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

Summersweet Shrub – Underplanted And Underappreciated

Posted by Hugh on June 11th, 2019

‘Pink Spire’ clethra

‘Hummingbird’ clethra

Summersweet clethra (Clethra alnifolia), aka sweet pepperbush, is a deciduous summer blooming shrub that ranges from coastal Maine to Florida (USDA hardiness zones 4-8). This delightful shrub grows 3-6 feet, although some cultivars grow 8 feet or higher. Flower colors (depending on variety) range from white, pink, and rose pink.

The sweetly fragrant flower clusters ( 4- 6 inches long racemes) are visited by multitudinous bees, a few butterflies, as well as by gardeners. When in bloom, the area is “a buzz” with bee activity lasting approximately 4 weeks in July and August.

Flowers give way to dark brown seed capsules that often persist through winter. The glossy dark green leaves (to 4 inches long) develop foliage shades of yellow to golden brown, which may linger for several weeks in autumn.

Summersweet is easy to grow in either full to partial sunlight and in average soil that is well- drained and mildly pH acidic. This native shrub thrives in wet sites and is both heat and cold tolerant. It tolerates dry soils after a two year period of establishment, but grows best and produces the greatest number of flowers when watered regularly. Avoid the hot afternoon sun in southern climes. Once a year feeding in late winter with a slow-release fertilizer such as Osmocote™ or Nutrikote™ is sufficient.

Summersweet is mostly disease- and pest-free. Pruning, if needed, should be done in late winter before spring growth begins. Little pruning is generally needed, unless it has outgrown its space. Every 5-6 years consider cutting shrub(s) to the ground in late fall. This tough reliable plant will bloom the following summer. Summersweet spreads by rhizomes and suckers; remove unwanted plants at any time.

Selected cultivars to try:

‘Hummingbird’ is a 3- 3 ½ foot tall compact form with deep green summer foliage

‘Rosea’ is a popular pink flowering form with pink flowers that fade to white.

‘Ruby Spice’ bears deep rose pink 3 ½ – 4 inch flowers; it grows into a 6 – 8 foot tall shrub.

‘Sixteen Candles’ bears larger 4 – 6 inch long flowers that stand upright and do not flop like most cultivars.

Grow Crocosmias In Your Summer Garden

Posted by Hugh on June 6th, 2019

Crocosmias are bulbous summer blooming flowering perennials that are closely related to gladiolas, also called montbretia and sword lilies. They’re actually corms, not bulbs, and are indigenous to South Africa (USDA hardiness zones 5b to 9).

Crocosmias enjoy lots of sun, soil moisture, and hot temps to produce flowers. Plants prefer nutrient-rich, slightly acidic, moist, well-drained soils. They begin blooming in mid-June and continue over most of the summer into fall. The brightly colored flowers emit a saffron fragrance. In northern gardens (zones 5b – 6), mulch in late fall for winter protection of smaller corms.

The gladiolus-like dark green foliage may be rippled or pleated. Usually disease and pest free, leaves may become sapped of their green color by mites and thrips in a dry summers; wash off foliage or resort to pesticide spraying.

Many cultivars are available; some grow vigorously and others at a slower rate. Color choices range from vivid reds, oranges, yellows and bi-colors. Flowers are followed by black berries. The fiery red cultivar ‘Lucifer’ is the most popular cultivar with scarlet red beauty. Set many many corms 3-4 inches deep and 8-10 inches apart to fill the space with showy clusters of flowers.

Over time a bed of crocomias may become overcrowded. Corms should be dug and divided in the fall. Cut the foliage down to the ground in fall or wait until late winter.

Crocosmia blooms are produced on 2-4 feet tall wiry arching stems, depending on variety. Plant shorter compact varieties in either flower beds or in containers. Crocosmias make excellent cut flowers, much in demand by florists.

In addition to ‘Lucifer’, I have listed five other varieties:

‘Prince of Orange’ – 2 ½ to 3 foot tall, red-orange blooms / burgundy speckled, gold centers

‘Mistral’- 2 to 2 ½ foot tall, orangey-red flowers

‘Star of the East’ – 3 foot tall, huge starry wide-open orange flowers

‘Tobias’ – 3 to 4 feet tall, 2-3 inch wide orangey-red blooms

‘Walberton Yellow‘ – compact 2 to 2 ½ feet tall; tightly-packed bright yellow flowers.

