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

Favorite Mountain Laurel Cultivars

Posted by Hugh on May 17th, 2012

'Carol' - dark pink buds / light pink flowers

Shopping for mountain laurels is like sampling sweets at a candy shoppe or ice cream parlour. There are so many great choices. Most plants grow 4-5 feet tall and wide. Most have plant foliage which is lustrous, dark green and leaf spot resistant. All cultivars need minimal pruning and fertilizing once a year. In great apprehension I have weaned my lengthy list of favorites down to ten:

‘Bullseye’ features a purple banded tint inside the floral corolla; exhibits a vigorous, upright growth habit and new foliage has reddish hue.

‘Carol’ features dark-pink floral buds, open light pink, and fade to white. Plant habit is dense, low and compact.

‘Carousel’ features flowers with a purplish-cinnamon inner corolla and a white edged border; shrub is a vigorous grower.

‘Heart’s Desire’ has red flower buds which open to reveal cinnamon-red colored corolla. Shrub has a dense, well-branched habit.

‘Minuet’ has light pink buds that open to stunning cherry-red banded corolla within. Minuet is a dwarf 3 foot tall mountain laurel.

‘Olympic Fire’ possesses deep red flower buds that open light pink.

‘Pink Charm’ has dark pink flower buds that open to luscious pink.

‘Pinwheel’ features cinnamon-maroon flowers with white centers and scalloped edges. Plant exhibits a compact form.

‘Sarah’ has flowers that are red in bud and open pinkish red.

‘Snowdrift’ displays pure white buds and white-flowers.

Growing Mountain Laurels in Your Landscape

Posted by Hugh on May 14th, 2012

Hybrid Mountain laurel

Mountain laurel (Kalmia latifolia) is a U.S. native evergreen broadleaf shrub (USDA hardiness zone 5). Mature sizes range from 5 feet (dwarf cultivars) to 12 feet in height and with equal spread. Over the past 30 years, mountain laurels have so improved, thanks to breeding efforts of Dr. Richard Jaynes*. He has released several dozen cultivars to date, including those with dwarf forms and with highly colorful flowers.

Flowers open over a two week period beginning in mid-May here in the Southern Appalachian region (USDA hardiness zones 6 and 7). In the wild, mountain laurel tends to grow near a woodland clearing. In the garden, plant in an open area for full or partial sunlight. Mountain laurel prospers a cool, moist, acidic (pH 6 or below preferred), compost rich soil which is well drained. Flowers and foliage are best protected from direct wind.

Pruning is best performed within a few weeks after flowering is finished. Prune to shape, to limit shrub height and width, and to remove dead or diseased twigs and branches. Pruning and feeding with an acidic water soluble fertilizer such as Miracle-Gro®, Hollytone® or Schultz® invigorates new growth and flowering the next year. Mountain laurel tolerates droughty soils once established for two years.

Mountain laurels tend to perform more reliably than rhododendrons. While several plant maladies are possible, gardener should be most aware of phytophthora root rot in poorly drained soils and lace bug damage on the spring/summer foliage.

*Dr. Jaynes’ book: “Kalmia: Mountain Laurel and Related Species”, 3rd ed.(Timber Press).

Next blog: list and descriptions of ten favorite kalmia cultivars.

Evaluating Weeping Bald Cypress Cultivars

Posted by Hugh on May 9th, 2012

‘Cascade Falls’ weeping baldcypress

Bald cypress (Taxodium distichum) is a large 75 -80 foot deciduous conifer tree. They are long-lived, often 100 years or more. Bald cypress is incredibly hardy from the warm humid Florida swamps to the cold winter temperatures and loamy soils of central Michigan. Bald cypress is tolerant of a wide range of soil and moisture conditions. It grows in full sun and in any average acidic (not alkaline) soil type.

‘Cascade Falls’ (CF) and ‘Falling Waters’ (FW) are two dwarf cultivars which are better fits in most gardens. Both exhibit a strong weeping habit. Their fern- like foliage is light green in spring and summer months, and finishes burnt orange to brown in the autumn. The small leaves fall and compose rapidly around the tree. Both are real standouts as small weeping trees. Their exfoliating bark is an added winter feature.

