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

Take A Second Look At Canadian Hemlock

Posted by Hugh on January 18th, 2015

Large hemlock hedge at Biltmore Estate, Asheville, NC

Hemlock at Yewdell in Louisville, KY

Canadian hemlock (Tsuga canadensis) is a native evergreen species which is available in many forms: prostrate, globose, weeping, fastigiate and variegated (USDA Hardiness Zones 3-7). Its tremendous versatility as a hedging tree or shrub in planting sites is also a great reason to continue to include hemlock in the landscape. Hemlock may be planted in full sun to moderate shade and does quite well.

Negative publicity continues hurt the sales of this evergreen. For nearly a half century, hemlock wooly adelgid, a serious insect pest from eastern Asia, has devastated hemlocks in the eastern U.S. forest lands. Adelgid infestations continue to move across the country.

Plant scientists have developed workable strategies for nursery producers and homeowners to combat wooly adelgids. In addition, the severe winter weather of 2013-14 reduced adelgid populations in large landscapes and forest lands. Parasitic beetle releases in state forests are helping to reduce adelgid numbers. Pesticides continue to be very effective in managing this pest without environmentally damaging the treated areas.

The American Conifer lists over 250 cultivars of just Canadian hemlock. Many are slow-growing and somewhat pendulous.

Short List of Cultivars to Plant…

‘Cole’s Prostrate’ or ‘Cole’ – slow-growing, ground hugger ideal for rock gardens; or graft on a short standard; 3 feet after 10 years.

‘Everitt Golden’ – new spring growth with golden tints; compact 5 feet high by 4 feet wide shrub after 10 years.

‘Frosty’ – white tipped new spring growth that fades; 3-6 feet globe form after 10 years.

‘Gentsch White’ – slow-growing, globe form with variegated branch tips; 5-6 feet after 10 years.

‘Jeddeloh’- mounding or nest-like habit; 3-6 feet height after 10 years.

‘Lewis’ – dwarf with upright branched; 3-6 feet height after 10 years.

‘Sargentii’ – aka ‘Pendula’, broad spreading weeping form that can reach more than 10 feet high and 20 feet wide.

‘Watnong Star’ – new shoots almost white; needle arrangement appears star-like on strong 2-inch to 2½-inch shoots.

Worldwide, there are five other major species of hemlock other than Canadian hemlock. They are Carolina hemlock (T. caroliniana), western hemlock (T. heterophylla), mountain hemlock(T. mertensiana), and Southern Japanese hemlock (T. sieboldii), and Northern Japanese hemlock (T. diversifolia).

Mt. Cuba Center Evaluates Heuchera (Coralbells) Cultivars

Posted by Hugh on January 16th, 2015

Heuchera ‘Mocha’

Heuchera ‘Apple Spice’

Over the past quarter century, gardeners have enjoyed the wonderful heuchera revolution (USDA hardiness zones 4-9). A great many hybrid cultivars have been introduced with more arriving every spring. Unfortunately, the flood of new cultivars has given us a huge number of poor selections. As I talk with gardeners across the U.S., it has become obvious that there are regional diffences among heucheras. A poor performing cultivar in the Southeastern U.S. may shine in the Mid-Atlantic or Midwestern U.S.

Heucheras are herbaceous perennials with palmate leaves attached by long petioles to a thick basal stem. Foliage emerges in spring with a second growth flush coming on in late summer if plants are not environmentally stressed. Leaves are reliably evergreen in plant zones 7-9.

There is an enormous number of hybrid cultivars including leaves with ruffled margins, colorful venation , et al. Plant breeders have made significant improvements in toughness, performance, and foliage. H. americana and H. villosa have lent hardiness, vigor, and color. Heucheras thrive planted in moderate shade or full morning sunlight (in zones 5-7).

From 2012-14 Mount Cuba Center near Greenville, Delaware evaluated 83 varieties. The best performers were: Citronelle, H. villosa Bronze Wave, Cajun Fire, Color Dream, Steel City, Carousel, Apple Crisp, Frosted Violet, Southern Comfort, Spellbound.

