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

American Hornbeam – Versatile Small U.S. Native Tree

Posted by Hugh on February 5th, 2019

American hornbeam at NC Arboretum in Asheville

Multi-trunk form is common

American hornbeam (Carpinus caroliniana), aka ironwood or muscle wood, grows primarily in moist, slightly acidic soils along woodland rivers and streams (USDA hardiness zones 3-9). This native hornbeam adapts to either wet or dry ground as long as soil moisture drains off, and it does not flood over long periods. This durable small tree copes with tough urban sites, including non-irrigated parking lots and the outer edges of rain gardens. It grows equally well in full sun or partial shade.

Its autumn foliage turns intense shades of yellow, orange, and at rare times scarlet red, depending on soil pH and the seed provenance of the species. Over the past quarter century Johnson Nursery (wholesale nationwide and retail locally) in Menomonee Falls, Wisconsin has introduced several forms with good fall red foliage. Firespire™ is a grafted clone with semi-upright branching and vibrant red fall color. ‘J N Strain’ is from a known seed population which delivers above average red fall leaf color.

Ironwood blooms in spring as separate male and female catkins, none of ornamental significance. In autumn female catkins produce showy clusters of winged nutlets, that are an important food resource to numerous forest fauna. The main trunk and branches exhibits a muscular beech-like bark, a singular trait that earns it the common names of “musclewood” and “ironwood”. Either single- or multi-trunked, the trunk(s) and boughs are singular assets in the winter garden.

American hornbeam grows 25-40 feet tall and variable in width depending on cultivar. It is free of disease and pest problems when properly sited. Fertilize and mulch the tree in early spring. The rich green summer, colorful autumn foliage, along with its gray muscular winter bark identifies this as an excellent small shade tree. Group several seedling together to develop a deciduous privacy screen.

American hornbeam is more difficult to transplant than European hornbeam (C. betulus), its taller European counterpart.

Tips On Amending The Soil In The Planting Hole

Posted by Hugh on February 1st, 2019

Soil Amendments Ready For Mixing on Site

Adding large amounts of compost or organic matter to a planting hole greatly improve the soil’s water-holding capacity and aeration. Simply throwing piles of leaves into the bottom of the planting hole helps improve a soil. However, amending the planting hole is not recommended by most plant experts. Why? According to soil scientists, the plant roots stay locked within the rich planting media in planting hole, like a pot, and roots don’t grow out into the surrounding native soil. This is especially true in heavy clay soils.

Newly planted tree + mulch

Doing it right: A wide shallow hole is more correct and a lot easier that one that’s narrow and very deep. Thoroughly mix organic amendments with the surrounding soil into the planting hole. Use a rototiller or 4-tine fork to turn and thoroughly mix humus, leaf litter, or compost into the planting hole.

Adding organic matter has good properties to improve the soil’s water- and nutrient-holding capacity. Humus rich soils are more porous and alive with beneficial organisms such as earth worms and beneficial fungi. However, too much is no good either. The ingredients peat, bark, and coarse sand make the backfill.

Finally, get the tree depth in the hole correct. Placing a heavy tree or shrub in the planting hole will compress the loose fill, often resulting in a tree being planted too deep.

Extra facts: Acidic organic materials are valuable to acid-loving shrubs such as rhododendrons, azaleas, mountain laurels, blueberries. Acidifying fertilizers, such as ammonium nitrate, ammonium sulfate, and sulfur-coated urea can also raise soil acidity levels. Mulch acid-loving plants with acidic materials such as pine needles, bark, and nuggets, and oak leaves; all eventually decompose into humus.

Organic mulches also cool roots of tree and shrub species, particularly in warmer climes Native trees, such as Beech (Fagus grandifolia)), paper , gray, and river birches (Betula spp.), sourwood (Oxydendrum), black gum (Nyssa sylvatica), silverbell (Halesia) and dogwoods (Cornus spp.).

Re-blooming Poinsettia This Fall

Posted by Hugh on January 26th, 2019

Poinsettia display at Biltmore Estates

Assorted poinsettias

The winter holidays may be over, but your poinsettia plant is likely still looking pretty. If you opt to grow and re-bloom your plant next Christmas, follow this growing schedule.

