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

Compass Plant – Prairie Giant

Posted by Hugh on June 26th, 2020

Compass Plant (Silphium laciniatum) are impressive prairie plants that look like – but are not – sunflowers. Native to the central U.S. (USDA hardiness zones 3 to 8), these sturdy prairie giants grow upwards of 5-8 feet in height (1.5 – 3 feet wide) on stiff, hairy, resinous stems. The group (Silphiums) are also called “rosinweed” because split or broken stems exude a gummy rosin (resin).

Their sunflower-like flowers measure 4-5 inches in width with yellow rays and yellow center disks. Flowers bloom in loose spikes on the upper parts of the plant in summer. Leaves are very large and deeply cut. The bottom (basal) leaves measure upwards of 18 inches in length. Basal leaves usually orient themselves on a north-south axis so as to minimize intense overhead sun exposure, thus giving rise to the common name.
The upper leaves are a lot smaller.

Compass plant is easily grown in average, medium moist, well-drained soils in full sun. This prairie giant tolerates poor soils and asks for little or no care. In partial shade, staking plants may be necessary.

No serious insect or disease problems trouble compass plant. Plants from seed may be slow to establish and may not flower until the second or third year. Flowers attract butterflies, bees, and other pollinators. Don’t be in a hurry to cutback plants in the winter as birds perch upon the stems of these architectural giants.

Because of their enormous height, compass plants are best sited in the rear of a flower border where they should prosper over many years. They make excellent additions to a prairie or wildflower gardens.

Prairie species like compass plants are rarely sold at local garden centers. Mail order seed companies like American Meadow, Inc. are your best place to shop.

Gaura (Wand Flower)

Posted by Hugh on June 21st, 2020

Gaura (Gaura lindheimeri), also known as wand flower, whirling butterfly, and bee blossom (Gaura lindheimeri) is one tough perennial that blooms through the summer into fall. Gaura is native to Texas and Louisana and is hardy to USDA plant zones (5)6-9. It lives many years in hot humid climates and requires very little care after the first year.

Plant heights range from 15 inches to 4 feet (see variety list below). Many cultivars are compact and that makes them container-friendly as well. Gaura foliage is lance-shaped, often tinted with pink, white, and cream (depending on variety). Wiry flower stems bear numerous 1-inch 4-petalled flowers. Color palette is white, pink, reddish, or color blends. Heaviest blooming occurs in early summer, but plants often flush full of flowers through summer / early fall and are visited by bees, butterflies, and an occasional hummingbird or two.

Flowers catch your eye as fluttering wands (stems) of white or pinkish flowers. Compact varieties of gaura are also make good pot fillers. Flowers may appear delicate but gauras are one exceptionally tough perennial. Cut taller varieties back by one-half in the early days of summer to promote compactness. Also, remove old spent cut floral stems back; new stems will rush up and plant(s) will re-bloom. Disease and pest problems along with deer rarely trouble gaura.

Plant gaura in a sunny location that captures 6 to 8 hours of direct sun daily and in average well-drained soil. Gaura develops a deep taproot and is rated as highly drought tolerant. Irrigate gaura the first year and enjoy not having to reach for a watering hose in subsequent summers. Feed plants with a slow release fertilizer in spring. Annual mulching is highly recommended for long term plantings.

Popular varieties:

‘Siskiyou Pink’ – favorite old-timey variety with deep pink flowers

‘Whiskers Deep Rose’ –ultra compact (14-16 inches tall) with rosy-pink petals and white stamens, all above burgundy-tinted foliage.

Whirling Butterflies® – bright white flowers with red sepals; compact (36 inches tall); free flowering and don’t self-seed.

Sparkle White (2014 All-American Selection (AAS) winner)- 24 inch tall compact.

Four Landscape Shrubs That Are Early Summer Stars

Posted by Hugh on June 16th, 2020

Bottlebrush buckeye (Aesculus parviflora) is one of our finest early summer native flowering shrubs for sun or shady sites. It is a dense, mounded, suckering, deciduous, multi-stemmed shrub which grows 6-12 feet tall and 15-18 feet spread. It flaunts unique palmate green leaves (5-7 leaflets) and white 10-12 inch tall floral candles. The dynamic bottlebrush florets reveal conspicuous red anthers and pinkish filaments. Glossy inedible, pear-shaped husks containing nuts (buckeyes) appear in early fall. Finally, the foliage turns yellow in autumn. (Zones 4-8)

Summersweet (Clethra alnifolia) is a deciduous native shrub found in the wild in moist woodlands, stream banks and seashores from coastal Maine to Florida and west to Texas (Zones 3-9). This rounded, suckering, densely-branched, deciduous shrub grows to 3-6 feet (less frequently to 8 feet) tall and is noted for producing a mid-summer bloom show of sweetly fragrant white (or pink), 2-6 inches long, upright flower panicles (racemes). Flowers give way to dark brown seed capsules which often persist into winter. Serrate, obovate to oblong, glossy, dark green 3-4 inch long leaves. Expect an attractive yellow to golden brown fall leaf color. Flowers attract to butterflies and bees.

