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

Colorful ‘Sugar Tip’ Althea ( Rose Of Sharon)

Posted by Hugh on July 15th, 2018

Hibiscus syriacus ‘Sugar Tip’ In mid-June in UT Gardens, Knoxville, TN

Lightly variegated foliage

Rose of Sharon or shrub althea (Hibiscus syriacus) is a vigorous, upright, multi-branched, deciduous shrub that generally grows 8-12 feet tall and 4-6 feet wide. Althea is native from eastern to central Asia (USDA hardiness zones 5-8).

Sugar Tip® is a patented variety that features variegated creamy-white and blue-green foliage and soft pink double flowers. Leaf variegation is its unique trait. It produces smallish pale-colored double flowers that do not garner as much notice as the large single flowered varieties.

The 5-petaled double flowers, up to 3 inches across, appear over a long, early-summer to fall bloom period. The pink double flowers have prominent floral stamens in center. Flowers are mostly sterile, resulting in no weedy seedlings to pop up around your property.

Altheas tend to leaf out in late spring. The 3-4 inch long, 3-lobed, medium green leaves are palmately-veined. The blemish-free variegated foliage remains attractive from late spring through mid-autumn. Fall foliage color is inconsequential.

Flowers

Altheas are easily grown in average, moist, well-drained, moderately acidic soils and in full to partial sun. Under partial shade altheas bloom less and can become weak wooded, and more prone to disease issues. Best flowering occurs in full sun. This shrub is highly summer heat and humidity tolerant. Altheas are frequently seen planted in downtown urban congested areas.

Altheas bloom on new wood, so pruning is performed in late winter or spring. Heavy pruning results in less blooms which are much larger in size. Altheas are easily propagated by softwood stem cuttings collected in late spring. Sugar Tip may be trained as a small tree or espaliered.

No serious insect or disease problems trouble this tough hardy shrub. Occasionally, leaf spots, blights, rusts and cankers may appear if site location is poor. Japanese beetles, whiteflies and aphids are occasional insect feeders. In some years Japanese beetles may severely damage foliage when left unchecked.

As with most shrub altheas, they serve as superior summer flowering shrubs. Plant single specimen shrub or tree; mass several together as foundation or border shrubs, or as a deciduous privacy hedge or screen.

Fill Summer Flower Beds With Annual Rudbeckias

Posted by Hugh on July 10th, 2018

Rudbeckia hirta ‘Tiger Eyes’ at NC Arboretum in Asheville

‘Indian Summer’ rudbeckia in Pittsburgh, PA

Black-eyed Susan (Rudbeckia hirta) is a native wildflower. Annual or biennial forms are also called gloriosa daisy and brown-eyed Susan. In recent years public urban gardens are growing annual types. From summer into early autumn, brown-eyed Susans produce showy daisy-like blossoms up to 3-inches across with light or deep yellow rays and brownish-purple centers (“buttons”). Their cut flowers will decorate households.

This coarse weedy plant has undergone a breeding improvements. Today’s varieties bloom most of the summer and with disease-resistant leaves. Colorful ray flowers are available in shades of red, yellow, bronze, orange and bi-colors. They bloom non-stop through the summer atop sturdy upright stems. Plant heights vary by cultivar from 1-3 feet high. Rough, hairy, lance-shaped leaves are 3-7 inches long.

This biennial or short-lived perennial is winter hardy to USDA Zones 3-7. It blooms the first year from seed set out in early spring. It grows in average, moist, well-drained soils and in full sun. Brown-eyed Susan is at its finest in moist, compost-rich soils. For maximum bloom time, start seed indoors in late February or the beginning of March. Garden centers sell them in cell/six packs. Set out seedlings or purchased plants after the last frost date has passed. At planting time feed the flower bed with a granulated fertilizer such as 10-10-10 or or equivalent plus a secondary feeding in early summer. Deadhead spend flowers to encourage lateral branching and additional bloom. Removing old spent flowers also prevents self-seeding.

Most disease and pest problems may be avoided if properly sited and care for. In some years aphids, rust, powdery mildew, and septoria leaf spots may trouble these annuals. Watch for slugs and snails on young plants.