Cascade Falls grows to about 20 feet tall and 20 or more feet in width. FW has a graceful arching form which is 15-20 feet tall by 8-12 feet in width (after 20 years). FW grows taller with less staking and holds its narrow tree profile.

In the early years, staking is a must for both cultivars. CF grows as tall as you stake it. It arches down, eventually forming a mound. Bend up and stake the leader until the desired height is achieved. If not staked, CF tends to grow like a ground cover.

Bald cypress requires little other maintenance, possessing few disease and insect issues. It is deer resistant.

Firethorns Make Good Utility Shrubs

Posted by Hugh on May 6th, 2012

6 Feet Tall Firethorn (Pyracantha) Hedge

Firethorn (Pyracantha spp.) is an old- fashion shrub that is making a comeback. Its white flowers makes a lovely presence in spring, followed by dark green leaves in summer, and bright orange or red fruits (berry clusters) in fall and winter. Firethorn tolerates close clipping and is often utilized as a short 6-8 foot tall privacy screen.

White clusters of foul smelling flowers cover the shrub in the spring. Fragrance is not detected from a few feet away. Fruit color depends on the cultivar planted. Firethorn prefers full to partial sunlight (6 hours minimum) and a well-drained average soil. Fertilize in late winter, but do not overfeed. Firethorn is susceptible to bacterial fireblight and scab leaf spot, but disease resistant cultivars are available.

Firethorn creates an effective 8-10 feet barrier or hedge. Sharp ½ – ¾ inch long thorns keep people and pets behind the sharp barrier and unwanted guests on the outside. The short stiff spines are mostly hidden among the foliage.

Firethorn tolerates close clipping and is easily pruned into an espalier against a wall or fence. You should wear leather or heavy canvas gloves to protect your hands during pruning.

Firethorn performs almost evergreen in the Southern Appalachian region (USDA zones 6 and 7), some years defoliating in mid to late winter. The leaves drop pale yellow, rarely catching your eye.

Here are 5 new hybrid cultivars are scab and fire blight resistant:

‘Apache’ grows to 5 feet high and 6 feet wide and forms large, bright red berries that last well into winter.

‘Fiery Cascade’ grows to 8 feet tall and 9 feet wide, and bears orange berries in the fall that turn red in winter.

‘Mohave’ grows to 12 feet tall and wide and develops many big orange-red berries which last well into winter.

‘Rutgers’ bears orange-red fruits on a low spreading 3 feet x 9 feet shrub. It demonstrates better winter hardiness than ‘Mohave’ and ‘Navaho’, writes Dr. Michael Dirr in the Manual of Woody Plants (6th ed.).

‘Teton’ has a tall upright growth habit (12 feet high and 4 feet wide) and is very cold hardy. Berries turn golden yellow in the fall.

Variegated Tapioca Plant Thrives In The Summer Heat

Posted by Hugh on May 3rd, 2012

Variegated Tapioca Plant (Manihot)

Add some tropical flair to your garden with variegated tapioca plant (Manihot esculenta ‘Variegata’), aka Cassava. Variegated tapioca is a spectacular foliage plant (zone 8 – 11) which excels as summer’s heat and humidity arrives and lingers.

Tapioca plant is not likely to be sold in every garden center and you’ll likely need to order one or more on-line. Young 12-18 inch tall plants grow to 5-6 feet tall and wide by late summer in full sun or partial sun (6 hours minimum). The first hard frost in autumn will kill this tropical plant.

Set out plants in mid- to late spring when all danger of frost has passed. Once temperatures climb into the seventy (70°F) plus degree range, plants will shoot up quickly. Tapioca plant thrives in poor soils and needs little attention once it becomes established after 4-5 weeks. Plant growth does excel with backup irrigation during long dry spells. Feed with a slow-release fertilizer at time of spring planting.

Its striking creamy yellow splashed foliage is a real eye catcher. It looks good in containers or in garden beds. Here in the Southern Appalachian region (USDA hardness zones 6 and 7), it is grown as an annual as it will not overwinter outdoors. Tapioca plant can be grown in large outdoor containers and brought indoors in early fall. Plants are cut back severely to fit inside a room to re-sprout.