Highly rated were: H. villosa ‘Autumn Bride’, Brownies, Creole Nights, Dark Secret, Guardian Angel, Miracle, Pinot Noir, Plum Pudding, Rachel.

How to use this data? Read the entire report on the Mt. Cuba website posted under” research”. If you garden in the Mid-Atlantic states or in zones 5-6, this regional report should be of value. For mid-westerners, a 4 year heuchera trial conducted by Richard Hawke was published by the Chicago Botanical Gardens (CBG) in 2003 and is still available for viewing on the CBG website. Dr. Leonard Perry at The University of Vermont has also evaluated heucheras in previous years.

What Roses Need

Posted by Hugh on January 13th, 2015

Double Pink Knockout at UT Gardens, Knoxville, TN

Rosa ‘Shockwave’

A goal of most rose gardeners (rosarians) is to grow them almost maintenance free. The improved shrub roses introduced almost two decades ago have brought this too reality. Rose series such as Knockout®, Home Run®, Drift®, OSO Easy®, Carefree® and Meidiland™ are among the best.

No matter the pedigree of the rose, selecting a poor site, doing something wrong, and new disease problems can disappoint your love affair with roses. Providing a good environment makes growing roses a lot more enjoyable:

Plant in soil with good moisture drainage
At least 6 hours of sunlight
Adequate spacing between shrubs to allow good air circulation
Shelter from high or drying winds
Little competition from other plants
Irrigate ground but keep foliage dry (drip, soaker hoses); best time to water is early morning
Fertilizers: either a water soluble fertilizer (3-4 times in growing season thru early September); or 10-10-10 (in early spring and mid-July); or slow release fertilizer once in early spring.
Organic fertilizers (as alternative):

N (nitrogen) -horse manure – yes!; cow manure –no! (full of weed seeds)
P (phosphorus) – roses crave P, very important; sources: bone meal, rock phosphate
K (potassium) – improve summer heat tolerance
Minors- Fe (chelated iron) and Mg (Epsom salts)

Mulch with 2-3 inch layer of pine needles, bark chips or nuggets around bushes, but not against trunks.
Keep roses weed-free as weeds compete and also attract harmful bugs and diseases
Prune roses in late winter or spring when dormant or starting to bud out
Prune in summer to remove disease wood, particularly rose rosette or other virus problems

Blue Atlas Cedar Becoming Very Popular In Urban Landscape

Posted by Hugh on January 10th, 2015

Blue Atlas Cedar at Dallas Arboretum

Blue Atlas cedar (Cedrus atlantica ) hails from the Atlas Mountains in northern Morocco and Algeria (USDA hardiness zone 6). The cultivar ‘Glauca’ has been the popular choice because of its blue green foliage. Blue Atlas grows to 40-60 feet in height, but individuals over 70 feet are hard to find. Mature forms, those 50 years or more age to become conifer aristocrats.

Atlas cedar is a “true” cedar. In its early years, Atlas cedars grow tall and narrow with rigid upright branches. Young tree framework is strongly pyramidal. As it ages, overall tree canopy widens, taking on a slightly weeping form. Tufts of 1-inch long deep blue needles develop from late spring through early fall. Needle color over winter washes out to slate blue; needle color plus medium gray bark are handsome winter features.

This conifer prefers a deep, well-drained, slightly acidic soil. Never plant on a tight poorly drained soil where water may stand over several days. Allow plenty of room for branches to spread gracefully. Its ability to handle snow loads is debatable. Pest and disease problems are rare if planted on an open site in full sun and with good air movement. Permit 2-years for establishment with backup irrigation over long dry spell. A multi-year old tree exhibits exceptional heat and drought toughness.

The 3-4 inch long cylinder shape cones lay above the needle foliage and need two years to mature. Purchase grafted nursery stock as seed produced plants do not hold their needle color year-round.