At Atlanta Botanical Gardens

Five popular annual rudbeckia cultivars

Cherry Brandy – cherry-red ray flowers

Prairie Sun – orange to lemon yellow petal with green button cone

Rustic Dwarfs – shorter form in a mix of flowers from yellow to rich mahogany

Tiger Eyes – golden yellow ray flowers; improved powdery mildew resistance

Toto – dwarf, compact plants and golden-yellow blooms

Heat Loving Annuals For Containers

Posted by Hugh on July 6th, 2018

Angelface’Blue Iimproved’ (photo from PW)

Ipomoea batatas ‘Cameo’

Not all annuals grow well in containers. An aggressively growing annual may not be a suitable companion plant in containers. Small containers dry out quickly. Large containers, a minimum of 16 inches across, should be your beginner size. For an eye-catching container garden, utilize plants that require the same care but differ in colors, heights, and textures.

I’ve selected a dozen annuals (list below) that beat the heat. They must stay hydrated (watered) and container size is of importance here. Group a variety of annuals that are compatible with one another. One does not outgrow another and they like to same diet that includes water plus fertilizer. Usually in spring, give them a drink every other day. Your container will likely need watering everyday or 3-4 days a week. To know for sure, poke a finger an inch or two into the soil (potting media).

If you rely on rain to water your plants, much of the precipitation will repel off the leaves and fall away, rather than moisten the soil. Don’t trust that rain is supply your plants during the growing season. Hand watering with a hose will do a better job.

To ensure that your annuals bloom all season, deadhead spent blooms that look wilted or dead. Provide a clean fresh appearance of new blooms all summer long. Fertilize at planting time using a slow release product such as Osmocote™ or Nutricote™ according to the label directions. By mid-summer plant nutrition is exhausted. Apply water soluble fertilizers such as Miracle-Gro™, Schultz™, or Peters™.

A Dozen Summer Heat And Humidity Tolerant Annuals

Globe amaranth at NC Arboretum

Persian Shield (Strobilantes)

Globe amaranth (Gomphrena)

Egyptian star flowers (Pentas)

Fanflower (Scaevola)

Marigold (Tagetes)

Mexican sunflower (Tithonia)

Summer snapdragon (Angelonia)

Setcreasa pallida ‘Purple Heart’

Lantana

Dichondra

Euphorbia

Ornamental Sweet Potato (Ipomoea batatas)

Smaller Alternatives To Limelight® Panicle Hydrangea

Posted by Hugh on July 2nd, 2018

‘Limelight’ hydrangea at the NC Arboretum in Asheville, NC

‘Little Quick Fire’ hydrangea

Beautiful panicle hydrangeas (Hydrangea paniculata) are among the best hydrangea choices for the summer garden (USDA hardiness zones 3 to 8). Flowers of some cultivars age gracefully with floral heads turning lightly pink. They are perfect for use in containers or in groupings or masses, shrub borders, hedges, and screens. Panicle hydrangeas are suitable as fresh cut or dried flowers.

Limelight® hydrangea is the current standard-bearer among panicle hydrangeas with huge 6 – 8 (some to 12) inches chartreuse (off white) flower heads. Limelight grows more compact compared to the species @ 6 to 8 feet tall and wide. Its yellow fall leaf color generally does not stand out.

Plants grow from 3 – 10 feet high depending on the variety chosen. For best flowering grow panicle hydrangeas in full sun to light shade and in moist well-drained soil. Feed hydrangeas in early spring with a slow release fertilizer such as Osmocote™ or Nutrikote™. Keep hydrangeas mulched during the hot dry portion of spring and summer. Shrubs bloom on new wood in summer, and are pruned to desired size and shape in early spring.

For smaller landscapes, choose from any of these smaller cultivars:

Bobo® hydrangea – fluffy, creamy floral spikes, that turn to deep pink with red highlights, on sturdy red stems. Earlier blooming Bobo opens 1-2 weeks before many H. paniculata varieties start blooming. Bobo grow 3–5 feet tall, and is a good option in small gardens and growing in large containers.

Little Lime® hydrangea – dwarf version of Limelight® grows 5-6 feet tall and wide and boasts creamy florets that age to rosy pink.

Little Quick Fire® hydrangea – smaller version of Quick Fire® @ 3-5 feet tall and to 2-4 feet wide. It blooms early in upright panicles. Panicles emerge white, change to pink, and mature reddish-purple by late summer.

