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

Summer Blooming Golden Raintree

Posted by Hugh on June 1st, 2022

Golden raintree (Koelreuteria paniculata)is a medium sized deciduous tree that grows 30 to 45 feet tall and 25-35 feet wide, a horizontally branched tree Zones 5-9). This tree has a medium to fast growth rate, blooms at an early age with upright twigs with yellow flowers, a rare color among flowering trees whenever the time of year. The bright star-like flowers sparkle for almost two-weeks long in early July (Tennessee/Virginia).

The tightly closed papery fruits are highly decorative and often included in dried floral arrangements. Its papery lantern-like fruits contain viable seeds that dehisce (explode) from the husks in late autumn.

Golden raintree tolerates a range of soil types but prefers moist, well-drained soil that is neutral to slightly alkaline. Raintree transplants easy and prefers full sun. The wide spreading branched tree is commonly planted in lawns and patios or as park, shade or street trees.

Identification features: Leaves are pinnate or bipinnate, feathery, compound leaves (to 18″ long), each leaf having 7-17 irregularly deeply lobed leaflets. Leaves emerge pinkish bronze to purplish in spring, mature to a bright green in summer and turn yellow (quality variable) in fall. Bright yellow flowers (1/2″ wide) appear in early summer in long, terminal, panicles (12-15″). Falling blossoms from several raintrees may lay down an attractive golden carpet around the trees. Stems also have prominent, shield-shaped leaf scars.

This great summer flowering tree tolerates summer heat and drought as well as urban air pollution. It is mildly resistant to deer injury and is pest and disease free. Sometimes suffers from coral spot fungus, root rot, and cankers. Branches are rated as brittle wood and may be damaged in seasonal storms. Golden raintree reseeds easily and can become weedy; listed as an invasive species in some states.

Cultivars: ‘Fastigiata’ has a narrow upright habit, 30 feet tall and 6 feet wide framework. ‘September’ blooms later in August-September and is not rated as cold hardy as species.

Cinnamon Clethra

Posted by Hugh on May 27th, 2022

*Clethra barbinervis* growing at the High Line in NYC

Japanese clethra (Clethra barbinervis) is a large, upright, deciduous shrub or small tree (USDA 5-8). As a small tree it generally grows 10-20 feet tall and features horizontally drooping, terminal racemes (4-6 inches long); the white flowers are pleasantly fragrant. Its bloom period continues over several weeks from mid to late summer. In autumn, its blemish-free, glossy, dark green foliage turns brightly yellow, sometimes taking on reddish tones.

This Asian clethra is larger in all respects than our native sweet pepperbush (Clethra alnifolia). As a multi-branched shrub, it typically grows 8 to 12 feet tall. In early summer, the small ivory flowers appear and later give way to peppercorn-shaped seed capsules borne on the branch tips in fall. The dark brown seed capsules persist through winter.

By mid-autumn the bark begins peeling off in small, irregular patches to expose a cinnamon inner-bark. It is often nicknamed “cinnamon clethra”. It is the plant’s most striking feature. As the tree ages, its polished exfoliating cinnamon bark stands out against newly fallen snow.

Clethras grow in average, medium to wet, well-drained soil in full sun to part shade. Shrubs prefer partial shade and moist, humus-rich, slightly acidic soils. In northerly climes (zone 5), the Asian form should be grown in locations protected from harsh wintry winds and where it may not be reliably hardy.

Cinnamon clethra is a good choice for a woodland garden. Flower spikes are less fragrant than those of C. alnifolia, but attract butterflies and bees. No serious insect or disease problems trouble this tough multi-branched shrub or small tree.

Japanese clethra is rarely sold by local garden centers but is available from on-line specialty nurseries.

Adding Compact Summer Flowering Shrubs

Posted by Hugh on May 24th, 2022

Yes, to reduce annual garden maintenance some gardeners are switching to space-saving flowering shrubs. Patio gardeners are popping compact shrubs into containers such as spireas, hydrangeas, crape myrtles, chaste tree, weigelias, and buddleias. They’re looking to add color and reduce their maintenance workload.

