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

‘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.

Pampas Grass – Have We Learned A Lesson?

Posted by Hugh on May 4th, 2015

Dwarf Pampas Grass

Many areas in the mid-South and northeast U.S. (USDA hardiness zones 6 and 7a) learned a hard lesson in the harsh cold winter of 2013-14. Over the past decade gardeners had been lulled into zone bending, insisting on planting species from a warmer zone. One of them was pampas grass (Cortaderia selloana). Very few clumps survived here in the Southern Appalachian region (USDA hardiness 6 and 7).

Pampas grass, depending on cultivar, grows 5 to 10 feet tall and 3 to 6 feet wide. It is a clump growing grass that thrives in full sun and medium soil moisture. A one year old clump displays exceptional drought tolerance. Showy plume flowers appear in mid-summer. Pink or white plumes (inflorescences) cultivars are available at most garden centers in the Southeastern U.S.

One of the most cold-hardy pampas grass varieties is dwarf pampas grass (C. selloana ‘Pumila’). Hardy to zone 6, winter snow plus a 2-3 inch layer of loose leaves provides a protective mulch covering before the start of winter.

Referring to ‘Pumilo’ as “dwarf” is misleading as some varieties of pampas grass are even shorter. Its showy silvery-cream plumes can be used in dried flower arrangements. Vegetative green grass portion grow 3 feet tall and wide. Add another 18-36 inches for the silvery white plumes to rise above the green mound.

Pampas grass establishes quickly, usually in one season. Feed and irrigate the first year after planting. One year old plants are very drought tolerant and require little care other than once a year pruning. Wait until late winter or early spring before cutting pampas grass back. Wear protective clothes as the leaves are razor-sharp!

Usually its enormous size, attractiveness, and architecture are good reasons to consider pampas grass. It is often planted as a stand-alone ornamental grass. Placement in front of tall evergreens helps to make it a statuesque landscape focal point.

Point of reference: at some garden centers you will find Hardy Pampas Grass. This grass is a different genus (Eranthus) and is cold hardy in zones 4b and 5.

Siebold Viburnum Makes Wonderful Small Tree

Posted by Hugh on May 3rd, 2015

Viburnum sieboldii ripening red (later black) fruits in late August

Newly Opened Flower Cluster

The genus Viburnum is no stranger to U.S. gardens. Many species and cultivars of viburnums are popular. Siebold viburnum (V. sieboldii) is a large spring flowering species from eastern Asia (USDA hardiness zones 5-7), but is under-planted in today’s gardens. This multi-trunk large shrub to 12 to 15 feet high or 25 to 30 feet tall as a small tree.

This large, coarsely-textured shrub is covered with clusters of creamy white flowers in mid-spring (late May into June). Clusters of edible berry-like fruits (drupes) follow, each 1/3 inches in diameter; drupes eventually turn pinkish red starting in late August. Birds and other wildlife snap up the ripened black fruits fall into winter. The smooth light gray bark is a winter asset.

Dark green prominently veined leaves hang on long into autumn, eventually turning yellowish green before abscising. This naturally large multi-branched shrub is easily trained into a small tree and is a good choice for planting under power lines. Fashioning a young shrub into a small tree via pruning is not difficult.

Siebold viburnum grows and blooms more abundantly in full sun on a well-drained, moist, moderately acid soil. Two-year established shrubs are moderately shade and drought tolerant. It is rarely troubled by diseases and pests.

Plant enmasse to develop a tall hedge or thicket to shelter wildlife and provide them a feeding station.

Two cultivars of note:

Ironclad™ (‘KLMfour’) grow 15 feet tall and 12 feet wide with rugged foliage which gives striking coarse textured look

‘Seneca’ (U.S. National Arboretum introduction) is exceptionally hardy (zone 4) with lustrous dark green leaves that often hold on until late November.

