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

Pest Alert -Laurel Wilt Disease

Posted by Hugh on April 1st, 2018

Granulate ambrosia beetle frass on red maple (Photo by Dr. Frank Hale, Univ. of Tenn. Extension Entomologist)

Granulate ambrosia beetle adult female (Photo by Dr. Frank Hale, Univ. of Tenn. Extension Entomologist)

Laurel wilt (Raffaelea lauricola) is an invasive deadly vascular wilt disease of red bay laurel and other trees in the Lauraceae family. The fungal disease is carried from tree to tree by a small beetle called the redbay ambrosia beetle (Xyleborus glabratus). This Ambrosia beetle bores into the wood and the fungus disease infects the tree. It is possible(?) that granulate ambrosia beetles may also transmit the disease. The disease spreads attacks the tree’s vascular system, blocking movement of water within, and the tree wilts and dies weeks or months later.

Key symptoms are beetle holes and frass tubes in the trunk of susceptible trees. Redbay ambrosia beetle is originally from southeastern Asia. Here is another example of how an Asiatic pest and fungus disease can be transported thousands of miles. It was likely introduced in wood products shipped from overseas.

Only plants in the Laurel family are susceptible to laurel wilt. The most severely affected species is redbay, which is a medium sized tree commonly found throughout the eastern part of the state. Sassafras (S. albidum), avocado, and spicebush (Lindera benzoin) are susceptible species, while mountain-laurel (Kalmia latifolia), rhododendrons, and sweetbay magnolia (M. virginiana) are not susceptible. So far, since 2011, Laurel wilt has been detected in North Carolina, Georgia, Mississippi, Alabama, Florida, South Carolina, Louisiana, Texas, and Arkansas.

Sassafras – susceptible host plant

About redbay ambrosia beetles
Female ambrosia beetles can fly and the males cannot. A single female beetle flies to a host tree, reproduces, and starts a new brood without mating. They’re wood borers and tunnel deep within the host trees.

The insect is tiny cylindrical brown to black beetle, about 1/16th inch long. Multiple generations of beetles are produced from late June through September. When you observe small “toothpicks” of sawdust and beetle excrement, called “frass”, form at ambrosia beetles entrance holes; beetles push materials out to create living space within the tree.

Management:

Currently, there is no effective control for this disease. Spraying the trunk of susceptible species with insecticides containing bifenthrin or permethrin in early spring can protect the tree from the beetle. Monitor this pest and and do not transport potentially-infested firewood. Insecticides are not totally effective in stopping beetle attacks. Fungicides are costly and must be re-applied annually. Properly disposed of diseased trees on site by burying or burning dead trees.

Four Large Street Trees With A Narrow Vertical Look

Posted by Hugh on March 26th, 2018

Liquidambar ‘Slender Silhouette’

‘Arnold’ tulip poplar

There is an old saying that they’re not making more land. This is particularly true in urban downtown areas where room to grow street trees is very limited. Here are four tall trees that also have a striking vertical accent. Their branching is upright. Because of their tall stature, they are particularly suitable planted along wide avenues or boulevards in urban areas. All 4 species adapt well to urban environs. They’re also perfect for small planting sites with no height restrictions (USDA hardiness zones 5-9).

During the first two years following planting, all street trees should be irrigated during dry spells (or very 2-3 weeks) from spring through late summer.

‘Slender Silhouette’ Sweetgum (Liquidambar styraciflua ‘Slender Silhouette’) (USDA 5-9) is a columnar 35 to 50 feet tree that spreads only 8 feet wide. ‘Slender Silhouette’ produces very few nuisance gumball fruits so typical for sweetgum trees. Yellow to red fall color is exceptionally nice. Bark develops deep furrows as the tree matures.

‘Beacon’ Swamp White Oak (Quercus bicolor Beacon) deserves more recognition. ‘Beacon’ is a tightly columnar cultivar with upright branches and mostly disease-free foliage compared to the species. Fall color is yellow and persists for 2 to 4 weeks. Its mature height is 30 to 40 feet and 12 to 15 feet wide. This oak produces acorns which might be a messy problem every 3 or 4 years unless picked up regularly curbside.