Numerous new [rose] varieties have been created that are relatively resistant to the defoliating fungus disease black spot that allows them to grow and flower non-stop for several months. They’re indeed easy to care for and highly fragrant.

Roses have changed so much over the past quarter century. More buyers are opting for the easy growing species roses such as Brindabella™, Oso Easy® and Flower Carpet® series, ‘Ringo’, ‘At Last’, and lots more. Many are very fragrant.

Many panicle hydrangeas (Hydrangea paniculata) bloom in July and, color-wise, the blossoms age gracefully, beautiful over two plus months. Best in the group are: ‘Bobo’, ‘Little Quickfire’, and reblooming H. serrata ‘Tuff Stuff’ and hybrid ‘Arriba’.

Dwarf chaste tree (Vitex agnus-castus) are now available in shorter forms. Breeders are just starting to work on these plants. Blue Diddley® and Blue Puffball™ are currently available and more are coming. Both varieties grow only 3-4 feet tall and 4-5 feet wide, a mound-shaped plant with deep blue, fragrant flowers from June to August. Flowers form on new growth. In colder climates dwarf forms can be used as a perennial or dieback shrub and emerge with new fresh growth in the spring.

Butterfly bush (Buddleia) have changed so much. I am in love with the Lo and Behold® and Pugster® series from PW and Walters Gardens’ Cascade series. The flower panicles are enormous at 12-14″ long and 4″ thick. The flower panicles continue to sprout new shoots until the cool fall weather arrives.

Vitex ‘ Blue Diddley’ (Photo courtesy of PW)

Whale’s Tongue Agave

Posted by Hugh on May 21st, 2022

Whale’s Tongue Agave

Over the past 10-15 years, interest in growing agaves has really caught fire, whale’s tongue agave (Agave ovatifolia) in particular. It grows to 3 to 4 feet tall and 4 to 6 feet wide in 5 to 8 years, especially with summer water. Like many agaves, whale’s tongue blooms after 15-20 years, and the main crown dies after blooming.

Whale’s tongue agave has distinguishing blue leaves, arranged in a spiral rosette. Leaves are cupped and can vary from long and narrow (24 inches x 8 inches) to short and broad (18 inches x 10 inches). The grand undulating leaves are lined with dark brown curved teeth measuring one-quarter to one-half inch in depth and end in a terminal 1- to 2-inch spine.

Whale’s tongue blooms only once. Sometime between 10 to 20 years, Whales’s tongue ends its life with a spectacular floral show. A multi-branched flower stalk arises 10 to 15 feet high with densely clustered chartreuse flowers. The resulting seed pods develop and mature before frost. Thereafter, the entire plant dies. Unlike most agaves, whale’s tongue does not produce offsets (pups).

Flowering Stage: whale’s tongue agave at Dallas Arboretum

Site selection is highly important. Agaves are exceptionally drought tolerant and suitable for xeric gardens. Whale’s tongue agave looks awesome in mass plantings. Agaves possess a large tap root and do not transplant well. The majority of the roots are surface roots and do not require a deep hole at planting.

Never overwater agaves! In fact, agaves perform best in high porosity soil. Agaves are highly drought tolerant and soil drainage, either in the ground or a container. They grow happily in soil with average to low fertility and in full sun to dappled shade. In a ground bed plant on a slope in soil generously amend to soil with crushed gravel, gritty sand or chit.

Agave hardiness is the most important concern (USDA hardiness zones 7-11) and in a protected area of zone 6b. When planting in clay soils, deeply amend bed or container soil with coarse sand or pea gravel in a 50:50 ratio. In early spring apply a slow-release fertilizer.

Two clones are available from tissue culture: ‘Frosty Blue’ (gray to powdery blue leaves) and ‘Vanzie’ (soft blue-gray leaves). Seed produced agaves vary in plant color, shape and size.

Caveats: keep plant(s) away from heavily trafficked areas. Agaves have dangerously sharp vicious spines; humans and pets need to be kept apart. Agaves attract birds, hummingbirds, and are deer resistant.

