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

Preventing Powdery Mildew Disease On Summer Plants

Posted by Hugh on May 18th, 2014

Early Stages Of Powdery Mildew on Beebalm (Monarda)

Powdery mildews are serious fungal leaf diseases infecting many garden plants. Each one is host specific. The powdery mildew that attacks summer phlox does not infect zinnias or pumpkin vines. Powdery mildew disease on crape myrtles does not attack lilacs or roses. In recent years new powdery mildew diseases have popped up on dogwoods and herbaceous peonies.

Powdery mildew appears as a white floury substance on the leaf surface. Infected leaves lose much of their photosynthetic efficiency. Poor air circulation and overhead irrigation in the garden creates an ideal environment for the fungus. Fungal invasion is generally worse during prolonged cool wet spring weather or the return of cool night temperatures on late summer.

Infections on annual zinnias, summer phloxes, squashes and pumpkins generally begin in late summer or at the start of cool autumn weather. High summer humidity can really trigger a mildew outbreak and result in leaf distortions. Multi-year infestations eventually weaken and kill dogwoods, lilacs, or rose bushes.

Planting mildew resistant varieties is one of your best alternatives. However, be aware that “disease resistance” does not mean that plant(s) are “disease immuned”. Generally, mildew resistant cultivars are less susceptible and leaf injury will be less.

Other tips: Over applying nitrogen-based fertilizers may worsen an outbreak of powdery mildew. A number of fungicides prevent, but do not cure powdery mildew. Susceptible plants must be sprayed every 7-10 days. During a heavy rain fungicides are easily washed off and must be re-applied. In the fall pull up diseased plants and rake up garden debris. Remove it from the property. Do not compost diseased leaves and stems.

Sweetbay Magnolia

Posted by Hugh on May 15th, 2014

Magnolia virginiana at Kingwood Center, Mansfield, Ohio

Sweetbay, aka laurel magnolia, (Magnolia virginiana) is a U.S. native tree. This small to medium-sized native species often 20-30 feet tall and 15-20 feet wide as a large shrub or multi-stemmed small tree. Finding a 50-60 feet sweetbay near by a lake or pond near where you live is not unusual (USDA hardiness zones 5-9).

Sweetbay blooms from mid-May through June, with occasional flowers in July. The flower petals of magnolias are called “tepals” and sweet bay flowers consist of 8-10 tepals. The creamy-white blooms are 3-4 inches across and last three to four days. Numbers of open flowers are rarely abundant at any one time. On occasion their sweet lemony fragrance becomes quite evident in the late spring garden.

The glossy light-green leathery leaves are 4-5 inches long. A slight fluttering breeze exposes the silvery underside of the leaves. Foliage is reliably evergreen in USDA hardiness 7-9 and semi-evergreen in zone 6. ‘Green Shadow’ and ‘Moonglow’ are leading cultivars that exhibit slightly larger flowers, darker green leaves, and better winter hardiness.

In early fall green cone-like seed capsules burst open to expose bright orange to red seeds within. Seeds may be collected in late September and stratified (refrigerated) in moist sand over three months @ 32 to 41°F; or may be sown directly in the garden. Seedlings emerge from the soil the following June.

Unlike most magnolia species, sweet bay flourishes in moist soils, including those that are flooded for short periods. It prefers an organic rich, acidic soil; summer leaves may turn chlorotic (yellow) in iron deficient alkaline soils. Disease and pest problems are rare.

Sweetbay is well-suited for a small urban garden near a patio or deck. Cut foliage is often included in holiday wreaths and garlands, and in table and floral arrangements.

Rooguchi Clematis: Let It Ramble

Posted by Hugh on May 12th, 2014

Clematis 'Rooguchi' in Jonesborough, TN

Combine two popular garden trends: climbing vines and vertical gardening. Vines may grow on a trellis or allow them to weave through an existing shrub or tree. In a small garden this can be a space saver. In the world of clematis, the cultivar Rooguchi, aka Roguchi, (Clematis integrifolia x C. reticulata) has become increasingly popular (USDA hardiness zones 4-9). This hybrid selection is from Japan.

