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

Winter Damage On Crape Myrtles

Posted by Hugh on June 2nd, 2015

Crape myrtles suckering from base

Winter damaged crape myrtle

Extremely cold winters of 2013-14 and 2014-15 have damaged many cultivars of crape myrtles (Lagerstroemia x indica). Don’t assume that new crape myrtles are hardy; many are rated hardy only to zone 7. Several of the U.S. National Arboretum cultivars are hardy in zone 6. Gardeners living in the Mid-Atlantic or the lower Midwest states, where crape myrtles are iffy, frequently start over by cutting them back near the ground in spring and fertilizing.

Is your crape myrtle dead? First, determine if the tree (shrub) is alive? Nick the bark with your fingernail or a knife to determine if the wood is still green (living). Use a chain saw, pruning saw or loppers to cut the trunk(s) close to the ground. Within a few weeks green shoots will begin sprouting around the base. Choose 3 – 5 well-spaced shoots to become the new main trunk(s) and cut off the rest. Large specimens can sucker back and even bloom in late summer and the early days of autumn.

Fertilize every 6 – 8 weeks with a high-nitrogen fertilizer until mid-August and no more through the end of the year. Maintain 2 – 3 inches of mulch and keep soil and mulch away from the shrub/tree base. Irrigate crape myrtles bi-monthly in the absence of rainfall.

When replanting, set crape myrtles in the ground shallow and never deep in the planting hole. Stop the practice of hat-racking, commonly called “crape murder”, as it places a tree under stress and more susceptible to winter freeze damage. Do not prune crape myrtles in the winter months (early March in most areas).

Finally, select exceptionally cold-hardy cultivars, such as ‘Natchez’ (tree form, white blooms), ‘Hopi’ (shrub, medium pink), ‘Acoma’ (shrub, white).

Modern Day Clematis Bloom Freely

Posted by Hugh on May 29th, 2015

Late Summer Blooming C. viticella 'Emily Plater'

Late Summer Blooming C. viticella ‘Emilia Plater’

Free-flowering ‘Rooguchi’ clematis

The old-fashioned clematis(es) in grandma’s garden bloomed one time in spring or summer and bore huge showy flowers (USDA hardiness zones 3-7). Vines took up lots of space in the garden. Old cultivars grew 8-9 feet tall; many bore one single large flower at the end of each growing stem. They bloomed at one time and, even today, are stunningly beautiful and still sold at many garden centers.

Today’s gardens are smaller in size. Clematis plants need to be more compact, free-flowering, and produce more flower power over several months in smaller spaces. Modern day clematis are fibrous rooted to withstand colder winters and have better mildew disease resistance. Many are double flowering, offer more color choices that do not fade and are easier to prune. Early flowering types are also available that bloom profusely on either old wood or new growth.

Many shorter types can be grown in pots and containers instead of walls and trellises. Some are “free-flowering” types produce a lot of flowers up along their stems. Some develop 5 to 7 leaf nodes that form multiple flowers buds over several months.

Many gardeners have a difficult time understanding how to prune clematis. Modern cultivars are a lot easier to prune. In early spring simply removed all but 6 to 9 inches of old vine wood above soil level. After pruning and fertilizing in early spring, vines and compact shrubby types grow rapidly and bloom over several months.

I highly recommend Raymond Evison 2007 book “Clematis for Small Spaces,” which details 150 of the best clematis cultivars for patios and decks.

Flame Azalea Favorite Among Native Azaleas

Posted by Hugh on May 26th, 2015

Young 4-year old Flame azalea (select seedling)

Flame azalea (R. calendulaceum) is a spectacular sight when it flowers in early May through June (depending on location). The mountainsides across the Appalachian region seem to be afire with their yellow, orange or red flowers (USDA hardiness zones 5 thru 8). Its native habitat is in open, dry sites in woods, on the hillsides, and on mountaintop open areas (“balds”) from 600 to 5,000 feet in altitude.

Flowers tend to be larger than other native azalea species. Each flower truss contains 3 to 10 flowers, which open before or when leaves are present. Funnel-shaped corolla is about 2 inches long and up to 3 inches wide. Long stamens protrude out from the corolla. The upper petal (lobe) on each bloom exhibits a prominent orange or pinkish blotch. Flowers tend not to be fragrant.