‘Princeton Sentry’ or ‘Fastigiata’ Ginkgo (Ginkgo biloba ‘Princeton Sentry’) is a deciduous conifer (a true gymnosperm) that grows to 30-50 feet in height, although a rare mature 100 feet trees is possible after a century or more. It features distinctive two-lobed, triangular or fan-shaped green summer leaves. Male trees (fruitless) should only be planted. Foliage turns bright yellow in fall. In most years, leaves drop rapidly and form a golden carpet around the tree.

‘Arnold’ tulip poplar (Liriodendron tulipifera ‘Arnold’) is a upright (fastigiate) grower to 50-60 feet tall and 8 to 10 feet wide. Unusual light green and orange tulip-like flowers appear in late spring, most blooms hidden under tree’s foliage. Fruits (seed pods) have no value ornamentally. The furrowed gray bark is showy and offers significant winter interest.

Favorites For The Shade

Posted by Hugh on March 23rd, 2018

Here are ten of my favorite perennial plants for shady areas (USDA hardiness zones 4-7). All prosper in 1-2 hours of early morning sunlight and in humus-rich, moist, well-drained soil. Mulch to conserve moisture and suppress weeds.

Astilbe chinensis

Fairy Wings (Epimedium)

Hosta – unquestionably the shade favorite of U.S. gardeners. A low maintenance plant that returns every spring with lush beautiful foliage and white or purple trumpet-like flowers. Choose from over 35,000 registered cultivars of different leaf shapes, variegations, sizes and textures. Select those that are proven performers in your region. Blue leaf types grow best in moderate shade.

Chinese Astilbe – colorful feathery plumes in summer and lacy, fern-like foliage. Flower colors range from white to dark purple depending upon the species. Astilbes are at their best in a shady area that receives 2-3 morning sunlight and adequate soil moisture.

Assorted Ferns – six choices to start planting: Autumn fern (evergreen), Christmas fern (evergreen), Japanese painted fern, Lady fern, Royal fern, and Northern maidenhair.

Variegated Solomon’s Seal (Polygonatum odoratum Variegatum) – pendulous, white, bell-shaped flowers appear in pairs beneath arching stems in spring. Plants grow 1-2 feet tall and blooms are slightly fragrant.

Heart shaped brunnera (Brunnera macrophylla) , aka Siberian bugloss, is a rhizomatous, clump-forming perennial with attractive heart-shaped mottled green foliage and airy light blue forget-me-not-like flower heads. Leading cultivars are ‘Jack Frost’, ‘Sea Heart’, and ‘Looking Glass’.

Fairy Wings (Epimedium spp.) aka bishop’s hat, spread via shallow underground rhizomes; plants spread slowly form close-knit colonies. Tiny flowers rise through last year’s foliage, before emergence of new spring foliage. Some epimediums have evergreen foliage.

Foamflower (Tiarella cordifolia) – clump-forming perennial that spreads rapidly by runners (stolons) to form dense, 1-2 feet wide clumps of foliage. Semi-glossy, heart-shaped, 3-5 lobed leaves (4 inches across) develop directly from stolons. Foliage is evergreen where winters are mild, otherwise turning reddish bronze in autumn and winter.

Old-fashioned Bleeding Heart (Lamprocapnos spectabilis) – Asian species and hybrids produce larger and showier flowers. Irrigating plants during dry spells keeps them looking good with repeat bloom.

Bigroot Geranium (Geranium macrorrhizum), aka cranesbill – vigorous ground cover filled with magenta-pink flowers that are conspicuously red veined in spring; develops into a dense leafy mat; foliage turns red in fall. Leading cultivar is ‘Bevan’s Variety’.

Bugbane (Actae racemosa) aka black cohosh, grows 4-6 feet (foliage + flowering spikes). Numerous small creamy white fragrant flowers on wiry stems rise well above the foliage in mid-summer.

Painted fern and bleeding heart (L. exima)

Woody Trees and Shrubs That Bees Like Most and Least*

Posted by Hugh on March 20th, 2018

Cornelian cherry is bee favorite

Ornamental crabapple

Recently, I saw this listing of woody trees and shrubs that are good pollinators. I grow a number of these great plants in my garden and will vouch for the accuracy of this list. The source is HRI Research and data was collected in the Ohio Valley region of the U.S. (includes Tennessee, Kentucky, southern Indiana and Illinois, and SW Pennsylvania).