Rooguchi’s flowers are not the typical star-shape clematis. A hundred or more bell-shaped blooms may be open on an established vine at any one time. The 1 to 2 ½ inch violet purple flowers appear from late May through September. Clematis seed heads can be quite showy. The bell flowers hang downward (pendant). The bell’s rim flairs outward into four distinct lobes.

Rooguchi is an herbaceous perennial that lives for many years when properly cared for. Plant it in a compost rich soil with adequate moisture and partial sunlight. In zones 4-6 it handles full day sunlight, but further south, protection from harsh afternoon summer sun is warranted. Mulching around the base of the vine helps to moderate soil temperatures and conserve moisture.

Allow Rooguchi clematis to weave through a Japanese maple, rose bush, or any open branched deciduous plant. Let it ramble along the ground. You may tie it to a wire or wooden trellis for vertical support. Leaf petioles wrap around a wire or lath trellis for added support.

A 2- year old trellised vine grows 6 to 8 feet high and 4 to 5 feet wide over the summer. It flowers on new growth. Prune this vigorous vine aggressively in late winter (Pruning Group 3), sharply cutting it back to its main branches or to a few strong buds near the ground.

Roseshell Azalea Thrives In Cool Mountain Woodlands

Posted by Hugh on May 9th, 2014

Rhododendron prinophyllum (photo by Jay Jackson, Appalachian Native Plants)

Roseshell azalea (Rhododendron prinophyllum, formerly R. roseum) is native from New England, a number of Midwestern states, south to Texas. In its natural habitat it is commonly grows on wooded, north-facing slopes, shaded ravines, or nearby a cool mountain stream. The plants are not stoloniferous.

Roseshell azalea grows best in organically rich, acidic, well-drained, and moderately moist soils. It thrives in morning sunlight, and should be partially shaded in the afternoon. It struggles in dry soils and high heat areas; Southern forms are being studied. Maintain a 2-3 inch organic mulch (e.g., bark, oak leaf or pine needle) to retain soil moisture and cool temperatures.

This upright growing shrub averages 4 to 8 feet in height and width. Prune as needed to manage shrub size. Leaves are bright green on the surface and covered with tiny hairs beneath; it is sometimes nicknamed “downy azalea”. Foliage turns copper brown in fall.

Flowers range from pale pink to dark vibrant pink and open slightly ahead of the foliage in May and June (date depending on location). Floral trusses average 5-9 flowers, each to 1.5 inches long. Hummingbirds and butterflies are attracted to the tubular flowers which emit a pleasant sweet clove-like fragrance.

Roseshell azalea is one of our hardiest native azaleas. The University of Minnesota bred the winter hardy Northern Lights hybrids using roseshell azalea as one of the parents. Western forms native to Oklahoma and western Arkansas are more heat tolerant and have been successfully trialed in Athens, GA area.

Use Roseshell azalea as a specimen or group several together in a woodland setting or as part of a foundation planting. While susceptible to numerous disease and pest problems, roseshell azalea performs well when located on a cool, partially shaded site.

Enjoy Moonvine In The Evening Garden

Posted by Hugh on May 5th, 2014

Moonvine (Ipomoea alba)

Moonvine (Ipomoea alba)is a fast growing tropical vine. Its dark green heart shaped leaves stay clean and pest-free the entire growing season. Pure white 6-inch wide flowers open non-stop from early summer until frost. Each showy white flower lasts one day, opening in late afternoon and withering late the following morning.

Plants may be purchased in the spring at garden centers. Moonvine is tropical vines and safe to set out when tomatoes and vegetable vine crops are also being planted. Moonvine can be trained on a trellis or permitted to ramble along the ground.

Grow in full sun and moist, well-drained soil. Transplant seedlings into garden and feed biweekly with water soluble fertilizer such as Miracle-Gro®, Daniels®, or Hyponex®. Vines generally grow 10-15 feet long, but up to 40 feet is not uncommon under optimum growing conditions.

Moonvine’s white flowers radiate in the evening garden. Purple pods form where once flowers bloomed. The pods contain plenty of viable seeds which can be collected and saved for next year’s garden.

Start seeds indoors in early spring or direct sow into the garden in late spring. The seed coat is very hard and should be nicked with a knife or soaked overnight in warm water. Plant seeds 1/2 – 1 inch deep and 6 inches apart. Cull out most seedlings to permit a few to prosper.