Buttonbush (Cephalanthus occidentalis) is a deciduous native shrub with an open-rounded shrubby form that typically grows 6-12 feet tall (occasionally to 20 feet). Tiny, tubular, 5-lobed, fragrant white flowers appear in dense, spherical, long-stalked flower heads (to 1.5 inches in diameter) in early summer. Long, projecting styles give the flower heads a distinctively pincushion-like appearance. Flower heads attractive bees and butterflies. Flower heads mature into hard spherical ball-like fruits consisting of multiple tiny two-seeded nutlets persist through most winters. Ovate to elliptic glossy bright green 4-6 inches long leaves form in pairs or whorls in late spring (May). (Zones 5-9)

Chastetree (Vitex agnus-castus) is typically grown in warm winter climates as a vase-shaped, deciduous shrub to 10-15 feet tall or trained as a single trunk tree to 20 feet tall. This non-native will grow as a 3-5 feet tall herbaceous perennial in colder parts of the U.S. (zones 5). Its grayish-green aromatic, palmately compound leaves are comprise of 5-7 lance-shaped leaflets (each leaflet to 6 inches long). In early- to mid- summer 9-12 inch floral panicles of tiny, fragrant, lavender to pale violet flowers attract loads of nectar hungry butterflies and pollinators. (Zones 6-9)

Hakone Grass – On The Shadier Side Of A Garden

Posted by Hugh on June 11th, 2020

‘Aureola’ hakone grass

Japanese Forest grasses, also called Hakone grasses (Hakonechloa macra), hail from Japan (USDA hardiness Zones 5-9). They are a wonderful choice in a drab woodland garden spot. You will love them for their bright foliage and low growing habit.

Hakone grass grows in a mounding clump. The foliage cascades over rocks, edges over garden walls, or off the rims of containers. It spreads slowly via rhizomes into a luscious ground cover.

The species itself (H. macra) has its green foliage, tolerates a bit more sun and drier soils, and is much faster growing compared to the brightly tinted cultivars. Four selections, including the species are highlighted here.

‘Aureola’ – this green and gold streaked cultivar was selected the Perennial Plant of the Year in 2009. Leaf coloring is more prominent in deep shade and less so in sunnier spots.

‘All Gold’ – foliage is chartreuse or all gold as its name implies, a wonderful accent plant associated with other colored foliage plants grown in containers or garden beds.

‘Fubuki’ forms a low mound of narrow green and creamy white striped 14 inches tall and 18 inches wide sedge; leaves develop pink tones in autumn; grows very compact than related cultivars.

‘Beni-kaze’ (Red Wind) produces short wide green blades which turn partially red in summer and most leaves take on a red to purple tint in fall.

Plant hakone grasses from spring thru mid-summer to allow adequate time for the plant’s root system to develop before the arrival of winter. Hakone grasses prefer a partial sunny to partial shade location and humus-rich, moist, well-drained, slightly acidic soils. In northern locales full morning sunlight or full day dappled sites are perfect. The grass tolerates almost full shade in the hot, humid deep South.

Feed lightly in spring with granular 20-10-10 or equivalent fertilizer or water soluble fertilizer 2-3 times in spring and summer months. Clip back (or mow off) last year’s clumps a few inches from ground in late winter.

Queen Of The Prairie Or Meadowsweet

Posted by Hugh on June 6th, 2020

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*Filipendula rubra* at Kingwood Center in Mansfield, Ohio

“Tall and pretty spectacular” very much describes Queen of the prairie (Filipendula rubra) (USDA hardiness zones 3 to 8). Twelve species comprise this genus of U.S. perennials (USDA hardiness zones 3-8). Best known species are meadowsweet (F. ulmaria).dropwort (F. vulgaris), both native to Europe, and queen-of-the-forest (F. occidentalis) and queen-of-the-prairie (F. rubra), both native to North America.

