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.

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.

Mighty Rodgersias For Your Shade Garden

Posted by Hugh on April 14th, 2014

Rodgersia In Vancouver Botanical Garden, BC, Canada

In a shade garden the large palmately compound foliage of rodgersias (Rodgersia spp.) make a bold statement (USDA hardiness zones 4-9). In recent years rodgersias are becoming more available at garden centers in the U.S. Three of five species are listed below. Hybrid forms are also available.

Rodgersias thrive in moist, organically rich soils. They want either half-day direct morning sun or partial shade all day long. They also prefer a cool location. Shoots emerge slowly in late spring. The edge of a bog garden, pond, or in a damp meadow are good places to grow rodgersias, along with other moisture loving plants as ferns, toad lilies (Tricytris spp.), sweet flags (Acorus gramineus), ligularias, astilbes, and hostas.

Give rodgersia three years to bulk up. Their size and leaf texture will make them a focal point in your shade garden. Plants grow 3 to 6 feet tall depending on species, soil quality, nutritional level, plant age, and soil moisture. In late spring/early summer, white flowers rise high above the foliage and the old floral heads age gracefully. Rodgersias exhibit few disease or pest problems.

Fingerleaf rodgersia (Rodgersia aesculifolia) is the most available in the U.S. Native to China it grows 3 to 5 feet tall and wide and features thick blackened rhizomes (USDA hardiness zones 5-9). The attractive non- petalled (apetulous) flowers are fragrant and the flower stalks, stems and leaf margins are covered with brown hairs. Flowers stand well above the foliage. The large, crinkled, coarsely-toothed, palmate, dark green, basal leaves span 12 inches across with seven (vary from 6-9) leaflets. The foliage of cultivar ‘Chocolate Wings’ remains dark bronze all season long.

Featherleaf rodgersia (Rodgersia pinnata) grows 3 to 4 feet tall and wide. Leaves arranged in pairs. Clusters of apetulous, white, creamy-pink, or rose-red flowers arise high above the foliage. Each of the 6-9 palmate leaflets range from 6-8 inches in length. By late summer foliage has turned reddish-bronze. ‘Superba’ is a popular cultivar with bronze-tinted foliage all season and bright pink flowers.

Bronze-leaf rodgersia (Rodgersia podophylla) exhibit 5 large, jagged palmate leaflets that emerge bronze-green in the spring, green in summer, and rust red in the fall (5-8). It grows 3 to 6 feet high and wide. The creamy white foot long flowers tower above the foliage.

Re-starting Summer Flowering Shrubs After Winter Injury

Posted by Hugh on March 9th, 2014

Chaste tree (Vitex agnus-castus)

Some non-hardy shrubs can be treated as hardy perennials. Crape myrtles (Lagerstroemia indica) and chastetree (Vitex agnus-castus) may emerge in poor condition after an unusually cold winter. Shrubs like butterfly bush (Buddleia spp.), and blue mist (Caryopteris spp.) often emerge in a ragged state, but recover quicker if cutback near the ground several weeks before spring bud break.

All examples are summer bloomers on current season’s wood. Renewal pruning is easy to understand, essentially cutting a shrub back to 3-6 inches above the ground. There is no advanced waiting required before grabbing a lopping shears or chain saw to perform this task.

After pruning follow-up by feeding the cutback shrubs. Each shrub or tree should receive a heaping handful of 10-10-10 or equivalent granular fertilizer. Fertilizer should be spread 12-18 inches away for the crown (base) of the tree or shrub. One caveat: the shrub should be healthy before renewal pruning is tried. A weak plant is unlikely to survive this technique, but will likely grow and bloom poorly if you had not acted.

By mid-spring, many shoots are likely to grow around the shrub base. A follow-up pruning may be needed if you desire a taller shrub. Leaving many multiple shoots will reduce plant height. Also, the amount of sunlight penetrating the plant will be inadequate, resulting in poor summer flowering.

Tips On Growing Sourwood Trees

Posted by Hugh on February 22nd, 2014

Awesome Fall Color Of Sourwood In Western North Carolina

Sourwood (Oxydendrum arboreum) is one of the most beautiful flowering trees in the U.S. Trying to establish one in your landscape can prove quite challenging. In the wild sourwood grows in shallow soils on steep craggy or rocky ground. Dry ground seems to be the rule. It grows either multi-stemmed (shrub-like) to 20-30 feet or tree form to 35-40 feet and half that in width.