Beware that seeds and plant foliage are poisonous to cattle and other foraging animals.

Blackberry Lily Is Easy Summer Perennial

Posted by Hugh on May 3rd, 2014

Fall Seed Heads On Blackberry lily at NC Arboretum, Asheville, NC

Blackberry Lily (Belamcanda chinensis) is a summer flowering perennial native to China and Japan (USDA hardiness zones 5 -10). Don’t be fooled by its name. It is not a “lily” as it belongs to the Iris family. The iris sword-like leafy stalks stand 2 to 3 feet high.

Blackberry lily blooms in early to mid-summer in the Southern Appalachian region (zones 6-7). Numerous 2-inch wide orange flowers strikingly stand out, dotted with red spots. Clusters of shiny black seeds mimic blackberries after capsules split apart.

Non-fussy blackberry lily grows under part shade to full sun and in average soil that is adequately drainage. Fertilize once at the start of spring with 10-10-10 or equivalent granular fertilizer.

Blackberry lily is a prolific seeder. If you do not desire a significant overpopulation in your garden, prune off seed capsules in late summer before they split open. Individual plants are not long-lived if winter soil is soggy. However, enough seeds are dispersed naturally that this short lived perennial is rarely lost.

Blackberry lily is easily started from division of rhizomes or by seed. If started in the garden, set rhizomes 1 inch deep. Sow the seeds in the fall to satisfy a 4 to 6 week cold stratification period. Seeds germinate the following spring and usually bloom the first year.

Ice Plant – A Cool Plant For Dry Sunny Spots

Posted by Hugh on May 1st, 2014

Ice Plant (Delosperma)

From the extreme heat and dry climates of east and Southern Africa come the hardy ice plants (Delosperma spp.). There are two popular species, Purple ice plant (D. cooperi) and Orange-yellow iceplant (D. nubigenium), plus hybrid cultivars galore.

Ice plants are dependable zone 6 winter hardy succulents. They’re excellent candidates for roof top and rock gardens, co-habitating with other dryland sun-loving succulents. A poorly drained clay soil or a winter soggy soil would be their death knoll.

Ice plants survive in hot parched soils from central Kansas south thru Texas. You even see them in the urban heat and soils around New York City if the growing media is properly drained. A gritty sand-based container mix appears perfect. A favorite planting spot is on a south-facing sunny slope.

Depending on species and cultivars, their bright clear yellow, orange, red or purple flowers carpet the ground. Butterflies and other pollinators love them. Ground-hugging ice plants form a thick 1 to 4 inches high mat.

Generally, ice plants are short-lived perennials, lasting 2 to 3 years unless their site is uniquely suited. Minimal plant nutrition is recommended. You can irrigate every 4-6 weeks with water-soluble fertilizers such as Miracle-Gro™, Daniels™, or Jacks™ through mid-summer.

Dependable species and cultivars have been identified by Dr. Panayoti Kelaidis and staff at the Denver Botanical Garden which has increased the popularity of ice plant.

New 'Jewel of the Desert Ruby' Ice Plant at NC Arboretum in Asheville

‘Summer Gold’ Kousa Dogwood

Posted by Hugh on April 27th, 2014

Gold-edged Variegated Foliage of 'Summer Gold Kousa Dogwood

Get ready to alter your mindset with ‘Summer Gold’ Chinese (kousa) dogwood (Cornus kousa) (USDA hardiness zones 5-8). Its diminutive size, 8 to 10 feet high and 4 to 5 feet wide, makes it a great fit for a small city garden. Branching is distinctly upright, which partially accounts for its narrow space needs.

‘Summer Gold’ exhibits dark green leaves with a wide golden edge. The green leaf portion turns a medium red in the fall. As the tree ages, the bark on the trunk and main branches flakes off, forming a patchy or mosaic pattern.

Masses of creamy white pointed bracted flowers cover this small tree in early spring, opening after 2-3 weeks after flowering dogwood (C. florida) has finished blooming. Spring flowers and late summer fleshy fruits attract butterflies and birds respectively. Deer do not bother kousa dogwood unless their populations are unusually high or their natural food supply is lacking.