Little Lamb® hydrangea – downsized version of H. paniculata ‘Grandiflora’ @ 6-8 feet tall and wide. Dense, cone-shaped panicles of mostly sterile, small white flowers. Panicles stand upright on stiff sturdy stems. Smaller, fluffy, fertile florets lie beneath showier sterile florets.

Pest Alert – Giant Hogweed

Posted by Hugh on June 29th, 2018

Giant Hogweed (Virginia Tech photo)

Leaves (Univ of Connecticut photo)

Giant hogweed plant (Heracleum mantegazzianum) is a large, invasive plant that can cause severe burns, blisters and rashes and vision loss in humans. As its name suggests, giant hogweed plant is enormous growing invasive species that originated from the Caucasus region of Eurasia. It produces large, towering purple stalks of white flower clusters. Don’t pick these flowers! Contact from its clear watery sap from all parts of giant hogweed (leaves, roots, stems, flowers, and seeds of the plant) results in blisters and rashes in humans. These serious reactions are called “phytophotodermatitis”).

The plant has been found in Canada, Northwestern U.S, New England and mid-Atlantic states, and North Carolina. It is listed among the most serious of invasive weeds. The plant may grow upwards of 15 feet high. Giant hogweed sap contains several photo-sensitizing compounds. Initial symptoms of skin injury after plant contact may not appear for several days. Sap can also burn and blind your eyes.

The sap from leaves and stems may also sensitize the skin so that it becomes easily sunburned. Children should be kept away from giant hogweed, wear protective clothing, and practice eye safety. If the skin has been exposed, wash the affected area(s) thoroughly with soap and water; and protected the exposed skin from the sun for 48 hours. If a rash develops or if eyes come in contact with sap, consult with a medical professional.

Control Options

Non-Chemical

Non-chemical controls may not be practical for large, dense stands of giant hogweed. Control options are best initiated when plants are small in size, preferably under 5 feet tall. Prevent plants from setting seed by removing flower heads; the seeds may remain viable in the soil for a number of years.

These controls are most effective when preventing seedling growth or when used in combination with a chemical control.

Digging is the most effective non-chemical control.

Mowing – repeated cutting back to the ground level. Protect skin and eyes from vegetation thrown from grass and string mowers.

Grazing – cattle, sheep and other livestock, unaffected by hogweed sap, can help control giant hogweed.

Chemical control

Hire a landscape professional pesticide applicator to apply an herbicide. Glyphosate and triclopyr, two common pesticide ingredients in herbicides, are labelled for control. Read and follow all label directions. Repeated applications will be necessary. Some states have set up a HELP hotline for people who came into contact with the plant and urged residents to report sightings.

Three July Blooming Trees (Other Than Crapemyrtles)

Posted by Hugh on June 25th, 2018

Vitex agnus castus

Chaste Tree (Vitex agnus-castus) is a 10-15 feet tall, vase-shaped, deciduous shrub or a small 15-20 foot tree. The species is native from southern Europe and Asia. Often mistaken as a purple-flowering crapemyrtle, vitex is grown where wintry weather is not severe (USDA hardiness zones 6-9). Its palmately compound grayish-green leaves, composed of 5-7 lance-shaped leaflets, are aromatic if you rub. Airy panicles composed of tiny, fragrant, lavender to pale violet flowers (to 12″ long) appear in early to late summer. Blooms attract numerous bees and butterflies.

Sourwood (Oxydendrum)

Sourwood (Oxydendrum arboreum), aka lily of the valley tree, is a deciduous understory tree that is native to the eastern U.S. from Pennsylvania south to Florida and Louisiana (USDA hardiness zones 5-9). A member of the Heath plant family, which includes azaleas, rhododendrons, and mountain laurels, plants prefer an acidic soil. This native tree (or multi-branched shrub) grows 20-25 feet tall (50 feet or more in the wild). Finely-toothed, 5-8 inch long, glossy green leaves produce one of showiest red fall hues. Terminal 4-8 inch long panicles of white lily-of-the-valley flowers drape off branch tips in early summer. Flowers are slightly fragrant. Long-lasting dried flower panicles are present through September, and attract many many bees and sourwood honey is a tasty result.

