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

New Christmas Roses (Hellebores) Greatly Improved

Posted by Hugh on December 18th, 2014

Newly planted Helleborus niger Gold Collection® var ‘Jacob’

Christmas roses (Helleborus niger) is a winter flowering perennial. It is native to central and southern Europe (USDA hardiness zones 4-8) and is not as winter hardy as lenten rose (Helleborus x orientalis). Christmas rose tends to flower 1 to 4 weeks earlier, around the Christmas holidays in southern climes (zones 7-8). New selections of H. niger are better garden performers than previous selections.

Large cup-shaped white or soft-pink flowers gradually age to a pale green color, but some individual blooms may take on a pinkish tint in cool weather. Colder than normal fall-winter temperatures frequently delays flower development.

Somewhat slow to establish, Christmas rose grows to 12 to 18 inches high and about as wide. Leathery dark green summer foliage loses much of its attractiveness through the winter months. Prune off basal (lower) leaves which age first. One-gallon size plants purchased in the spring and sited correctly start blooming within two winters.

Christmas rose performs best in partial sun to partial shade and in compost-rich, moist, low acid to mildly alkaline pH soils. Morning light exposure is best; avoid direct afternoon sunlight in southerly climes (zones 7-9). Keep plant(s) watered during long dry spells. Overwatering leads to plant decline and death.

This long-lived perennial rarely need to be divided. Christmas rose may prolifically self-sow nearby the “mother plant” and most seedlings should be grubbed out. Insects and diseases rarely trouble hellebores. Slugs and aphids are occasional pests.

Fertilize plants in early spring to stimulate new growth. Feed with a slow-release fertilizer such as Osmocote™ or Nutricote™. An alternative is to feed bi-monthly (until mid-August) with water soluble products such as Miracle-Gro™, Nature’s Choice™, or Schultz™.

Their leathery leaves are utilized for winter holiday decorations. Caution: when handling plants, protect exposed arms and hands with a long sleeved shirt and gloves as foliage and sap are serious skin irritants.

Nellie R. Stevens Holly

Posted by Hugh on December 16th, 2014

UT Rose Garden in Knoxville, TN with ‘Nellie R. Stevens’ holly in background

Hollies and the winter season work well together. Female hollies with bright red fruits (yellow-fruited forms also) contrast with their glossy evergreen foliage. ‘Nellie R. Stevens’ holly (NRS), a female form, is a cross between English (Ilex aquifolium) and Chinese (I. cornuta) hollies. NRS is the popular holly choice in Southern landscapes (USDA hardiness zones 6 to 9).

Hollies are dioecious, requiring both a male and female parent for fruit formation. NRS holly exhibits the trait of bearing small numbers of seedless parthenocarpic fruit, without a male pollinator being present. More fruits are produced when NRS is properly mated with male holly cultivar ‘Edward J. Stevens.’ One male holly adequately pollinates 8-10 female plants located within 200-300 feet.

Hollies should be spaced apart according to their mature size and purpose in a planting. A single NRS makes an outstanding stand alone specimen shrub or tree; or mass several together to form a tall privacy screen. Plant them on 12 foot centers (between plants). NRS is a strong grower at 20-30 feet height and 15-18 feet width over 30 years. NRS is long-lived and asks for very little maintenance.

Hollies prefer a mostly sunny location and moderately acidic, well-drained soil. Established hollies are good foragers for nutrients, and do benefit from regular feedings with acidic-based fertilizers such as Hollytone®, Miracid®, or Miracle Gro® according to package directions.

Dr. Ed Gilman, at the University of Florida in Gainesville, writes that NRS has been successfully planted in urban areas on soils that are droughty and poorly drained, and on sites with poor air quality.

Provide Space For Weeping Blue Atlas Cedar

Posted by Hugh on December 13th, 2014

Weeping Blue Atlas Cedar at Biltmore Estate in Asheville, NC

Atlas cedar (Cedrus atlantica) hails from the Atlas Mountains in northern Morocco and Algeria (USDA hardiness zone 6-9). ‘Glauca Pendula’ is a popular weeping form with blue green needle foliage. It is found in limited quantities at full service garden centers.

Mature forms of weeping blue atlas cedars take up lots of space. When young its natural weeping form perform as a ground cover and requires support on stout vertical stakes, trellises, pergolas, or espaliered against a wall. It may reach heights of 30-40 feet if purposely supported on a vertical pole to grow skyward. Each year the wire or nylon ties must be loosened and retied to avoid stem girdling. Spread, height and plant form is dependent on how the tree was trained (and pruned).

