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

Colorful Pentas Bloom In Summer’s Heat And Humidity

Posted by Hugh on March 3rd, 2013

Egyptian Star Flower (Pentas lanceolata) Cope with Summer’s Heat and Humidity

Pentas, aka Egyptian starflower, (Pentas lanceolata) excel in the summer flower garden. Only a few years ago, pentas were only found decorating window boxes and other containers. Today, they have becoming a popular bedding plant in geographic areas where summer temps get hot.

Pentas grow best in full to part sun (6-hours minimum), and preferably, in a compost-rich, well-drained garden soil with regular watering. Soil pH may range from moderately acidic to slightly alkaline(pH 5.8 to 7.5). Established plants become moderately drought tolerant by mid-summer. Adding a 2-3 inch layer of organic mulch is also beneficial to retain soil moisture.

The 3- 3 1/2 inch long leaves are dark lustrous green. Disease and pest issues are few if plants are properly spaced and irrigated when needed. Spring-planted pentas bloom non-stop to the first autumn hard frost. The flat-topped 3-5 inch wide flowers (corymbs) are clusters of brightly colored star-like blooms– available in red, pink, lavender purple, and white. The non-fragrant flowers attract huge numbers of butterflies to the summer garden.

At spring planting time, broadcast a slow release fertilizer over the flower bed. Supplement with a water-soluble product such as Miracle-Gro™, Jacks™, or Schultz™ according to package directions biweekly from mid-July to early September.

There are numerous pentas varieties including Graffiti, Kaleidoscope, New Look, Butterfly, Pinata and Starcluster series. Plant heights (2 to 4 feet range) will vary from one series to another.

Zelkova Becoming Dominant Urban Street Tree

Posted by Hugh on March 1st, 2013

Winter Outline of 'Green Vase' Zelkova in Charlotte, NC

Japanese zelkova (Zelkova serrata) is a 60-90 feet tall shade tree with structurally strong branches. Fast growing zelkova may grow 2 feet or more in a single year. Belonging to the elm family (Ulmaceae), zelkova exhibits several elm-like features, including a vase shaped branching habit. Its very different exfoliating mottled bark distinguishes it from elms.

Dark green leaves are 3-5 inches long with blunted teeth along the margin. Leaves turn bronze yellow in the fall, somewhat dependent on the cultivar and previous summer’s growing conditions. Tiny insignificant flowers appear in the spring. Fall seeds are consumed by birds and wildlife, and its dense tree canopy offers shelter to birds.

Zelkova trees tolerates wind, summer heat and drought, and urban air pollutants. Tree form varies from a narrow upright 20 to 25 feet spread of ‘Musashino’ to the wide 40 to 50 feet strongly horizontal branching of ‘Village Green’. Until recently, upright branched ‘Green Vase’ had been a popular favorite for urban/suburban street planting.

Zelkova is best sited in full to partial sunlight (6 hours minimum). Soil should be acid to slightly alkaline, and preferably moist and well drained. Plant either container grown or balled-and-burlapped (b&b) nursery stock. In urban/suburban street plantings irrigate newly planted trees deeply for 2-3 years until established. Feed annually in late winter with 10-10-10 granular fertilizer or equivalent.

Through the growing season, the dark green foliage remains disease or pest free. On rare occasions leaf feeding beetles may cause some defoliation, but fast growing zelkova recovers quickly. The shallow roots of a large zelkova may lift up the sidewalk.

‘White Shield’ – New Thornless Osage Orange

Posted by Hugh on February 26th, 2013

Messy Osage Orange at Bartlett Tree Lab in Charlotte, NC

Osage orange (Maclura pomifera) has been declawed and neutered. Also called Bois D’Arc (pronounced “bow-dark”) by native Americans, this tough native prairie tree species (USDA Zones 5-8) produces large 4-6 inch diameter yellowish green fruits (“hedge apples”) which may weigh 2 to 3 pounds. They fall from the tree in October to create a maintenance nightmare. Its fierce ½- inch long thorns, hidden among the thick branches, can snag clothing or puncture a car tire.

‘White Shield’ thornless cultivar (M. pomifera var. inermis) has arrived. It is a handsome medium-sized landscape tree, averaging 35 feet in height and spread. It can be utilized as a specimen shade tree or as a deciduous windbreak.

Osage orange is fast growing at 2 ½ to 3 feet per year. Its wood is hard and does not easily split. Mature tree bark is deeply fissured, with an orange-brown inner wood peeking through. Pruning helps in the early years to develop a well-branched tree.

Summer foliage is dark green and glossy. Yellow-green fall foliage color may vary widely from tree to tree, sometimes brightly golden. In late spring fruitless White Shield bears tiny green flower clusters that are mostly inconspicuous.

