Potential Epidemic In Your Car Trunk Or Camper?

Photo: walnut twig beetle infestation

Tennessee Department of Agriculture (TDA) officials urge state residents and visitors to the state to help prevent the spread of Thousand Cankers Disease in black walnut (Juglans nigra)trees and Emerald Ash Borer in ash species (Fraxinus spp.). Take the following steps:

 Don’t transport firewood, even within Tennessee. Don’t bring firewood along for camping trips. Buy the wood you need from a local source. Don’t bring wood home with you.

 Don’t buy or move firewood from outside the state. If someone comes to your door selling firewood, ask them about the source, and don’t buy wood from outside the state.

 Watch for signs of walnut twig beetle infestation in your black walnut trees. If you suspect your black walnut tree is infested with TCD, visit www.TN.gov/agriculture/tcd for an online symptoms checklist and report form or call TDA’s Regulatory Services Division at 1-800-628-2631.

Mulching- Not Always a Good Practice

A generation of gardeners have extolled the benefits of mulching around trees and flower beds. Sometimes, mulching is not a good practice.

Often, a heavy clay soil retains too much moisture over the winter months. Some dryland perennials, such as cheddar pinks (dianthus), euphorbia, and delospermum, prefer dry to moderately wet winter soils. Amending with coarse sand improves soil drainage, but adding mulch may be counter-productive.

Quality mulch contains very little cellulose (wood) fiber. A wood based mulch attracts structural wood -feeding insects such as termites, carpenter ants, and wood beetles. Wood-based mulches should not be spread around home foundations.

Fresh wood-based mulch grabs up available soil nitrogen. Nitrogen -starved plants appear yellowed (chlorotic). You may need to apply 2-4 times the amount of fertilizer to counteract the wood mulch.

Piling up mulch around the base of trees, called "mulch volcanoes", will damage tree trunks. Surface roots are deprived of oxygen. Often, weak adventitious roots grow in the mulch. When the mulch dries out, the weak roots die and scar the trunk.

Young fruit trees should not be mulched in the fall and winter where field mice (voles) are suspected. The voles create a home in the mulch and feed on live roots and soft tree bark.

Zones 6 Winter Hardy Encore Azaleas™

'Autumn Ruby' Encore azalea in April 2009

Photo credit: Dr. Alan Windham, Extension Plant Pathologist, University of Tennessee

Encore Azaleas™ bloom twice: in the spring and from late summer into the fall season.
Ten varieties consistently exhibited cold hardiness throughout zones 6-a and 6-b: Autumn Amethyst, Autumn Carnation, Autumn Cheer, Autumn Lilac, Autumn Royalty, Autumn Ruby, Autumn Sangria, Autumn Sundance, Autumn Sunset, and Autumn Twist.

In Zone 6-b, nine additional varieties also consistently exhibited exceptional cold hardiness: Autumn Bravo, Autumn Carnival, Autumn Debutante, Autumn Embers , Autumn Empress , Autumn Monarch, Autumn Princess, Autumn Rouge, and Autumn Sweetheart.

For best results in plant zones 6-b and colder, gardeners should plant in the spring or early summer. In Zones 7-9, Encore Azaleas benefit from fall and late summer planting schedules. Their multi-season blooms make them ideal for container gardens.

Encore azaleas™ begin blooming each spring like traditional azaleas. These evergreen azaleas enjoy more sun than traditional azaleas. Encore Azaleas were bred by Robert E. “Buddy” Lee of Independence, Louisiana and are available at many independent garden centers.

Chinese (Kousa) Dogwood Doesn't Like Extreme Heat

photo: leaf curl on kousa dogwood
Never forget the adage: "the right plant in the right location". In USDA hardiness zone 7 and warmer parts of zone 6-b, Chinese dogwood (Cornus kousa) does not cope with excessive summer heat well. A typical stress response is leaf curling. On more stressful droughty sites, leaf margins and centers will likely burn.

The young tree pictured above is planted along a suburban street, with a concrete sidewalk and street curb on two sides. Thick turf sod covers the ground beneath the tree, competing with the tree for available soil moisture and nutrients. On a hot 90°F day, this tree is likely to experience heat indices above 120°F.

