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

Why Peonies Do Not Bloom

Posted by Hugh on April 20th, 2013

Herbaceous Peonies In May Garden

Herbaceous peonies (Paeonia x lactiflora) are among the easy to care for and long-lived garden perennials. If you plant them correctly in compost rich, well-drained soil and a minimum of 6 hours of sunlight, they will bloom for the next 30+ years. If peonies fail to bloom, here are 8 probable causes:

1. Planting crowns too shallow or too deeply. Proper soil depth from the top of the crown is 2 inches.

2. Proper planting date – plant anytime from late August thru November in the Southern Appalachian region (USDA hardiness zones 6 and 7). Container plants may be planted anytime and do not to disturb the tender fibrous roots unless badly potbound.

3. Buy strong 3-eyed or more peony crowns from a reliable peony source on-line or local garden shop.

4. Inadequate sunlight – plants full sunlight or at least 6 hours daily (USDA hardiness zones 4-7a). Shade from harsh afternoon sun in zone 7b).

5. Overcrowded plants – Space 3-4 feet apart to prevent plants from competing for light and soil nutrition. Overcrowding increases disease pressure, particularly leaf spot diseases such as Botrytis blight and Phytophthora stem blight. Flower buds do not open, turn black and drop off weeks later.

6. Too much nitrogen fertilizer – Peonies tend to feed constantly through the growing season. A slow release fertilizer applied in late winter is more than adequate.

7. Deficient Phosphorus (P) and/or potassium (K) in the soil. Both nutrients initiate flowering in peonies.

8. Late spring killing frost injure unopened floral buds. Protect tender flower buds by placing a cloth, not plastic, tarp or blanket over plants.

Summer Flowering Heleniums Should Not Make You Sneeze

Posted by Hugh on April 18th, 2013

Helenium 'Moerheim Beauty'

Helenium, named for Helen of Troy from Greek mythology, is U.S. prairie perennial. In times past powdered disk flowers and leaves of some heleniums were used as snuff, hence the common name. It’s difficult to sell ‘sneezeweed” and many garden catalogs now list it as “helenium”. A number of good hybrid selections have been introduced including Moerheim Beauty (Helenium ‘Moerheim Beauty’) and Mardi Gras (H. x ‘Mardi Gras’).

Moerheim Beauty stands 2 ½ to 3 feet tall and 1 to 1½ feet wide on sturdy stems. It develops deep roots, and rarely needs staking as many seed varieties do. The showy 2-inch wide coppery red ray flowers surround a dark dome-like center. Flowers gradually fade to burnt orange.

Mardi Gras grows slightly shorter and bears bright fiesta-like yellow petals, splashed with orange-red over 6-8 weeks from mid- to late- summer. Petals age to clear red with a gold edge, all surrounding a dark brown button center.

Heleniums grow in full sun and in an average moist, well drained soil. They tolerate wet, sometimes flooded soils, and are great choices for rain gardens. Long summer dry spells can devastate the foliage and flower count, and they should be watered regularly. Flowers may sometimes be nipped by an early autumn frost in USDA hardiness zone 5 and colder.

Fertilize sparingly to prevent weak stems and crowns, and the need for staking. Plants may benefit from being cut back in late spring to encourage branching and more flower formation. Deadhead old blooms to encourage additional ones. Crowns should be dug up and divided every 2-3 years.

Flowers attract many kinds of butterflies; deer and rabbits stay away from toxic heleniums. Plant heleniums in flower borders and meadow gardens. They look great growing in containers and their sturdy long stems and a long vase life make them great cut flowers. Above recommended cultivars exhibit exceptional disease resistance.

A Marigold Revival

Posted by Hugh on April 14th, 2013

Marigolds and Ageratums at Kingwood Center, Mansfield, Ohio

Over the past 2-3 years marigolds are regaining their popularity. Marigolds are easy to grow and come in vibrant shades of yellows and oranges. Tall African type marigolds grow 24-42 inches tall and belong in garden beds. Intermediate (15-24 inch height) and dwarf French types (10-12 inch height) are suited for both bedding and container plantings.

Plant marigolds in full open sunlight and do not crowd or overwater plants. They require very little maintenance if planted in compost-rich garden soil that is well drained. Marigolds handle summer heat and short dry intervals if they have been properly cared for the first six weeks after planting. A well established bed of marigolds will bloom non-stop through the summer into autumn.