Few trees prosper better in poor infertile, acid or alkaline pH soil, dry or wet ground. Summer foliage is impervious to urban air pollutants. Overall, disease and pest problems are rarely an issue.

White Shield is ideally suited for large residential or commercial properties, municipal parks, and golf courses.

‘White Shield’ osage orange (photo courtesy of J.Frank Schmidt Nursery, Boring, OR)

‘Green Giant’ Arborvitae: A Terrific Green Privacy Screen

Posted by Hugh on February 23rd, 2013

22-year old Western Arborvitae (T. plicata) Specimen in Conlon Garden

Western arborvitae (Thuja plicata) is a large native evergreen tree from the Western U.S. (USDA hardiness zones 5-7). As many as 30 cultivars are available among dwarf, weeping, and variegated leaf forms. One of the most popular selections is ‘Green Giant,’ a hybrid between T. plicata and T. standishii, a Japanese arborvitae.

In its native Oregon the species (T. plicata) attains heights greater than 100 feet with a strong vertical presence (see photo). In the Eastern U.S., western arborvitae typically matures to 60 to 70 feet tall and 25 to 35 feet wide.

Established Green Giant arborvitaes grow at a torrid pace, as much as 2 to 3 feet per year. During its initial 2 years growth rate may be slow, as it adapts to the new site. A single row, planted 10-12 feet apart, should provide a dense privacy screen within 10 years. I recommend minimum 16 feet spacing.

Its narrow pyramidal form stands tall under winter ice or snow. The lustrous dark green summer foliage naturally bronzes off in cold winters, and greens back up with spring’s arrival. Green Giant is disease and pest resistant. Deer seem to leave it alone. Young trees exhibit a grayish bark, which ages to fibrous reddish-brown. Small ½-inch long cones mature dark brown in the fall.

Green Giant retains its lower branches longer than most evergreens. Pruning is rarely necessary except to remove multiple leaders or to hedge them for a shorter privacy screen. Over the years, lower branches near the ground may root and form a mini-forest or thicket.

Green Giant prefers a cool, moist, well-drained soil. The soil pH should be mildly acidic to near neutral. It can be planted on a sunny or partially shady site. An established plant handles moderate shade and summer dry periods. It is tolerant of heavy clay or urban disturbed soils where few other needle evergreen trees survive. Roots are deeply anchored and Green Giant is unlikely to be blown over by strong winds.

More Winter Hardy Encore Azaleas Now Available

Posted by Hugh on February 21st, 2013

Encore Azaleas at Dallas Arboretum in September

For spring 2013, 22 of 32 Encore™ Azalea varieties are cold hardy in the Southern Appalachian region (USDA hardiness zones 6 and 7). Thirteen (13) varieties are reliably cold hardy throughout Zone 6-a&b. They are: Autumn Amethyst, Autumn Carnation, Autumn Cheer, Autumn Jewel , Autumn Lilac, Autumn Lily, Autumn Royalty, Autumn Ruby, Autumn Sangria, Autumn Sunburst, Autumn Sundance, Autumn Sunset, and Autumn Twist.

Nine (9) additional varieties are rated as cold hardy in zone 6-b: Autumn Bravo, Autumn Carnival, Autumn Debutante, Autumn Embers, Autumn Empress, Autumn Monarch, Autumn Princess, Autumn Rouge, and Autumn Sweetheart.

Selecting the proper garden site is most important. Encore Azaleas are tolerant to full day sun exposure in zones 6 and 7. On the shady side, Encore Azaleas do need 4 to 6 hours minimum of sunlight daily for repeat bloom in the autumn. The soil should be acidic and compost rich. Optimum soil pH should range between 5.5 and 6.5. Good soil drainage is an absolute must! Following a heavy rain, if water is still standing 12 hours later, growing them in a raised bed is advised.

Irrigation during summer dry and excessive heat periods is highly recommended. Fertilize with an 8-9 month rated slow-release fertilizer from late winter to mid-spring. An alternative is to feed azaleas with water-soluble fertilizers (Miracle-Gro™, Jack’s™, Schultz™, or other brands) bi-weekly. Do not feed azaleas after mid-August.

Container-grown plants may be added to a garden from late winter to early fall. Dig a hole 6-8 inches deep and twice as wide as the nursery container. Fill with compost rich soil in the hole and spread 2-3 inches of pine bark or needles around each azalea. Slowly pour 3-5 gallons of water into the planting hole.