Arborvitae Fern

Posted by Hugh on June 1st, 2019

Selaginella braunii (winter bronzing)

Arborvitae fern (summer look)

Arborvitae fern (Selaginella braunii) is native to China (USDA hardiness zones 6-9). It is not a fern at all, but a Lycopod or “club moss”, a descendant of ancient spore-producing plants which date back to the Carboniferous and Permian Ages. Its small club shaped cones give it the plant moniker – ”club moss”.

Arborvitae fern is a slowly creeping rhizome with semi-evergreen leathery frond-like leaves. In early spring the tender light green emerges and stays brightly green if seasonal moisture is adequate. During cold winters the foliage is often bronze-tinted.

By the end of its 3 season, a small 3-inch wide plant may fill-in an 18-24 inch wide space. Arborvitae fern grows 6-12 inches (15-30 cm) high. Its textural and seasonal color make for a lovely landscape groundcover in partially to fully shaded areas. It also looks great in hanging baskets and large ground planters combined with other taller plants.

Arborvitae fern loves a moist well-drained, organically rich soil and in full to part shade. Amend a sandy or clay soil by generously incorporating a two- or three-inch layer of compost or humus. Plant quart or gallon-sized containers a foot or so apart. Water as needed to maintain moist soil. Once established, give it 1-2 years, it will tolerate moderately dry sites over short periods. Fertilize in early spring just as new growth begins with a slow-release fertilizer at low rates.

Arborvitae ferns are easy to grow, disease and insect resistant and deer proof. These and other club mosses can be easily divided at any time of year. They do not flower in the traditional sense, but you can nurture them from spores.

Best of The Oakleaf Hydrangeas (So Far)

Posted by Hugh on May 26th, 2019

‘Snowflafe’ oakleaf hydrangea

Fall leaf color of ‘Snow Queen’

More than 30 available oakleaf hydrangea (Hydrangea quercifolia) cultivars, you can select the perfect specimen to complement any size garden USDA hardiness zones 5 -9). Oakleaf hydrangea is a native plant that delights gardeners with four seasons of distinct features. In spring, oak-shaped leaves are followed by summer’s white-panicled flowers. When it sheds its colorful leaves in autumn, they reveal cinnamon-colored exfoliating bark that adds texture to the winter garden.

Oakleaf hydrangeas are native to the southeastern United States, and hardy in oakleaf hydrangea adapts better to different climates than the recognizable bigleaf hydrangea with mophead blooms.

Its superior disease resistance makes this shrub a low-maintenance choice for beginning gardeners. Oakleaf hydrangea are tolerant of moderate shade, an excellent choice as an understory shrub. Expect smaller numbers of flowers.

Large… For larger gardens pick your choice of either ‘Alice’ or ‘Allison’. Both grow 12-15 feet tall and wide with enormous 12 inch cone-shaped flower clusters may be longer than 12 inches. Additionally, Alison’s” handsome burgundy fall foliage. A third tall variety is ‘Harmony at 10 foot tall . Individual florets of panicles are densely packed,

Medium… One of the most popular oakleaf hydrangeas was introduced in 1971 when nurseryman Eddie Aldridge patented a cultivar that had double flowers. Snowflake grows 8 feet high and wide and the double florets bloom longer than other cultivars. Snow Queen is an equal beauty with single-flowered panicles and upright shrub form.

‘Little Honey’

Small… Two of the best dwarf oakleaf hydrangea cultivars are ‘Ruby Slippers and ‘Munchkin’ are plants that feature the desired qualities of their larger relatives, but in compact form. Munchkin’s blooms open white, as all oakleaf varieties do, and gradually turn pink with age. Ruby Slipper’s bears white flowers that fade to pale pink and finish rose color. Both shrubs grow to 5 to 5 ½ feet after 7-10 years. These dwarf forms are perfect for large containers on decks and patio.