Flame azalea forms an upright branched shrub 5 to 12 feet high with an open spreading canopy. The medium green leaves take on yellow, bronze, and red hues in fall before abscising. Leaves are deciduous, about 1-3 inches long, medium to dark green above, and tiny hairs beneath. Both leaves and branches often develop in whorls.

Flame azaleas are difficult to propagate from cuttings, but are easily started from seeds collected in the fall. The tiny seeds are sprinkled on a fine peat /bark soil-less medium, lightly covered, and frequently misted with water daily. Seeds germinate over 2 – 3 weeks. It may take 3 or more years for seedlings to bloom for the first time.

In the garden flame azalea grows best in morning sun and afternoon shade. Soil drainage must be well drained and supplied with adequate moisture. Mulch around shrub with pine needles or nuggets. Avoid soppy soils! Feed lightly once or twice during the late spring during its growing period with an acidic water-base fertilizer such as Miracle-Gro™, Schultz™, or Natures Source™. Prune primarily to control shrub height and spread.

Flame azaleas are the “asked-for” native azaleas by gardeners, yet are rarely sold at garden centers. Find them at e-commerce nurseries on-line.

Red Abyssinian Banana For Tropical Looking Landscapes

Posted by Hugh on May 24th, 2015

Red Abyssinian Banana in container

Ensete banana

Red Abyssinian banana (Ensete maurelii ‘Red Abyssinian’) is a tropical banana from high in the mountains of Ethiopia in eastern Africa. Its enormous reddish to purplish foliage and red – burgundy trunk adds a tropical presence to any garden. Compared to hardier banana genus Musa, Ensete does not produce root suckers (pups) nor is it a clump grower. All foliage originates from one trunk. By late September plant may grow 8 – 10 feet tall and 6 – 7 feet wide in temperate gardens and double that size in tropical regions.

Individual leaves expand to 10 feet or more in length. The green leaves orient upright and are splashed with vivid burgundy splotches over the new stems and foliage. Foliage color is more vivid if grown in full sun. Red Abyssinian can be planted in large containers or troughs and set on your deck or patio.

Red Abyssinian holds its foliage very upright on a burgundy colored pseudo-trunk. Spring/summer growth is extremely vigorous. This tropical banana excels in hot, humid, wet summers and rich fertile soils and fails when soil moisture and nitrogen fertilizer are lacking.

At the garden center your initial purchase may be a 18-inch starter plant from tissue culture, and in only 4 – 5 months it develops into a 6 – 8 foot giant. Beautiful flowers form only in tropical climates with a much longer hot weather to permit uninterrupted growth.

Select a large container greater than 24 inches in diameter at the base and weighted down to support what will be an enormous plant by late summer. Maintain your banana on the luxury diet with sun, water and liquid fertilizer.

Choose flowering bedding plants, large leaf hostas, vining ground covers, and/or ferns to complement Ensete banana in a container. In zone 8 and further south combine tropical gingers, spiky-leaved phormiums, and various palms.

‘Short and Sassy’ Helenium (Sneezeweed)

Posted by Hugh on May 21st, 2015

‘Short and Sassy’ Helenium (Skagit Gardens Photo)

Sneezeweed (Helenium autumnale) is a bee/butterfly friendly perennial that blooms heavily from mid-summer into early fall. Helenium (“sneezeweed”) does not cause hayfever or irritate sinus passages. The genus Helenium is named for Helen of Troy. Its dried leaves were once crunched to make a snuff to promote sneezing.

This tough prairie native thrives in full sun and in a moist well-drained soil (USDA hardiness zones 4-8). ‘Short n Sassy’ is a new dwarf cultivar introduced by Skagit Gardens in Mount Vernon, WA. Those who garden in a small space or in containers will appreciate this diminutive form.

As its cultivar name hints, Short and Sassy plants grow in a compact mound-like habit reaching a height of 12-18 inches and 24 inches width. It never requires staking and the brightly colored flowers stand tall above the foliage. It starts flowering a week or two earlier than other heleniums.

Their charming flowers fill the late summer garden with vibrant fiesta colored blazing orange and yellow ray flowers centered by a coffee-brown button. Petals open almost red and fade to bright orange. Narrow slender leaves are a rich glossy green color and stay disease and pest-free.

Spring-planted heleniums establish quickly and demonstrate good heat and drought tolerances as flowering begins. Bloom period can be extended if spent flowers are quickly removed. Bees and butterflies work the flowers; birds feast on the seeds in the fall. Deer generally stay clear from helenium plants.

Plants should be divided every 2-3 years to retain clump vigor.