Marigolds are best planted in early to mid-May in the Southern Appalachian region (USDA hardiness zones 6 and 7) after the spring frost period has passed in your gardening area. Marigolds are great as late garden fillers where other flowers may have fizzled out. You may plant marigolds up to mid-August and they will bloom up to the first hard freeze in October or November.

Feed with a granular 10-10-10 fertilizer or a water soluble products such as Miracle-Gro®, Jack’s Classic®, or Daniels® fertilizer at package directions.

Their principal nemesis is spider mites which are easily eradicated with environmentally mild pesticides. Botrytis is a flower disease best prevented by selecting varieties that shed water and by not watering overhead. Short French type marigolds are known to repel insects in vegetable gardens with their strong fragrance. You must plant large numbers of marigolds which will cut down space veggie beds.

Recommended cultivars:

‘Perfection’ series @ 30 -36 inch tall and 15 inches wide.

‘Marvel’ series @ 18 inch tall by 10 inches wide.

‘Moonsong Deep Orange’ @ 15 inches tall by 10 inches wide.

Moonstruck Series @ 12-15 inches tall

Bonanza series (French type) @ 10-12 inch tall

Cool Blooming Osteospermums

Posted by Hugh on April 11th, 2013

Osteos at UGA Gardens in Athens, GA

Osteospermums (Osteospermum x hybrida ) are members of the daisy (Asteraceae) family, commonly called African Daisy, Blue-eyed Daisy, or Cape Daisy. Osteos are cool season annuals that excel in northern and less so in southern U.S. gardens. Osteos bloom more profusely in full sun, but want some cooling relief during the summers.

Osteos have always been a popular cutflower, but are now becoming a annual bedding plant. They should be planted early with petunias and million bells (Calibrachoa). The heat of summer knocks osteos out of bloom, but they often recover to bloom again in late summer. Keep them adequately watered the first month after planting.

Flat daisy-like petals radiate out in a tubular or spoon shape. Every year new color choices continue to win over gardeners. Plant breeders are improving summer heat-tolerance and introducing more compact growing cultivars. Color choices abound from lavender, pink, white, yellow and bi-color, with more introduced every year. Their dark green foliage may vary with the cultivar from lance- , ovate, and/or lobed- shaped.

They prefer an acidic soil, but perform well between 5.5 to 6.5 pH. Feed osteos on a bi-weekly basis with a water soluble fertilizer such as Miracle-Gro™, Jack’s™, or Schultz™ according to package directions. Although drought tolerant once established, osteos need one inch of water weekly to look their best.

During periods of intense heat and drought, growth slows or plants go dormant. Cut osteos back in late summer to stimulate new stems and leaves. Remove wilted flowers and old worn foliage to induce new flowering.

Osteos are super performers in hanging baskets and window boxes. Cultivar series vary from 12 – 36 inches in height by 12 – 24 inches in spread. Among the popular osteos are the Voltage®, 3D®, and Margarita® series.

U.S. Native Pagoda Dogwood Wonderful Woodsy Tree

Posted by Hugh on April 11th, 2013

Late Spring Flowering of Cornus alternifolia

Pagoda dogwood (Cornus alternifolia), aka alternate leaf dogwood, is a small deciduous tree or large multi-stemmed shrub. It typically grows 15-25 feet tall and spreads slightly wider than tall. It exhibits a very distinctive layered horizontal branching.

Small creamy white non-bracted flowers appear as flattened cymes in mid to late spring, about 3-4 weeks after flowering dogwood (C. florida) has finished. Its sweet flower fragrance, in my opinion, would not be an outstanding trait.

While the leaves of most dogwoods (Cornus spp.) are arranged opposite, pagoda dogwood’s leaves are alternate. The medium to dark green leaves are unusually parallel-veined; leaf size varies from 2-4 inches in length.

Bluish-black fruits (drupes) ripen in late summer and are favorites of many species of birds. Autumn leaf hues are insignificant. Disease and pest problems are rare when the pagoda dogwood is properly sited. Deer appear to pester it very little.

Grow pagoda dogwood in acidic, compost-rich, and well-drained moist soil. Pagoda dogwood is hardy to northerly zone 3 where it grows in full day sunlight. Protection from afternoon sun in southerly climes (zones 6 and 7) is highly recommended.

Plant this small flowering tree where it can be seen such as near a patio or in a woodsy area to attract hungry birds. Pagoda dogwood needs little annual maintenance other than to prune off occasional basal suckers.

Two variegated leaf forms are sold at garden centers and e-commerce nurseries. ‘Argentea’ features attractive silvery white variegated foliage on layered horizontal branches. It grows into a 10 to 15 ft. tall shrub. Golden Shadows® also grows shrub-like with layered horizontal branching and gold variegated foliage.