Queen of the prairie is a popular favorite, native from Pennsylvania to Georgia west and north to Iowa and Missouri. This long-lived beauty will dominate its garden spot for many years. Unlike most Filipendula spp. which bear white flowers, F. rubra flaunts wonderful pink flowers,

Queen of the prairie is valued for both its bold foliage and flowers. This clump-forming perennial grows 6-8 feet tall. Many 6-9 inch wide panicles (corymbs) tiny, fragrant, pale pink flowers fill the tops in early to mid summer. Bright green, deeply cut, pinnately compound leaves comprise 7-9 lance-shaped large leaflets, each leaflet 7-9 lobed. Leaves are fragrant.

In Zones 3 to 7, filipendulas grow naturally in mostly full sun sites. In the South (Zones 7b – 8), plants are best lightly shaded from mid-afternoon sun. Plant in moist acidic soils, but they also will prosper on poorly drained, calcareous sites. More soil moisture means taller plants.

Few serious disease or insect problems trouble filipendulas when plants are not crowded and roots are kept relatively moist. Leaf spots, powdery mildew, rust are occasional problems. Though quite tall, this sturdy stemmed perennial usually does not ask for staking unless grown in moderate shade.

Filipendulas are tall plants for large gardens. Plant three or more for an
early summer spectacular floral show.

Landscape use: borders (rear), cottage gardens, rain gardens, wet meadows or in moist ground along streams or ponds.

F. rubra varieties include:

‘Albicans’ (‘Magnificum Album’) has white flowers and grows shorter.

‘Venusta’ (‘Magnifica’) has deep pink flowers.

Related species:

Siberian Meadowsweet (F. palmata) – 4 feet tall with medium-green palmate leaves with fuzzy white undersides. Flowers range from pale to deep pink and are borne inclusters on erect stems. Zones 3 to 9. Russia, China, Japan.

Japanese Meadowsweet (F. purpurea) – 4 feet tall with medium-green toothed, lobed leaves and erect purple-red flower stems with deep reddish pink blooms. Zones 4 to 9. Japan.

Queen of the Meadow, Meadowsweet (F. ulmaria) – 2 to 3 feet tall with toothed, lobed medium-green leaves and erect, branched flower stems with dense clusters of creamy white blooms.

Six Easy Perennials To Grow

Posted by Hugh on June 1st, 2020

‘Rozanne’ hardy geranium at Biltmore Estates, Asheville, NC

Rozanne (‘Gerwalt’) Cranesbill (Geranium X ‘Rozanne’) – low growing flowering groundcover that forms a 20 inch tall by 24 inch wide mound; blooms almost non-stop from mid-spring to early fall. For a cranesbill, its 5-petaled, violet-blue flowers are huge (2.5 inches wide) with off-white centers; in bloom from late spring to early summer. (Zones 5-8).

‘Millennium’ Ornamental Onion (Allium x ‘Millennium’) – produces a dark green strap-like leaves in spring, topped by soft pink umbels on long stalks starting in June. Dried round seedheads add slight interest to the winter landscape; drought tolerant; deer resistant; prefers full to partial day sunlight. (Zones 5-8)

‘Cardonna’ Sage (Salvia nemorosa ‘Cardonna’) – bears showy violet-blue flowers on tall dark purple flower stems; grows 24 – 30 inches high and 18 – 24 inches wide; deadhead to keep in bloom; attract hummingbirds; deer-resistant; prefers full sun and well-drained soil. (Zones 4-8).

‘Angelina’ Stonecrop (Sedum rupestre ‘Angelina’) has striking chartreuse needle-like evergreen foliage; best in sunny areas; inconspicuous yellow flowers in summer. Leaves develop a reddish tinge in winter; highly drought tolerant and spreads prolifically; thrives in mixed containers; rock and roof gardens. Prune (mow) back rambling plants to keep bed neat and tidy. (zones 5-8).

Balloon flower (Platycodon grandiflorus) – clump-forming perennial with puff up like balloon shape buds that burst open into bell-shaped
five pointed purple-blue flowers (to 2-3 inches across); long blooming stems grow to 30 inches tall; 1.5 – 2 inch long blue-green leaves stay blemish-free all summer. (Zones 3-8).

‘Raydon’s Favorite’ aster (Symphyotrichum oblongifolium ‘Raydon’s Favorite’) – one of the most reliable native perennial asters with masses of violet-blue, daisy-like flowers on 2-3 feet tall multi-stemmed plants in mid to late autumn; prefers full sun in well-drained acidic to low alkaline soils. Cut back plants by one-half in late June to develop a well branched plant; flowers attract many butterflies and bees. (Zones 3-8).

Two Kinds Of Maidenhair Ferns

Posted by Hugh on May 26th, 2020

A.-peltatum at Chanticleer Gardens in Pennsylvania

A. pedatum at Chanticleer Gardens in Pennsylvania

Northern maidenhair fern

Maidenhair ferns (Adiantum spp.) are deciduous hardy perennial ferns. Two native species are commonly planted in U.S. gardens. These delicate-looking ferns typically grow 1 to 2 feet tall and frequently grow in rich soils in eastern and Midwest U.S. woodland gardens.