Their enormous size makes them ideal selections planted in spacious public areas such as urban parks, golf courses, industrial parks, wide boulevards, and cemeteries. For narrow restricted spaces, select the upright cultivar ‘Fastigiata’. ’Glauca Pendula’ is an awesome weeping form, but requires staking in its early years to attain its desired height and form.

Personal note: I have seen 100+ year old specimens in the northeastern U.S. which stand tall and majestic for a century and more.

Many Shapes and Sizes Of Cryptomerias

Posted by Hugh on January 7th, 2015

Cryptomeria ‘Radicans’

Cryptomeria ‘Globosa Nana’

Japanese cedar, aka cryptomeria, (Cryptomeria japonica) is the national tree of Japan and is also indigenous to China (USDA hardiness zones 5 to 8). Cryptomeria cultivars vary greatly from very dwarf to rounded shrubs to large tree forms. Needle-like foliage may be dark green, medium green, golden or contorted leaves.

Cryptomerias tolerate hot humid summers and prefer deep, moist, well-drained soils with an acidic to neutral pH, and in full to half-day sun. Two-year trees are moderately drought tolerant.

Spring-summer foliage is bright green; leaves of many cultivars often turn bronzy in winter. Gold needle cultivars are available but not listed here. The rusty red bark, peeling in vertical strips, is also very attractive; older trees are frequently limbed up to show off the bark.
Cryptomeria contracts no major pests and diseases. On occasion, a fungal blight causes inner needles to turn reddish brown; prune out discolored foliage and toss from the property.

This mighty evergreen is wind tolerant, standing up to strong hurricanes; needles are salt tolerant. The upright branches hold up well to snow loads. Tall cryptomerias are easily trained and maintained as a tall single leader tree and utilized as privacy screens or windbreaks.

Cultivars to plant:

Tall tree forms…

‘Yoshino’- the most popular cultivar at 30-40 feet height; bright green needles bronze off in winter in zone 6.

‘Ben Franklin’- difficult to find at nurseries; similar to Yoshino in size and form; needles retain their green color through most of winter.

‘Radicans’ – tall upright pyramidal form, 20 to 30 feet tall x 7 to 10 feet wide; eventually to 40 feet high at maturity; holds its very dark green color throughout winter compared to Yoshino.

Intermediate…

‘Black Dragon’ –medium height @ 10-12 feet high x 6 feet wide; deep green needle-like leaves.

‘Gyokuryu’ – compact upright pyramid habit @ 10-15 feet high; dark green foliage with slight winter bronzing.

Shrub forms…

‘Globosa Nana’ – compact shrub form 2 to 3 feet high and wide, almost ball shaped.

‘Elegans Nana’ – globose compact form to 5-6 feet high.

‘Tansu’ – 2 feet x 3 feet dense compact form with rich green foliage; slow grower.

Twelve Days Of Christmas Showcase At Dallas Arboretum

Posted by Hugh on January 3rd, 2015

Seven Swans A-Swimming

Ten Lords A-Leaping

The Dallas Arboretum in Texas is hosting a festive holiday exposition: The Twelve Days at Christmas. It is an elaborate collection of 25-foot Victorian gazebos themed to “The Twelve Days at Christmas”. Each of 12 gazebos is comprised of charming costumed characters and whimsical animals made famous by the beloved Christmas carol.

Each gazebo is richly decorated and encased in glass, permitting a 360º three-dimensional view. Each of the 12 showcases are mechanically animated and accompanied by holiday musical classics that bring the characters almost to life. Around each gazebo Arboretum staff have decorated with many kinds of large evergreen trees for a wintry feel.

The Arboretum has extended daily visitation hours into the evening hours (until 9 p.m.) during the exhibit’s run which ends on January 4^th. Each gazebo is illuminated for magical nighttime viewing. In addition, visitors will become further immersed in the Victorian-era holiday theme by live carolers and holiday treats served in the arboretum’s cafe.

