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

‘Summer Snowflake’ Viburnum

Posted by Hugh on September 18th, 2014

‘Summer Snowflake’ viburnum at UT Gardens in Knoxville, TN in mid-September

Autumn may be coming or has arrived, but spring-flowering ‘Summer Snowflake’, a selection of doublefile viburnum (Viburnum plicatum var. tomentosum) continues to bloom. Native to Japan, doublefile viburnums are in a league of their own. Summer Snowflake grows 15 to 18 feet tall and a narrow 6 to 9 feet width or roughly 2:1 height to width.

Floral clusters of layered white flowers rest on the horizontal branches. Days later, prominently veined green leaves begin to emerge. Blooming is showiest, at its best around the end of April (in east Tennessee), nearly a week after flowering dogwoods (Cornus florida) have finished. Single snowy white flowers measure the size of a quarter, and each flat cyme averages 4 inches across.

Summer Snowflake is uniquely different because its branching tends to be upright and its repeat blooming. The spring bloom cycle is very showy. Secondary flowering extends almost 3 seasons. Bright red berries follow in late summer and fall, and rusty red fall color completes the season. Leaves are prominently veined. Birds quickly devour the small crop of berries.

Summer Snowflake viburnum is at its best in full sun and in a rich loamy well-drained soil. It fares well in partial sun (4 hours minimum sunlight). Shrub exhibits good drought tolerance within 2 years after planting, but repeat blooming declines if summer is exceptionally dry. Disease and insect problems are generally minimal unless shrub becomes environmentally stressed.

Summer Snowflake may be grown as a large specimen shrub or group several together for an informal hedge or screen. It rarely needs pruning except to control shrub size and form.

Sparse fruit load on doublefile viburnum

Autumn/Winter Garden Dressup

Posted by Hugh on September 15th, 2014

Silvery artichoke at Dallas Arboretum

Ornamental cabbage & kale at Dallas Arboretum

It’s fall and many gardeners take leave of their garden until spring. Autumn is a great time to create new color schemes that will carry over into the winter garden. It’s just like spring all over again! Frost hardy flowering plants get their turn, such as pansies, violas, snapdragons, and diascias (USDA Hardiness zone 7), a recent addition to this list. Plant them in containers or in ground beds.

Tough winter foliage plants such as Swiss chard, giant red mustard, bull’s blood beets, artichoke, and ornamental cabbage or kale are great garden companions. Add fragrant evergreen herbs around a porch, deck or patio areas such as rosemary, lavender, sage and thyme.

Design with in fall/winter plants in containers or garden beds. A good container assortment contains various plant forms and leaf colors. Spiky narrow evergreen shrubs such as ‘Green Arrow’ Alaskan cedar (Chamaecyparis nootkatensis), ‘DeGroot Spire’ arborvitae (Thuja occidentalis), ‘Sky Pencil’ holly (Ilex crenata), or ‘Dee Runk’ boxwood (Buxus sempervirens) add height to a bed or container design.

Weeping and spreading evergreens make colorful “spillers” such as yellow needled ‘All Gold’ juniper (J. conferta ‘All Gold’), winter bronze-leaf Russian arborvitae (Microbiota decussata), or green needled Prostrata plum yew (Cephalotaxus harringtonia ‘Prostrata’).

To insure winter survival, blanket the soil with 2 to 3 inches of organic mulch for root insulation and to conserve soil moisture. Prune off dead blooms and unsightly foliage. Flowering annuals, particularly pansies and violas, benefit from bi-monthly feeding with 10-10-10 or equivalent fertilizer or monthly watering incorporating water-soluble Miracle-Gro™, Jack’s™, or Daniels™.

Fall Blooming ‘October Skies’ Aster

Posted by Hugh on September 12th, 2014

‘October Skies’ aster (Photo by Andrea Sessions, Sunlight Gardens, Inc., Andersonville, TN

From Maine to Texas, the aromatic asters (Symphyotrichum (Aster) oblongifolius) are great garden performers in the fall garden (USDA hardiness zones 5–8). The cultivar ‘October Skies’ is one of the best. Plants are covered with lavender blue flowers (up to 1 ¼ inches in diameter) from late September thru late October. Each flower displays a gold button center. Its grey-green foliage smells minty when crushed.