Lungworts- Perfect Shade Companion With Hostas

Posted by Hugh on February 18th, 2013

Pulmonarias at Terra Nova Nurseries in Oregon

The lungworts (Pulmonaria spp.) are very popular in shade gardens with hostas, astilbes, Solomon seals, and ferns (USDA hardiness zones 4-8). Their green or silver-colored foliage may be dusted with green, silver or white spots. Lungworts are divided into two distinct foliage forms: narrow long-leaf (P. longifolia) and silvery or speckled oval leaves (P. saccharata). Longifolia types possess better cold tolerance. New hybrid cultivars exhibit totally awesome silver foliage and better heat and disease tolerance than ever before.

In late winter clean up the garden area, removing old foliage and flower stems. By late winter new flowers poke up through the litter before the spring foliage develops. On some varieties the flowers may start out one color and age to another. Blooms attract early arriving butterflies, bees, and hummingbirds.

An ideal garden spot is in partial to full shade. It has good air circulation to avoid potential leaf disease problems. A moist, well drained, compost-rich soil is crucial. Lungworts prosper with proper irrigation and mulching practices the first two years. Older established plants tolerate short two week long dry spells before leaves wilt and dry out. Overwatering and overcrowding plants will likely invite mildew diseases and slug problems.

Lungworts tend to be light feeders. Once a year feeding with granular 10-10-10 fertilizer or bi-monthly with a water-soluble product such as Miracle-Gro®, Jack’s Classic®, or Daniels® is usually adequate. Lungworts tend to be short-lived and should be divide every 3-5 years in early fall.

There are over 50 hybrid cultivars to shop for, varying from 6 to 24 inches in height to 24 to 30 inches in spread. If starting a lungwort collection, try any of the following 6 cultivars:
• ‘Roy Davidson’ – white spotted foliage; flowers open pink and age to blue.
• ‘Dark Vader’ – dark green, silver spotted foliage; blue flowers.
• ‘Excalibur’ – heat tolerant silvery foliage; rose colored flowers.
• ‘Janet Fisk’ – heavily marbled leaves; pink flowers fade to lavender.
• ‘Sissinghurst White’ – silvery white speckled leaves; large white flowers age to pale pink.
• ‘Spilled Milk’ – leaves with silvery surface with green spots; pink flowers.

Growing Pear Trees Too Challenging For Southeast Gardeners?

Posted by Hugh on February 15th, 2013

Pears To Be Harvested in Two Months

For many reasons growing pears in the Southeastern U.S. is very challenging. First, European (Pyrus communis) and Asian (P. pyrifera) pears are susceptible to fireblight (Erwinia amylovora). This bacterial disease is very difficult to manage. Two of the leading European pear varieties, ‘Bartlett’ and ‘Bosc’, are highly susceptible to fireblight. Varieties found to be fire blight resistant include: ‘Warren’, ‘Aires’, and ‘Moonglow’. ‘Shinto’, an Asian pear variety with russet brown fruits, exhibits above average fireblight resistance.

European pear varieties do not ripen on the tree. Fruits are harvested on the scheduled date for the variety and ripened indoors. Unripened pears should be stored in a closed plastic or paper bag (sack) for 7-10 days at room temperature (60-70 °F). Fruits may then be refrigerated to slow down their ripening. As with apples, Asian pears ripen on the tree, and are ready to eat when harvested. Asian pears are picked from late August to early October, depending on the variety grown.

European pear varieties will not pollinate Asian pears. Asian pears tend to bloom several days later than European varieties. Both European and Asian pears require cross-pollination from two or more different varieties which bloom near the same time.

Both European and Asian pears are notorious for “biennial bearing”. A tree may overproduce one year, and yield a small crop the next (the “off” year). Biennial bearing in the “on” year often results in limb breakage and smaller fruits. To prevent or break the biennial bearing cycle, remove excess fruit by hand within 30 days after full bloom in the “on” year. As a rule, 30-40 leaves support one pear fruit.

Finally, pruning pear trees can be a chore. Pears have a strong vertical branching form. Trees often grow tall and narrow, not easily within reach without a tall step ladder. Current pear dwarfing rootstocks have not been reliable, although better types may be available a few years away.

‘Pink Lemonade’ Blueberries Will Delight Your Taste Buds

Posted by Hugh on February 12th, 2013

Luscious pink fruits ready to eat in late July

Pink Lemonade blueberry (Vaccinium x ‘Pink Lemonade’) is a new variety introduction from the USDA. It combines the benefits of growing a beautiful landscape plant and one that produces a tasty crop of pinkish red blueberries. Pink Lemonade is also very winter hardy (USDA hardiness zone 4).