Keep the soil evenly moist and set the plant in bright daylight. Feed bi-monthly with a house plant fertilizer. Inspect and rid your plants of all pests, particularly aphids, scale, or white flies by spraying from with insecticidal soap or Neem oil.

Spring –Summer Care:

Around mid-March prune the main stem and side branches back hard to 4 – 6 inches above the soil. On warm days, move the plant outdoors into bright light but not direct sunlight. Re-pot into a larger pot, one that is at least 2 inches wider, and contains good potting media (soil). Water thoroughly and set in a sunny window. On days with outdoor temps in mid-fifties or higher, move the plant outdoors and bring it back indoors if temps drop below 55°F. Once the danger of frost outdoors has passed, set the plant outdoors in a semi- shady to partial sunny site. Sink the potted plant in your flower bed over the summer. Periodically rotate the pot every 2-3 weeks to prevent roots from growing through the bottom hole into the garden soil. Prune to maintain a uniform plant shape by pinching out the growing tips every 2-3 weeks to encourage branching (until mid- August).

Fall Care:

At the start of the fall season, as night temperatures drop below 55-60°F, bring the poinsettia indoors to a sunny window or a greenhouse. Continue to water and feed.

Poinsettia, including Thanksgiving and Christmas cactus (Schlumbergera spp.) and kalanchoe, are short-day or long-night plants. Flowers are initiated when the night (dark) period is greater than 12 hours for 10-12 continuous weeks. If the dark period is interrupted or broken, the poinsettia will not flower and will produce leaves only.

Put your poinsettia on an exact photoperiod schedule, such as at dusk (5 p.m.) every day cover with a heavy paper bag, black cloth, or set in a dark closet. During the daytime hours, let the plant receive daylight in an east- or south-facing window. Any short light interruption at night, such as turning on the light in the closet, may break the flower cycle. A streetlight outside a window may prevent flower formation.

Begin scheduling the poinsettia in late September or early October. Remember– the dark period must be 12 or more uninterrupted hours to initiate flowers. A dark period from 5 p.m. to 8 a.m. over 10-12 weeks is ideal for many folks.

By early December your poinsettia should have colorful bracts and flowers for late December holiday season.

All About Soil Drainage

Posted by Hugh on January 20th, 2019

Flood barrier from walkway

Trunk filled with amended soil

Many landscape plants die because they were planted in soil that was too wet or soggy. Poorly drained soils are generally poorly aerated. A high water table in an area limits your choices of plants that you may grow. Plants that grow naturally along streams and ponds are good candidates for poorly drained sites.

During periods of heavy rainfall, water may stand on the ground surface. Consistently wet soils eventually becomes a breeding area for anaerobic soil bacteria; an odor may indicate their presence. Soils that are poorly drainage may have a dull or slate gray color.

During construction heavy equipment may compact the soil reducing air space or create a hard pan. Frequently, on construction sites, contractors may pile up topsoil and return it to plant grass seed or sod. Unfortunately, some topsoil may be remove and sold off leaving only subsoil for new homeowners.

Drainage issues may result from poor grading of land, permitting road, street, or sidewalk runoff to flow onto garden beds or lawn. Runoff water may also come from plugged eaves and downspouts.

Excellent soil drainage a must with Daphne shrub

Perform A Perk Test before planting a new garden or lawn. Dig a hole 12 inches deep and 2-3 feet wide. Fill the hole with water and time how quickly the water drains out the bottom. If water drains out slowly or stands for longer than 24 hours, your soil is poorly drained.

Alternative Perk Test… remove the top and bottom from a large 3 lb. coffee or tin can. Dig a 4-inch deep hole and as wide as the diameter of the can; insert the can into the hole and fill soil around the outside of can. Fill can with water and measure the water level after one hour. If the water level drops 2 – 5 inches, soil drainage is good. If the water level drops less than 2 inches, soil drainage is poor.

