soft blue-gray leaves). Seed produced agaves vary in plant color, shape and size.

Caveats: keep plant(s) away from heavily trafficked areas. Agaves have dangerously sharp vicious spines; humans and pets need to be kept apart. Agaves attract birds, hummingbirds, and are deer resistant.

Silk Tassel Sedge

Posted by Hugh on May 17th, 2022

‘Silk Tassel’ Japanese sedge is an outstanding Japanese sedge cultivar of Carex morrowii temnolepis. It is ornamentally grown in shade areas for its narrow (1/8 inch wide) variegated foliage (USDA hardiness zones 5 to 9). This dense, grass-like clump grows 12 inches high and 1 to 1 ½ feet spread.

‘Silk Tassel’ sedge on The Ohio State Test Garden in Columbus, OH

Let’s start with an old well-worn adage — “sedges have edges”. ‘Silk Tassel’ has ultra-narrow leaves, that weeps as a fountain of fine-textured foliage. In mid-spring greenish-brown flower spikes arise atop triangular stems and are of no consequence. This sedge is evergreen in the deep South, holding its attractive foliage in summer, fall and much of winter.

Silk Tassel was introduced and named by Barry Yinger who brought it from Japan. The 18-inch-wide clump is deer-resistant and shimmers in the winter garden. ‘Silk Tassel’ lights up the woodland garden either utilized in a mass planting or several individual specimens spaced around a garden pond.

Silk Tassel tolerates moderate sunlight if the garden soil starts out humus-rich and is mulched in summer; otherwise, plant in partial to full shade. Foliage hues are cooler under shady conditions and appear washed-out in partial sun. Soils should not be permitted to dry out. Plants generally dislike hot and humid summers. In the northern part of its range, crop foliage down to the ground in late winter.

No serious insect, occasionally aphids, and diseases trouble sedges and, to repeat, deer tend to leave sedges alone

Group or mass as a ground cover in shade areas such as along paths and borders in woodland gardens. Also, an appropriate choice for low areas that may flood for short 1–2-day periods like low spots and stream/pond edges.

Annual growth rate is slow. Don’t wish to wait…buy in 1 or 2-gallon sizes to fill-in the planting more rapidly. Keep the media evenly moist. Avoid overwatering. Fertilize using a slow release, low-rate fertilizer.

Silk Tassel is a super companion accent plant added to containers on decks and patios and gardens. Use as a “spiller” in decorative containers next to hostas, coral bells (heuchera) and other bold-leafy plants.