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

How To Grow Milkweeds

Posted by Hugh on June 2nd, 2014

Common milkweed (Asclepias tuberosa)

Milkweeds, aka butterfly weed (Asclepias spp.), are the favorite food of the Monarch butterfly. Farmers and most gardeners rate them as a noxious weeds. They’re commonly spotted growing along roadsides or in unplowed ground (USDA hardiness zones 3-9). Milkweeds average 3 feet in height, but may vary from 2-6 feet depending on species. Most species are classified as herbaceous perennials.

As its common name suggests, milky sap pours out from the stems when cut. Leaves vary in shape with species (see below) and are either light to dark green in color. Flower color also varies by milkweed species, from pink, purple, or orange. They bloom from June to August and flowers of some species are fragrant. The cucumber-like seed pods set in autumn. Seed pods open and release hundreds of aerodynamic seeds carry over many miles by the wind.

Beginning in the southern U.S. and progressing northward U.S., milkweed blooming time coincides with the arrival of Monarch butterflies in your growing zone. Flowers are an important source of nectar for many insect pollinators, including butterflies and hummingbirds. Milkweeds are the primary host for monarch butterfly larvae (caterpillars). Female monarchs deposit their eggs on the milkweed plants and emerging caterpillars (larvae) emerge feast on the leaves. The resting pupa stage is on milkweeds.

Milkweeds are toxic to most predators of Monarchs, but are not harmful to feeding Monarch caterpillars. The caterpillars do not die, but the leaf toxins make the Monarchs poisonous to predators! There is tremendous variation in the poison levels of the foliage. A. tuberosa are rated low; A. verticillata and A. viridis are rated among the highest. Historically, milkweeds have been valued for their medicinal properties.

Milkweeds grow best in full sun and in a well-drained soil. Some are very drought tolerant and thrive in ordinary soils; they need little or no fertilizing. Some cope with wet soil conditions and others do not. Milkweeds blend well among other butterfly floral favorites in mixed borders, meadows and natural areas.

You may collect and save milkweed seeds in early fall. The seeds are best sown in the soil to overwinter there and germinate in the spring. You may also opt to sow vernalized (pre-chilled) seeds in a greenhouse or sun room in late winter or transplanted into outdoor beds after the danger of frost has passed in spring. Keep the soil moist but not soggy.

When plants have two sets of leaves, transplant them to their permanent, sunny location outside. Space plants about two feet apart, if planting in a row. A milkweed plant produces a long taproot which does not like to be disturbed after planting. Mulch can help conserve water.

The following seven (7) milkweed species are favorites of Monarch butterflies, bees, and other butterflies. Most are available from perennial and wildflower sources on-line.
Butterfly weed (A. tuberosa) – showy orange flowers; popular garden choice because of hardiness, long-life, and non-invasiveness; 1-2 feet height
Common milkweed (A. syriacus) – purple flowers blooms; aggressively spreads by rhizomes and self-seeds; 3 feet height.
Swamp milkweed (A. incarnata) – red flowers; 3-4 feet height
White milkweed (A. variegata) – striking clusters of snowy white flowers; 1-4 feet height
Whorled milkweed (A.verticillata) – small white flowers; bland narrow needle-like leaves; 1-3 feet height
Spider milkweed (A.viridis) – spring blooming green colored flowers; 1 foot height
Purple milkweed (A. purpurascens) – magenta colored flowers; 3 feet height
Scarlet milkweed (A. curassavica) – red and orange flowers; 2-3 feet height; annual (zone 9-11)

Doghobble for Shady Landscape Areas

Posted by Hugh on May 30th, 2014

cultivar -'Rainbow'

Mountain doghobble (Leucothoe fontanesiana) is native to woodland areas in the Southern Appalachian region (USDA zones 6 and 7). Florida coast leucothoe (L. axillaris) is another regional favorite, native from Virginia south to Florida. Over time it grow tall, usually 3-4 feet high as a rambling ground cover. Every 3 to 4 years hand pruning is needed to hold doghobbles to a desired location and height.

In nature doghobbles grow in acidic, well-drained, organically rich soil, often in close association with other U.S. native acid-loving shrubs such as rhododendrons, azaleas, and mountain laurels (Kalmia spp.) and selected ferns. Soil pHs in the range of 5.0 to 5.5 are preferred. Two-year established plants exhibit good drought tolerance; newly planted doghobbles require periodic watering when seasonal moisture is not plentiful from rain or snow. Mulching is often beneficial. Established plants rarely require fertilizing; use an acidifying fertilizer such as Miracle-Gro™ or Schultz™ as needed.

Doghobble is dominant under dappled or partial shade and grows less vigorously under deep shade. Florida coast will grow in full sun under good moisture. Both species are excellent choices as a shrubby ground cover planted under landscape shade trees, areas formerly occupied by ground hugging junipers. Often, new landscapes are bathe in full sun, but sun-loving ground covers like cotoneasters and junipers decline as the trees cast more shade.

Doghobbles produce creamy white fragrant flowers in May; their slight fragrance filters through their small space over the 2-3 week bloom time. Doghobbles are mostly insect and disease resistant, but leaf spot problems may occasionally ramp up in wet hot summers. Florida coast doghobble appears to be more leaf spot resistant than mountain doghobble.