Soils with good porosity (drainage) in the top 12-18 inches are ideal for most plant species. Amend planting soil with perlite or coarse sand to improve soil drainage or opt to grow plants in containers or raised beds.

Selecting A Good Landscape Shade Tree

Posted by Hugh on January 15th, 2019

‘Duraheat’ river birch

Medium to large shade trees increase the value of your property. Their summer shade and wintry wind protection may also reduce utility bills by 20 to 25%. Trees attract wild birds for nesting, protection, and as a food source. Some deciduous species will brighten up the landscape with dazzling fall color. Choosing a fast growing tree, yet some may not be good option. Know the maintenance level of the tree(s) before purchasing. Is the tree susceptible to disease and/or insects? Are better resistant cultivars available? Fit the right tree to the right location.

Much of the information comes from the Morton Arboretum in Lisle IL (near Chicago) and is highly reliable. Trees are ranked by their actual growth rate the first 10 years after planting. I have added some outstanding cultivars that you should purchase.

Category 1. Fast-growing trees (at least 25 feet tall) after 10 years:

Acer rubrum ‘October Glory’

Silver Maple (Acer saccharinum)

London Planetree (Platanus x acerfolia) ‘Columbia’, ‘Yarwood’

Sycamore (Platanus occidentalis)

American Elm (Ulmus americana) ‘Washington’, ‘Princeton’, ‘Jefferson’

Category 2. Moderately fast growing trees (18 to 25 feet tall):

Hybrid Freeman Maples (Acer freemanii)

Red Maple (Acer rubrum) ‘October Glory’, ‘Red Sunset’

Sugar Maple (Acer saccharum) ‘Green Mountain’, ‘Legacy’, ‘Sweet Shadow’

River birch (Betula nigra) -‘Heritage’, ”Duraheat’

Thornless Honeylocust (Gleditsia triacanthos var. inermis)

Silver linden

Kentucky Coffeetree (Gymnocladus dioicus) ‘Espresso’

Sawtooth Oak (Quercus acutissima)

Shingle Oak (Quercus imbricaria)

English Oak (Quercus robur)

Pin Oak (Quercus palustris)

Little leaf Linden (Tilia cordata)

Redmond Linden (Tilia x euchlora ‘Redmond’)

Silver linden (Tilia tomentosa)

Tuliptree (Liriodendron tulipifera) ‘Little Volunteer’

Category 3. Slower growing trees (less than 18 feet tall after 10 years):

Young ‘Happidaze’ sweetgum

Ohio Buckeye (Aesculus glabra)

European Hornbeam (Carpinus betulus) ‘Fastigiata’, ‘Frans Fontaine’

Common Hackberry (Celtis occidentalis)

Yellowwood (Cladrastis kentukea)

Ginkgo (Ginkgo biloba) (male clones)

Ironwood (Ostrya virginiana)

Norway Maple (Acer platanoides)

Sweetgum (Liquidambar styraciflua) ‘Slender Silhouette’, ‘Happidaze’

Category 4. Medium sized landscape trees:

Trident maple (Acer buergerianum) Aeryn®

Golden raintree (Koelreuteria paniculata)

Crape myrtle (tree forms) (Lagerstroemia x) ‘Natchez’, ‘Muskogee’

Black gum, tupelo (Nyssa sylvatica) ‘Wildfire’, ‘Green Gable’, ‘Red Rage’

Japanese pagoda tree (Styphnolobium japonica) ‘Regent’

Willow oak (Quercus phellos)

Live oak (Quercus virginiana)

Bald cypress (Taxodium distichum) ‘Shawnee Brave’

Lacebark elm (Ulmus parvifolia) ‘Athena’, ‘Bosque’

Japanese zelkova (Zelkova serrata) ‘Green Vase’

Editor’s note: all ash species (Fraxinus spp.) have been delisted from the Morton Arboretum study because of their susceptibility to Emerald Ash Borer.

Winter Honeysuckle Totally Ignored In The landscape

Posted by Hugh on January 6th, 2019

Lonicera fragrantissima at Biltmore Estates, Asheville, NC

Shaggy base of shrub

Winter honeysuckle, aka fragrant honeysuckle (Lonicera fragrantissima) is a treasured heirloom shrub (USDA hardiness zones 4 to 8). Plantings of this late winter blooming large woody shrub are still found in historical (older) urban neighborhoods and city parks planted prior to the 1960’s.