Placement is often the worse mistake a plant buyer makes. Allow plenty of room for branches to spread. Set a specimen many feet away from a home and garage. Also, keep distant from walkways and public sidewalks. Older trees become flat-topped and are a beautiful sight to behold

Tufts of 1-inch long deep blue needles develop from late spring through early fall. Needle color over winter washes out to slate blue; it may lose most needles where winter temps are severe. The 3-4 inch long cylinder shape cones lay above the needle foliage and need two years to mature.

Blue Atlas prefers a deep, well-drained, slightly acidic soil. Heavy snow loads may result in some breakage. Pest and disease problems are rare if planted on an open full sun site along with adequate air movement. Permit 2-year establishment period; keep adequately watered in a hot dry summer. A multi-year old specimen develops exceptional heat and drought toughness.

Young specimen in Staten Island, NY Garden with other dwarf conifers

All About Mulches

Posted by Hugh on December 10th, 2014

Delivery of Hardwood Bark Mulch

Pine needle mulch around azaleas at Callaway Gardens

Mulches aid in retaining soil moisture and reducing weeding chores. Over the years organically-based mulches gradually improve garden soils. Organic mulches are basically recycled bark, branches, twigs and leaves (including needles). Frequently they are organic by-products from the logging industry. Grass clippings and straw are also mulch sources. Hay is usually full of weed seeds which defeats the purpose for using it.

Over the years pine bark, nuggets, and needles tend to slightly acidify as they decompose in the soil. Oak leaves also tend to be acidic. These mulches are highly beneficial around acidic-loving shrubs such as blueberries, azaleas, rhododendrons, mountain laurels (Kalmia spp.), and others. Hardwood based mulches, ground from wood waste from most trees and evergreens, turn the soil slightly alkaline (raise soil pH) as it decomposes.

Fall applied mulches tend to act as a warming blanket, trapping in ground heat. The mulch blanket prolongs root growth in autumn by many weeks. Spring applied mulches may retard plant growth around newly planted perennials and annuals. Year-round mulching keeps ground surface temperatures cooler that benefits certain tree and shrub species. Never pile mulch up against the trunks of trees and shrubs as it often results in wood decays and/or formation of above ground roots.

Mulch should not be spread around recently planted fruit (and maple) trees unless the trunks have been protected by rodent guards around their base. In the winter pine voles will nest under the mulch and gnaw on the sugary sap of the fruit trees. Fruit trees after two years no longer need to be protected.

Finally, a warning about mulch quality. If a mulch pile is excessively steamy (over 100 ºF) or exudes a distinct alcohol smell, do not purchase or accept delivery. The product will likely burn young landscape plants, particularly herbaceous perennials and annuals. Yes, mulches may attract termites, carpenter ants and other wood boring insects.

Conifers For Poorly Drained Soils

Posted by Hugh on December 7th, 2014

Trimmed yew hedge

Before planting conifers in your landscape, it’s absolutely important to know the drainage (percolation rate) of the soil, particularly if it is clay-based. Most conifers prefer well-drained sandy and clay loam soils.

To determine your soil type and rate of drainage, try the “hole test” recommended by Virginia Tech University horticulturists. Dig a hole approximately one foot deep and fill it with water. Time the rate (on an hourly basis) of water drainage out of the hole. If the water drains away at about one inch per hour, you have a desirable, well-drained soil. If drainage is much faster, your soil is probably high in sand, and if much slower, your soil is probably high in clay.

You might try replacing the soil in an extra wide planting hole with coarse sand or pea gravel. To prevent plant losses on soggy wet soils, set conifers on an incline plane or rolling slope so the roots will not drown in the low oxygen soil. A final alternative is to plant the root ball shallow on high soil mounds or berms.

Some conifer species adapt to poorly drained soils such as bald cypresses (Taxodium spp.), dawn redwood (Metasequoia), and arborvitaes (Thuja spp.). Eastern larch (Larix laricina) lives in swamps in the northeast U.S. and Canada, but most Larix species do not like wet feet. Nootka or Alaska cedars (Xanthocyparis nootkatensis) prefer moist soils that must be adequately drained. Coastal populations of Atlantic Whitecedar (Chamaecyparis thyoides) inhabit swampy environs, but many treasured collector cultivars don’t seem to prosper on wet sites.

Yews (Taxus spp.), pine (Pinus spp.), spruce (Picea spp.), and firs (Abies spp.) demand ideal drainage all the time. Plant with good soil with the proper amounts of soil amendments.

Emerald™ Arborvitae

Posted by Hugh on December 4th, 2014

Emerald™ Arborvitae at NC Arboretum in Asheville, NC

Emerald™ or ‘Emerald Green’ arborvitae (Thuja occidentalis ‘Smaragd’) is not new shrub or cultivar. More than 3 generations of gardeners have used this unique form of eastern arborvitae as their “go to” evergreen shrub up and down the eastern coast and through the Midwest (USDA hardiness zones 3-7). Emerald is a semi-dwarf evergreen shrub with a compact, narrowly pyramidal habit.