Cassava is native to South America but is cultivated in tropical and subtropical zones throughout the world. It is one of the most important tropical food crops in the world. It requires at least 8 months of frost-free weather to produce usable roots. Cassava (tapioca) roots are poisonous and must be properly cooked to become edible.

Pinxterbloom Azalea

Posted by Hugh on May 1st, 2012

Pinxterbloom Azalea at Jenkins Arboretum in Philadelphia, PA

Pinxterbloom (Rhododendron periclymenoides), formerly R. nudiflorum, is a hardy deciduous azalea native to a large geographic area of the eastern United States. Pinxterbloom naturally grows nearby streams in a light woodland setting, but appears to tolerate dry rocky sites equally well after 2 years established. Shrub heights vary from 4-8 feet. Pinxterbloom spreads by underground stolons and shrubs may become quite dense.

Flowers open in mid to late spring and are often mistaken for honeysuckle blooms. Flower clusters (called “trusses”) appear just before the leaves emerge and bear 6 – 12 blooms each, which open 1½ – 2 inches wide. Flower colors vary among species populations from white to dark pink, most pale to pastel pink. The open petals curve back to show off the long extended stamens and styles. Flower fragrance also varies among plant populations.

Pinxterbloom azalea prefers an acidic, organically rich, moist, well-drained soil. Root rot and plant death often occur on poorly drained sites; planting on raised beds may be a good option on a heavy clay site. Partly shaded or dappled sun exposure is best.

Disease and insect problems are infrequent when pinxterbloom azalea is sited correctly. Soil moisture and acidity are key factors for successfully growing U.S. native azaleas.

Sapsucker Feeding May Blacken Maple Trunks

Posted by Hugh on April 29th, 2012

Sapsucker Holes Create Sappy Trunk

You see or hear a sapsucker tapping in a yard tree and pay little attention to it. The bird perforates the tree or shrub trunk and main branches with numerous shallow holes, similar to a riveter working with sheet metal. A sapsucker feeds on the cambium sap and on insects under the bark.

The holes are deep enough to cause sap leakage, particularly in the winter months when sap pressure in maples (also dogwoods, elms, birches and yellowwoods) is the highest. The sugary sap coats the trunk, and sooty mold fungi grow over the sap secretions. The result is a yucky black stain similar to pitch!

What to do? Nothing!! The sapsucker is at work, doing his/her natural thing. Sapsuckers are members of the woodpecker family. They serve an important function: listening and removing damaging insect borers which may be feeding on the tree sapwood.

Unfortunately, sapsucker feeding does not always indicate that the bird has found insects inside the tree. Yes, the numerous holes are unsightly, but are not injurious to the life of the tree. The black sooty appearance on the trunk should wash off in the months ahead.

According to University of Arkansas Extension horticulturist Dr. James Robbins, favorite tree species for sapsuckers include maple (Acer spp.), pecan (Carya), birch (Betula spp.), pine (Pinus spp.), elm (Ulmus spp.) and some oaks (Quercus spp.). Sapsuckers are attracted to old holes and other bark injury and may return to the same tree(s) for several years.

Pest Alert- Boxwood Blight

Posted by Hugh on April 27th, 2012

Leaf Spotting and Black Stem Canker Symptoms (Photo credit: Craig Adkins, NC State Extension)

Boxwood blight is a disease caused by a fungus (Cylindrocladium pseudonaviculatum) which is a serious threat to most boxwood (Buxus) and related species such as sweetbox (Sarcococca spp.). To date there is no evidence of resistance to boxwood blight in any Buxus species.

Plant pathologists in England first identified the disease in the mid-1990’s. It was first detected in the United States in North Carolina and Ohio in late 2011. The disease is now confirmed in 8 additional states (CT, MA, MD, NY, OR, PA, RI, VA) and in British Columbia.

Initial symptoms of boxwood blight include leaf spotting, rapid leaf drop, blackened stem cankers, and severe dieback. Most boxwoods are not immediately killed by the disease, but the plant(s) will become badly defoliated and unsightly.

Boxwood blight is spread primarily by water (rain splash, irrigation, runoff, etc.), by sale or exchange of plants in the nursery/garden center trade, and through contaminated tools, equipment, boots, etc. The sticky spores infect pruners and other tools, clothing, tires, and, of course, boxwood leaves.