Cornelian cherry (Cornus mas)

Dwarf fothergilla (Fothergilla gardenii)

Winter honeysuckle (Lonicera fragrantissima)

Higan weeping cherry (Prunus subhirtella ‘Pendula’)

Higan cherry (Prunus subhirtella ‘Autumnalis’)

Flowering cherry (Prunus spp.)

Fothergilla

Flowering crabapple (Malus spp.)

Burkwood viburnum (Viburnum burkwoodii)

Cherry laurel (Prunus laurocerasus)

Red horsechestnut (Aesculus x carnea)

American holly (Ilex opaca)

Foster’s holly (Ilex x attenuata)

Winter king hawthorn (Crataegus viridus)

Serviceberry (Amelanchier spp.)

Eastern redbud (Cercis canadensis)

Black gum (Nyssa sylvatica)

Ninebark (Physocarpus opulifolius)

Fuzzy deutzia (Deutzia scabra)

Firethorn (Pyracantha spp.)

Japanese tree lilac (Syringa reticulata)

American yellowwood (Cladrastis kentukea)

Mock orange (Philadelphus spp.)

Virginia spiraea (Spiraea virginiana)

Wild indigo (Amorpha fruticosa)

Buttonbush (Cephalanthus occidentalis)

Climbing rose (Rosa setigera)

Common winterberry (Ilex verticillata)

Sweetspire (Itea virginica)

Bottlebrush buckeye (Aesculus parviflora)

Linden (Tilia cordata)

Basswood (Tilia americana)

Golden raintree (Koelreuteria reticulata)

St. John’s Wort (Hypericum frondosum)

Devil’s walking stick (Aralia spinosa)

PeeGee hydrangea (Hydrangea paniculata)

Summer sweetshrub (Clethra alnifolia)

Bee bee tree (Tetradium danielii)

Winged sumac (Rhus copallinum)

Crape myrtle (Lagerstroemia spp.)

Glossy abelia (Abelia x grandiflora)

Seven-son flower (Heptacodium miconioides)

Chaste tree (Vitex agnus-castus)

Trees & Shrubs That Attract Few Bees*

Forsythia (Forsythia spp.)

Star magnolia (Magnolia stellata)

European boxwood (Buxus sempervirens)

Sassafras (Sassafras albidum)

Japanese Kwanzan cherry (Prunus ‘Kwanzan’)

Mulan magnolia (Magnolia liliiflora)

White azalea (Azalea spp.)

Koreanspice viburnum (Viburnum carlesii)

Carolina allspice (Calycanthus floridus)

White fringetree (Chionanthus virginicus)

Hybrid tea rose (Rosa spp.)

Smooth hydrangea (Hydrangea arborescens)

Bigleaf hydrangea (Hydrangea macrophylla)

*For more information: GrowWise.org and HRIresearch.org

Native Serviceberry

Posted by Hugh on March 17th, 2018

Fall color of A. laevis in container

Mult-trunked Amelianchier x laevis

Serviceberry (Amelanchier arborea) is a medium-sized native tree. Its native range stretches from Ontario to the Gulf Coast (USDA hardiness zones 4-9). However, it performs well across the Western and Central U.S. Serviceberry is regionally known by many names, including shadbush, shadblow, sarvisberry, sarvis tree, and Juneberry. The latter refers to the small greenish-blue, ripening red fruits in late May here in East Tennessee (USDA hardiness zones 6 and 7).

A frosty sighting on a mountainside in an early spring morn is likely serviceberry in bloom. Serviceberry’s small white blooms signals that the winter season is coming to an end. Flowering usually lasts 7-10 days. Its purple fruits attract multiples of birds. Soon thereafter, hundreds of seedlings will germinate in your landscape. In 5 to 6 years you may be enjoying a shade from one of these seedling trees.