Goldenrain Tree (Koelreuteria paniculata) is a medium-sized, open-branched, deciduous tree with a rounded crown (USDA hardiness zones 5-9). Native to China, it grows 30-40 feet tall and almost as wide. Its pinnate or bipinnate compound leaves, up to 18 inches across, are comprised of 7-17 irregularly lobed leaflets. The bright green, blemish -free summer foliage turns yellow in fall. Bright yellow flowers (each 1/2 inch wide) appear in early July as part of terminal 12-15 inch panicles. Flowers give way to brown lantern-like, papery seed capsules in fall. Caution: many seedlings may arise and become troublesome.

Goldenrain tree flower panicle

General care recommendations: all three trees prefer a moisture, mildly acidic, well-drained soil and full sun. Sourwood prefers a more acidic pH soil. Vitex is best planted in sheltered sites in zones 6. In colder zone 5 winters, vitex can be grown as a 3-5 foot herbaceous flowering perennial. New compact vitex shrub forms are coming to garden centers.

‘Herbstsonne’ Rudbeckias Fill Their Spot

Posted by Hugh on June 20th, 2018

Rudbeckia lacinata Herbstsonne’

Rudbeckia ‘Herbstonne’ at Biltmore Estates

For an old fashion plant ‘Herbstsonne’ (Rudbeckia laciniata) still pops up in many modern day gardens. It is a tall upright growing, clump-forming perennial black-eyed Susan (USDA hardiness zones 5 to 9). This vigorous North American perennial grows 4-7+ feet tall and 2-3 feet wide. ‘Herbstsonne’ is also synonymous with the cultivar ‘Autumn Sun’. Formerly cataloged as Rudbeckia nitida, many plant experts believe that it is a hybrid between the two species.

Large daisy-like flowers, 3-4 inches across, with drooping sulphur yellow rays petals stand out in the late summer – autumn landscape. Flower centers have elongated bright green long “nubbins” or cone centers. Flowers bloom singly atop slender branching stems. Bright green cutleaf leaves vary in size from 3-6 inches in length and are coarsely toothed. Flowers attract numerous butterflies and winter feeding birds relish their nutritious seeds.

Herbstonne prefers a rich, moist, well-drained soil and mostly full sun. This aggressive perennial tolerates hot and humid summers and exhibits above average drought resistant after its first year in the garden. Tall growing plants, particularly those grown in partially shaded areas, may require staking. Deadheading old spent flowers encourages additional re-bloom. Herbstonne (aka Autumn Sun) has no serious disease and pests and is deer proof.

Herbstonne spreads slowly by rhizomes. Propagate by seed, division or terminal cuttings. They’re outstanding for inclusion into mass plantings on large properties such as public parks, golf courses, and industrial sites. Include them in border plantings, meadows, prairies, and in rain and cutting gardens. In rain gardens plants cope in average soils and seasonal moisture extremes. Cut flowers will fill vases in your home and friends.

Personal note: Clumps of this aggressive growing rudbeckia are long-lived. I’ve fallen in love with old plantings near the conservatory at Biltmore Estates in Asheville, NC and at Chanticleer Gardens in Wayne, PA. Give ’em lots of room as plants eat up lots of garden space.

Stunningly Beautiful Three-Flowered Maple

Posted by Hugh on June 16th, 2018

Acer triflorum on NYC Hi-Line

Leaf color change in late October

Three flower maple (Acer triflorum), often called trifoliate maple, is native to eastern Asia (USDA hardiness zones 4-7). The latter pseudonym is misleading as A. triflorum is actually one of many compound-leafed maples identified as “trifoliate maples”. This small deciduous understory maple typically grows 2o-25 feet tall with a densely-branched, rounded crown. Specimens often grow to 35-40 feet in height range.

The tree’s outstanding features include its attractive shape, exfoliating tan brown bark, and fall leaf color. The young fully expanded spring leaves show off a fine pubescence. As autumn approaches, the medium green trifoliate leaves (leaflets to 3 inch long) take on vibrant shades of orange to red in autumn.

Tan brown bark exfoliates in vertical strips to reveal orange-brown inner bark. Greenish-yellow flowers appear in April in clusters of three, hence the species and common names. As with most maples, the flowers are not showy. Fruits are double winged samaras (1-1.25 inches long). Some individuals may confuse the tree with paperbark maple, Acer griseum, another beautiful trifoliate maple.

The tree grows in average, medium moist, mildly acidic (5.5-6.5 pH), well-drained soil and planted in full sun to part shade location. Keep in mind that three flowered maple is an understory species. In its southerly zone 7 range, full-day sunlight may be too harsh. Good soil fertility, moisture and drainage are keys to growing these small maple species.