American Yellowwood Deserves To Be Planted More

Posted by Hugh on May 19th, 2015

Yellowwood in flower

Gray beech-like Bark

American yellowwood (Cladrastis kentukea) is a beautiful native tree which is rarely planted in U.S. landscapes (USDA hardiness zones 4-8). Yellowwood is a tree for all seasons. It is both a lovely shade and flowering specimen. Long white wisteria-like flowers appear in mid- to late-May. It eventually matures into a lovely 35 to 45 foot landscape tree.

Yellowwood develops a narrow upright branching stance; its light gray smooth bark is very beech-like. Tree branches low to the ground. White fragrant pea-like blossoms, 8-14 inch long, drip from the tips of branches like wisteria. New spring compound leaf foliage starts off pale green, turns medium green by early summer, and turns lemony yellow in the fall. Each compound leaf is comprised of 7-leaflets, each 3-4 inches long. The species name is derived from the yellow color of its inner heartwood.

Yellowwood is the perfect tree for the patient gardener who is willing to wait 5-6 years (sometimes longer) after planting for first flowers to appear. The tree does not flower every spring and no one can predict what factors trigger the blooming response.

Plant this mid-sized tree around sunny patios and terrace areas, and take advantage of its cooling summer shade. Yellowwood prefers a moist, well-drained soil and is not drought tolerant. The species is pH insensitive and frequently grows in limestone-based soils. Disease and insect pests are rare, and do irrigate tree during periods of severe drought stress.

Yellowwood tree forms a deep legume root system; plant balled and burlapped (b&b) in late winter to early spring or container-grown nursery stock in any season. Prune in summer to avoid excess sap leakage observed in winter pruned trees. As the tree ages, upright branching sometimes leads to limb breakage. Main branches of older specimen trees may be cabled or braced to avoid or postpone limb loss.

‘Perkins’ Pink’, a rare pale pink flowering cultivar, is available from a few e-commerce nurseries.

Cosmos For Sunny Gardens

Posted by Hugh on May 15th, 2015

Cosmos Flowering in September

Reliable Cosmos

Cosmos, indigenous to Mexico and South America, are one of the easiest-to-grow flowering annuals. They start blooming in early summer and are at their best in late summer and early autumn. Two most popular species are Cosmos sulphureus and C. bipinnatus. Flower heads are composed of disc and ray flowers.

Cosmos is a member of the aster family. Today’s hybrids are brightly colored (red, pink, orange or white) that bloom freely like wildflowers. They attract birds and butterflies, particularly Monarchs. Blooms make terrific floral bouquets that will last for 7 – 10 days. Cosmos light green foliage is very fern-like.

Be aware that cosmos self-seeds freely. You may self-seed directly into the spring garden after the last spring-frost date or purchase plants at garden centers. Space plants approximately 1-2 feet apart; with tall varieties, space plants closer and let them support one another.

Cosmos thrive in average to subpar soils at neutral or slightly alkaline pH and that are well-drained. Plant heights vary from 1 to 5 feet depending on soils, cultivars, moisture, and fertilization. Excess soil nutrition will cause plants to grow luxuriantly at the expense of flower numbers. Plants tend to flop over in rich soil and may require staking to prevent stem breakage in high winds.

Pinch off spent flowers to encourage continuous bloom. Pinching stem tips reduces plant height and encourages branching, although is rarely necessary. Cosmos are mostly free of disease and pest troubles.

Fill Flower Gardens & Containers With Sweet Alyssums

Posted by Hugh on May 12th, 2015

White Alyssum (border) & angelonia (in back)

Sweet alyssum (Lobularia maritima) is one of the easiest annuals to grow. A member of the mustard family (Brassicaeae), it is native in the Mediterranean region and the Canary and Azores Islands (AHS heat zones 3-8). Modern day cultivars possess exceptional heat, humidity, and drought tolerance in summer months once fully established. Alyssums may be utilized in mixed containers and hanging baskets; they are used to edge garden beds and borders.

Low growing alyssums lay down a fragrant spreading carpet of floral color. Medium green leaves are barely 1-inch in length. Alyssums grow 4-9 inches high and 18- 36 inches wide depending on variety. Flowers are self-cleaning and available in numerous color choices, including pink, rose, lavender, purple and apricot.