The tree naturally develops multi-trunked unless trained as a single trunk tree at the nursery. Serviceberry can be utilized as a street tree and a yard tree. Leading cultivars (hybrids) are ‘Autumn Brilliance’, ‘Forest Prince’, ‘Princess Diana’ and ‘Robin Hill’. They’re listed as hybrid crosses (A. x grandiflora) and Downy serviceberry (A. arborea). Shrubby Allegheny serviceberry (A. laevis) is also commonly planted.

Annual growth rate is rapid, 20 to 30 feet tall and 15-20 feet wide in 20 years. Serviceberry tolerates many kinds of soils, preferring moist, acidic, well-drained soil, and partial to full day sun. Irrigate and mulch a newly planted tree until it is established. Within two years a tree can handle moderately dry spells. If pruning is needed, do so in the spring after flowering.

In most years, serviceberries suffer from few disease and pest issues. In a rare wet summer, severe leaf spotting may result in an early leaf loss in August and dash all hopes of fall color.

Serviceberry’s multi-trunked branching fashions a wonderful winter silhouette on a dreary snowy day.

Jazz Up Shady Garden Areas

Posted by Hugh on March 14th, 2018

Dicentra ‘GoldHeart’

Hosta ‘Golden Scepter’

From brilliant green to rich gold hues, fabulous foliage and flowers can wake up any dark or colorless, shade area. See below a list of great plants that wake up a blah area of your shade garden. Plant list is suitable for gardens in plant hardiness zones 5-8. Exciting colorful and/or tropical-like foliage or showy flowers.

Hostas, coral bells and liriopes are the first plants that gardeners think of and there are many cultivars to select from. A number of gold colored plants such as variegated liriope, ‘Sun King’ aralia, and many gold and variegated leaf hostas. Some variegated shrubs include ‘Brigadoon’ St. John’s wort, boxwood (Buxus), ‘Girard’s Rainbow’ doghobble (Leucothoe), and variegated forms of euonymus. They add a splash of foliage color, provided that they receive a minimum of 2-3 hours of dappled sunlight.

Plant suggestions:

Golden Japanese forest grass (Hakonechloa macra ‘Aureola’, ‘All Gold’)
Golden sweet flag (Acorus gramineus ‘Ogon’)
‘Evergold’ or ‘Evercolor’ sedges (Carex oshimensis)
Gold Heart Bleeding heart (Dicentra spectabilis ‘Gold Heart’)*
Creeping liriope, monkeygrass (Liriope spicata ‘Variegata’)
Lilyturf liriope (Liriope muscari ‘Peedee Ingot’)*
Sun King aralia (Aralia cordata ‘Sun King’)*
Black mondo grass (Ophiopogon planiscapus ‘Nigrescens’)
Gold leaf hostas (Hosta ‘Golden Tiara’, ‘Golden Scepter’, ‘August Moon’, others)
Variegated forms of hostas (Hosta ‘Patriot’, ‘Gold Standard’, ‘Francee’, others)
Autumn fern (Athyrium erythrosora)
Lungworts (Pulmonaria x ‘Miss Moon’, ‘Raspberry Splash’, ‘Dark Vader’, ‘Trevi Fountain’
Variegated Solomon Seal (Polygonatum odoratum ‘Variegatum’)
Ligularias (Ligularia dentata ‘Britt-Marie Crawford’)
Heart shaped brunneras (Brunnera macrophylla ’Jack Frost’, ‘Sea Heart’, ‘Looking Glass’)
Hypericum Brigadoon’
Brick red leaf rodgersia (Rodgersia podophylla ‘Rotlaub’)
Foam flowers (Tiarella x ‘Spring Symphony’, ‘Iron Butterfly’, ‘Mystic Mist’)
Colorful coral bells (Heuchera ‘Caramel’, ‘Southern Comfort’, ‘Citronelle’, ‘Georgia Peach’)
Various heucherellas (Heucherella x ‘Sweet Tea’, ‘Stoplight’)
Variegated boxwood (Buxus sempervirens ‘Elegantissima’)
Moonshadow wintercreeper (Euonymus x ‘Moonshadow’)
Golden St. John’s wort (Hypericum calycinum ‘Brigadoon’)*
Spotty Dotty Chinese mayapple (Podophyllum ‘Spotty Dotty’)

*2-3 hours of morning sunlight to maintain variegation and gold colors thru the season.