Disease spread is rapid, often in less than a week if weather is warm and humid. The disease is carried by splashing or wind driven rain. At this time there is no cure for boxwood blight. Here are some key steps for gardeners and landscapers to follow:

Know the primary symptoms of boxwood blight and check boxwoods in the garden regularly
Before purchasing inspect boxwoods at garden centers, and reject any with yellow spotted leaves and black stem cankers
During pruning, dip clippers into a 1-to-10 ratio of bleach to water or 70 percent ethanol solution for 1-2 minutes before moving on to a new plant.
Properly dispose of all diseased plants or clippings; do not compost them
Limit buying of new boxwoods and avoid combining new with existing plants
Take suspect boxwood plants and clippings to a county Extension office or to a full service retail garden center for proper diagnosis.

Exceptional Describes ‘Major Wheeler’ Climbing Honeysuckle

Posted by Hugh on April 25th, 2012

'Major Wheeler' Climbing Honeysuckle (photo courtesy of North Creek Nurseries)

Climbing or coral honeysuckle (Lonicera sempervirens) is a native vine. It can be spotted growing on fence rows along roadsides and in woodlands from Connecticut to Nebraska, and south to Texas and Florida. ‘Major Wheeler’ is one of the better climbing honeysuckles noted for its non-stop production of bright red trumpet flowers and green mildew resistant foliage.

Red tubular flowers cover the vine in mid- to late spring, and it continues to scatter blooms all summer long. Major Wheeler becomes a major hummingbird and butterfly magnet from miles around. Flowers form on both previous year’s and current season’s wood.

Climbing honeysuckle grows in full sun to partial shade and in average soils. Flower numbers are heaviest in full sun. Fertilizing is generally not needed unless growth and flowering are not prolific in infertile soils. Once established, Major Wheeler is very drought tolerant.

Rate of growth is fast, estimated at 8-12 feet per year. Prune annually to tidy up the enormous mass of growth. Ideal pruning time is immediately after the major spring bloom flush. Pruning will spur re-growth and new flowering. Expect removal of 50-80% of the old growth after pruning is completed.

Train on a sturdy fence, trellis or arbor from the beginning. Major Wheeler will quickly cover over any old fence that may be an eyesore. Its mildew resistance is outstanding compared to other varieties. Occasionally, aphids and scale insects may infest climbing vines, necessitating spraying with Bayer Advanced Garden Insecticide™, Malathion, or acephate (Orthene™).

‘Major Wheeler’ climbing honeysuckle was found by Charles Wheeler, the former president of the NC Botanical Gardens and is winter hardy to USDA zone 4.

‘Fireworks’ Pennisetum

Posted by Hugh on April 23rd, 2012

'Fireworks' Pennisetum in late August at Dallas Arboretum

Fountain grasses are popular annual grasses that thrive in Southern Appalachian gardens (USDA zones 6 and 7). The new cultivar ‘Fireworks’ is totally spectacular. The mid-vein of the grass blade is burgundy red and edged in hot pink.

Fireworks displays three seasons of awesome foliage color before dying off in the fall. Red plume foxtail flowers bloom from mid-summer to early fall. Fireworks grows as a thick clump that is 3-6 feet tall and 1-3 feet wide. Utilize Fireworks as an accent plant in landscape beds and containers.

Fireworks flourishes in full to partial sunlight (6-hours minimum) in average well-drained, low acidic soils (pH 6.0 to 7.0. Weekly irrigation is a plus. It establishes rapidly and tolerates short summer dry spells.

The vibrant tri-colored grass blades intensify in the early autumn cooler temperatures. In the deep South (USDA zones 7-b to 9), foliage colors often fade under extreme sunlight and heat (see photo above).

Fireworks should be fertilized at planting time with a 5-6 month rated slow release fertilizer. Another alternative is to feed monthly with water soluble Miracle-Gro™, Schultz®, or a similar product according to package rates.

Grass blades turn brown in the first hard autumn freeze. Snow or ice embedded ornamental grasses can be quite beautiful. You may opt to shear them back in early fall as the old floral heads (plumes) often self-seed. Fireworks fountain grass is relatively disease and pest free and is deer resistant.