Kousa grows best in well-drained soils with adequate moisture. Irrigate weekly the two years to develop a deep, extensive root system that will support the small tree. In general, kousa dogwood usually does not need feeding its first year. Thereafter, supply a handful or two of granular 10-10-10 or equivalent fertilizer in late winter.

Newly-planted trees are both heat and drought susceptible and should be irrigated the first two years after planting. Cooling the soil by watering helps. Irrigate weekly from mid-June thru early September when summer temps are consistently in the 90’s and rainfall amounts are deficient.

Generally, kousa dogwood requires very little annual pruning. Control tree shape as needed and prune off unwanted shoot and root suckers, particularly those near the graft union (swollen area on trunk near ground surface).

Don’t Shy Away From Annual Vincas (Periwinkles)

Posted by Hugh on April 23rd, 2014

Annual vinca or periwinkle (Catharanthus roseus) is a summer flowering annual popular in Southern and Midwest gardens (USDA hardiness zones 9-11). When summer’s heat and humidity soars, vincas look their best and bloom the heaviest. Vincas sparkle in containers, in flower beds, or in front borders around building foundations.

Transplants are set out in mid-spring after soils have warmed up and all threats of frost have passed. Vincas grow best in well-drained, organically rich, loamy soil and in full or part sun. Fertilize at planting with a second application in late July. Vincas enjoy occasional watering during prolonged dry spells but avoid sprinkling overhead. Established plants (after 4 to 5 weeks) are rated moderately drought tolerant.

Most modern day cultivars grow short and compact. They vary from 6 to 18 inches in height and spread. An individual flower is composed of five flattened petals attached to a tubular base. A wide range of flower colors include lavender, red, rose, salmon, several shades of pink, and white. Some cultivars exhibit a center eye in the flowers. Old blooms are self-cleaning and never messy. The 1-2 inch long leaves are dark green and glossy.

Most new cultivars contract few, if any, serious insect or disease problems. Plant vincas on an open site with good air circulation to prevent stem and root rot diseases (phytophtora) and bacterial leaf spots. Slugs and snails can occasionally become pesky in wet summers.

Popular vinca series at garden centers are Aztec, Cooler, Cora, Pacifica and Viper. Vincas often self-seed and re-appear in garden beds several years hence.

Growing Sunflowers Fun Family Activity

Posted by Hugh on April 20th, 2014

Sunflowers Growing In Front Of Home

Growing sunflowers (Helianthus annuus) are the current rage. Sunflowers are native to Central America and have been cultivated for thousands of years. Sunflowers are classified as annuals, living one growing season, and often returning the following spring from seeds dropped the previous fall. Some gardeners put out large beds to feed the birds.

Sunflowers come in many varieties, some 3-5 feet tall with yellow, cream, or red flowers; others 10 feet and more tall giants with sturdy stems and blooms nearly a foot across. Most varieties mature in 70 to 90 days or more. Read the seed package for plant heights and harvest time (ripening).

Sunflowers are easy to start from seed. Sow seeds 4-6 inches apart and cover them with plastic mesh or screen until several have poked their heads up (germinated). Otherwise, birds and animals may dig the seeds up. You can also start seeds in a small protected seedbed, seed flat, or pot and transplant each individually when they’re a few inches tall. For a head start on spring, you may opt to begin 2 to 3 weeks earlier indoors in individual peat pots. Sow 1 to 2 seeds per pot, and thin to one before planting outdoors after the spring frost period.

Sunflower plants grow well in average to rich soil. They grow best in full sun, but do tolerate light shade. They perform better in deep soil for roots to become firmly anchored to withstand strong winds and dry spells.

They do benefit from heavy feeding with 10-10-10 or an equivalent fertilizer at planting time and again 8-10 weeks later. Nitrogen (N) promotes plant growth and sturdiness. Adequate phosphorus (P) and potassium (K) in the soil increases flower bud numbers and bigger blooms.

Tall sunflowers serve as good companions interplanted with ground trailing cucumbers, melons, pumpkins, or squashes. Plant only 5-6 sunflowers per 100 square feet, so not to shade the vines below.

Insects and diseases are seldom problems, particularly on new ground. The birds and squirrels are primary invaders of a sunflower crop, all coming to feast on the delicious oily seeds.