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

Benefits Of Mulching

Posted by Hugh on April 22nd, 2018

Trunk filled with compost

Mulching benefits garden soil and enhances the landscape appearance.

Here is how:

Pine needle mulch at Biltmore Estates in Asheville, NC

Prevents weed seeds from germinating, thereby reducing hand weeding.
Mulching keeps plant roots moist and cool in summer.
Fall mulching acts like a thermal blanket and aids newly set plants to establish their roots quickly.
Reduces the need to water the garden as often.
Conservation measure via soil runoff protection.
Reduces soil compaction which permits rainfall and irrigation water to penetrate the soil surface.
Encourages beneficial insects and microorganisms.
Mulch decomposes and improves the organic level of the soil.
Offers a tidy appearance to the garden.
Certain kinds of mulch increase or decrease soil pH over time. Decomposition of oak leaves, holly leaves, and pine needles will lower pH over time. Mulch derived from hardwood bark tends to raise soil pH slightly over time.

Acid-loving plants such as blueberries, rhododendrons, azaleas, mountain laurels (Kalmia), and many evergreen shrubs benefit from low pH soils. To raise soil pH, apply hydrated lime (contains calcium) or dolomitic limestone (contains magnesium). Mulches derived from fresh sawdust or wood chips may tie up available soil nitrogen and plant foliage turns yellow (chlorotic). Do not over apply uncomposted mulches around landscape plants.

Typically, spring mulching entails adding 3-4 inches of composted mulch which may be purchased from garden centers or big box stores. Your city may sell or giveaway partially decomposed yard waste, a mix of cut tree/shrub prunings plus lawn clippings and leaves which have been ground up and composed for 3-6 months.

When not to mulch: do not mulch fall-planted fruit trees and shrubs the first year. Vole and other critters make their winter homes in the mulch and gnaw on the sweet soft bark of these plants. After the winter is over, fruiting plants may be permanently mulched.

Uniquely Different Spider Azalea

Posted by Hugh on April 19th, 2018

R. stenopetalum ‘Linearfolium’ at Biltmore Estates in Asheville, NC

Although rarely seen, spider azalea (Rhododendron stenopetalum ‘Linearfolium’) will be a pleasing addition to your woodland garden (USDA hardiness zones 6-8). Few people would ever guess that it is an azalea. This airy shrub grows 3-4 feet tall and a whole lot wider. It is slow growing, but is worth the wait. This unique semi- evergreen azalea hails from Japan.

April blooming spider azalea.

The very narrow (ribbon-like) leaves of spider azalea are mostly deciduous, nearly 3 inches long, and crinkly textured. The pink April/May flowers are very spider-like and appear in terminal clusters of three. Flowering may last 4-6 weeks in a dappled shade garden locale and are lightly fragrant up close.

Flowers are unique in that the 1 1/4 inch-long pink sepals tend to be slightly larger than the pink petals. Flowers are borne on tips of branches. The overall shrub is finely textured and will catch the attention of friends and visitors to your garden.

Spider azalea thrives in cool shade, best in partial day sun, preferably in the morning. Roots demand a moist, humus-rich, well drained, acidic soil and high shade that permits filtered sunlight. Do not plant in deep shade. The foliage is easily harmed by dry winds.

Feed spider azalea at the same time as you fertilize other azaleas and rhododendrons — once annually in late winter or early spring. Use a slow release fertilizer such as Osmocote™ or Nutrikote™. Maintain a 2-3 inch layer of an acidic based mulch comprised of pine needles or pine bark chips. Pruning is rarely needed and performed to shape the plant or to remove a dead or broken small branch. Irrigate as needed the first year to establish new shrub. Disease or pest troubles are rarely seen.

A number of sources, including Niche Gardens in Chapel Hill in North Carolina and Woodlanders Nursery in South Carolina, NC, list the variety ‘Seigai’.

Growing Celosia In The Summer Garden

Posted by Hugh on April 16th, 2018

Celosia ‘Arrabona Red’

Cutflower celosias sold at a Brooklyn, NY market

Celosias (Celosia argentea), aka cockscomb, feather, and plume amaranths, are summer flowering annuals in most of the U.S. (USDA hardiness zones 10-11). Mature plant height varies by cultivars, generally between 6 inches and 3 feet in height, taller types grown for the florist market. Celosia plants are classified into three groups: a crested type (C. cristata), plume type (C. plumosa), and spike or wheat type (C. spicata).

Celosias prefer full-day sun, although a minimum of 6 hours of direct sunlight is adequate. A compost rich, mildly acidic, well-drained garden soil is ideal. Plants are set outdoors in the garden when spring daytime temperatures stay above 60 °F. Add 2-3 inches of an organic mulch after planting and deeply water newly set plants. Mulching aids to suppress weed infestation and in soil water loss from evaporation. Celosias are not water hogs, but need irrigation during long summer dry spells.

At planting time apply a slow release granulated fertilizer such as Osmocote™ or Nutrikote™ according to package directions. Over the summer months, if plants need additional feeding, use a water-soluble fertilizer such as Miracle-Gro™ or Jacks™ every 2-3 weeks through mid-September. With taller cockscomb varieties, tie flower stalks to stakes to keep them from falling over; or simply pinch back shoots by one-half to develop a bushier plant. In addition, remove spent flowers to promote new blooms.