Hardy or Not– Grow Agapanthus

Posted by Hugh on April 8th, 2013

Lily of the Nile (Agapanthus)

Lily-of-the-Nile (Agapanthus praecox orientalis) is native to South Africa (USDA Zones 8–11), and is not reliably hardy in the Southern Appalachian region (USDA zone 6 and 7). However, many gardeners are successfully growing it as a “tender perennial”. Agapanthus grows in an outdoor flower bed or in a container.

The ball shaped light blue or white tubular shaped flower clusters first appear in late spring and early summer. By promptly deadheading spent flowers, agapanthus may produce another 1-2 flushes in summer and early fall.

Agapanthus grows 2-3 feet in height and 1 ½ -2 feet in spread with dense tuft of 1 inch wide strap-like dark green leaves which measure a foot or more in length. It prefers a compost rich soil (media), constant moisture and partial sunlight. Weekly watering promotes a deep, extensive root system.

During the winter months lay a thick 3 inches of organic mulch over the crown to protect the roots from frost. Remove the mulch once warm spring weather returns.

Container-grown plants should be cut back and brought indoors by early November and nurtured as house plants through the winter. Divide crowded root clumps every 2 to 3 years in early spring.

If you garden further north (USDA zone 5) tender agapanthus should be dug up and stored inside for the winter. Allow plant(s) to thoroughly dry out and trim back the foliage. Keep the dormant crown in a cool, dark location for the winter between 35 – 40ºF. In late winter move the dormant corms into a warm area and moisten the soil to force new growth. Bring plants back outdoors in mid-May to enjoy another summer in the garden.

Mealy bug and red spider mite can be major pest problems.

Silverbell Tree Are Great Additions To Your Garden

Posted by Hugh on April 6th, 2013

Carolina silverbell (Halesia diptera) in Conlon Garden

Carolina silverbells (Halesia spp.) bloom as the last bracts of flowering dogwood (Cornus florida) have fallen. Clusters of white or pale pink bell-shaped flowers open along the branches. Flowers appear first and medium green leaves emerge a few days later. Silverbells vary tremendously in the wild. Some grow large shrub-like, or as small multi-trunked trees to 20-25 feet in height, or as medium 30 to 50 feet high and 20 to 35 feet wide.

Over the past decade botanists have reclassified Halesia. Two-winged silverbell (H. diptera) grows a small 20-30 feet tall and wide, and fruits are 2-winged drupe seed capsules. Carolina silverbell (H. tetraptera, formerly H. carolina) is the taller species at 30-40 feet high and 25-30 feet wide, and fruits are 4-winged drupe seed capsules.

Young multi-stemmed shrubs are easily trained into single trunk trees. Fall leaf color is variable, in most years turning pale yellow in the Southern Appalachian region (USDA hardiness zones 6 and 7). Dry brownish seed capsules persist through most of the winter. In the winter months the dark gray-furrowed bark, marked with thin black vertical lines, is more noticeable.

Silverbell is primarily an understory tree, preferring partial sun (full morning sun, afternoon shade). Ideally, it prefers a slightly acidic, compost- rich, moist, well-drained soil. summer foliage often yellows (turns chlorotic) in high pH soils. Irrigate a newly planted tree in years 1 and 2 until it adapts to moderately dry summers. Fertilize lightly in late winter or before the tree blooms.

Leading cultivars: H. tetraptera ‘Rosea’ opens rose-pink and fade to pale pink. H. diptera ‘Magniflora’ bears 25% larger blooms than the species. ‘Wedding Bells’ is a new multi-branched shrub form from Dr. Mark Brand at the University of Connecticut.

Silverbells are disease and pest free if properly sited. This wonderful native provides food and shelter for birds and pollinating insects.

Coastal Azalea Copes With Heavy Clay Soils

Posted by Hugh on April 4th, 2013

Rhododendron atlanticum at Duke Gardens in Durham, NC

Coastal Azalea (Rhododendron atlanticum) is a deciduous native azalea that grows along coastal plains of the Mid-Atlantic and Southeast U. S. Their white 1 to 1 ½ inch tubular flowers appear about the time that lilac petals are beginning to fading. Flowers are snowy white with a pinkish blush, and emit a distinctly clove fragrance. Blooms open a few days before the new spring foliage.

