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

Stewartia- A Tree for All Seasons

Posted by Hugh on June 1st, 2011

Lovely Japanese stewartia at Biltmore Estate in Asheville, NC

June flowering stewartia

Japanese stewartia (Stewartia pseudocamellia) is a truly beautiful 20-30 foot small tree or multi-trunked shrub. Stewartia may be finicky to grow, but a great plant nonetheless. Although rarely seen in U.S. gardens, Japanese stewartia is the most commonly grown of the six stewartia species. All are winter hardy in the Southern Appalachian region (USDA zones 6 and 7).

Visually, stewartia provides four seasons of ornamental beauty. Lovely 2 to 2 ½ inch camellia-like white flowers appear in early June and are in bloom for 2 – 3 weeks. The 3 – 4 inch blemish-free green summer foliage turns yellow and/or crimson red in mid- autumn, depending on its location. Its patchwork mottled bark becomes more attractive with age.

The trick to growing stewartia is selecting a proper site. Stewartia may flourish for many years if the soil drainage and sunlight exposure are near perfect. Japanese stewartia grows similar to flowering dogwood (Cornus florida), requiring a compost rich, acidic pH and almost perfectly drained soil.

Filtered all-day sunlight or six hours of morning /early afternoon sunlight is ideal. Prolonged periods of scorching summer heat and low rainfall may be fatal to Japanese stewartia. Irrigate to cool and refresh the tree(s) and keep adequately mulched.

Does Mulch Attract Termites?

Posted by Hugh on May 29th, 2011

Recently mulched shrubs

Mulching, in itself, does not attract termites to your home. That’s the conclusion of two university studies. Soil moisture appears to be the key factor that attracts termites to the home. The subterranean termites found in scattered, localized areas are routinely found in wood chip mulch.

While landscape mulches are good for woody and herbaceous plants, they’re admittedly favorable for termites and other insects as well. Soil moisture favors termite exploration, tunneling and feeding.

University of Maryland entomologists found that termite populations were detected beneath many kinds of mulches, including eucalyptus, hardwood, pine bark, and pea gravel. However, termite activity was significantly higher beneath the gravel mulch. Scientists concluded that termite activity is more about a suitable habitat.

A University of Florida study reported that termites can be found in mulch, but their survival is poor. Why? – because the ability of termites to survive the chipping process that manufactures mulch is not good. Mulch-fed termites suffer significantly lower survivorship.

Overall recommendations: Keep mulch 12-18 inches away from the house foundation. Termites do need a cellulose materials like mulch to feed on. Always watch for signs of termites and their location (activity) around your home.

Is Paulownia Invasive?

Posted by Hugh on May 24th, 2011

Paulownia uninvited!!

Paulownia or Empress tree (Paulownia tomentosa) is a medium to large 30-50 foot tree. It is extremely fast growing, brittle wooded tree, as much as 4 feet per year. Across the Southern Appalachian region (USDA zones 6 and 7), the large pale violet flowers of paulownia are easily visible in May, perched on branch tips.

Its enormous 10-12 inch large medium green leaves are pushing out at the same time. The leaves dump considerable litter beneath the tree in the fall. Fall foliage color is of little importance.

Paulownia is an exotic from China which many plant experts have labelled “invasive”. A large paulownia tree produces many thousands of viable seeds which are dispersed by wind. The seeds are very susceptible to damping off disease (Pythium) and many do not survive. Seeds do germinate on “sterile” soil such as recently cleared ground and burned areas.

Paulownia is rarely seen in open fields already containing vegetation, compared to other serious invasives such as tree-of-heaven, privet, honeysuckle, et.al. It may grow on the edge of forests, but does not survive or compete in woodland shade.

Paulownia wood is highly prized by the Japanese for furniture, cooking utensils, owls, etc. There are several growers in the Southeastern U.S. who grow the fast growing paulownia wood for its export value.

Yellowwood Not Every Year Bloomer

Posted by Hugh on May 22nd, 2011

Yellowwood's gray beech-like bark

American yellowwood (Cladrastis kentukea) is a medium-sized flowering tree. In the month of May, a beautiful yellowwood tree is in bloom somewhere in the Southern Appalachian region (USDA zone 6 and 7). The 1- 1 1/2 inch white pea blossoms comprise the 8-14 inch long wisteria-like panicles which drape from branch and twig tips.

Yellowwood may bloom 2 to 3 consecutive years and not flower again for 1 to 2 years. The triggering mechanism for flowering is not clearly understood. A complex of environmental and physiological factors may be involved.