If you missed it 2014, the Arboretum plans to make The Twelve Days at Christmas exhibit an annual holidays showcase.

What A Plant Costs

Posted by Hugh on January 1st, 2015

Moderate growing Hinoki Cypress not pricey

Costly, Slow-growing, and Hard To Propagate Paperbark Maple

I overheard a customer complain about the “outrageous” prices for plants, particularly the newly introduced ones. Here is some of the whys:

Certain plants are difficult to reproduce. Occasionally, stores may stock some expensive items like paperbark maple (Acer griseum) and fringetree (Chionanthus virginicus). These two plants are difficult to propagate, slow growing, and demand will overshadows supply. Both will find a customer.

Some plants are slow growing. Some dwarf hinoki cypress (Chamaecyparis obtusa ‘Nana’) sell at two price points. Some cultivars are faster growing and lower priced compared to very dwarf types that may be 3-4 times more expensive. Slow dwarf grower will likely never outgrow its garden space or rarely need pruning maintenance.

Is the plant cultivar branded. Some examples:

Roses that are part of the Knockout, Home Run, Meidiland, Oso Easy, or Easy Care programs
Reblooming Evergreen Azaleas -Encore®, Bloom-A-Thon®,
Mophead (Hortensia) hydrangeas are part of Endless Summer, Let’s Dance^® or Cityline® series.

Large nurseries tend to brand the plants they sell, such as Monrovia, Proven Winners (PW), HGTV Gardens, Green Leaf, Gardeners Confidence, Plants That Work, Iselei, and many others.

New daylilies, hybrid lenten roses (Helleborus x) and hostas are very expensive the first 5-7 years after introduction. Prices come down as inventory numbers increase. In the 16th century Tulipmania created such a craze for tulips; they became more expensive than gold. In the 1990’s ‘Black Magic elephant ears (Colocasia) tubers were very costly because supply was low. Within 3 years, prices had dropped.

Is the plant trademarked or patented? Plant royalties to the breeder range from a few cents to several dollars. Heritage™ river birch and Double Red Knockout® rose are examples of trademarked or patented plants.

Price mark ups at garden centers range from 100-300%. Most items that we purchase, such as clothing, appliances, electronics, are marked up 200% or more. A sweater, bathing suit, or lawn mower enjoys a relatively long sales window. Most live plants have a short or limited shelf life.

New patented hydrangea

Is Your Tree A Hazard?

Posted by Hugh on December 30th, 2014

Fall Leaf Color of Silver Maple With Good Form

Is a dangerous tree lurking in your yard, ready to tumble down on your house or car? A well shaped landscape tree with a full canopy (top) and undergoes a safety checkup every 3-5 years is rarely at risk. When the weather forecaster is predicting a hurricane or an ice storm, it’s generally too late to call a local certified arborist.

Category storms are out of the ordinary and even healthy trees are likely to receive some injury. You should not wait until a storm has caused damage. Tree maintenance goes along with tree ownership. A tree’s health, like people’s, changes over time. Middle aged trees are less hazardous than old mature trees. Age plus a category storm may inflict significant damage to render a tree hazardous.

Different tree species possess different mechanical strengths and decay mechanisms. Weak-wooded species considered hazardous include silver maple (Acer saccharinum), cottonwood and hybrid poplars (Populus spp.), willows (Salix spp.), boxelder (Acer negundo), and tree-of-heaven (Ailanthus altissima).

Location is a key factor. A tree not growing around people, homes, and autos is not likely to inflict serious damage if it falls. A tree growing in a public park should be inspected periodically, then pruned or removed. However, a residential tree with a large decay cavity likely should be removed at once.

Trees may show decay or cavities along the main trunk(s) and branches. Timely pruning usually cures most ills. It’s kind of like going to the dentist. A cavity represents wood decay and branch weakness. Decay can be slowed by cleaning out the wound and spraying a pesticide to prevent wood boring insects from habitating.