Photo: ‘Rainbow’ is a popular cultivar with 3-color, variegated foliage.

Allium ‘Millennium’ Outstanding Summer Blooming Ground Cover

Posted by Hugh on May 26th, 2014

‘Millenium’ allium at Kingwood Center, Mansfield, Ohio

Allium ‘Millennium’ is a rhizomatous type allium (onion) introduced by plant breeder Mark McDonough over a decade ago (USDA hardiness zones 5-8). In nursery catalogs it is sometimes listed Allium nutans‘Millennium’. Fleshy strap-like 12-inch long glossy green foliage emits a slight oniony smell when crushed.

‘Millennium’ is a rhizomatous (clump growing) long-lived perennial. Individual plants grow vigorously, 15-20 inches high (in bloom), and spread 10-15 inches. Round-headed rosy purple flowers, 2 inches or more in diameter, appear in mid to late July. They stay in bloom well into August. Millennium tends to bloom 7 to 10 days later, compared to ‘Pink Feathers’, another clump forming cultivar.

Tight mounds of glossy foliage, beautiful flowers, and striking seed heads offer multi-season interest. Nectar-seeking honeybees and butterflies hone in on the flowers. Clumping alliums do not seed-in and become weedy like the bulbous onion types. The dry flower stalks stand upright thru the winter months.

Clumping alliums grow in average well-drained, slightly acidic soils (pH 5.5 to 7.0). They are frequently found in open moist sites such as in rain gardens. One-year established plants become exceptionally drought tolerant and thrive in xeric rock garden soils. Grow in either full to partial sunlight (minimum 4-5 hours) is preferred to maintain their tight clumping ground cover.

Plants may be dug up and divided either in mid-autumn or in early spring before new growth emerges. Alliums are also deer and rabbit proof and usually disease and pest free.

How Hardy Is Chinese Fringe Flower (Loropetalum)

Posted by Hugh on May 24th, 2014

7-8 feet tall fringe flower at Atlanta Botanical Gardens (early April

late in flower cycle

Loropetalum or Chinese fringe flower (Loropetalum chinensis) has clearly caught on with professional landscapers and gardeners (USDA hardiness zones 7 thru 9). It is rated as marginally hardy in northerly zones 6-b, and has succeeded in consecutive mild winters in the past decade. The winter of 2014 had killed some established plants to the ground, but most had re-sprouted by late spring.

This early flowering fringe flowering shrub is a member of the witchhazel family (Hamamelidaceae). Fragrant creamy white flowers open from mid- April into May and in late March in Southern states. Fringe flower occasionally may re-bloom during the summer and fall. Reddish and purple foliage forms are now available in addition to dark green cultivars.

Depending on variety, shrubs grow from 6 feet to 15 feet and 4 to 5 feet wide. New compact cultivars may reach only 2 to 3 feet tall. Short compact cultivars are perfect as borders or as groundcovers in foundation plantings. Taller forms may be utilized as screens and some Southern gardeners train them into small trees.

Fringe flower excels in full day sunlight, but also grow well under light afternoon shade. Plant in moderately acidic (ph5.5-7.0), well- drained soil. Fertilize shrubs in spring and water regularly over summer dry periods.

The return of an old fashioned cold winter could alter your opinion of fringe flower. You might consider the following five cultivars as perhaps cold hardier: ‘Burgundy Blast’, ‘ZhuZhou’, ‘Cherry Blast’, ‘Garnet Fire’, and ‘Purple Diamond’. A new semi-dwarf cultivar named ‘Crimson Fire’ may also be slightly hardier.

At this writing gardeners should continue to rate fringe flower as not reliably hardy north of zone 7.

Japanese Tree Lilac Is Excellent Late Flowering Form

Posted by Hugh on May 21st, 2014

Multi-trunk Form At Biltmore Estates in Asheville, NC

Spent Floral Heads of Japanese Tree Lilac

Japanese tree lilac (Syringa reticulata) is a late flowering lilac, often 2-3 weeks later than the popular common and hybrid shrub lilacs (USDA hardiness zone 3-7). Tree lilac is tall growing, often 20-25 feet tall with a 15-25 foot spread. It forms a nice small multi-trunked street tree.

Tree lilac is the last of the lilacs to bloom. In the Southern Appalachian region (USDA hardiness zones 6 and 7) it blooms in late May and later further north. Large 6 to 12 inch long clusters of creamy white flowers form on the terminal branches and are both showy and fragrant. Two popular cultivars are Ivory Silk® and ‘Summer Sun’. Ivory Silk was chosen as a 1996 Gold Medal Plant by the Pennsylvania Horticultural Society.

Its form and flowering makes it a great choice around a deck or patio as an accent plant. Dark reddish brown bark is white speckled and becomes quite showy when wet following a summer shower. Fall leaf color is usually a non-event.

Tree lilac favors a northerly climate. Fall leaf colors are better in the northern part of its range. Good air circulation is important to prevent leaf diseases that plague other Syringa species. Lilac borers may be problematic if weather is extremely hot and dry. It needs a few hours of afternoon shade in the mid-South.

As with most spring flowering shrubs, prune within a month after flowering. Tree lilac tends to bloom heavier one year and lighter the following year. Removal of seed heads tends to promote annual blooming. Annual pruning controls plant height and shape.

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.