Celosia is rarely troubled by disease and insect problems. Inspect plants for mites over a hot dry summer. Good soil drainage is absolutelyessential to avoid root rot problems. Leading plumosa varieties: ‘Arrabona’, ‘Fresh Look’, ‘Dragon’s Breath’, ‘Prestige Scarlet’. ‘Intenz’, Century® series, and ‘Flamingo Feathers’ are spike type celosia. Cristata types include Bombay® and Kimono® series. Floral color range is purple, deep red, wine red, gold, and yellow gold.

Simple Care of Crape Myrtles

Posted by Hugh on April 13th, 2018

‘Muskogee’ crape myrtle

‘Acoma’ crape myrtle on City Street in Charlotte, NC

Crape Myrtle Hardiness: Know how hardy the cultivar is. USDA hardiness zones 6 to 9).

Site Location: Crape myrtles love sunlight. Flower numbers decline in light to medium shade. Plant in average soil that is well-drained. Select the right cultivar that fits the allotted planting space. Mulch plant and water as needed the first growing season.

Planting Time: In most regions plant in early- to mid-spring. Summer and early fall will also work in southern areas. Water newly planted crape myrtle deeply at planting time and mulch around them to conserve soil moisture and prohibit weeds. Apply a granular fertilizer such as 10-10-10 or equivalent in early spring. Keep plant(s) irrigated through the summer months.

Pruning crape myrtles: grow naturally as small upright or vase shaped trees with multiple trunks (except small shrub types). Late winter (late February thru March) is the best time to prune crape myrtles. Crapemyrtles generally require only minimum pruning annually. STOP THE CHOP! –do not prune back crape myrtles to the same point every spring as you often see landscapers doing at shopping malls and industrial buildings. This is “crape murder.” Removing seedpods is an optional activity.

Avoid Disease / Insect Problems
In general, crape myrtles contact few disease and insect problems if you select the best cultivars for the area where you garden. In southerly regions (zones 7-9) inspect newly emerging spring foliage for crape myrtle aphids, particularly on the leaf underside. Sooty mold fungus usually follows. Leaves and stems turn black, that is clear evidence of aphid feedings. Aphids are rarely seen in northern areas (zone 6).

Aphid Resistant Cultivars: ‘Muskogee,’ ‘Natchez,’ ‘Tuscarora,’ ‘Acoma,’ ‘Tuskegee,’ ‘Hopi,’ ‘Zuni,’ ‘Biloxi,’ ‘Miami,’ ‘Wichita,’ ‘Apalachee,’ ,’Lipan,’ ‘Osage,’ ‘Sioux,’ ‘Yuma,’ ‘Tonto,’ and ‘Fantasy.’ Target aphids using any of the following insecticides: malathion, diazinon, or summer horticultural oils. Read and follow package directions.

Crape Myrtle Bark Scale is becoming a significant problem in the deep South.

Powdery Mildew Resistant Cultivars: ‘Hopi’, ‘Lipan’, ‘Osage’, ‘Regal Red’, ‘Sioux’, ‘Tonto’, ‘Tuscarora’, ‘Tuskegee’, ‘Apalachee’, and ‘Fantasy’. For susceptible cultivars, spray leaves at first sign of disease with Funginex™, Immunox™, Bayleton™, or Strike™ to reduce the spread of powdery mildew; repeat spraying as necessary.

Cercospora Leaf Spot Resistant Cultivars: ‘Fantasy,’ ‘Tonto,’ ‘Tuscarora,’ ‘Tuskegee’, among others.

Credit: South Carolina Extension for listing of disease and insect resistant cultivars.

Landscape Ideas Using Crape Myrtles

Posted by Hugh on April 10th, 2018

30 feet tall ‘Natchez’ crape myrtle

‘Cherry Dazzle’ crape myrtle

If you live in zone 7 and points southward, you are likely growing crape myrtles (Lagerstroemia indica x fauriei). Additional hybrid cultivars (varieties) are hardy in zone 6. Crape myrtles are loved for their spectacular summer flowers, colorful fall foliage, and exquisite peeling bark over trunks and branches. Cultivars range in size from dwarf selections that grow less than 5 feet tall to several that reach upwards of 30 feet plus. Know the mature height of the cultivar before you purchase it.

Landscape uses: Planted several together to create a large deciduous hedge or privacy screen; utilize low shrub types in the front foundation. Plant 1-3 specimen trees as a distinctive focal point near the patio. Select the right size for your needs. Larger types should not grow into power lines. Medium-size cultivars (12 to 15 feet) are a perfect choice in a narrow side yard or a small urban garden. Dwarf selections are suited for large containers in zone 7 and points south.