And lastly… ‘Little Honey’, a branch sport of H. quercifolia ‘Pee Wee’, is a unique gold leaf oakleaf hydrangea. This compact spreading beauty grows 3-4 feet tall and 4-5 feet wide and is frequently utilized as an accent plant. Its flowers do not standout, but its gold colored foliage surely does.

Sacred Lily (Rohdea)

Posted by Hugh on May 21st, 2019

Sacred lily (Rohdea japonica), aka nippon lilies, are native to Japan and China. Rohdeas are truly collector’s plants (USDA hardiness zones 6-10). In the Orient these lovely shade perennials are highly revered. In traditional Japanese horticulture, sacred lilies (known as o moto) came to be associated with long life and good fortune. Containers are planted near the entry to courtyards and homes. Over the past two centuries colorful, contorted, ridged, dwarf, giant, or variegated leaf forms have been bred, almost all with Japanese names.

Rohdeas are members of the asparagus family (Asparagaceae). Plants are rhizomatous perennials that grow 8-18 inches high depending on cultivar.

Well-established clumps produce short-stemmed, creamy to greenish, white bell shaped flowers. The racemes appear in early spring. found at the base of the plant. Blooms are mostly hidden within the dense leathery foliage and therefore mostly inconspicuous. Red or orange ornamental berries follow in late fall and last through most of the winter.

Sacred lilies are simple to grow and live for many years. Plants prefer a moderately moist, humus-rich, well-drained garden soil. They’re especially adapted to deep shade. Several varieties appear to be reliably hardy to Zone 6. Rohdeas are not troubled by diseases, pests or deer.

Sacred lilies produce dark green, evergreen, strap-like (lanceolate) leaves. They look like a garden-hardy snake plants (Sanseviera). New plants start off slowly, but do multiply and form large colonies of ground covering. Numerous divisions over time can help you build a collection which you can trade back and forth with other collectors.

Where to shop for Rohdea japonica: www.plantdelightsnursery.com lists 7 varieties, the most that I’ve seen from a single nursery source. Plants are also traded on Ebay.

Try Maple-leaf Viburnum In Woodsy Areas

Posted by Hugh on May 16th, 2019

Maple-leaf Viburnum in bloom in late May In Tennessee Garden

Maple-leaf Viburnum (Viburnum acerifolium) is a small to medium deciduous shrub that is indigenous to many areas of the Eastern U.S. (USDA hardiness zones 3-8). This underutilized native viburnum is at its finest in a dappled shady woodland landscape. Slow-growing at first, a single plant may reach heights of 4-6 feet and 2-4 feet in spread. Maple-leaf viburnum displays multi-season interest for its spring bloom, late summer fruiting, and fall color.

Terminal clusters of white flowers (flattened cymes) form about a month emergence of the leaves in May to June. Oval green fruits soon follow that begin turning bluish-black in late summer. Flower clusters measure 2 – 3 inches across. Birds and other wildlife munch on the fruits during the winter.

Coarsely toothed, mostly three-lobed, medium green leaves turn reddish-purple to magenta color in fall. Leaves usually have small black spotting on the undersides.

Mapleleaf viburnum is more shade tolerant than most Viburnum species. It grows in average, medium moist, well-drained soil and in full sun to part shade; it tolerates a wide range of soils. Established 2 year old plants demonstrate good drought tolerance. Feed once in early spring with a granular fertilizer such as 10-10-10 or equivalent @ 1 -2 lbs. per 100 square feet. Keep shrub(s) mulched to retain soil moisture and reduce weed pressure. Irrigate during establishment and extended dry periods.

Within 4-5 weeks after flowering, prune to shape and maintain the shrub as desired. Plants will naturalize via root suckering to form colonies unless suckering is held in check. Suckering is a lot less in dry shade. In an open woodland area, it may take 5 or more years before it starts to naturalize.

No serious insect or disease problems trouble this woodsy viburnum. It may be utilized in shrub borders, foundations or hedges. Maple-leaf viburnum is primarily available from e-commerce native plant nurseries.