Over the past two decades the weather across the Southern Appalachian region can only be described as “extreme”, unusually dry, hot summers and unseasonably mild winters. A physiological condition called “biennial bearing” may be in play here. If a tree sets an unusually heavy seed load one summer, few to no flowers are initiated the following spring.

Whether it flowers or not, yellowwood makes a fine landscape shade tree for any sized landscape. Plant in well drained, slightly acidic soil in full sunlight. Its dark green compound leaves remain pest free from spring until early autumn. Yellowwood’s bright yellow fall color arrives at a time when many trees have already defoliated. Its smooth gray colored bark is very beech-like and has multi-seasonal interest.

Summer Wine™: The Taming of The Ninebark

Posted by Hugh on May 19th, 2011

Physocarpus 'Summer Wine'

Over the past 25 years our native Eastern ninebark (Physocarpus opulifolius) has been reborn. Its overly vigorous nature has been tamed. Latest up is Summer Wine™ ninebark with small, deeply cut, wine burgundy leaves, quite different from the medium green foliage of old-fashioned ninebarks. Summer Wine is a more compact (5-6 feet in height and width) grower.

Grow ninebark in full sun to retain its reddish leaf color longer. Ninebark grows in any soil type, tolerates wet soggy ground, and is pH insensitive. It demonstrates exceptional heat and drought tolerance after one year in the garden. Annual pruning, right after spring flowers have faded, further limits growth and presents many design choices.

Summer Wine fits a multiple of landscape uses: grouped enmasse as a dense growing deciduous hedge, screen or border, or grown by itself as a landscape specimen or in a patio container. Ninebark grown in outdoor containers is winter hardy here in the Southern Appalachian region (USDA zones 6 and 7).

White spirea-like flower clusters, 1 ½ – 2 inch wide, open in May. White blossoms and dark foliage playoff each other. The reddish leaf tint has bled out by mid-summer, now dark green and usually blemish-free. Autumn leaf color is of no consequence.

Select Hollies for Privacy

Posted by Hugh on May 16th, 2011

: Ilex opaca ‘Greenleaf’

I continue to witness the overplanting of Leyland cypress (Cupressocyparis x leylandii) across the Southern Appalachian region (USDA zones 6 and 7). This is followed by Japanese cedar (Cryptomeria japonica) and western arborvitae (Thuja x plicata). These three evergreen species have a rapid growth rate and eventually attain heights of 40-60 feet, sometimes in less than 20 years. Ask yourself the question: “do you really need a huge green barrier around your property?”

Hollies offer the benefits of lustrous green foliage and colorful fruit. The following evergreen species create a dependable privacy screen: Dwarf Burford holly (I. cornuta ‘Dwarf Burford’), Inkberry (I. glabra), American holly (I. opaca), Foster #2 holly (I. x attenuata), and Nellie R. Stevens holly (I. x ‘Nellie R. Stevens’).

A few simple tips about growing hollies:

Hollies prefer a slightly acidic, well-drained, and organically rich soil.
Hollies prefer full to partial sun location.
Established hollies demonstrate good drought tolerance.
Space plants a minimum of 12 feet apart.
Hollies should be properly mated. Fruit are produced on female cultivars and a matching male pollinator should be planted.

Growing Azaleas in Outdoor Containers Year-Around

Posted by Hugh on May 10th, 2011

'Elsie Lee' azalea (photo by Sam Kinsey)

In the Southern Appalachian region (USDA zones 6 and 7), if you desire to grow azaleas in above ground containers year around, you must select winter hardy cultivars. Two of the best for containers are ‘Elsie Lee’ (2½- inch wide semi-double light lavender blooms) and ‘Herbert’ (1 ¾- inch wide bright purple with dark blotch). ‘Elsie Lee’ boasts a neat, compact shrub form while ‘Herbert’ has a dense, slightly more spreading habit.

Both exhibit exceptionally long flower period. Spring – summer leaves are medium green, changing to bright yellow, orange, and/or red shades in the autumn. They’re mid-season bloomers and vigorous growers, attaining 3-4 feet in height and width in 10 years.

Grow azaleas to keep roots cool inside the lightly colored (not black) containers. Follow a regular watering and nutrient feeding schedule to establish a deep, extensive root system. Pot in a well drained peat and bark based potting soil or medium with a 2-3” surface layer of mulch. Feed with an acid-based liquid fertilizer like Miracle-Gro™ or Miracid™. Prune azaleas as needed to shape plants and to eliminate dead or diseased twigs.

