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

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.

‘Prestige’ Red Poinsettia

‘Ice Crystal’ poinsettia

Determining A Plant’s Cold Hardiness

Posted by Hugh on December 21st, 2014

U.S. Hardiness Zone Map

On-line nursery catalogs and plant labels at garden centers list the hardiness of the trees, shrubs, vines, and perennials that they sell. Many years ago the U.S. Department of Agriculture (USDA) developed the hardiness rating scale based on geographic location from northern Canada to southern Mexico. Most U.S. gardeners live within Zones 3 to 11. Don’t know the hardiness zone where you live and garden? This information is easily found on-line by simply entering your zip code.

If a plant originates from another country, for example China, the USDA has estimated its hardiness in North America. For example, hardiness zone 6 records an average low winter temperature between 0º F – 10º F; colder zone 5 falls between -10º F to -20º F.

Minimum temperature ranges of a particular hardiness zone are just averages. In some years temps may turn out to be colder; some “hardy” plants may not survive if winter is unusually cold. Sometimes a label designates only one zone, such as Zone 4. That represents solely the cold hardiness of the species; the plant is also be winter hardy in zones 5, 6, and 7. But it may be heat tolerant in the south. It will not survive in zone 3 winters.

There are many factors that affect a plant’s ability to survive cold temperatures. Environmental factors such as soil type, sun and wind exposure, slope, proximity to buildings, and snow cover create microclimates that could influence the over-winter survival of plants. Hardiness zone ratings are guidelines; cold temperatures, microclimates and other factors can influence plant survival following an abnormally cold winter.

When ordering plants on-line, utilize hardiness zone information to determine the proper shipping date in your area. For example, a Minnesota gardener may want to delay receiving plants to mid-spring when the cold weather is subsiding; a Tennessee gardener may want delivery 2 – 3 weeks earlier.

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.