Black Mondo Grass

Posted by Hugh on May 11th, 2019

Ophiopogon planiscapus ‘Nigrescens’

Black mondo under shade tree

Black mondo grass or black lilyturf (Ophiopogon planiscapus) is sold as a number of cultivars – ‘Arabicus’, ‘Black Dragon’, ‘Nigrescens’, or ‘Ebony Knight’. This stoloniferous grass-like perennial belongs to the lily family (Liliaceae) (USDA hardiness zones 6-9). Its blackish-purple foliage (3/16 inch wide leaf blades) forms lush arching clumps. For the patient gardener, know that black mondo starts off slowly. Compared to other mondo grasses, this black form grows shorter @ 8 -12 inches in height.

Indigenous to Japan, black mondo typically grows in slow spreading clumps with arching, slowly-spreading clumps. The dark purple foliage appears almost black in most sites. In southern climates, black mondo is often planted under the shade of trees, because leaf blade color will fade under intense sunlight. White, bell-shaped flowers (up to 1/4 inch long), with pink to lilac tints, bloom in summer. Dark purple globular berries mature in fall.

Black mondo grows best in humus rich, slightly acidic, moist, well-drained, soils and in partial to full shade. Mondo prefers consistent, evenly moist soils. Although not reliably winter hardy in USDA Zone 5, many northern gardeners have been successful growing it in a protected area. Plant foliage is evergreen in Southern winter climates. Black foliage color is best in cool sunny locales of zones 6 and 7 and in light shady spots in zones 8-9.

In the landscape black mondo makes for a great edging plant or utilize it as a filler plant in containers. Its dark grassy foliage makes a great accent feature. As garden edging space plants 4-5 inches apart and they should fill within 3-4 years. Feed with a slow release fertilizer such as Osmocote™ or Nutricote™ in early spring. Rake away fallen leaves from nearby trees and shrubs in the fall so mondo grass can continue to grow through the winter months. Irrigate a new planting the first season and during prolong summer dry spell.

Annual Geraniums Make Garden Comeback

Posted by Hugh on May 6th, 2019

‘Calliope Dark Red’

Geranium basket

Once popular annual geraniums (Pelargonium x) are making a comeback with U.S. gardeners. Geraniums are also planted in window boxes or hanging baskets. Three types of geraniums are sold at garden centers: zonal or bedding geraniums (P. x hortorum), ivy-leaf geraniums (P. peltatum), and Martha Washington geraniums (P. x domesticum). Color choices include red, pink, rose, salmon, orange, lavender, violet, or white.

Of the 3 types, zonal geraniums are the most widely planted. Ivy-leafed geraniums (Pelargonium peltatum) have a trailing habit with ivy-shaped foliage. They are principally planted in hanging baskets and window boxes. Martha Washington geraniums (P. x domesticum) are primarily sold by florists as flowering pot plants and do not perform well outdoors.

High summer heat is challenging for all types of geraniums. Some types of geraniums stop blooming completely and perk up when cool temps return. Over the past quarter century plant breeders have given gardeners more heat-tolerant types, such as the Americana™, Eclipse™, Rocky Mountain™ cutting series; Maverick™, and Orbit™ seed series; and the interspecific hybrids trademarked as Caliente and Calliope.

Plant geraniums outdoors after all threat of frost has passed. Depending on the geranium type and variety, plants are spaced about 8 to 12 inches apart and around the same depth as their original planting pots. Mulch around plants to retain soil moisture and suppress weeds. Deadheading of spent blooms also encourages additional blooming. Avoid overhead irrigation, as this may bring on disease problems. Geranium cuttings root easily and held over as house plants.

Geraniums must have a moist well-drained soil and should be planted in a garden receiving at least 6 – 8 hours of sunlight. Let the soil go slightly dry between waterings. Do not overfertilize. Fertilize with a slow-release, granular product once in spring and/or with a water soluble fertilizer such as Miracle-Gro™ or Jacks™ 1-2 times over the summer. Remove old spent flowers to keep plants blooming. Ideal light exposure is in full morning sunlight and in light afternoon shade.

Russian Arborvitae For Cool Areas Of The U.S.