‘Elsie Lee’ is a Tony Shammarello hybrid from Ohio. ‘Herbert’ azalea (R. yedoense var. poukhanense x R. ‘Hexe’) is a fabulous David Gable hybrid from Pennsylvania. Bred more than 50 years ago, they’re winter hardy to -15 degrees F (USDA Zones 5-9).

Stop Ignoring Enkianthus

Posted by Hugh on May 7th, 2011

'Red Bells' enkianthus

From the photo, looks like a pieris? No, it’s redveined enkianthus (Enkianthus campanulatus) and its brightly colored bell-shaped flowers are attention getters in the early May garden. Lovely cream yellow to orangy red bell shaped flowers are faintly red veined. The bell shaped blooms exude a slight scent, one that you may like or not.

From the start, growth rate is slow, but once established, shrubs mature to 8 to 12 feet in height and about the same in spread. Culture is similar to azaleas, pieris and rhododendrons which they are related to. Enkianthus grows well in full sun to light shade. They are not as fussy regarding pH and moisture needs, provided the soil is well drained. Enkianthus becomes well established within two years, and are rated as moderately drought tolerant. Do provide supplemental irrigation during the driest periods of summer.

Over twenty cultivars are listed, varying in flower colors from near white (pale cream), pink and red. Fall color is quite variable among vcultivars and growing site from yellow, orange or red. Enkianthus has no serious disease or insect problems.

Callaway Gardens

Posted by Hugh on May 2nd, 2011

Perhaps, azaleas (Rhododendron spp.) offer the broadest color array of any shrub category in the spring garden. Very few public or private gardens display azaleas better than Callaway Gardens in Pine Mountain, GA. In late March, Jane and I enjoyed a 2-day visit at Callaway.

We arrived to catch the early blooming azalea sequence and were not disappointed. Vivid reds, pinks, and whites surrounded us in Callaway’s Azalea Bowl and Overlook Azalea Garden. Azalea series labelled Kurume, Glendale, Girard, Encore, and a lovely white cultivar labeled ‘H.H.Hume’ were stunning. The pale pink native Piedmont deciduous azaleas (R. canescens) were also starting to open. Azalea bushes in the hundreds were in bloom and many thousands more awaiting their turn over the five week of Callaway’s Annual Azalea Festival.

'H. H. Hume'

Many early flowering perennials, woodland beauties, shrubs and trees joined the spring floral chorus. To list just a very few: Oriental cherries, ornamental pears, dogwood, forsythia, several viburnum species, trilliums, Jack in the Pulpits, woodland poppies, and Lenten roses. Hundreds of Japanese maples (Acer palmatum) and (A. japonicum) complimented the azaleas. Azaleas and Japanese maples do make a perfect pair.

Not a gardener? Callaway is a visual masterpiece with hundreds of acres to be enjoyed by outdoor and sports enthusiast from golfing, tennis, swimming, biking, hiking, and fishing. We also stopped at the Sibley Horticultural Center and Day Butterfly Center at Callaway. A Birds of Prey show is presented daily at the Discovery Center Amphitheater.

You may pre-register for a scheduled cooking or gardening class. There are additional workshops held throughout the year. Several moderately priced restaurants are on the property or in nearby towns. For further information go to the Callaway Gardens website: www.callawaygardens.com

Light a Candle in Your Garden

Posted by Hugh on May 1st, 2011

'Giles van Hees' veronica

Speedwells (Veronica spp.) are long-blooming, easy-care perennials. Speedwells are outstanding for their color rich floral candles (spikes). The candle-like flowers rise like sentinels in the late spring-summer garden and attract lots of butterflies and bees.

The small individual 5- pedaled blossoms range in colors from white, pink, blue, and several shades of purple. The floral spikes open at the base and continue upward. Cultivar sizes vary, making veronicas a great choice as the front, middle or back border in any flower bed. Personal picks include V. ‘Giles Van Hees’ (6- inch bright pink spikes) and V. ‘Royal Candles’ (15-inch blue-purple spikes).

Speedwells belong in full sun, planted in a moist, well-drained soil. Soggy soils may lead to a root rot and foliar mildew diseases. Summer irrigation and mulching aids to conserve soil moisture and suppress weed competition.

Quick removal of the old flower spikes (deadheading) encourages growth of new basal foliage and almost continuous flowering through the summer months. Pruning back taller cultivars by one-third reduces the need for staking plants. Dividing perennial crowns every 2-3 years in early spring maintains overall plant vigor.