Dwarf (less than 5 feet height) – ‘Cherry Dazzle’, ‘Berry Dazzle’, ‘Chickasaw’, ‘Centennial’, ‘Victor’

Semi-dwarf (5-12 feet) – ‘Hopi’, ‘Zuni’, ‘Tonto’, ‘Caddo’

Intermediate (13-20 feet) – ‘Acoma’, ‘Lipan’, ‘Osage’, ‘Sioux’

Tree type (21-33 feet) – ‘Muskogee’, ‘Apalachee’, ‘Tuskegee’, ‘Natchez’

Crape myrtles perform best in full sun and are not finicky regarding type of soil, as long as it’s well drained. Soil pH may be acidic to mildly alkaline. Keep them properly mulched and irrigated over the first summer. Feed crape myrtles with granular 10-10-10 or equivalent in early spring just before budbreak. Young trees benefit from one additional feeding in early summer. Do not fertilizer crape myrtles after mid- August. Mature trees do not benefit from annual fertilizing and frequently draw off adequate nutrition from a nearby lawn area that has been fertilized.

When To Cut Back Foliage Of Spring Flowering Bulbs

Posted by Hugh on April 7th, 2018

Tulip planting

Narcissus + hyacinth

Once your tulips, daffodils and other spring flowering bulbs have bloomed, don’t be in a hurry to cut off the stems and leaves. Plant foliage serves an valuable role in the health and growth of bulbous plants. The green leaves absorb sunlight and carbon dioxide as a part of the process of photosynthesis.

The spent blossoms are no longer needed and should be removed as soon as the flowers fade. Leaving the old flowers may encourage seed formation which further exhausts the food supply in the bulbs. Unless you are interested in growing daffodils or tulips from seed, the old blooms should be pruned off. Bulb growth, including the formation of new bublets is promoted.

It is not unusual to see garden workers at large public and private gardens pulling up bulbs right after they have bloomed. Several hours later, they may be planting annuals and perennials for spring – summer garden displays. In this instance the bulbs are considered annuals and are dug up and discard. These bulbs are mostly depleted of food material and most will not re-bloom next year without new carbohydrates being produced. In fall, garden staff will plant new bulbs.

Most home gardeners want their bulbs to perennialize, e.g. come back every spring. For small gardens the following suggestions should help minimize the impact of spent foliage in your garden. About a month after the flowers have faded, the leaves will turn yellow. At this time cutback the all stems and leaves about an inch above the ground. If there is space, at least 3-4 inches between the bulbous stems, plant bedding plants between. For this purpose, I attach an augur bit to my power drill to set summer annuals. Add a layer of an organic mulch to the bed and you’re ready for a summer of dazzling color. Feed bulbs and new annuals in spring and summer. Your bulbs will be back again next spring.

Another idea is to interplant spring blooming bulbs with winter hardy pansies, wallflowers, diascias, dianthus, et.al. in the fall. Bulbs and pansies will offer a full bed of color. Once the pansies have finished flowering in the heat of late spring, you may fill the void with summer annuals

Bugleweed (Ajuga) Groundcover

Posted by Hugh on April 3rd, 2018

Bugleweed (Ajuga)

A. reptans ‘Catlin’s Giant’

Bugleweed, aka carpetweed (Ajuga reptans), is low-growing semi-evergreen groundcover that offers almost year-round appeal (USDA hardiness zones 3-9). It develops a low prostrate habit and spreads by runners that root into the soil. Attractive vertical spikes of flowers arise in mid- to late- spring. Cultivars abound with multi-colored flowers. Foliage variants range from light green, dark green, bronzed, purple, or variegated leaves.

Vegetatively, ajuga grows 2 to 5 inches tall, depending on cultivar. Attractive flower stalks rise 6 to 10 inches above the foliage. Small flowers come in blue, purple, pink, or white, depending on cultivar. Flowers are covered by bees and skipper butterflies. Tiny brown seeds follow on the persistent fruiting stalks.

After flowering you may raise your mower height to clean off spent flowers and seed heads, and to renovate old winter beaten foliage. Ajuga grows best in partial sun to full shade and thrives in humus-rich soil; it will grow in average, well-drained soil. Utilize ajuga to cover large flat areas and minor slopes, to edge walkways, and for rock gardens.

Feed with spring application of granular 10-10-10 or equivalent fertilizer and irrigate regularly during the hot and dry summer intervals. It is susceptible to crown rot under extremely wet conditions. Ajuga is easily propagated from daughter plants (runners) and from crown divisions. Over the years ajuga will intrude into lawn areas and flower beds.

Leading cultivars:*

‘Bronze Beauty’ – bright green-bronze foliage turns glossy deep purple in fall and winter; lilac-blue flower spikes.
‘Burgundy Glow’ (aka ‘Burgundy Lace’) – pink, white, and green variegated foliage; blue flower spikes.
‘Catlin’s Giant’ – vigorous growing, glossy, bronze purple/near black, crisp foliage; deep blue flowers.
‘Chocolate Chip’ – compact growing, small, glossy, bronze-maroon and green foliage; 2 inches tall lilac-blue flower spikes.
‘Metallica Crispa’ (also known as ‘Cristata’) – bronzed foliage is small and crinkled, resembling dark spinach, but is not as vigorous as other cultivars; blue flower spikelets

*Note: some variegated forms may revert to green or bronzed foliage.

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.