Baptisias – Long-Lived Native Perennials

Posted by Hugh on March 10th, 2018

‘Carolina Moonlight’ baptisia

‘Purple Smoke’ baptisia at Mt Cuba Center, Greenville, DE

Wild indigos or Baptisias (Baptisia spp.) are long-lived native perennials. Baptisias are tap rooted perennials that will reward you for many years. They’re sometimes mistaken for Carolina lupine (Thermopsis caroliniana).

Modern day cultivars are hybrids of 4 Baptisia species: purple (B. australis), lavender blue (B. minor), white (B. alba), bright yellow (B. sphaerocarpa). Several bicolors are also available. Baptisias bloom for 3 to 4 weeks. Their blue-gray foliage and sturdy upright shrubby habit are pluses in the summer garden.

Baptisias perform at their best in full sun. In the shade they bloom less and stems are weak and frequently require staking. Baptisias prefer a deep humus-rich well-drained soil, but tolerate average soil. Mulch with organic matter to keep the soil cool and weed-free.

Vigorous plants grow 3 to 4 feet high and 4 to 5 feet wide after 3 to 5 years. Do not overcrowd. Newly planted baptisias should be watered until established, usually within 1-2 year. Plants are slow to establish and begin blooming, usually a few flowers in their first year and are covered with flowers in 3 to 4 years.

In early spring add 1-2 handfuls of a slow-release fertilizer around plants. Older well established plants require little to no fertilizer as they produce their own nitrogen. Yellowing of leaves in the summer is a symptom of iron deficiency or high soil pH. In such cases, feed with chelated iron or a water-soluble fertilizer such as Schultz™ or Miracid™. Established plants are heat and drought tolerant and are almost invincible to disease and insect problems.

Stunning stalks of colorful pea-like flowers appear in mid-spring. Flowers stalks give way to black seedpods by late July. Gardeners may opt to remove the seed pods before they mature. Flower arrangers utilize the ripe blacken seedpods in arrangements.

Cultivars with the deeper shades of blue and yellow blooms stand out in a garden. Popular cultivars include: ‘Purple Smoke’ (lavender flowers), ‘Solar Flare’ (yellow), ‘Alba’ (white), and ‘Twilight Prairie Blues’.

Tips On Repotting Container Plants

Posted by Hugh on March 7th, 2018

Canna in container

Banana (Musa) in container in Fort Worth Gardens

Eventually, all potted plants outgrow their containers. This includes potted roses, Japanese maples and other small trees, shrubs, dwarf conifers, elephant ears (Colocasia, Alocasia), cannas, lotus, papyrus, and lots more. A rule of thumb is to transplant every 2 years in early spring before bud break. In the case of perennials and tropicals, this is a good opportunity to divide plants. Tropicals may need to be set back into a greenhouse until it is safe to move outdoors.

Plants tend to deplete the soil of nutrients and soil pH may change. Select a container large enough to provide adequate space for plant roots, one that is one or two sizes larger. New soil media should be well-drained and retain moisture. Add a one inch deep layer of coarse to medium sized gravel or other rocks in the bottom of the container for extra drainage.

Spread out plant roots and fill in around the roots with the remaining soil media. Press down firmly, but do not injure roots. For grafted plants such as roses, Japanese maples, or certain conifers, don’t bury the bud union. Settle the soil (media) in the container and finish filling to within 1 inch of the lip of the pot.

The container may be plastic or clay. During hot weather clay containers provide a cooler soil environment for roots compared to plastic pots. Clay pots usually dry out faster than plastic. Choose light colored pots so dark shades heat up faster. Thin plastic and clay pots may crack during freezing winters.

Set the container in a location with adequate light and good air circulation. Allow 2 feet or more space between containers for adequate sunlight and proper air movement. For example, roses should have 6-7 hours of direct sunlight. Don’t crowd plants too close together as this may create a favorable environment for disease and insect troubles.