The palmately compound fronds are finely-textured along with thin wiry black stems. Coiled young fiddleheads (crosiers) emerge with a pinkish tint in spring.

Northern or Common Maidenhair (A. pedatum) grows 10 to 26 inches tall on thin, wiry stems (USDA hardiness zones 3-8). On older plants fronds develop in a distinctive horseshoe or crab framework. It is deciduous and grows in part to full shade in the mountains and piedmont regions.

Southern or Venus Maidenhair (A. capillus-veneris) grows 12 to 24 inches tall on thin wiry stems with delicate leaves (USDA hardiness zones (6)7-10). It will tolerate zone 6 winters in Virginia, Kentucky and Tennessee if dormant clumps are grown in dappled shade and sheltered from dry wintry winds.

Maidenhair ferns grow in average, medium, well-drained soil in partial to full shade. Clumps flourish in moist, humus-rich, in neutral to alkaline (high calcium) moist soils. Maintain moist cool soils with generous amounts of mulch or pine needles. In their northerly range, maidenhair ferns will prosper in 1-2 hours of morning sunlight, but dappled light in southern climes is adequate.

Despite their lacey appearance, maidenhair ferns are tough, easy-to-grow shade perennial ferns that are free of serious insect or disease problems and are deer resistant. By late summer, summer heat sometimes scorches the thin tender fronds, especially if soil moisture levels are inadequate and/or plants receive too much sunlight.

Maidenhair ferns are perfect for rock gardens, or in mixed container arrangements. Plants spread slowly by creeping, branching rhizomes to eventually form large colonies.

For accent, combined them with broad leaves of small leaved hostas, coral bells (Heuchera), lungworts (Pulmonaria), and fairy wings (Epimedium).

Garden Phlox Attract Pollinators

Posted by Hugh on May 21st, 2020

Phlox (Phlox spp.) are popular perennials that are also U.S. natives. A multitude of species and hybrids are available to landscapers and gardeners for almost any type of garden environment, including containers.

Here is a list of the intermediate garden species: Border phlox (Phlox paniculata), Meadow phlox (P. maculata), Carolina phlox (P. carolina), Smooth phlox (P. glaberimma), Downy phlox (P. pilosa), Alabama phlox (P. pulchra), and Large leaf phlox (P. amplifolia). Of these, Border or Garden Phlox (P. paniculata) is the most popular.

Many varieties of garden phlox are particularly susceptible to powdery mildew. While this foliar disease may be only a cosmetic nuisance, severe cases will result in significant leaf loss and plant death. Overcrowding plants often result in outbreaks with powdery mildew disease.

Proper siting – full to partial sun and humus-rich soil – are key to successfully growing phlox. Phlox ask for minimal care of seasonal fertilizing, mulching, and supplemental watering in periods of drought. Deadheading also extends the plant’s flowering potential. Select truly superior cultivars and never over-irrigate the garden bed.

2015-17 MT. Cuba Center’s Phlox Trial in Greenville, DE. The best performing cultivars of Phlox paniculata are: Phlox paniculata ‘Jeana’, ‘Glamour Girl’, ‘Delta Snow’, ‘Lavelle’, ‘Robert Poore’, ‘Dick Weaver’, ‘David’, ‘Ditomdre’ (Coral Crème Drop), and ‘Shortwood’.

The best performing selections from other species and hybrid phlox are: Carolina phlox (Phlox carolina ssp. carolina) ‘Kim’ (light pink), Phlox glaberrima ssp. triflora ‘Bill Baker’, sweetly aromatic, reddish purple flowers (P. glaberrima ‘Morris Berd’), purplish-pink flowers of P. x ‘Forever Pink’, large leaf P. amplifolia, and P. x ‘Minnie Pearl’ (pure white).

Three P. paniculata favorites:

‘David’ – large, pure white, fragrant flowers; foliage is highly mildew resistant; 2002 Perennial Plant of The Year

‘Delta Snow’ – grows 3-4 feet tall. Fragrant, snow white tubular flowers with purple eyes; mildew resistant foliage.

‘Jeana’ – long blooming summer phlox cultivar; deep green foliage is topped by conical lavender-pink flowers and mildew resistant foliage.

All three varieties make colorful additions to fresh cut flowers.