Dense clusters of sweetly fragrant white 4-petaled flowers cover the foliage mounds from spring to early summer. Individual flower clusters measure 2-3 inches in diameter, and they bloom from planting time up to hard frost. Alyssums are frequently planted as a winter annual in zone 9 and further south. In regions with long hot summers, alyssums tend to decline in summer’s heat unless planted sited under partial afternoon shade.

Plant alyssums in sun to partial sun and apply slow release fertilizer at planting time. Plants are shallow-rooted and do benefit from mulching and moderate irrigation in the summer heat. In mid-August alyssums may look tired, leggy or seedy; if so, clip back a few inches, irrigate, and re-fertilize. Plants will return to their glorious best within 1-2 weeks. Alyssums are not troubled with serious disease or pest problems.

Alyssum varieties:

‘Rosie O’Day’ – All-American Selection (AAS) winner with rose pink flowers.

Snow Princess® – AAS winner with outstanding performance and is very heat tolerant.

White Knight® – new in 2014 with dark green foliage and covered with fragrant white blossoms

Stream®series – Lavender Stream and White Stream are real performers.

Caution: Gardeners with sensitive skin should wear gloves when working with alyssums

Chinese Fringetree Gains In Popularity And Availability

Posted by Hugh on May 9th, 2015

Chinese fringetree (Chionanthus retusus)

When in bloom in mid-spring (May), the fringetrees (Chionanthus spp.) definitely will catch your eye. Chinese fringetree (C. retusus), is one of the finest small to medium sized flowering trees, not to be confused with the U.S. native fringetree (C. virginicus) (USDA hardiness zones 5-9). Both produce spectacular white lacy flowers in late spring. Flower panicles are larger and showier on American fringetree, and its growth form is often wild without some annual pruning.

Over the past quarter century the Chinese form has developed a growing “fan base” among American gardeners. Its high gloss, dark green foliage holds its sheen through the spring and summer months and are disease and pest free. Fall color is non-distinct yellow and is rarely spectacular. The aged furrowed bark on Chinese fringetree is very attractive.

Fringetrees are dioecious; male flowers are non-fruiting while female flowers bear ½ inch long egg-shaped blue-black fruits (drupes). Seeds collected and sown in the fall will germinate 2-3 years later.

Chinese fringetree prefers a full sun location. It tolerates a wide range of soils provided they’re well-drained. A 3 to 5 gallon plant will grow to 25 to 30 feet tall and wide in 20 years. Two-year established plants demonstrate good drought tolerance. It performs better sited in light afternoon shade in southern climes.

‘Tokyo Tower’ is a columnar form that matures to 15 to 18 feet height and only 6 to 8 feet in width. ‘China Snow’ is a slow-growing shrub form from Tennessee nurseryman Don Shadow; it grows 8 feet tall and 5 feet wide in ten years with snowy white fringed blooms.

Caveat: People often confuse the name “fringetree” (Chionanthus) with “fringe flower” (Loropetalum)

Cardinal Flower Attracts Hummingbirds and Butterflies

Posted by Hugh on May 6th, 2015

Cardinal flowers at Biltmore Estate, Asheville, NC

With their vibrant red colored blooms in July and August and a strong vertical growth habit, you visually can’t miss with our native cardinal flowers (Lobelia cardinalis) (USDA hardiness zones 3-9). Hummingbirds and butterflies won’t pass them by either.

Cardinal flowers are also called scarlet lobelias. Their vibrant red single raceme flowers single them out from other summer-flowering perennials. The non-branching flower stalks are covered from top to bottom with small flowers. In the garden blooms can be present from early to late summer, particularly if you keep them deadheaded. In the wild, they tend to bloom 3-4 weeks later if moisture is adequate.

Cardinal flowers prefer a compost-rich moist site in full sun. Mulching is highly recommended for even soil moisture. Set plants 2 to 3 feet apart. You may also opt to submerge pots of cardinal flower in a water garden, plant them in a rain garden, or on the edge of a stream or lake. Periodic flooding makes it look better; again, roots crave soil moist.

This clump-forming perennial has no serious pest or disease problems. Deer seem to leave it alone. It is best divided after three years in early spring. There are several cultivars available including the popular red, pink and white. Some of them include ‘Alba’ (white blooms), ‘Heather Pink’ (pink) and a ‘Black Truffle’ (dark chocolaty-purple foliage and bold red flowers). Black Truffle’s dark foliage holds throughout the spring and summer months.

L. cardinalis serves a parent in the breeding of new hybrid lobelias. Some of the hybrid forms may not be as hardy as cardinal flower itself.