Emerald arborvitae differs from 12-15 feet high and 4-5 feet wide at maturity. A row of these “cookie cutter” shrubs shows very little variability as a lovely privacy hedge or foundation planting. Leaves are glossy, bright green, and scale-like in flattened sprays. Color rarely bronzes off in a cold winter in east Tennessee (zone 6). Urn-shaped ½ inch long cones turn reddish brown in late autumn.

Eastern arborvitae grows in any well-drained soil in full sun or part shade. Deep watering is highly recommended over long summer dry spells. This conifer struggles on a poorly drained site. Foliage is more open (less tight) when planted on shady sites. Under southeast U.S. heat and humidity Emerald arborvitae excels, far better than the species.

Feed in late winter with a slow release fertilizer specially designed for evergreen shrubs such as Osmocote™, Nutricote™, or Schultz Nursery Plus™. Add to organic mulch in the spring. Prune arborvitaes in late winter before onset of new spring growth. Remove broken branches and inspect hedges for possible bagworm infestations.

The tightly bundled branches may break apart under excessive ice and snow loads. Arborvitaes are rarely troubled by disease or pest problems and are quite tolerant to air pollutants in large urban centers. Bagworms and spider mites are occasional insect pests. Protection against deer browsing is imperative.

Lacebark Pine Is An Arboreal Gem

Posted by Hugh on December 1st, 2014

Lacebark Pine Blooming in mid-May

Lacebark pine (Pinus bungeana) is an arboreal gem which few gardeners are privileged to own (USDA hardiness zones 4-8). Hopefully, this will change. Lacebark is a lovely 3-needle pine with exquisite exfoliating bark which becomes more attractive as it ages. Bark mottling begins after 8-10 years, that’s worth the wait if you’re a young patient gardener.

Lacebark is a 30 to 50 foot tall pine. Frequently, most gardeners start out planting an affordable 2 – 3 foot multi-branched shrub. A young lacebark starts out slow, but growth rate picks up (4-5 inches annually) after 4-5 years on-site. The lovely cinnamon colored candles tip the branches in May, similar to candles decorating a cake. When fully expanded, the 2 – 4 inch long bristly needles are sharp to the touch.

Lacebark requires no special care other than fertilizing in the early spring and mulching until it is established after 2 years. Plant lacebark in full sun and in above-average garden soil that is well-drained. An older tree is moderately drought tolerant. Occasionally, you may want prune off a few side branches to show off the exfoliating bark pattern within. Young tree bark tends to color olive green and gradually bleaches out to an oft-white many years hence.

Most potentially serious disease and insect pests may be avoided through proper siting and care. Select a visible landscape location which is frequently visited, such as near a patio, carport, driveway or a window which looks out at lacebark.

Lacebark pine can be purchased from specialty mail-order nurseries via the internet. Lacebark is a long term investment, an evergreen that you and future generations will cherish for its exquisite patchwork bark.

Patchy bark

List of Zone 6 Hardy Camellias Grows Longer

Posted by Hugh on November 29th, 2014

‘April Tryst’ Camellia

‘April Remembered’ Camellia

If you live and garden in USDA hardiness zone 6, several camellia cultivars are winter hardy. The past decade has seen an increase in the list of hardy cultivars. These same cultivars are also reliable planted in zone 7. Here is a sampling of the best Zone 6 Hardy Camellias:

Fall Bloomers:

Londontowne Blush

Long Island Pink

Snow Flurry

Sweet October

Winter’s Interlude

Winter’s Joy

Winter’s Star

Spring Bloomers:

April Dawn

April Remembered

April Snow

April Tryst

Korean Fire

Pink Icicle

Spring’s Promise

Winter of 2013-14 was the roughest in my 9 years of growing camellias in northeast Tennessee (zone 6). All March-April bloomers lost their flower buds. All camellias in my garden survived the cold and looked great by summer.

Subjecting camellias to direct winter winds and planting them late in the year are two big mistakes. Don’t plantafter October 1st; spread 2-3 inches of an organic mulch around newly planted camellias as a soil heat blanket. October tends to be a dry month in the mid-South region; irrigate new camellias during rainfall deficit. Caveat: do not overwater camellias; November-December rainfall is usually plentiful. One-year old planted camellias acquire good drought tolerance. Irrigate only when summer months are exceptionally dry.

As a holiday promotion local big box stores may sell the camellia cultivar ‘Yuletide’ with bright red blooms and dark green leaves which open around late October. Most flowers will not open as frigid temperatures will arrive shortly. Open flowers are immediately injured and temperatures below 15º F will kill (blast) unopened floral buds. Yuletide may be zone 7b hardy.