Good News About Garden Impatiens

Posted by Hugh on May 1st, 2015

Impatiens Bounce Pink Flame at Univ. of Georgia Trial Gardens (photo by Meg Green)

Gardeners no longer have to give up growing garden impatiens (Impatiens walleriana). No, the worldwide disease outbreak of downy mildew on garden impatiens is not over. But new disease resistant cultivars of impatiens are arriving at garden centers this spring.

Two of the newest are: SunPatiens® Spreading Shell Pink and Bounce® Pink Flame (‘Balboufink’). Sunpatiens thrives in half-day to full sun. Bounce impatiens are New Guinea types and grow either in modest shade to half-day morning sunlight (zones 6-8).

Spreading Shell Pink, the newest addition in the series, is covered with lovely soft pink flowers from late spring to first fall frost. After transplanting a strong rootsystem takes hold quickly and these impatiens thrive in summer’s heat, rain and humidity. Plants have a vigorous spreading habit and plants maintain excellent plant form through the summer in full sun to light shade.

Bounce impatiens are interspecific hybrids with New Guinea impatiens (I. x hawkeri); they look like old-fashioned garden impatiens in plant habit, flower form and count, but are completely downy mildew resistant. One of four new cultivars in the Bounce series for 2015, Pink Flame boasts massive numbers of stunning, bright pink bicolor blooms on plants that are 12 to 18 inches high and spread.

Bounce and Sunpatiens are low-maintenance flowering annuals to grace your garden this year and many more. Both new impatiens are highly disease and pest resistant. Feed plants monthly with a water soluble fertilizer such as Miracle-Gro™, Daniels™ or Schultz™. Mulch at transplanting time and irrigate during moderate dry spells through the season.

All-America Selections (AAS) has picked out these two impatiens for their exceptional performance in the AAS container trials.

Sooty Mold Is Symptom Of Aphid Feeding

Posted by Hugh on April 29th, 2015

Sooty mildew on hackberry leaves (Photo courtesy of Dr. Alan Windham, UT Ext. Plant Pathologist, Nashville, TN

Wooly Asian hackberry aphids (A. S. Windham photo)

Aphids are small (1 to 10 mm long) and pear shape. Infestations are often worse during wet cool days of spring; they are frequently feed on new growing shoots and leaves. Actively growing weeds also harbor aphids and may migrate over to favorite garden plants. Summer feeding aphids should never be counted out. Feeding aphids may spread a number of bacterial and virus diseases from sickly to healthy plants.

Color varies by aphid species and are capable of changing their color. Common colors include green, dark pink, yellow, and black. Many are smooth and shiny, and a few are wooly or covered with fluff. Most aphids are wingless, but some may form wings a new aphid colony to find a new food source when plants they’re feeding on are in poor shape.

Aphids do not possess chewing mouthparts. They don’t nip chunks out of leaves or stems. Instead they have piercing or “stylet” mouthparts to draw out the sap from sugary phloem tissues. Plant damage shows up as leaf curling, stunted growth, yellowing (chlorotic), or any combination thereof.

Their reproduction rates are very rapid. Aphids can reproduce without mating. Aphids also molt 4 times before maturing as adults. The old flakey skins are frequently seen over leaf surfaces. A wet or sticky honeydew deposit builds up over leaves and stems; later, black mold fungus colonizes over leaf surfaces. The sooty appearance looks unattractive. The sooty mold may be partially hosed off.

Several pesticides are effective against aphids in a garden. Insecticidal soaps and oils kill aphids on contact. Systemic pesticides like neonicotinoids provide longer activity, but may harm many beneficial insects such as bees and butterflies. Products containing Beauveria bassiana, Azadirachtin (neem oil) and Endeavor (pymetrozine) control aphids without harming most beneficial insects.

The soft bodied aphids have numerous natural enemies including ladybugs, lacewings, fly larva, wasps, true bugs. Parasitic wasps may be purchased and released to reduce aphid populations.