This tough, durable shrub can reach 10+ feet tall and wide. You may opt to limb up its shaggy lower branches for show. The longevity of winter honeysuckle is incredible. If shrubs get out of control, cut the back to the ground after spring blooming is over. Vegetative cuttings root easily, and you can pass-along this old fashion shrub to gardening friends as it is rarely sold in garden centers.

Flowers are a harbinger of spring. Budded branches may be cut for an early, fragrant, indoor arrangement. In the southeastern U.S., small creamy flowers often emerge during a warm January – February spell. Winter honeysuckle continues to bloom on and off through March. Your nose will catch its sweet lemony fragrance. The deciduous blue green summer foliage offers no fall color. Further southern (zones 7 and 8), the foliage is almost evergreen.

Fragrant honeysuckle grows in average, dry to medium, well-drained soil, and in full sun to partial shade. This vigorous shrub asks for little care other that annual corrective pruning. Susceptible to a limited number of disease and pest issues, winter honeysuckle usually grows out it. Potential pests include aphids, scale, sawfly, whitefly, and webworm. Early native bees are especially glad to find it on winter days and are drawn to the pollen and nectar. If fruits (berries) are formed, hungry birds come and fest.

Yes, winter honeysuckle is a “true” honeysuckle and you should check whether if it is invasive in your state. It is not invasive in Tennessee and Virginia, but North Carolina and Texas forbids new plantings. Since it blooms so early in the year, e.g., compared to most honeysuckle species, few fruits (and seeds) form. In southern locales where winters are mild, it may seed-in prolifically.

Landscape use: clipped or informal hedge, screen or background border shrub.

Update On Boxwood Blight Disease

Posted by Hugh on January 1st, 2019

Samples of boxwood blight (photo by Dr. Alan Windham, Univ. of Tennessee Plant Pathologist)

A decade ago, boxwoods (Buxus spp.) were the quintessential shrubs, particularly for formal hedges. Over the past half century, many new boxwood varieties have been introduced into nursery commerce, a boxwood variety that will work in most garden situations. Just five years ago, boxwood production at U.S. nurseries was greater than for azaleas, hollies, hydrangeas, and arborvitaes.

The impact of boxwood blight (Calonectria pseudnaviculata) on sales has been crippling. Professional landscapers and homeowners can no longer be certain that they are purchasing diseased plants, that may contaminate healthy boxwoods already planted on site. While other diseases and pest problems – such as Volutella canker (Volutella buxii) and boxwood leafminer and midge – injure boxwoods, boxwood blight has become the foremost concern here in the U.S. and around the world.

Boxwood blight can be found on container and landscape-grown plants, as well as on greenery and wreaths used for Christmas decorations. All popular boxwood cultivars are thought to be susceptible to infection, although they do vary in susceptibility. Boxwood relatives, such as Japanese spurge (Pachysandra terminalis), Allegheny spurge (P. procumbens), and Sweetbox (Sarcococca spp.), are also susceptible to boxwood blight.

Research has determined that the fungus that causes boxwood blight usually moves short distances, mostly by rain splashing or wind driven rain. The fungal spores are large and are not carried via air currents. Nurserymen and landscapers are cleaning tools, work boots, and gloves when working with boxwoods in the field to prevent its spread. Drip irrigation systems are preferred rather than overhead systems. Mulching around plants reduces rain splash and distribution of boxwood fungus. Fungicide applications slow down disease spread, but do not eradicate the disease.

Field and landscape sanitation is most important. After hedging (or pruning) boxwoods, disinfect tools with bleach, ethanol (rubbing alcohol), Lysol®, and others. Awareness and better diagnoses are important criteria at garden centers. Consumers should avoid purchasing suspicious boxwoods if the foliage looks discolored or leaf drop is significant.

Still no sure? Collect boxwood samples (see picture above) and send them to your local Extension office.

