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

A Perfect Year for Hortensia Hydrangeas

Posted by Hugh on August 13th, 2010

2010 has been an exceptional year for big leaf hydrangeas (Hydrangea macrophylla), also called “hortensia” hydrangeas. Consecutive year blooming rarely occurs here in the southern Appalachian region (USDA zones 6 and 7). ‘Nikko Blue” hydrangea, which has not bloomed for over 15 years, has been beautiful in my garden this summer.

Why have big leaf hydrangeas been so “on” this summer? I asked Dr. Sandra Reed, USDA hydrangea breeder at the TN State University Nursery Crops Research Station in McMinnville. Sandra’s response… “the weather”. The 2009 autumn was unusual. October and November temperatures gradually declined. The winter was cold and temps stayed cold, not fluctuating wildly. Across most areas a perfect spring followed with no severe freezes or frosts.

Finally, new hardier cultivars are available such as Endless Summer®, ‘Penny Mac’, and ‘Pia’ (lacecap type). These varieties are remontant, able to bloom on either old or new wood.

If your hydrangea(s) did not bloom this year, check the plant’s light exposure and nutrition. Hortensia types want a minimum of one-half day sunlight, preferably in the morning. Feed shrubs in early spring with a water soluble or slow-release fertilizer according the manufacturer’s package directions.

Cardinal Flower – A Hummingbird Magnet

Posted by Hugh on August 11th, 2010

Cardinal flower (Lobelia cardinalis) is a hardy perennial native in USDA zones 5-8. Clumps should be divided every 2-3 years to retain plant vigor. Soil moisture determines its height and vigor.

Cardinal flower prefers half-day direct morning sunlight, particularly in more southern climes. The brilliant red flowers bloom from late July through most of September, making it a standout on their own or mixed with other perennials. Deadheading (pruning off the old floral stems) extends out its flowering period.

Cardinal flower grows 3 feet high and 2 ½ feet wide, and is taller when planted at the edge of a pond or water garden. This lobelia is at home in a rain garden, particularly when summer moisture is plentiful. Fertilize with a water soluble product monthly or feed bi-monthly with agricultural grade fertilizer (10-10-10 or equivalent) from late winter to the end of the flowering period.

Select these two cultivars — ‘Fried Green Tomatoes’ exhibits bright green foliage which turns a deep olive color on the leaf upper surface and maroon on the underside; flowers are bright red. ‘Monet Moment’ bears exquisite rose-pink flowers. Blooms on both cultivars are exceptionally larger than species.

Summertime Is Here…So Is Locust Leaf Miner

Posted by Hugh on August 8th, 2010

Photo: ‘Freesia’ black locust tree
Some trees take on a dead brownish look along highways in the summer months across the southern Appalachian region (USDA zones 6 and 7). Over the past month, locust leaf miner have been feeding on black locust (Robinia pseudoacacia) trees, stripping chlorophyll from the leaves.

Something to worry about? Generally, no. Spraying insecticides is usually not necessary. By late June black locust trees have completed their “photosynthetic life cycle” and foliar injury does not prevent old established trees from starting fresh next spring.

Generally, American gardeners have always had a low opinion about our native black locust. However, new black locust cultivars are awakening our interests. To list three exciting cultivar introductions- try Twisty Baby™ with lacy foliage and twisted shoots, ‘Purple Robe’ with dark red-rose flowers, and golden leaved ‘Frisia’. These young trees need insect protection.

A time-saving, environmentally safe treatment is a soil application of imidaclopyrid (Bayer Advanced Garden Insecticide™) in early spring. Simply, the pesticide is applied to the ground under the tree and watered in (according to label directions). This prevents beetle larvae development in the spring, and eliminates the threat of the summer leaf skeletonizing adults.

An alternative summer treatment is to spray any pyrethoid insecticide labeled for landscape trees and shrubs. Spraying large trees are a chore, requiring two or more applications over a 4-6 week period.

‘Notify Grounds Crew’ Daylily

Posted by Hugh on August 5th, 2010

What’s in a name? During our July pilgrimage to Kingwood Center in Mansfield, Ohio, I photographed this unlabelled daylily. It towered over all other daylilies in the large display bed. Of course, my curiosity go the better of me, and I had to know its name.