Coastal azalea forms a low compact deciduous shrub. It rarely grows taller than 4 feet in height and 4 to 6 feet wide. It should be grown in full sun (in zone 5b -6) and in partial shade (zones 7-8). Coastal azalea grows best in a well- drained acidic soil. It should be watered during prolonged summer dry spells. Its bluish-green foliage remains disease and pest free if plants are not environmentally stressed.

Coastal azaleas are highly stoloniferous, spreading by underground stems and forming small plant colonies around themselves. They tend to sucker a lot less in clay soils. The cultivar R. atlanticum ‘Winterthur’ has an outstanding compact growth habit and tends not to sucker.

R. atlanticum is parent to a number of hybrid deciduous azaleas:

‘Fragrant Star’ (R. canescens x R. atlanticum) – fragrant white flowers (slightly larger than ‘Snowbird’); 4 by 4 foot compact shrub with blue green foliage, introduced by Briggs Nursery in Olympia, WA.

‘Snowbird’ (R. atlanticum x R. canescens) – 4 by 4 foot compact shrub with blue green, mildew resistant foliage; introduced by Biltmore Estates in Asheville, NC.

‘Marydel’ (R. atlanticum x R. periclymenoides)- abundant pinkish-white, fragrant flowers from late April into May; introduced by the late Polly Hill.

‘My Mary’ [R. atlanticum x R. periclymenoides] x R. austrinum – very fragrant yellow flowers in late April.

‘Appalachian Spring’ Dogwood Highly Disease Resistant

Posted by Hugh on April 1st, 2013

Flowering dogwood (Cornus florida)

This may be old news, but definitely worth repeating. Twenty five years ago a dreaded dogwood disease threatened to eliminate our beautiful spring flowering tree from our gardens. Appalachian Spring flowering dogwood (Cornus florida ‘Appalachian Spring’) was found at the Camp David Presidential Retreat atop Catoctin Mountain in Maryland.

Currently, Appalachian Spring is the only dogwood cultivar resistant to dreaded anthracnose (Discula destructiva) disease. It was introduced in 1990 by plant scientists at the University of Tennessee in Knoxville. These same scientists have also released four additional dogwood cultivars which are resistant to powdery mildew. Appalachian Spring is not resistant to powdery mildew disease.

Flowering dogwood is a small understory tree, preferring partial sunlight (morning and early afternoon hours are best). The white bracted flowers open in early spring in the Southern Appalachian region (USDA hardiness zones 6 and 7). Dogwood blooms heaviest in full day sun, but the tree’s life span is generally shorter. Two-year old established dogwoods exhibit good drought tolerant, but do benefit from irrigation during long dry spells. Mulching conserves soil moisture and cools the soil. Possible infestations of dogwood borer are also reduced.

Flowering dogwood grows in average garden soil that is well drained. Adding generous amounts of compost spread over the planting site (not the hole) is recommended. Young trees grow vigorously, often reaching 15 to 20 feet in height in 10 years. Feed dogwood(s) in late winter with 10-10-10 or equivalent fertilizer. In the fall green drupe fruit turn bright red, usually 2-3 weeks before the dogwood foliage turns bright red. Birds and other wildlife are dependent on dogwood mast over the fall and winter months.

Golden Hakone Grass Is Worth The Extra Care

Posted by Hugh on March 29th, 2013

Hakonechloa 'Aureola' Awakens Shady Garden Spot

Awaken dark zones in your shade garden with this wonderful golden treasure from Japan. Golden hakonegrass (Hakonechloa macra ‘Aureola’) grows 12-18 inches tall and 18-24 inches wide in a cascading mound form.

Very thin green stripes (veins) line the mid-rib of the ½ inch wide golden leaf blades. Tiny, relatively ininsignificant, floral spikes (inflorescences) appear for a short time in late summer. The grass blades take on a pink to reddish tinge in the cool fall air before all vegetation withers away for a long winter’s nap.

Golden hakone prospers in moist, humus-rich, well-drained soil. Contrarily, it grows poorly in compact heavy clay soils. Hakone prefers a partially shaded garden spot. Feed with a water soluble fertilizer (Miracle -Gro®, Schultz®, or Hollytone®) at package directions every 4-6 weeks from early spring thru mid-summer.

In its first year golden hakone starts off very slowly, and spreads from underground stolons. Soil moisture is in maximum need the first two years to successfully establish hakone grass. This extra attention will be worth your patience. Hakone grass will rarely trespass on spaces occupied by neighboring hosta, astilbe, heuchera, and others in the shade garden.

Golden hakone is rarely bothered by disease or insect pests and is not troubled by deer. ‘Aureola’ hakone grass was selected the Perennial Plant of the Year in 2009.