Ten Grow Facts About Perennials

Posted by Hugh on March 4th, 2018

Daylilies

Before purchasing and planting perennials, here are ten helpful tips to assist you in garden planning:

Perennials die back to the ground in fall or winter and regrow from plant crowns or roots the following spring.
Most perennials should be divided when they are dormant: Spring bloomers in the fall and Fall bloomers in the spring. Some (Shasta daisies, coneflowers, black eyed Susans) may need dividing every 3 years; hostas and daylilies every 5 years.
Perennials from cool temperate regions must undergo a cold winter to encourage new buds to grow in spring. Examples: asters, irises, lupines, wallflowers, peonies, and primroses,
Many perennials spread from underground roots (termed “rhizomatous”) which send up new stems in spring. Examples: bleeding heart, iris, coreopsis.
Some perennials, such as lupines, columbines and delphiniums are short-lived, lasting only 2-3 years in zone 6 and south.
Perennials are not totally maintenance-free. Some do clean up easier than others.
Deadheading, the practice of removing the old spent flowers often results in additional flowering 4-5 weeks later. Examples include beebalm (Monarda), blanket flower (Gaillardia), speedwell (Veronica), yarrow (Achillea), Shasta daisies (Leucanthemum), and many more.
Grand expectations: most perennials do not reach their full potential (size and flower numbers) until 3-4 years after planting. Many gardeners say “first they sleep, year 2 they creep, year three they leep”.
Most perennials bloom in a specific timeline. Reblooming daylily and iris cultivars flower 2-3 weeks in summer and re-bloom again in fall (with extra care). Select lots of different kinds to lengthen the blooming cycle in your garden. Since perennial bloom is periodical, interplant with lots of colorful longer flowering annuals.
Some perennial species may be invasive in your state. Check with your state’s Department of Agriculture or Natural Resources to find which plants are listed as invasive.

Why No Fruit On My Tree?

Posted by Hugh on March 1st, 2018

Espaliered apple tree

Why trees fail to bear fruit or only produce fruit every other year? There are 8 common reasons:

Excessive Tree Vigor – Primary cause is over-fertilizing and/or over-pruning fruit trees. Heavy applications of nitrogen will stimulate excessive growth at the expense of flower production. A nearby fertilized lawn may supply too much nitrogen to adjacent fruit trees. Heavy winter pruning also stimulate excessive growth. Apple and pear trees are pruned differently than peach, plum, and cherry trees.
Frost Damage – Late spring frosts or temps below 30 °F will damage flower parts. Do not plant fruit trees in low land areas. Fruit trees bloom at different times in the spring. Early flowering apricots are frequently damaged by spring frosts. Peaches bloom first before cherries, plums, pears, peaches and apples (last). Apple varieties flower at different times, such as Gala and MacIntosh bloom before Rome Beauty.
Severity of winter temperatures. Extremes in temperatures over winter months can damage dormant flower buds. Areas where winter temperatures consistently drop below -15 °F will not support consistent fruit production. Flower bud hardiness (most hardy to least cold hardy): Pears > Apple > Apricots > Tart Cherries > Sweet Cherries > Plums > Peaches > Nectarines.
Poor Pollination by Bees – Weather factors like rain or high winds will reduce bee activity and pollination. Improper spraying of pesticides will also reduce bee populations. Avoid the use of insecticides during bloom that may kill honeybees.
Cross vs Self-Pollinated – Apples, pears and sour cherries must be cross pollinated for maximum fruit crops. Plant 2 or more different varieties for optimum fruit set. Peaches, nectarines, tart cherries and most plums are self-fruitful and only one variety is necessary to produce fruit.
Over-production – Heavy crops the previous year, particularly apple and pear trees, can reduce shoot growth and/or prevent flower formation. Remove some fruits by hand within one month after petal fall. With apples and pears, thin to 1 to 2 fruit cluster per 6 to 10 inches of branch length. Heavy crop loads on peach and nectarine trees reduce shoot growth and less fruit buds will form the following year. With peaches and nectarines, thin to one fruit per 10 inches.
Tree age – Apples and pears should not bear fruits until 3-4 years after planting (depending on rootstock). For example, apple varieties are grafted on semi-dwarf rootstock like M111 or EM7.
Sevin™ (Carbaryl), sprayed on apple and pear trees when they’re flowering or within first month after petal fall, will cause some or all fruits to drop. Read the label of pesticides to avoid unintentional thinning of the fruit.