Mystery solved, thanks to Mr. Charles Applegate, Kingwood gardener for the past 42 years. Charles called me, and provided the pedigree of ‘Notify Ground Crew’. What a great name, one that I will not likely to forget.

‘Notify Ground Crew” is a mid-season tetraploid bloomer. It exhibits extremely tall 72-inch high floral scapes and is well-branched (see photo). Cheery, 5 inch wide, bright yellow flowers tower above all other daylily varieties in the bed. It was bred by Curt Hanson in Michigan and introduced in 2000. It is very modestly priced and available from several on-line nurseries.

Arkansas Amsonia – 2011 Perennial Plant of the Year

Posted by Hugh on August 2nd, 2010

Since 1990, the Perennial Plant Association (PPA) has annually selected one outstanding perennial for gardeners to enjoy. Last week, at the annual PPA Symposium in Portland, OR, members selected Arkansas amsonia (Amsonia hubrichtii) as the 2011 Perennial Plant of the Year.
Why wait until next year to purchase amsonia? It is available now through many garden centers, mail order, and on-line nurseries. Amsonia begins its rapid growth in early April. A month later, the 3 foot tall and wide plants are blooming. Pale “bluestar” flowers bloom over 2-3 weeks in the southern Appalachian region (USDA zones 6 and 7).
Flowering is just a prelude to its other attributes. Blue-green, fine textured summer foliage is devoid of serious disease and insect problems and is deer proof. In October, its foliage turns a spectacular lemony yellow. To achieve maximum autumn foliar impact, plant three or more amsonia spaced 3 to 4 feet apart.
Amsonia forms strong stems under full day sunlight; branches are weak or floppy in partial shade. It grows in any well-drained soil with a pH range from 5.6 -6.8. Established plants are heat, humidity, and drought tolerant.
Furthermore, don’t overlook another perennial favorite, bluestar amsonia (A. tabernaemontana), which will be featured in a future blog.

Thousand Cankers Disease Found in Knoxville, TN

Posted by Hugh on July 29th, 2010

Photo: walnut canker from Dr. Alan Windham, Extension Plant Pathologist, University of Tennessee

A black walnut (Juglans nigra) sample collected by Dr. Scott Schlarbaum, research forester at the University of Tennessee, has been confirmed as thousand cankers disease (TCD) (Geosmithia sp. nov.). Also found in the Knoxville TN walnut sample was one adult male beetle, verified as walnut twig beetle (Pityophthorus juglandis).

This is the first report of the walnut twig beetle and TCD in the native range of black walnut. TCD has killed thousands of walnut trees in the western United States and could potentially be devastating in the eastern United States as well. The extent of the outbreak in the Knoxville area is unknown at this time. The affected trees are in an urban area. Judging the sample, the disease has been present in the region for a number of years and is causing mortality.

Based on our experience TCD will be difficult, if not impossible, to stop. The hope is that the beetle and disease will behave differently in the eastern U.S. It takes 3-5 years to kill a large walnut tree. There are probably other outbreaks in the East that have not yet been noticed.

Dr. Alan Windham, UT Extension Plant Pathologist, urges foresters and others to be on the lookout for unusual dieback or mortality of walnuts, especially in urban areas. This is where TCD is likely to occur first because of movement of the beetle in wood (firewood, fresh lumber).

At this time the USDA has no federal quarantine on TCD, and this disease is not on any action lists. For further information, search: http://www.ppdl.purdue.edu/PPDL/pubs/walnutthousandcankersdisease.pdf

Pennisetum ‘Karley Rose’

Posted by Hugh on July 25th, 2010

Asian fountain grass cultivar ‘Karley Rose'(Pennisetum orientale) is a four season eye-catcher. It is reliably hardy in USDA zones 5-9. It produces smoky rose colored flower spikes (plumes) in early summer, which persist thru the winter months. Its dark green foliage begins upright in form, 2 1/2 feet tall, achieving 3 feet in height in flower. By mid- summer the grass blades cascade down, true to the name “fountain grass”.