Likely, the tree will survive, but not bloom dependably every spring. Leaf burning and curling reduce the tree’s ability to photosynthesize, resulting in less (or more) flower bud set. The tree will either flower poorly or bloom heavily in future springs, resulting in an alternate flowering cycle or "biennial bearing".

Kousa dogwood will handle full sun locations, provided heat and drought stresses are managed through timely irrigation. Currently, the University of Tennessee is evaluating several seedling kousa selections for better heat and drought tolerances here in the mid-South.

'Dee Runk' is Best Upright Boxwood

Looking for the best upright boxwood for your garden or landscape? According to wholesale boxwood growers, Saunders Brothers Nursery in Roanoke, VA and Weigel Farms near Greensboro, NC, the best is 'Dee Runk' (pictured).

Over the past quarter century, the boxwood cultivar 'Graham Blandy' had been the standard bearer, but commercial landscapers have increasingly complained about losing plants to pythium and phytophthora root rot diseases. 'Dee Runk' and another called 'Fastigiata' possess better disease resistance. ‘Dee Runk’ is also more reliable than the root rot prone ‘Sky Pencil’ holly (Ilex crenata 'Sky Pencil').

Buxus sempervirens ‘Dee Runk’ is remarkably winter hardy (USDA hardiness zones 5-8). Growth rate is medium, reaching 10 feet in height and 3 feet in width after 15 years. New foliage begins with a bluish-green tint and matures dark green. Boxwoods are deer-resistant and pollution tolerant.

In general, boxwoods tolerate most garden light conditions from full sun or moderate shade at the edge of a woodland garden. ‘Dee Runk’ also handles poor clay sites, provided soils are well-drained.

Landscape uses: specimen, screens/formal hedges, in containers, and a foundation shrub that won’t interfere with roof eaves in future years.

Intensia® Phlox Stand Up to Summer Heat

Photo: 'Intensia Lilac Rose'
The Intensia® Phlox series are the result of a cross between P. drummondii and a southwestern U.S. phlox species. Growth is low and cascading which makes this annual phlox ideal for planting in the front garden border. Equally, Intensia® Phlox excel in mixed containers, window boxes, and hanging baskets.

Intensia® phlox grow to a uniform 8-12” mature height in full to partial sun (best in 6 hours or more sunlight). Intensia phlox possess exceptional heat and humidity tolerances and flower freely all summer long. Insect and disease problems are minimal, exhibiting above average powdery mildew resistance.

Annual phlox thrive in well-drained garden soil which has been generously amended with organic matter. After planting, water on a 7-10 day schedule, particularly when rainfall is not plentiful.

By mid-summer plants may appear seedy and overgrown. Mow them back to 5 inches high, add fertilizer, and irrigate. The phlox bed will perk up and re-bloom within a few weeks, and right into the autumn season.

Blooms are slightly fragrance and attract frequent visits from nectar-hungry bees and butterflies.Flower colors of the Intensia® series range from white, several pink shades, lavender, and purple.

Pruning Big Leaf Hydrangeas

photo credit: Dr. Ken Tilt, Auburn University

When mophead and lacecap hydrangeas (Hydrangea macrophylla) get too tall, leggy, or have outgrown their garden space, prune them now from mid-July thru mid-August. Our native oakleaf hydrangeas (H. quercifolia) are pruned at this time as well. Remove withered or faded flowers; some new flowers may replace those that you have deadheaded in September.

These two hydrangea species set their flower buds for next spring on old or current season’s growth on the terminal bud. Pruning in the fall or winter may remove flower buds or stimulate soft late shoots which die over the winter. Make all cuts at 1/4 inch above the last set of leaves (see photo) or cutback flush to a main branch.

Pruning improves the health of the plant, increasing vegetative growth. On older 4-5 year old hydrangeas, remove larger, thicker canes and prune them at the base of the stem. Remove one-quarter to one-third of these older branches. In 3-4 years the hydrangea will be completely rejuvenated.

Dead, dying, diseased stems and flowers can be removed at any time of year.