With a low mounding habit these compact asters grow to 18 – 24 inches in height and spread and rarely require pinching. It is shorter and bushier and bluer (flowers) than sister seedling ‘Raydon’s Favorite’. Plant is a vigorous grower with sturdy stems that stand up well when covered with blooms.

October Skies, along with other aromatic asters, excels in full sun. It prefers a moist well-drained, organically rich soil, but adapts to average dry sites. Spring-planted aromatic asters establish quickly and develop good heat and drought tolerance by mid-summer. Asters do benefit to mulching and feeding at planting and once a year in the spring. Asters attract numerous pollinators, particularly many species of butterflies. Deer usually turn their noses up on aromatic asters.

October Skies ranks as one of the easiest to-grow perennials. As a rule, aromatic asters are highly disease and pest resistant. Plants can be cut back in late fall after flowering.

Kingwood Center In Mansfield, Ohio

Posted by Hugh on September 10th, 2014

Mall area leading up to Kingwood Gardens Office and Library

Floral Display at Kingwood

Over the years Kingwood Center in Mansfield, Ohio (60 miles north of Columbus) has been a popular public gardens to visit. Formerly the home of Charles King, the 47 acre former estate garden has been open to the public since 1953. The former King home now houses Kingwood’s administrative offices and horticultural library.

Kingwood is not an enormous property, but is beautifully laid out and cared for. The talented garden staff creates lasting memories through floral displays. Kingwood is blessed with outstanding collections of hostas (Hosta) and daylilies (Hemerocallis). A formal rose garden displays the newest AARS winners from the American Rose Society. The newly redesigned herb garden (we called it the “Peter Rabbit garden”) offers visitors lots of take-home ideas.

Enter the Greenhouse Conservatory and move from house to house viewing tropical, temperate, and desert plants from around the world. In the rear of the greenhouse is fabulous selection of plants for sale; several gems have found a place in the Conlon garden. Displays of flowering annuals are always well-done, best viewed after summer’s heat has pushed the gardens to their peak from early July to autumn frost. Most annuals and perennial varieties are labeled. Past blog readers have seen many photos from Kingwood Center.

Kingwood’s showcase garden is a formal allee’ of shrubbery and hostas edged with colorful annuals. Displays change every summer with colorful begonias, coleus, geraniums, etal. On one side of the manicured grassy mall is a glorious bubbling fountain and on the other end is Kingwood’s offices and horticultural library.

Walk among the majestic trees and shrubs at Kingwood. Ten of my favorites include: bald cypress (Taxodium), dawn redwood (Metasequoia), Amur corktree, Lawson cypress, coffeetree, silver linden (Tilia tomentosa), Alaskan cedar, Japanese stewartia (S. pseudocamellia), red horsechestnut, and a fabulous collection of crabapples (Malus).

A large pond with lots of ducks (and optional feeding stations) delights visitors, young and old as do the peacocks which have full run of the grounds.

Some mid-Ohio craft groups, such as quilt and lapidary (rocks and gems) societies call Kingwood home. On selected summer weekends, members display and sell their handiwork, including artistic crafts and gems.

Location: 900 Park Avenue West, Mansfield, Ohio 44906 • 419-522-0211. Admission fee: $5.00 (non-members).

Wingstem Common Along Roadsides In Late Summer

Posted by Hugh on September 6th, 2014

Wingstem (Verbesina alternifolia ) in northeast Tennessee

Ridged stem of wingstem

In late summer several wildflowers, golden rods (Solidago spp.)and ironweeds (Vernonia spp.) to name two, start blooming along many Midwestern and Eastern U.S. roadsides. Wingstems (Verbesina alternifolia) are another 4-8 feet tall native perennial wildflower that grows nearby (USDA hardiness zones 4-7). Many people ask what they are.