Lastly, some zone 7 rated cultivars demonstrates exceptional plant cold hardiness. Their flowers (Sasanqua types) open in early autumn. Their winter foliage bronzes slightly, but shrubs rarely lose a leaf. More about these cultivars at a future blog

Species Tulips Thrive in Tough Spots

Posted by Hugh on November 27th, 2014

Tulipa bakeri ‘Lilac Wonder'(photo from Brent and Becky’s Bulbs, Gloucester, VA)

T. ‘Peppermint Stick’ (photo from Brent and Becky’s Bulbd, Gloucester, VA)

T. clusiana ‘Cynthia’ (photo from Brent and Becky’s Bulb in Gloucester, VA)

Species tulips (mini-tulips) are tough! In the wild they grow in the winter environs and dry soils of Central Asia, the Middle East, and China (USDA hardiness zones 3-7). In gardens they prosper for many years in full to partial sun and in average soil with good drainage.

Over the centuries mini-tulips have been improved. Color choices include red, bright yellow, orangey-red, pink, orchid, white, and bi-colors. Bloom times vary from early thru late spring.

Mini-tulips partner well with low-growing varieties of stonecrops (Sedum), which also thrive in subpar soils and hot, dry sites. Avoid planting in poorly drained or soggy soils. Voles may become a serious pest.

Plant mini-tulips at the same time you’re sowing other spring-blooming bulbs from October thru December when average day temperatures are in low 4oºF range and the ground is not frozen. Bury them just 4-5 inches deep. No fertilizer or soil amending is needed.

To maximize their potential to naturalize, do not trim foliage after flowering ends; allow foliage to die back on its own. New bulblets (offsets) and new bulb should develop underground. Mini-tulips suffer in southern U.S. zones if winter soil temps stay too warm to initiate flowers; plants also may germinate weakly and not bloom.

They’re small… so bunch a handful in pockets in flower borders, in rock gardens, along fences or walks. Tuck some around the base of late leafing deciduous trees.

Mr. Brent Heath, Brent and Becky’s Bulbs in Gloucester, VA, provided the following info:

T. sylvestris – stoloniferous, naturalizes in light shade, yellow, sweet fragrant outwardly facing flowers.

T. clusiana var. chrysantha –high desert mountain type from Iran to northern India is perfect for rock gardens; varieties ‘Lady Jane’ and ‘Cynthia’.

T. whatalei – orange cup-shape flowers in light shade (South) to full sun (North).

T. bakeri – ‘Lilac Wonder’ and ‘Honky Tonk’(soft yellow-pink hybrid) prefer full sun.

T. linifolia – dark red flowers and narrow edged leaves; ideal for sunny rock garden.

Tips On Crape Myrtles In Fall And Winter

Posted by Hugh on November 24th, 2014

Poor Pruning of Crape Myrtles

“Crape Murder” In Early February

Hardy cultivars of crape myrtles are best left alone in the fall. Light pruning to remove a broken branch or the seed capsules is ok, but major pruning should wait until early spring. “Crape murder” is a common practice in the Southeast U.S. and is not recommended any time or place. It involves lopping down tree and shrub crape myrtles to 5-6 feet height. The reason often cited by professional landscapers is that retail merchants want customers to see their signage.

The severe 2013-14 winter caught many landscape companies pruning in January and February. The aftermath was that many crape myrtles died to the ground. Fortunately, most did sucker back up and flower in summer (about 4-6 weeks later than normal). Plants had to be pruned to redevelop their branching habit.

If you must dig one up to transplant, wait until mid-March or later. Fall planting can be risky. Crape myrtles are cheap to replace or to start over. Often a fall or winter transplanted crape myrtle starts off weak, particularly if the previous winter weather has been severe.

Andrew Bunting, plant curator at the Scott Arboretum (campus of Swarthmore College in Swarthmore, PA) lists these cultivars that came through the winter 2013-4 with virtually no damage:

fauriei ‘Fantasy’
fauriei ‘Townhouse’
indica ‘Carolina Beauty’
indica ‘Pink Velour’
‘Acoma’
‘Lipan’
‘Muskogee’
‘Natchez’
‘Osage’
‘Tuscarora’
‘Tuskegee’

In northeastern cities such as Boston, New York, Philadelphia, Wilmington, and Baltimore, crape myrtles are rated as hardy perennials and not woody shrubs or trees. Following a severe winter, expect some to dieback to the ground. Some of the hardiest forms originate from the U.S. National Arboretum. If you desire to trial only 3 or 4 cultivars, ‘Natchez’ and ‘Muskogee’ (tree forms) and ‘Acoma’ and ‘Osage’ (shrub forms) are most reliable.