Weeping Landscape Trees

Posted by Hugh on December 28th, 2018

Salix babylonica

Weeping forms of willows (Salix spp.), flowering cherries (Prunus spp.), pines (Pinus spp.), spruces (Picea spp.) and European beeches (Fagus sylvatica) are magnificent landscape features. Weeping forms of evergreen and deciduous trees develop strong upright central leaders, and their outward branches cascade downward. Among conifer species there are over 150 different cultivars with pendulous habits.

Here is a list of 28 weeping tree species. I have tried to choose the best cultivars available in the U.S. nursery trade. Weeping cultivars tend to be a bit more pricier than non-weeping forms. A nursery usually must put an additional 2-4 years in staking and pruning young trees.

Weeping Japanese Maples (Acer palmatum) –‘Ryusen’, ‘Matsukake’, ‘Omuyarama’, ‘Green Cascade’ among others
Styrax japonicus ‘Pendula’
Weeping river birch (Betula nigra) ‘Summer Cascade™’
Weeping birch (Betula pendula) ‘Youngii’, ‘Carelica’, ‘Dalecarlica’, ‘Golden Cloud’, ‘Gracilis’, ‘Laciniata’, ‘Purpurea’
Weeping katsura tree (Cercidiphyllum japonicum) – ‘Pendula’, ‘Tidal Wave’, ‘Amazing Grace’
Weeping redbud (Cercis canadensis) – ‘Traveller’, ‘Ruby Falls’, Lavender Twist® (‘Covey’), ‘Whitewater’
Weeping Blue Atlas cedar (Cedrus atlantica) ‘Pendula’
Weeping Himalayan cedar (Cedrus deodara) ‘Pendula’
Weeping beech (Fagus sylvatica) – ‘Pendula, ‘Purpurea Pendula’, ‘Pendula’, ‘Atropunicea’, ‘Atropurpurea’, ‘Purpurea Pendula’
Weeping Japanese Larch (Larix kaempferi) ‘Pendula’)
Weeping crabapple (Malus x ) – ‘Red Jade’, ‘Louisa’, ‘Luwick’, Molten Lava™ (‘Molazam’), ‘Royal Fountain’, several others
Weeping white mulberry (Morus alba) – ‘Pendula’ (female clone –sets fruits); ‘Chaparral’ (male clone – no fruits)
Weeping blackgum (Nyssa sylvatica) ‘Autumn Cascade’
Weeping Norway spruce (Picea abies) ‘Pendula’
Weeping Serbian spruce (Picea omorika) ‘Pendula
Weeping white pine (Pinus strobus) ‘Pendula
Weeping Flowering Apricot (Prunus mume) ‘Pendula’
Weeping cherries (Prunus serrulata) ‘Kiku-shidare-zakura’
Weeping Higan cherry (Prunus subhirtella) ‘Pendula’, ‘Pendula Alba’, and ‘Pendula Rubra’
Yoshino cherry (Prunus x yedoensis) ‘Snow Fountains’
Weeping willow (Salix spp.) – many weeping cultivars listed S. babylonica; add Contorted leaf willow (Salix matsudana ‘Tortuosa’)
Morus alba ‘Pendula’
Japanese styrax (Styrax japonica) – ‘Pendula’, ‘Carillon’
Japanese Pagoda Tree (Styphnolobium japonicum) ‘Pendula’
Bald cypress (Taxodium distichum) – ‘Cascade Falls’, ‘Falling Waters’ (both grafted shrub forms that may be trained into small weeping tree forms)
Little leaf linden (Tilia cordata) – ‘Pendula Nana’ and ‘Girard’s Pendula Nana’ (both are dwarf forms)
Weeping Silver Linden (Tilia petiolaris) ‘Pendula
Canadian hemlock (Tsuga canadensis) ‘Pendula’ – several weeping shrub forms
Camperdown elm (Ulmus glabra) ‘Camperdownii’
Weeping Alaskan cedar (Xanthocyparis nootkatensis) ‘Pendula’, ‘Jubilee’, ‘Strict Weeping’

Prevent Leaf Burn on Evergreens This Winter

Posted by Hugh on December 24th, 2018

Natural needle drop on white pine in the fall

Natural winter color of PJM rhododendron

Winter foliage burn on evergreens is often most prevalent on boxwoods (Buxus), hollies (Ilex), rhododendron, and many kinds of conifers. Symptoms often develop when temperatures warm up in late winter and early spring. This type of winter damage is often misdiagnosed as an infectious disease or damage from excessively cold temperatures.