Sturdy stems, mostly unbranched, stand tall and are topped by panicles of bright yellow flowers. Raised ridges (called wings) line the stem; this feature makes it easy to identify. Numerous white hairs cover the stems. At first sighting the lower leaves in late spring are ovate-shaped and arranged opposite along the stem. Summer leaves are alternate and lanceolate, 5 to 9 inches long and 2-3 inches wide, and are tapered at the base. Leaf surface is medium green and sandpapery in feel.

Starting in late summer the dome-shaped panicle flowers open. Blooming period lasts a month or more. Blooms, composed of both ray and small disc flowers, are 1-2 inches across. The ray blossoms are daisy-like and showier. Seeds quickly ripen in the fall and most drop to the ground or carried away by the wind.

Wingstem prefers moist organically-rich fertile soils and full sun, but can handle light shade. Habitats are usually adjacent to woodland areas or bodies of water, such as moist prairies, meadows, pastures, and roadside ditches. Lower leaves often shrivel and drop off when summers are exceptionally hot and dry.

Foliar diseases are rare unless plants are under weather stress. Nectar feeding bees, particularly bumblebees, butterflies, and moths frequent the flowers. Some caterpillars of the Silvery Checkerspot butterfly (Chlosyne nycteis) gnaw on the foliage, and caterpillars of the Gold Moth (Basilodes pepita) feed on the flowers and developing seeds. Deer, rabbits, and other herbivores usually bypass wingstems.

Wingstem, sometimes called “yellow ironweed” and purple-flowered ironweed are often observed growing together. Both plants bloom in very late summer, grow to similar heights, have similar foliage, and prefer moist sunny habitats. Root systems of both species are rhizomatous and tend to form vegetative colonies.

‘Tamukeyama’ Japanese Maple One Of The Best

Posted by Hugh on September 4th, 2014

Acer palmatum ‘Tamukeyama’ In Early Summer

Tamukeyama Japanese maple (Acer palmatum ‘Tamukeyama’) is a long-lived botanical treasure (USDA hardiness zones 5-8). Tamukeyama is a short 6-8 feet tall multi-stemmed deciduous tree. It grows slightly taller and its foliage tolerates hot summer sun better than ‘Crimson Queen’.

Tamukeyama grows best in full sun to partial shade. It prefers moist well-drained soil and shouldn’t be allowed to dry out. It is not particular as to soil pH, but performs best in compost-rich soil. Don’t plant on a hot dry site and protect from strong winds.

Its lovely cascading branches spread 12 or more feet wide. The finely dissected palmate leaves are 2-4 inches with 5 to 7, sometimes 9 lobes or points. Foliage color changes with the season and may scorch in southerly climes in full sun (zones 7b -8). In mid-spring small reddish-purple flowers open. Pairs of winged samaras ripen in September-October.

In the spring deeply-cut fine palmate leaves emerge crimson red, loses much of its deep burgundy color over the summer, and finishes bright red in mid-fall. Its gray (with reddish tints) bark and thin wiry cascading branches are impressive winter features.

When properly sited, Tamukeyama is rarely troubled by diseases or pests. Stem cankers and leaf spots are problems when soils are arid in a summer drought. Verticillium wilt may also occur on poor sites. In most springs Tamukeyama tends to avoid frost problems by leafing out 7-10 days later than many other cultivars.

If you worry about growing Japanese maples, Tamukeyama is a good reliable cultivar to select. It is very low maintenance. Summer is the best season to prune Japanese maples to prevent bleeding sap, a common malady observed in trees pruned in late winter or early spring.