Posted by Hugh on May 1st, 2019

Russian arborvitae and Siberian cypress (Microbiota decussata) is an underutilize ground cover (USDA hardiness zones 3-7). This tough juniper-like evergreen hails from Siberia and demonstrates exceptional cold hardiness to -40 ° F. In extreme northerly sites, the lacy evergreen foliage may turn complete brown in the dead of winter and re-sprout in spring.

In the cool temps of zones 5 and 6 microbiota really prospers. It struggles (melts down) in zone 7 unless cozied up under afternoon shade. Its soft feathery green foliage develops a purple to russet cast where winters are abnormally harsh. An early spring warm-up quickly restores its cool medium green hue.

Growth rate is slow to medium. Feed, if needed, in early spring with a general purpose granular fertilizer such as 10-10-10 or equivalent. Pruning is rarely necessary except to check its spread or to remove any broken branches.

The flat sprays of low growing microbiota range between 8-15 inches in height and 6-8 feet in width over several years. Microbiota is a great alternative to some disease plagued ground cover junipers. It is tolerant of dry shade. Deer and most disease and insect pests don’t bother it. It wants good soil drainage and cool summer temperatures.

Adjacent to my driveway I use microbiota to cascade over a low retaining wall. Foliage tolerates windy exposed sites once it becomes fully established in 2 years.

I am seeing more independent garden centers selling this terrific ground cover. E-commerce specialty nurseries also sell it. Plant container grown nursery stock in late winter thru spring.

Varieties: Celtic Pride™ – an exceptional cold hardy form.

Enjoy Two Kinds Of Stachys In Your Summer Garden

Posted by Hugh on April 26th, 2019

S. monieri ‘Hummelo’ (photo provided by North Creek Nurseries, Landenberg, PA)

Stachys ‘Countess Helene Von Stein’

Many gardeners are acquainted with the wooly leaf perennial called lambs ears (Stachys byzantina). But the genus Stachys is also home to betony (S. officinalis) / (S. monieri). Alpine betony (Stachys monieri) is native to Europe and Asia (USDA hardiness zones 4-8).

‘Hummelo’ betony is very different in appearance from its gray velvety leaf relative called lamb’s ears (e.g., Stachys byzantina). Instead of silvery foliage, Hummelo betony’s foliage is dark green and glabrous (hairless). In Southern climes the foliage is evergreen. This colorful and compact growing plant makes an excellent addition to the full sun perennial border. Wiry stems make for a great cut flower as well.

Hummelo exhibits an upright plant form @ 18 to 20 inches tall and wide. Pollinators can’t resist the striking lavender-rose flower spikes in late June thru July, emerging above basal glossy green foliage mounds. The bright flowers can be easily mistaken for salvias.

In comparison, lamb’s ear (S. byzantina) forms a dense mat of woolly silver-gray leaves. Plants grow 12 -15 inches high and 18 – 20 inches wide. Spikes of purplish pink flowers appear on tall stems in early summer that detract from the foliage and, in my opinion, should be pruned off. Bloom stalks often re-develop and necessitate more pruning. Seedlings from this weedy species will spread to other parts of the garden.

The cultivar ‘Countess Helene von Stein’, aka ‘Big Ears’, is the preferred choice among landscapers. It exhibits showier velvet (hairy silver) foliage, better heat and humidity tolerances, and best of all, it rarely flowers and seeds-in. Over time Big Ears develops a wider vegetative mound than the species.

Both types of Stachys are easily grown in moist well-drained soils and full to part day sun (6 hours or more recommended). Soils should be kept evenly moist, but established plants have some drought tolerance. Plants spread by underground stolons. Set multiple plants 12-18 inches apart as a ground cover. Feed in early spring at planting time with granular 10-10-10 or equivalent fertilizer.

No serious disease or insect pests trouble either species. Pollinators can’t resist the striking midsummer colorful floral spikes. Deer and rabbits generally stay away. Snails and slugs may be troublesome in wet summers.

The Perennial Plant Association has selected Stachys monieri ‘Hummelo’ as 2019 Perennial Plant of the Year.