Sourwood is a pioneering species. Tiny dehiscent seeds are dispersed into the wind and blown like dust over many acres of land. Tens of thousands of seedlings germinate each spring on new ground that may have been previously clear cut for reclamation. If available, supply water intermittently over dry periods the first two summers. Established trees tend to better cope with heat and dry soils.

For a home gardener the challenge seems to be getting one established. Site them in the type of soil and environmental conditions which rhododendrons and mountain laurels enjoy. They prefer a loose, gravelly, acidic soil containing some organic matter and excellent drainage. A newly-planted sourwood prioritizes by establishing its root system first.

Purchase primarily nursery container-grown trees, if you can find them. Plant in well-drained soil and prune the new tree or shrub back to 6-12 inches from the ground in early spring. Essentially, you are starting over with 100% root system and 10-15% top (shoot). What comes up is your new tree, more vigorous than one not pruned.

In nature sourwood seem to prefer the eastern facing slope of the woodland where they receive midday sun. Young transplants respond to fertilizing; older well-established trees do not. Sourwood requires little pruning and has few serious insect or disease problems.

2014 Plant Winners Announced

Posted by Hugh on February 8th, 2014

Echinacea (coneflower) named 2014 Perennial of the Year by National Gardeners Bureau

Petunia Declared Annual of 2014 by NGB

At the start of each year the Motion Picture Industry awards their Golden Globes and Oscars. The Music Industry has the Grammys. Gardening associations also announce the award-winning plants.

The National Garden Bureau (NGB) has declared 2014 Year of the Echinacea (coneflower) in the perennial category. NGB declared the mighty cucumber as Vegetable of The Year, and Petunia as Annual of The Year. Their primary purpose is to create buzz among gardeners about these great plants. NGB’s website there is lots of reliable cultural information about these plants and other plants. It helps growers and garden centers to increase plant sales.

All American Selections (AAS) trials annuals and vegetables varieties across the United States annually. AAS awards now includes perennials and the 2014 perennial picks are: Gaura Sparkle White (Bedding Plant Award) and Penstemon Arabesque Red F1 (Flower Award).

Perennial Plant Association (PPA) selected Northwind switchgrass (Panicum virgatum ‘Northwind’) as the 2014 Perennial Plant of the Year. This native grass grows 5 to 6 feet tall with a narrow upright form and steel green foliage.

2014 Hosta of the Year (American Hosta Society) – Hosta ‘Abiqua Drinking Gourd’ features deeply cupped, thick textured leaves. The rich blue-green leaves are large size, heavily corrugated.

2013 Stout Silver Medal Winner (American Hemerocallis Society) – ‘Heavenly Angel Ice’ is a re-blooming daylily with 8-inch wide flowers/white petals and green-yellow throat. Flower scapes grow 36 inches high. Note: 2014 winner is designated late in 2014.

2014 Dykes Medal Winner (America Iris Society) – Iris ‘That’s All Folks’ is a tall bearded iris with giant brilliant golden flowers with ruffled and laced edge petals.

2014 Ivy of the Year (American Ivy Society) – Hedera helix ‘Teneriffe’ – an old ivy variety with yellow-cream colored variegated, small-leafed ivy.

Winter Sap Bleeding From Trees Not Harmful

Posted by Hugh on January 28th, 2014

Icicle Off Poor Pruning Cut in Fall

Winter can be a cruel period for trees. Day-night temperatures may wildly fluctuate and drying winds tend to injure tender buds. Maples (Acer spp.), flowering dogwoods (Cornus florida), birches (Betula spp.), yellowwoods (Cladrastis kentukea), walnuts (Juglans spp.) and elms (Ulmus spp.) are “bleeders”. The sap pressure inside branches is highest during the winter months.

If any tree jeopardizes a house, property, utility lines, and human safety, it should be pruned no matter the time of year. The bleeding sap phenomena is over-rated. Winter-pruned bleeder trees will not die. If it humanly bothers you, prune these “bleeder” species in the summer when sap pressure is lowest.

Leaky sap may drip on pedestrians, cars, and walkways resulting in stains on trunk bark and sidewalks. Puddles on walkways may freeze and create slippery pavement.

Bleeding or sap loss will eventually stop on its own. Quickly, the pruning wound cuts have internally sealed off and the healing process started.

Spraying paint (wound dressing) does not help. Many times the sap flow is so plentiful as to wash the wound paint off. You may want to irrigate the tree during dry spells to speed wound healing.