Swamp White Oak Gaining In Popularity

Posted by Hugh on September 1st, 2014

Young Swamp White Oaks in Pittsburgh

Exfoliating trunk on Swamp White Oak

Swamp white oak (Quercus bicolor) is an underutilized large native oak whose ornamental attributes have captured the attention of municipal arborists (and perhaps you as well). (USDA hardiness zones 4 to 8). Swamp white oak is a medium to large sized deciduous shade tree, 50 to 60 feet tall and wide, and a broad, irregularly shaped canopy. Compared to some oak species, its growth rate is moderate, 12-15 inches annually. Larger specimens over 70 feet tall exist but are not common.

As its common name indicates, this native oak is indigenous to moist to swampy locations in bottomlands and lowlands, along streams and lakes, on floodplains, and on the edge of swamps. It is not fussy growing in average soil, dry, medium or wet, and moderately acidic (4.5 – 6.5), and in full sun. Established trees turn out to exhibit good drought resistance and are long-lived. Tree is widely adaptable to adverse soil conditions such as periodic flooding or prolonged drought. Yellowing of the foliage in the summer (chlorosis) may occur when the soil is not acidic enough. Additions of chelated iron to the soil will correct the problem over a few years.

Leaves are 3 to 7 inch long with 3-7 pairs of rounded lobes and very short petioles. Its deep green summer foliage color holds late into fall, turning russet-brown in early winter before abscising. Young trees tend to hold their leaves into the early winter. In mid-spring strings of male and female catkins flowers emerge and hang from branch tips shortly before leaves emerge.

Acorn fruits are sweet and can be eaten right off the tree; they’re an important food source for many forms of wildlife. Young trees show off a pale gray bark that exfoliates; older mature trees exhibit a sturdy furrowed bark of winter interest to some who love the outdoors.
Swamp white oak is a member of the white oak group along with white oak (Q. alba), bur oak (Q. macrocarpa), Chinkapin oak (Q. muhlenbergii), English oak (Q. robur), and post oak (Q. stellata). This group is identified by their rounded (not pointed) leaf lobes and acorns that mature in one growing season.

Swamp white oak is susceptible to numerous diseases and pest problems, including anthracnose, cankers, leaf spots, rusts, galls, caterpillars, borers, leaf miners, lace bugs, and mites. Most occur in late summer and are of little consequence.

A balled and burlap (b&b) tree should best planted from late winter through spring. Swamp white oak has no cultivars to select from, but hybrid forms do exist. In recent years many urban communities have been planting swamp white oak in parks, golf courses, and in large commercial and residential properties.

Swamp Milkweed Is Monarch Butterfly’s Favorite

Posted by Hugh on August 29th, 2014

Swamp Milkweed at Chicago Botanical Gardens

Swamp milkweed (Asclepias incarnata) is an erect, clump-forming, U.S. native plant indigenous to swamps, bottomlands and wet meadows (USDA hardiness zones 3 to 6). Obviously, it prefers moist soils but grows equally well in average, well-drained garden soils. Full sun is best, but copes with some light shade.

As its common name indicates, it makes a great choice for planting in moist spots such as in rain gardens and along stream/pond banks. No butterfly garden is complete without swamp milkweed. The flowers of swamp milkweed attract several species of butterflies including Monarchs. Monarch larvae (caterpillars) prefer swamp milkweed foliage for a nourishing food source over butterfly weed (A. tuberosa).

New plants emerge slowly in late spring. It develops a deep tap rootsystem which is best left undisturbed once established. Swamp milkweed grows 3 to 4 feet tall (sometimes to 5 feet) and 2 to 3 feet wide on branching stems. Narrow, willow-like leaves are 3-6 inches long with a tapered point. Stems exude a toxic milky sap when cut.

The clustered flowers are very attractive and fragrant. Small individual ¼-inch wide blooms are a pink to light lavender color; tight clusters (umbels) of five reflexed petals sit atop tall stems in July and/or August. Flowers are followed by attractive 2-4 inch long seed pods.

Swamp milkweed is short-lived, often 2-3 years, but it frequently re-seeds itself. In the fall the mature pods split open to release silky-haired seeds that are carried away on a blustery autumn day.

Swamp milkweed has no serious insect or disease problems. Aphids may be a significant pest. Deer generally leave milkweeds (Asclepias spp.) alone.

