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

Virginia Bluebells – An Early Spring Wildflower

Posted by Hugh on March 15th, 2013

Virginia bluebell (Mertensia virginica)

In early spring Virginia bluebells (Mertensia virginica) is an ephemeral woodland wildflower. In early April their lovely presence is to be enjoyed for a short 8-10 week period. Clusters of pinkish-blue nodding buds burst forth into soft pastel blue flowers. Gradually, the bell -shaped flowers age to pale pink hues. The lovely blue flowers are a perfect foil against the pale green foliage beneath. Plants grow in partial to full shade to 18 to 24 inches tall and 12 to 18 inches wide.

Plant tubers purchased from mail order nurseries in the autumn as you would tulips or daffodils. Space them 2 feet apart. Virginia bluebells will bloom next spring. Flowers attract early arriving butterflies and hummingbirds. Plants fade away in late May until next spring.

Mark the garden spot where they are planted. Space the plants about 2 feet and more apart. Bluebells will spread by seed and form small colonies.

Virginia bluebells rarely need fertilizing. They usually receive adequate nourishment in moist, slightly acidic, compost rich soil. When necessary, water plants when in flower. Often, plants bloom sparsely the first year after planting, and alot better in subsequent years.

You may interplant with other shade inhabitants such as ferns, foam flowers (tiarellas), lungworts (Pulmonaria spp.), hostas, and brunneras which may compete for open ground formerly occupied by the bluebells.

‘Alba’ is a white-flowering cultivar that mixes nicely with the traditional blue flowers, but it may be hard to find.

Treat Colorful Caladiums As Tender Annuals

Posted by Hugh on March 12th, 2013

: Caladiums at Yewdell Gardens in Crestwood, KY (near Louisville)

Caladiums (Caladium bicolor) are tropical foliage plants which are grown as annuals. Caladiums brighten up shady to sunny spots. Their brightly colored foliage is either heart and lanced shaped in color combinations ranging from red, rose, pink, chartreuse, green, and white.

Caladiums absolutely prefer a warm, moist, well-drained, compost rich soil. Don’t plant caladiums in questionable ground. If your garden soil is questionable, plant them in a raised bed or in containers with soil-less media. Add mulch to conserve soil moisture.

Caladiums thrive in shady areas, but can grow under modest amounts of direct sunlight if regular soil moisture is provided. Caladiums can survive Texas summer heat and sunlight if irrigated daily.

Plant caladium tubers about 1½ to 2 inches deep with their growing points or “eyes” right side up. Buy jumbo or large sized tubers and space them 12 to 18 inches apart for more and larger foliage in the summer months.

Caladium tubers should be planted in warm 70°F soil in the spring. If planted in cool garden soil, tubers tend to rot rather than sprout. If you’re planting caladiums in northern areas, start them out in a warm greenhouse or cold frame 5 – 6 weeks before last frost in your growing area.

Feed with a high phosphorus based fertilizer such as 5-10-10 or equivalent once in spring and again in early summer. An alternative is to feed caladiums with water soluble fertilizers such as Miracle-Gro®, Jack’s Classic®, or Schultz® products according to package directions.

In the Southern Appalachian region (USDA zones 6 and 7), tender caladiums tuber must be dug up in early autumn. Allow tubers to dry out for 7-10 days, clip off all leaves and roots, and store tubers in dry sphagnum peat, vermiculite, or perlite in a warm spot above 50°F for planting next spring. Storing in mesh or paper bags also works. Do not allow tubers to freeze.

Leaves tend to be larger in shady areas compared to those in sunlight. Foliage colors may vary according to the amount of sunlight, soil nutrition and water quantity.

Caladium bulbs and leaves are highly poisonous, although a person must eat lots of leaves to cause death or serious injury.

Early Blooming Cornelian Cherry In The March Garden

Posted by Hugh on March 9th, 2013

Cornelian cherry on ETSU Campus in Johnson City, TN in mid- March

Cornelian cherry (Cornus mas) is a multi-stemmed, low-branched dogwood tree or shrub. It typically grows 20-25 feet tall and slightly less in overall width (USDA hardiness zones 4-7). Tiny, golden yellow flowers appear in late winter, around March 1st in my east Tennessee garden, and remain in bloom through most of the month despite cold winter nights and snow.

Leavess emerge around the first day of spring. Small drupe fruits (called “cornels”) ripen in late summer, and are tasty morsels for birds. Most of the fruits may stay hidden inside the dense foliage until late fall. In eastern Europe, where Cornelian cherry is native, the sour tasting fruits are made into syrups or jams.

In the autumn the dark green oval-shaped leaves turn a dull purple tinge before dropping. No serious insect or pests bother Cornelian cherry, and surprisingly, deer don’t seem to relish either foliage or fruits. A prominent feature on this long lived tree/shrub is its flakey gray-brown bark which exfoliates over the main trunk(s) and older branches as it ages.