A certified arborist can measure the extent of the tree decay using a Resistograph®. A hollow tree cavity is not always hazardous. Tree cavities that are surrounded by at least one inch of solid wood per six inches of tree diameter are unlikely to fail according to good scientific support.

You should hire only a certified, licensed and insured arborist. Certification is awarded by the International Society of Arboriculture (ISA) following extensive study and testing.

Beware Of Short-Lived And Overly Aggressive Plants

Posted by Hugh on December 27th, 2014

Lysimachia nummularia ‘Aurea

Chameleon Plant (Houttuynia)

Gardening does involve some work, sometimes a lot more if you select the wrong plants. A good purchase may even reduce annual maintenance. Some of them are beautifully tempting at the garden center.

Non-hardy woody trees and shrubs often sold by box store garden centers. For example, it is not uncommon to find zone 7 hardy trees and shrubs for sale in zone 6 store lots. Store plant buyers may be responsible for ordering for 100 or more stores over a large geographic area.
Disease or insect prone plants such as Alberta spruce (Picea glauca ‘Conica’), hybrid tea roses, redtips (Photinia spp.), some evergreen euonymus (Euonymus fortunei), and most lilacs (Syringa spp.).
Overly aggressive perennials are garden thugs. Here is a short list of the worst offenders: bishop’s weed (Aegopodium podograria), sundrops (Oenothera speciosa), yellow archangel (Lamium galeobdolan), gooseneck loosestrife (Lysimachia clethroides), creeping Jenny (Lysimachia nummularia), and chameleon plant (Houttuynia). Some (not all) varieties of English ivy (Hedera helix) are aggressive and potentially invasive in the adult stage.
Short-lived trees or shrubs, such as Bradford pears (Pyrus x calleryana), flowering peach (Prunus persica), and ornamental plums (Prunus cerasifera).
Trees and shrubs with aggressive rootsystems. Examples include: staghorn sumacs (Rhus typhina) and (R. glabra), willows (Salix spp.), and many poplar species (Populus spp.).
High maintenance plants such as sycamores (Platanus spp.), most willows (Salix spp.), and poplars(Populus spp.)
Invasive plants are absolute no nos. You should review your state watch list for plants you should avoid purchasing. Many states have eradication programs in place to exclude multiflora rose (Rosa multiflora), autumn olive (Eleagnus umbellata), Japanese honeysuckle (Lonicera japonica), oriental bittersweet (Celastrus orbiculatus), Japanese knotweed (Polygonum cuspidatum), and purple loosestrife (Lythrum salicaria). Some states also list east Asian honeysuckles (Lonicera spp.), specific varieties of Japanese barberry (Berberis spp.), Chinese privet (Ligustrum chinensis), maiden grass (Miscanthus spp.), and some species of euonymus (Euonymus spp.).

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Holiday Poinsettia Requires Basic Care

Posted by Hugh on December 24th, 2014

Lemony White ‘Polar Ice’ Poinsettia

Gifts have been opened and a great dinner served. The holiday season may be waning, but your beautiful poinsettia plant (Euphorbia pulcherrima) will require some minimal care. Generally, the same weekly care that you provide your house plants will keep your poinsettia looking beautiful most of the winter. Here are some basic tips:

Place poinsettia in bright natural light but not in direct sunlight. Turn the plant weekly.
Keep the plant away from hot or cold breezes, particularly away from heating ducts.
Keep away from children and pets. No, your poinsettia is not poisonous, but protect it from injury.
The brightly colored bracts should remain fresh if room temperatures do not exceed 75º F or drop below 55º F.
Water plant thoroughly when the top of the soil feels dry to the touch. Never leave the plant sitting in water over several hours. Drain off excess water in the bottom saucer within 30 minutes.
Feed plant every two week with any water soluble fertilizer recommended for house plants. Examples include Schultz™ and Miracle-Gro™. Closely follow package instructions.
Poinsettia quality tends to decline by late February in the home. You may opt to prune it back severely (at much as 70-80%) and begin developing a new plant. Otherwise, you may opt to discard the plant.