English Oak Demands A Moist Well-drained Soil

Posted by Hugh on August 27th, 2014

Leaves of Quercus robur ‘Skyrocket’

Thinking about English oak (Quercus robur) brings to mind Robin Hood and Sherwood Forest. This majestic oak forms a broad spreading crown supported by a short sturdy trunk with a medium-brown, deeply-fissured bark (USDA hardiness zones 4-8). A young tree exhibits a pyramidal form. In a city park or golf course, it typically grows 50-70 feet tall and 40-50 feet spread. Wild specimens across Europe have been measured over 100 feet tall and hundreds of years old.

English oak has small 3-5 inch long deciduous leaves with 3-7 pairs of rounded lobes and very short petioles. Its deep green foliage color holds long into the fall before turning brown and persisting on the tree most of the winter. In early spring strings of hanging catkins flowers emerge shortly before the leaves.

English oak is a member of the “white oak group”. Its rounded leaf lobes appear similar to white oak (Q. alba), a U.S. native which has ear-like basal lobes and very short petioles. Small 1-inch oval acorns form in the fall. English oak may take up to 25-30 years to bear its first crop of acorns that are an important source of food for wildlife. Acorns (nuts) are edible after poisonous tannins are boiled or leached out. Keep acorns away from grazing animals (horses, cattle, etc.).

English oak wants full sun and a moist well-drained, acidic or alkaline (pH 5.8-7.5) soil. This oak does not tolerate extended droughts. A balled and burlap (b&b) tree should best planted from late winter through spring. Young trees tend to grow slowly – 12 to 15 inches annually. Few disease and pest problems trouble it. In some years aphids, several species of caterpillars, and leaf miners feed on the leaves, rarely damaging the tree. Powdery mildew can become serious in hot, humid climates such as in the Midwest and Southeastern U.S.

There are many selections of English oak, as well as hybrids with other oak species.’Skyrocket’ has erect branches and a narrow pyramidal form. ‘Pendula’ has a weeping habit. ‘Crimschmidt’ (Crimson Spire™), a hybrid between English oak and white oak, exhibits a fastigiate habit and leaves turn reddish in autumn.

English oak is native to Europe, western Asia and northern Africa. It is widely planted across Europe, Canada, and the northeastern U.S. as a landscape shade tree and as a tall privacy hedge. For centuries its hard wood has been utilized in the construction of sailing ships.

Mexican Sunflowers Thrive In A Hot Summer

Posted by Hugh on August 24th, 2014

Tithonia + swallowtail (photo by Joy Stewart, Bristol, TN

Mexican sunflower (Tithonia rotundiloba) is a fast growing annual that produces vivid orange-red zinnia-like flowers from early summer to autumn frost. It is native to Mexico and Central America. Dark green leaves remain blemish-free all summer long. Snails and slugs are occasional pests during wet summers or when irrigated overhead.

Plants grow 3-4 feet tall and 2 feet wide by the end of summer, and may reach 5-6 feet high. Its brightly colored summer flowers are supported on strong stemmed plants. Blooms make excellent cutflowers.

As its name hints, Mexican sunflower (tithonia) thrives in hot sunny location and languishes where summer is relatively cool. In the spring do not rush to plant; wait until all dangers of frost has past in your area. Plant in well-drained, moderately fertile soil. Mulch and feed the flower bed with a slow release fertilizer such as Osmocote™ or Nutricote™ at planting time. Staking may be needed if set in a part sun and/or windy location. Those growing in containers may also need some support.

Flowers are butterfly magnets, particularly swallowtails. Monarchs, bees, hummingbirds, and other pollinators visit the blooms for nectar. Generally, deer leave tithonia alone.

Leading cultivars include old-time favorite ‘Fiesta Del Sol’ and ‘Torch’ (series includes orange and yellow cultivars). Established plants, usually after 6-8 weeks in the garden, demonstrate exceptional drought resistance.