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

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.

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.

Unusual Forms Of Umbrella Pine Are Really Cool

Posted by Hugh on December 11th, 2018

Umbrella Pine at NC Arboretum in Asheville, NC

Gold shrub form of Umbrella pine

Japanese Umbrella Pine (Sciadopitys verticillata) is a prized ornamental evergreen (USDA hardiness zones 5b -9). It is not actually a pine. The only species within genus Sciadopitys, this conifer dates back to the dinosaurs. Umbrella pine is a mid-sized landscape tree with several fine attributes: 1. glossy green long narrow needles arranged like the spokes of a wheel; 2. peeling reddish brown bark; and 3. conical form.

In its early years after planting, umbrella pine is a notoriously slow grower. Eventually, it reaches 30 to 40 feet in height and 20 feet wide. Specimens 70 feet tall are not unusual. Shedding reddish brown bark is noticeable on mature trees. Umbrella Pine prefers full sun with light shade around mid-day. Plant the tree in humus-rich, moist, well-drained soil with slightly acidic to neutral pH. Their long rigid needles, along with a sturdy limb structure, allow the tree to withstand heavy snow and ice loads.

Several forms, including variegated, pendulous, columnar, and dwarf cultivars, along with striking foliage are available at specialty conifer nurseries.

Four Unusual Forms of Umbrella Pine:

‘Gruene Kugel’ – slow-growing compact form from Germany (30 inches x 18 inches in 10 years); rounded form when young, develop slowly into a small compact tree with glossy deep green foliage year-round.

‘Mr. Happy’ – upright coniferous tree with lush dark-green needles and /or clear yellow variegation. According to Buchholz & Buchholz Nursery in Gaston, OR, needles may be entirely green or entirely yellow or variegated half-and-half. It prefers sun/partial shade in well-drained soil; 5 feet tall x 3 feet wide in 10 years. Zone 4

‘Joe Kozey’ grows tall and very narrow at 20 feet high and 6 feet wide. Needles are held more tightly to the trunk than other types. At maturity, this slow-growing variety becomes a large, spire-like tree.

‘Picola’ – a dwarf, conical selection with short, 2 inch (5 cm) long, shiny dark-green needles. After 10 years years of growth, a specimen will stand only 30 inches (80 cm) tall and 15 inches (35 cm) wide, suggesting an annual rate of growth of 2.5 inches (8 cm).

Outdoor Holiday Decorating With Poinsettias and Cyclamens

Posted by Hugh on December 6th, 2018

Outdoor planting of hardy cyclamen

Poinsettia in Jacksonville, FL landscape

If you live in U.S. hardiness zones 3-7, December weather is ordinarily is too frigid to grow poinsettias and cyclamen outdoors. Southeastern U.S. cities like Charleston, SC, Savannah, GA, and northern parts of FL like Jacksonville, Tampa and Orlando enjoy mild December temperatures 50 º F. lies in zone 8 as well as most of the Dallas TX.

Whether planted in front of a shopping center, a restaurant, or your home, these brightly colored plants should put you into the holiday spirit. Poinsettias are native to Mexico (USDA hardiness zones 9 to 11. If poinsettias and cyclamens are planted nearby a building foundation, they often enjoy a micro-environment protection of 4-5 º F.

Hardy cyclamen (Cyclamen spp.) are native to the Mediterranean region and flowers are available in a wide range of white and pink shades. Breeders have developed several plant sizes ranging from small, medium and large. Some varieties are fragrant. At Black Friday sales around Thanksgiving, poinsettias may sell for less than $2.00 at the big box stores.

Here are some basic care tips for outdoor care:

Place poinsettias and cyclamens in bright natural light to morning only sunlight.
Keep plants away from high winds.
Brightly colored poinsettia bracts should remain fresh if outdoor temperatures do not exceed 80 º F or drop below 50 º F in November and December.
Water plants thoroughly weekly if set bare-root in planter beds or every 3-4 days in pots if natural rainfall is low. Never leave plants sitting in water over several hours.
Feed plants every 2-3 week with a water soluble fertilizer such as Schultz™ and Miracle-Gro™ at recommended rates for house plants.
Plant quality will begin to decline in early January. You may opt to discard plants or grow them on for their foliage.

Spring Star Flowers (Ipheion)

Posted by Hugh on November 28th, 2018

Starflower (Ipheion)

Spring star flowers (Ipheion uniflorum), native to Argentina and Uruguay, feature grass-like foliage and 6-petaled star-shaped flowers on 3-6 inches tall stems in early spring (April). Each bulb produces multiple flowering stems. Flowers range in color from almost white to violet blue and emit a mild spicy fragrance. In addition the grassy foliage gives off an oniony or garlic aroma when crushed. They are in the Liliaceae plant family and their scent repels deer and rabbits.

Star flowers are one of the easiest bulbs to grow. These minor bulbs grow in average, medium, well-drained soils in full sun to part shade. They’re tolerant of a wide range of soils. In fall, sow bulbs 2-4 inches deep and 2-4 inches apart. Bulbs naturalize rapidly by bulb offsets and also by self-seeding. Plants go dormant by late spring. Lightly feed the planting in early spring with 10-20-10 or equivalent fertilizer.

Bulbs may start out slowly the first year, but star flowers eventually naturalize. Once established, star flowers produce masses of quarter size blooms lasting 3-4 weeks even if planted in the home lawn. Star flowers flourish in the Southeastern U.S. west to Texas (USDA hardiness zones 4-9).

Star flowers are great planted in a rock garden, containers, front borders or mixed among peonies, heucheras, hostas, et al. Sow masses of bulbs under recently planted shade trees. Branches should be limbed up high enough to permit the early spring sunlight to filter down to the bulb foliage.

I have found the largest variety selection listed in Brent and Becky’s fall catalog @Brent and Becky’s Bulb, Inc. in Gloucester, VA. A few favorites include: ‘Jessie’ (described as the darkest blue); ‘Rolf Fiedler’ (bright deep blue), ‘Tessa’ (light pale blue), ‘White Star’ White stars), and ‘Wisley Blue’ (variable shades of blue).

Decorate your spring kitchen table with a small vase of these beauties.