A newly planted tree should be adequately irrigated the first two years after planting. Feed annually (in late winter or early spring) with a slow release fertilizer such as Osmocote® or Nutricote®. according to package directions. Maintain a 3-4 inch deep, weed-free, organic-mulched zone around the tree.

Disease and insect issues are rare if tree(s) are properly well cared for. Leaves may turn chlorotic (yellowed) if soil acidity climbs above 6.8 pH. In most years little annual pruning is necessary.

American Basswood Tree

Posted by Hugh on June 12th, 2018

Large American linden

Summer foliage and winged seed

American basswood (Tilia americana) is a common deciduous native tree in midwestern and eastern U.S. forests (USDA hardiness zones 2-11). This large majestic tree is remarkably fast-growing but not weak wooded. Basswood is planted as a large residential shade tree, street tree along wide avenues, or tall privacy screen. A mature specimen may grow 50 – 80 feet tall and 30 – 40 feet wide although individual trees 90 – 100 feet tall are not unusual. Basswood may be either single or multiple trunk.

Sweetly fragrant pale yellow flowers opened in June and attract numerous insects, including butterflies, nocturnal moths, bees and flies. Basswood honey is highly prized for its sweet honey. Early colonists knew to identify trees because where you saw basswoods, bee hives (and honey) were nearby.

The large, showy cream-colored bracts persist well into fall. Bobwhites, squirrels, chipmunks, and deer feed on the nutlets. Its large growth buds are very noticeable in late winter. Basswood’s dark green heart shaped leaves are large (to 6 inches long), serrated along the margin, and sharply pointed at the tip. Leaf undersides are silvery in spring and less so later in the summer.

Basswood grows in average, medium moisture, well-drained soils in full sun to part shade. Young trees are drought susceptible, but older established trees are highly drought tolerant. Generally, basswood is intolerant of air pollution and urban conditions.

No serious insect or disease problems trouble basswood trees. Aphid and lacebug feedings on leaf surfaces are evident by early summer; Japanese beetles may also mar foliage. Newly planted trees should be sprayed for 1-3 years, but after 3 years, the tree’s growth rate makes pesticide spraying unnecessary. Powdery mildew, leaf spots and stem cankers may occur but pesticide spraying is not practical. Spider mites can also cause significant damage, particularly over hot, dry summers.

Multi-Use Bowles’ Golden Sedge

Posted by Hugh on June 8th, 2018

Bowles’ Golden Sedge With Hosta in Vancouver, BC

'Bowles Golden' Sedge at Kingwood Center in Mansfield, Ohio

‘Bowles Golden’ Sedge in part shade at Kingwood Center in Mansfield, Ohio

Bowles’ golden sedge (Carex elata ‘Aurea’) is an easy to grow sedge (USDA hardiness zones 5-8). Golden sedge was introduced by English plantsman and garden writer E.A. Bowles who discovered it growing in eastern England.

Bowles’ Golden sedge grows 1 ½ to nearly 3 feet high (in flower) and 2-3 feet wide. It features bright lemon- yellow leaves with dark green margins. Its fine-textured foliage turns lime-green in heavy shade. In late May (in zone 6), tiny brownish-colored flowers appear, but are mostly insignificant. You may opt to clip them off and put all energy into growing the plant.

Bowles’ Golden can be utilized for erosion control along stream banks. It freely naturalizes and eventually may dominate its wet surroundings. Clumps 3 years and older can be easily divided and/or transplanted in late winter or early spring before new growth begins. Fertilize the planting with a slow release organic fertilizer in early spring or feed with a water soluble product such as Miracle-Gro™ or Peters™.

Grow it in a moist loamy acidic soil and in partial shade. Bowles’ Golden will tolerate moderately dry soils in a shady garden spot. Plant it on the edge of a pond or water garden submersed in 1-2 inches of water. It can be planted in full sun under frequent irrigation where its golden color will shine. Golden sedge may also be planted in containers among other moisture-loving plants. You may substitute with other gold leaf favorites like golden sweet flag (Acorus gramineus ‘Ogon’) or Aureola hakone grass (Hakonechloa macra ‘Aureola’).

Golden sedge has no serious pests and is deer resistant. The foliage on established clumps may brown or grow shorter during temporary dry spells and recovers as soil moisture is more plentiful.