If you’re seeking advice about pruning large shade trees, consult a certified arborist first. The International Society of Arboriculture (ISA) website should list one or more in your area.

Soil Sampling Is Good Insurance

Posted by Hugh on January 25th, 2014

Soil sampling is good gardening insurance!

Do you know what your soil needs to grow a great lawn, flower, or vegetable garden? If you haven’t analyzed the soil in the past five years, get it done in any season. Most gardeners do it in late winter when university, state, and private soil labs are busiest.

The local Extension office or a garden center can supply you with one or more sample kits with instructions and forms detailing how to sample. Mail the soil, form, and money to the soil lab.

If soil conditions have drastically changed because great amounts of organic matter, topsoil, etc. were added or accidentally spilled fertilizer or another chemical, retest your soil. Do you have a special problem area? Separately test this spot and explain the problem. Photos are optional.

In early fall, before you’re ready to tackle a major fescue/bluegrass lawn renovation, soil test before the work starts. Be sure to mark on the form that you want recommendations for a lawn. With a lab results in hand, they detail how many pounds of fertilizer to apply. If lime or sulfur to raise or lower the soil pH, that is included on your report.

If you’re planting acid-loving plants such as azaleas, blueberries or mountain laurels (Kalmia app.), inform the soil lab; they will estimate when and how much sulfur to apply. Planning a home fruit orchard (apples, peaches, plums, grapes, brambles), tell the lab intended use of the land.

Basic sampling instructions: using a trowel, take 8-10 random samples of topsoil from various parts of your yard. Dig only 5-6 inches deep. Mix all together thoroughly in a bucket. Place a small amount of the soil mixture in a paper (not plastic) bag or box, enough to fill a small baby food jar. Do not ship wet soil.

“Death By Mower” Disease

Posted by Hugh on January 22nd, 2014

Dead Dogwood By “Mower Disease”

“Mower disease” is a totally preventable human malady caused by permitting lawn grasses and weeds from growing near the crown of trees and shrubs. The problem is commonly seen on large properties such as church grounds, cemeteries and public parks. Large gang mowing machines (with many reels) cut 95-98% of the turf area. Workers follow along with push mowers and string, blade weed-eaters or “weed wackers” around trees and shrubs.

String mowers are blamed for most of the unsightly bark injuries. The tree or shrub is eventually weakened by sap leakage and nutrient loss. The damage also exposes the tree/shrub crown to numerous disease infection and insect borers.

A better management practice is to maintain a thin organic mulch zone around the tree or shrub base. The mulch should never be piled up against the trunk. A mulch layer more than 4 inches is not recommended.

Weeds will eventually grow on surface of decaying mulch barrier. Periodically, hoe or hand-pull invading grasses and weeds atop the mulch. An alternative is to spray a weed herbicide such as Round-up™ or an equivalent product according to label directions. When done, add 1-inch of mulch for a fresh clean appearance.

Moving Large And Mature Trees

Posted by Hugh on January 5th, 2014

Mature ‘Crimson Queen’ Japanese maple at Samara Farms Nursery, Nashville, TN

Perhaps tree lovers can’t plant wonderful trees such as shagbark hickory (Carya ovata), American beech (Fagus grandifolia), or white oak (Quercus alba). They can purchase property with the tree(s) growing on them. Most nurseries do not grow these difficult species or guarantee their success after planting. But, all is not lost!

Modern nurseries, backed by university research, have debunked many tree planting myths. For example, the recommended size and shape of a planting hole has changed. Digging a wide shallow hole is better than a narrow deep one.

Perhaps an old 100 year old Japanese maple may require a new home. There are specialty nurseries which are able to transport old mature trees hundreds of miles. We know more about how trees grow and the best time to lift and transplant one to a new hole several hundred miles away.

Some difficult to transplant trees can be moved during a narrow window of 4 to 6 weeks commencing in mid-winter. Digging is performed by a knowledgeable certified arborist and a specialty nursery with the proper equipment. These tree experts are listed on the International Society of Arboriculture (ISA) website: www.treesaregood.org

Some tree species are reputed to being difficult to move. Blackgum or tupelo (Nyssa sylvatica) is one such tree. Perhaps, this was true 50 to 100 years ago, but better cultivars have come along. Cultivars ‘Wildfire’ and ‘Red Rage are improved blackgum selections.