Branching tends to be upright and is easily trained into a small single-trunked tree by clearing away all suckers around the base. Plant it in well-drained, slightly acidic soil, and in full to partial sunlight (6-hours minimum). Cornelian cherry makes a fine specimen tree or utilize as a deciduous hedge or privacy screen.

Among plant nerds it has been long debated whether Japanese cornel (C. officinalis) is prettier in bloom than Cornelian cherry. My suggestion is to plant both! ‘Golden Glory’ and ‘Spring Glow’ are major cultivars sold at many garden centers. ‘Aurea’ is a golden yellow leaf form available from on-line nursery sources. Reportedly, ‘Spring Glow’ produces very few fruits annually.

Epimediums Excel As Dry Shade Groundcovers

Posted by Hugh on March 7th, 2013

Epimedium's New Spring Foliage

Epimediums, aka barrenwort or fairy wings, are slow-growing groundcovers which are hardy in USDA hardiness zones 4-9. Foliage varies by species, variety, and the season of the year. Most are deciduous, but some evergreen in the Southern Appalachian region (zones 6 and 7).

The leaves of some may be chartreuse in spring, green in summer, and red in the fall. Some varieties have red or silver leaves in the summer. The leaves are asymmetrical heart shaped which attributes the name “fairy wings”.

Also, floral shapes earn them the name “bishop’s cap”. There are dozens of species and varieties. Epimediums bloom from late winter (March) to mid- spring (early May) over a 1 to 2 week span. Colors range from pink, red, violet, white, or yellow flowers. Flowers attract early-arriving butterflies and hummingbirds.

Trying to predict the ultimate dimension of a groundcover is foolhardy, particularly the genus Epimedium with so many species and varieties. Epimediums vary between 6 -12 inches in height and 12 – 18 inches in spread. Water them thoroughly and apply an organic-based mulch at planting time.

Epimediums are slow growing the first 2-3 years. Epimediums thrive in part sun to part shade (morning sun and afternoon shade). They handle average garden soils that are well-drained and moderately acidic. They ask for little maintenance once established.

Get plants off to a good start by regularly watering and feeding them. Use a slow-release fertilizer according to label directions at planting time and again each spring thereafter. An alternative is to feed monthly from April to mid-August with a water-soluble plant food.

In late winter cleanup fallen leaf matter by mowing over the debris before flower buds appear. The groundcover looks better and allows all to visually enjoy the spring flowers and new foliage. Epimediums have few disease or pest problems, including deer and rabbits.

Epimediums make excellent groundcovers beneath trees because they don’t compete with tree roots. These four are among my favorites:

• Red barrenwort (E. × rubrum) – reddish spring foliage; reddish fall foliage; deciduous and semi-evergreen in z-7; red and white bicolor flowers
• Bicolor barrenwort (E. × versicolor ‘Sulphureum’) – evergreen foliage (z-7); mottled red early spring foliage; bright yellow flowers
• Longspur barrenwort (E. grandiflorum ’Rose Queen’) – deep bronze spring foliage; dark red flowers with white spurs
• ‘Frohnleiten’ (E. x perralchicum ‘Frohnleiten’) – bronze spring foliage; large yellow flowers

A Variegated Ornamental Grass Is ‘River Mist’ Sea Oats

Posted by Hugh on March 5th, 2013

'River Mist' Sea Oats With Dwarf Variegated Solomon Seal in Container

River Mist Northern sea oats (Chasmanthium latifolium ‘River Mist’), formerly Uniola latifolia, is a recent plant introduction with striking green and white variegated foliage on slightly arching stems. River Mist grows shorter than the species, 30-36 inches tall and 24-36 inches wide.

Northern sea oats is one of the more shade tolerant of the ornamental grasses, from full sun to light shade in northern gardens (USDA hardiness zones 5-6) and in partial shade further south (zones 7-8). River Mist thrives in an average, medium to wet, well-drained soil. Soil nutritional needs are minimal, perhaps 2 lbs of 10-10-10 or equivalent fertilizer per 100 feet of garden bed.

River Mist is most distinguished by the flat, drooping oat seed heads in late summer. Seed heads flutter in the slightest of summer breezes. Seed heads emerge green and turn purplish bronze in very late summer. By early winter most seed heads may collapsed under heavy snow loads. Otherwise, withered foliage and seed heads may contribute some winter landscape interest. All growth should cut back and gathered up by late winter.

Sea oats has no serious insect or disease problems and is deer resistant. It may require staking if grown in a too shady a location. Seed heads and foliage are excellent in dried floral arrangements.

Its delicate arching habit and bright variegation makes River Mist a great choice for a front flower border, in naturalized areas, or mixed with other plants in large containers. It easily self-seeds and may spread or naturalize aggressively.

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.