Grow ‘Karley Rose’ in full sun or partial areas with 6 hours sunlight to maintain optimum grass form and plume color. Despite proven drought tolerance, it prefers to grow in compost rich, well-drained soil. It has a wide soil pH preference from acidic to slightly alkaline (6.2 to 7.5).

This clump growing grass is quick to establish and prospers for many years. Annual maintenance is minimal. In late fall or late winter cut back the old foliage to 3-4 inches and feed with a high nitrogen lawn grade fertilizer. Fountain grass has no serious disease or insect problems and is deer resistant and salt tolerant.

The handsome foliage and attractive flower spikes of ‘Karley Rose’ provide excellent texture and seasonal color. Use as an accent specimen or group together in mass plantings.

‘Buttered Popcorn’ Daylily- Performs In The Mid-South

Posted by Hugh on July 22nd, 2010

Daylily ‘Buttered Popcorn’ (Hemerocallis ‘Buttered Popcorn’) produces buttery yellow 6″ flowers from late June thru mid-July. The 32-inch tall floral scapes are well branched and flowers are mildly fragrant. Bud count on each scape may average 10 or more.

This tetraploid cultivar is also well known for its incredible fall re-bloom. In the Southern Appalachian Region (zones 6-7), ‘Buttered Popcorn’ is rated as a better re-blooming daylily than popular favorite ‘Stella de Oro’.

Daylilies require little care. They grow in almost any well-drained soil type. Daylilies grow best in full to partially sunny areas. Allow 6 hours of sunlight for high bud bloom count. Although drought tolerant, re-blooming varieties perform best with 1-inch or more of water (or rainfall) per week during the summer months.

In late fall, cutback daylilies to 3-6 inches in height. Remove the old plant debris. Daylilies possess good disease and pest resistance. Fertilize once with 10-10-10 and mulch plants in late winter or spring. Feed a second time in early June before flowering begins.

Daylilies are great additions to large containers or plant them in garden beds. The short (under 24-inch tall) daylily varieties are also utilized as ground covers on steep slopes.

‘Diabolo’ Ninebark as Small Patio Tree

Posted by Hugh on July 18th, 2010

photo: ‘Diabolo’ ninebark trained as a small tree

I saw this idea several years ago at an Ohio nursery. Common ninebark (Physocarpus opulifolius) is basically a utility shrub, inexpensive to purchase in large quantities. This midwest native grows in almost any soil or landscape environ except shade and bog areas. Over the past decade ninebark has gone to “beauty school”, and a number of new cultivars, including purple leaved ‘Diabolo’, are currently available.

Ninebark is a vigorous grower and possesses a unique exfoliating bark trait. In the hands of a capable pruner, ninebark can be easily shaped into a small 10-12 foot single stemmed tree. The purple ‘Diabolo’ foliage plus its inner light tan-colored ninebark adds up to a winning landscape combination.

I suspect that suckering at the crown will likely continue, necessitating sucker removal by a hand pruner (do not use a weed wacker) every few months. ‘Diabolo’ ninebark purple leaf color holds the longest under full sun and bleaches out to green by mid-summer. ‘Diabolo’ offers pinkish white flowers from mid-May into June, followed by red fruit clusters (seed capsules) through the summer months.

Windmill Palm

Posted by Hugh on July 15th, 2010

Photo by Dr. Tim McDowell, East TN State University Botanist of an 8 year old windmill palm (now deceased)
Windmill Palm (Trachycarpus fortunei) is not reliably hardy in the Southern Appalachian region (zones 6-7), even when planted in an outdoor protected area. An alternative is to grow in a container for ease of moving it indoors before the cold weather in late autumn arrives. Windmill palm is hardy to +15° F.

If planted in a protected garden spot, dig a hole wide twice as wide and no deeper than it came in the nursery pot. Palms, particularly those which you are trying out, are best planted in very late May. Frequent watering is crucial for a newly-planted palm. The well-drained porous soil should not be allow to completely dry out. Windmill palm should be fed bi-monthly during the warm months with a water-soluble fertilizer applications.

Windmill palm may eventually grow from 10 – 20 feet in height. Its medium green palmate leaves are circular, increasing in diameter to approximately 3 feet after 20-30 years. The trunk is covered with dense, light brown, hair-like fibers, easily damaged, and made vulnerable to insects and fungus.