Select a sunny location, preferably with an eastern or northern exposure. Ground prep should begin at least one year ahead of planting date to lower the pH (recommend 4.5 – 5.5 range) and to raise the organic level of the soil. The ground must also be well-drained and compost-rich. Reduce weeds with frequent soil tillage and/or applying herbicides according to label directions.

Attractive pinkish-white, bell-shaped flowers open in the spring. Fruits ripen to a deep pink color in mid to late July in the Southern Appalachian region (USDA hardiness zones 6 and 7). Blueberry leaves have an attractive glossy green cast and exhibit few disease and insect problems. In autumn leaves turn bright orange to deep red color and fruit stems are bright red at the start of winter.

Pink Lemonade is vigorous, reaching 4 to 5 feet in height and width. The medium-sized, glossy, bright pink blueberries ripen in late season compared to other varieties. Berries have a mild sweet flavor with good fruit firmness.

Many gardeners cover plants with netting as harvest time nears and the birds invade the blueberry planting. In late summer remove the netting to allow the hungry birds and other wildlife to consume unharvested fruits.

Wait two years for the blueberry plants to establish before producing the first crop. Space blueberry bushes 5 to 7 feet apart in rows 8 feet apart. Mulch with 3 to 4 inches of sawdust, wood chips or pine needles to maintain soil acidity and retain moisture.

Plants are shallow rooted and should be irrigated regularly, particularly if natural rainfall amounts are low. Feed plants in late winter with 10-10-10 or equivalent fertilizer @ 2 lbs per 100 square feet. Blueberries are pruned in late winter.

Design A Garden Path For Greater Garden Enjoyment

Posted by Hugh on February 9th, 2013

Beautiful slate pathway in Richmond VA garden

Inexpensive Path from 16-inch concrete squares

Are you receiving full enjoyment from your garden landscape year-round? Gardeners spend so much time tied up with chores- planting, cultivating, and weeding. The fall and winter months are a great time to enjoy the garden, particularly if your footwear is dry and not muddy. A network of garden paths permits you, also neighbors and friends, to enjoy the 12 months of beauty created from your labor.

Nasty spells of weather hit many parts of the U.S. in fall and winter. On pleasant days you can walk through your garden. A path serves as a focal point of discovery such as viewing flowering bulbs poking through or witchhazels (Hamamelis spp.) and lenten roses (Helleborus spp.) in bloom. You are likely to gain a different perspective strolling through the garden.

Landscape designers recommend a spacious path, 20 inches or more in width. The path may be straight or curvilinear. You can construct a series of paths inexpensively from pea gravel, fine grit, or wood shavings. Garden centers and hardware stores sell metal or plastic edging to contain the gravel or shavings from spreading into lawn areas. You may utilize 16-inch wide concrete stone pavers, either attached or spaced several inches apart according to the pre-measured stride of your step.

Paths add new dimensions to your garden space. You may discover new areas for planting a shrub or tree, or set additional planters and containers. Perhaps a water feature, some statuary, or accent lighting along the path to extend the hours of enjoyment outdoors in your garden.

‘Vanderwolf Pyramid’– Reliable Mid-sized Limber Pine

Posted by Hugh on February 6th, 2013

Winter silver green foliage color of 'Vanderwolf Pyramid'

Limber pine (Pinus flexilis), native to the Rocky Mountain region, has proven to be a reliable landscape evergreen tree in the Midwest and is gaining new fans in mid-South gardens (USDA hardiness zone 7-a). ‘Vanderwolf Pyramid’(VP) is a beautiful dwarf pine being planted by conifer collectors. It is hardy in USDA zone 5, and displays poor heat tolerance in 7-b and further south.

Vanderwolf Pyramid was introduced by New Jersey nurseryman Peter Vermeulen in 1967 and is a real eye catcher. Bluish-green needles are 4-6 inches long, bundled in fives, and are distinctively twisted. VP has an unusually long needle life of 5-7 years. Spring candle growths flaunt electric bluish-green needles which gradually turn a silvery green during winter.

VP has a fastigiate (upright) branching tree form, which tends to open up as the tree ages. VP is a medium-sized pine which matures 30 to 35 feet in height and 15 to 20 feet in width. Young trees transplant reliably, but older trees are less dependable because of a deep tap root system.

In general, limber pine thrives in a moist, well-drained soil in full sun and is tolerant of high pH soils. It has few serious diseases and pests problems, and deer don’t seem to bother it.

VP typically grows slowly at the start and eventually 1 to 2 feet per year. Its common name refers to its flexible (“limber”) branches which bend (give way) under heavy snow loads. The cultivar is commonly grafted onto P. flexilis understock. Utilize as a single landscape specimen or as a privacy or wind screen.