Evergreens transpire (lose water from needles or leaves) over the course of a day. For a large pine or fir tree, that may be hundreds of gallons of water daily on a dry winter day. Conditions may worsen if the soil is dry or frozen. Roots in frozen soil are incapable of replacing moisture loss and leaves desiccate, die, and turn brown.

Major Causes: Leaf burn or water loss is frequently greater on plants located on the south and west sides of homes where the late afternoon air is warmest because of sunlight exposure and heat. De-icing salt spray from nearby streets (roads) or sidewalks may also burn evergreen foliage. High winds may dry out needles.

To Prevent Winter Burn (in order of priority):

Select trees and shrubs that are hardy to your region.
Plant broadleaved evergreens such as rhododendrons, needle conifers, and hollies (Ilex) in areas sheltered from high winds.
Around Thanksgiving (mid-November) holidays, irrigate plants deeply before the ground freezes if little precipitation is expected.
On windy sites plant a natural tree/shrub windbreak around your home, composed of fast-growing evergreen and deciduous trees.
Construct physical barriers from landscape tarp or slatted snow fencing to protect problem plants with burlap or landscape fabric.
Use of chemical anti-transpirants (available at most garden centers) should be your last resort. Follow package recommendation closely, but do not overuse these products.
Maintain a 3-4 inch layer of organic mulch around evergreens to retain soil moisture.

Assessing winter injury and recovery rate of foliar burned evergreens is a waiting game. Hold off until late spring before pruning away dead and damaged branches. Burnt needles will not recover. Dead appearing branches may still possess surviving buds that will green up and fill in some bare patches. Prune off all dead branches that have not greened up.

“Got The Winter Blues”- Go For A Walk At A Garden Center

Posted by Hugh on December 16th, 2018

Begonias for sale

Assorted ferns

Tired of being a shopping mall walker this winter? Instead, visit a local full service garden center. This is a garden center that is open year round and generally does not include the big box stores unless you live a southern climes like Florida, Texas, Arizona, or California.

Stores are likely to have walkways, likely concrete or pea gravel, to accommodate a walker or wheelchair. Exercise not only your legs but other senses with an array of colors and fragrances. Lush greenery may surround you in the greenhouse, no matter what the weather is outdoors.

Out in the parking lot winter-hardy pansies, snapdragons, and dianthus maybe peaking through the snow. Truckloads of pre-forced spring flowering bulbs, such as tulips, daffodils, and fragrant hyacinths, should have arrived by mid-January. Some garden centers also offer outdoor display gardens. Walk through the gardens as warm spring temperatures are arriving and trees, shrubs and perennials are waking up.

Wander down the aisles of tropical house plants. Check out dumbcanes (Dieffenbachia), Chinese evergreens (Aglaonema), fiddleleaf figs, palms, ferns, or snake plants (Sansevieria). You’ll feel as if you are in a tropical paradise. Overhead may be several hanging vines like philodendrons, ivies, and pothos.

How about those flowering plants? Spring may be months away, but moth orchids (Phalaenopsis), begonias, amaryllises, colorful bromeliads, African violets (Saintpaulia), peace lilies and anthuriums. Desert plants, including cacti, jades, aloes and other succulents, are lush this time of year and many sporting colorful blooms. Over in the herb department, inhale the sweet smells of pineapple sage, rosemary, lavender, mint, and chocolate. Miniature orange, lime and lemon trees full of super fragrant blooms.

Spend 30 to 60 minutes walking through our greenhouses and come away refreshed, renewed, and rejuvenated at no charge. Some garden centers offer yoga and pilates classes to help get in shape for spring. Stop by the gourmet coffee bar for a hot (or cold) brew.