Calibrachoas (Million Bells*)

Posted by Hugh on May 16th, 2020

Gardeners have discovered Million Bells* (Calibrachoa x hybrida), a small flowering cousin of the petunia. Million Bells are prolific bloomers and produce one-inch mini-blossoms. They were first marketed to home gardeners in the 1990’s. They’re native to Peru, Brazil, and Chile, and are commonly grown as annuals in the U.S.

Over the past twenty years plant breeders have increased the range of bloom colors, bigger flowers, and improved plant vigor. Plants display a low sprawling habit reaching 12-24 inches in width and 6-12 inches in height. Trailing varieties extend up to 30 inches in length. Million Bells bloom best with at least six hours of sun, and can tolerate partial shade.

Blooms include solid and bicolors, stripes, patterns, and doubles. Million Bells are available in all shades of the rainbow. Plants are prolific bloomers with self-cleaning flowers, so no deadheading needed.

Container mix at NC Arboretum, Asheville, NC

These cool tolerant annuals can be set outdoors in early to mid-spring in most localities – literally during spring frosts until early autumn. Grow them in containers or hanging baskets, or plant in front garden borders and in raised beds. They can be planted in bedding displays providing the amended soil is compost-rich with good moisture drainage.

Occasionally, pinch back growing tips to encourage branching and more flowers. To rejuvenate plants in mid-summer, cutback branches to half their length and fertilize to spur new growth.

General care: Million Bells are heavy feeders and should be fertilized regularly for prolific, continuous bloom. Use a water-soluble fertilizer such as Miracle-Gro™ or Jacks™ every two weeks as recommended, or add a slow-release granular fertilizer such as Osmocote® or Nutricote®. Foliage color looks best when the soil pH is maintained between 5.5 and 6.0. If the soil or media pH gets too high, leaves will turn yellow (chlorotic). Irrigate during hot weather, particularly containers which can dry out quickly.

Overwatering can lead to root rot. Heat stress can make plants susceptible to spider mites, and aphids. Million Bells are not particular favorites of deer, but are not deer resistant.

Million Bells combine well with most annuals. They are also great container fillers with perennials such as coral bells (Heuchera), sweet flags (Acorus), or sedges (Carex).

*Million Bells® is the common name for Calibrachoa, a trademarked name of Ball Horticulture, Inc.

The Mountain Mints – The Pollinators’ Favorite

Posted by Hugh on May 11th, 2020

Mountain mints (Pycnanthemum spp.) are clump-forming native perennials. They typically grow 1-3 feet tall depending on species (USDA hardiness zones 4 – 8). About 20 species of mountain mints are found in the southeastern U.S. As their name suggests, they belong to the mint family, very evident by their square stems and aromatic leaves when crushed. Botanically, they’re also closely related to beebalms (Monarda). Mountain mints grow in open woodlands, dry prairies, and grassy meadows.

Mountain mints are rhizomatous perennials that grow 2 to 3 feet tall and spread as wide as site conditions allow. Their slender upright stems have oppositely arranged leaves that are either broadly lanceolate in form or narrow and willow-like in appearance.

Only two mountain mint species will be highlighted here. Slender mountain mint (P. tenuifolium), also called common horsemint or Virginia thyme, is easily identified by its narrow, almost needle-like foliage and are covered with small ¼ inch white tubular flowers with purple anthers in mid-summer (in Tennessee).

Number two is short-tooth mountain mint (P. muticum) which grows slightly more compact and its growth rate is more aggressive. Its foliage is very different and more lustrous, 1-3 inch long, broader (½ -1 inch across) and pointed leaf tips. Clusters of tiny tubular white to pinkish flowers appear in mid-summer. Flowers are accompanied with showy frosted (silvery) bracts.

Blooming period lasts 4-6 weeks, from early to mid-summer. Leaves emit a mild mint fragrance and flowers are not fragrant. Slender mountain mint is highly rated by the Xerces Society, with designated “Special Value” to Native Bees, Bumblebees, and Honey Bees. Flowers of mountain mints attract a wide range of insects including many kinds of bees and butterflies.

For best flowering, mountain mints should be grown in full sun, but do tolerate light shade. Slender mountain mint is rated as more drought tolerant. No serious insect or disease problems trouble the mountain mints. Foliar rust disease may occur in wet summers.

Easily grown from seed, these two species can be started indoors in late winter. OR, sow seeds outdoors after the threat of frost has past in your area; plants should be well established by the end of their first growing season. Established plants have a taproot and spread via rhizomes. Control their spread by mowing or trimming. Mountain mints are easily propagated by cuttings and clump division.

Mountain mints naturalize freely in native plant gardens, butterfly gardens or meadows, garden borders. The foliage is a natural mosquito repellent; the minty leaves can be added to teas.