Silk Tassel Sedge

Posted by Hugh on May 17th, 2022

‘Silk Tassel’ Japanese sedge is an outstanding Japanese sedge cultivar of Carex morrowii temnolepis. It is ornamentally grown in shade areas for its narrow (1/8 inch wide) variegated foliage (USDA hardiness zones 5 to 9). This dense, grass-like clump grows 12 inches high and 1 to 1 ½ feet spread.

‘Silk Tassel’ sedge on The Ohio State Test Garden in Columbus, OH

Let’s start with an old well-worn adage — “sedges have edges”. ‘Silk Tassel’ has ultra-narrow leaves, that weeps as a fountain of fine-textured foliage. In mid-spring greenish-brown flower spikes arise atop triangular stems and are of no consequence. This sedge is evergreen in the deep South, holding its attractive foliage in summer, fall and much of winter.

Silk Tassel was introduced and named by Barry Yinger who brought it from Japan. The 18-inch-wide clump is deer-resistant and shimmers in the winter garden. ‘Silk Tassel’ lights up the woodland garden either utilized in a mass planting or several individual specimens spaced around a garden pond.

Silk Tassel tolerates moderate sunlight if the garden soil starts out humus-rich and is mulched in summer; otherwise, plant in partial to full shade. Foliage hues are cooler under shady conditions and appear washed-out in partial sun. Soils should not be permitted to dry out. Plants generally dislike hot and humid summers. In the northern part of its range, crop foliage down to the ground in late winter.

No serious insect, occasionally aphids, and diseases trouble sedges and, to repeat, deer tend to leave sedges alone

Group or mass as a ground cover in shade areas such as along paths and borders in woodland gardens. Also, an appropriate choice for low areas that may flood for short 1–2-day periods like low spots and stream/pond edges.

Annual growth rate is slow. Don’t wish to wait…buy in 1 or 2-gallon sizes to fill-in the planting more rapidly. Keep the media evenly moist. Avoid overwatering. Fertilize using a slow release, low-rate fertilizer.

Silk Tassel is a super companion accent plant added to containers on decks and patios and gardens. Use as a “spiller” in decorative containers next to hostas, coral bells (heuchera) and other bold-leafy plants.

Lion’s Tail

Posted by Hugh on May 11th, 2022

Lion’s tail (Leonotis leonurus) is a tropical plant native to south Africa (USDA hardiness zones 8-11). I have seen used as a late summer – fall blooming annual in public gardens. Lion’s tail’s bright burnt orange flowers are standouts and receive great notice. The common name “Lion’s Ear” comes from the flowers resembling the color and shape of a lion’s ear.

Lion’s Tail (*Leonotis leonurus*) at Longwood Gardens

Lion’s Tail is a semi-evergreen upright shrub in the mint family with a woody base and herbaceous stems. It boasts very showy rings of bright orange hairy two-lipped tubular flowers. Utilize as a cut flower in floral arrangements. Indigenous to South Africa, this plant is tolerant of extreme heat, drought, and dry soils. Where hardy, plants may freeze to the ground in winter and often resprout from hardened wood in the spring. Mulching the crown in winter aids to perennialize the plant. Prune annually after flowering to maintain a bushy dense shape.

Lion’s Tail at Chanticleer Garden, Wayne PA

Give this 4-6 feet tall and wide plant adequate room to grow in full day (in 6 hours minimum) sun and well-drained soil with average moisture. Hairy tubular orange flowers in whorls with two lips appear late spring through fall. The plant is also moderately drought tolerant once it has been established in spring and early summer planting.

Lion’s tail should be grown in a spacious garden location or container. The plant is disease and pest-free as well as deer resistant. Its tubular orange flowers attract hummingbirds, as well as bees and butterflies. In public gardens it should be coupled with some other fall bloomers like fall sunflowers (Helianthus), late summer-blooming salvias, cannas, and others.

Chinese Fringetree

Posted by Hugh on May 6th, 2022

Chinese fringetree (Chionanthus retusus) is native to China, Korea and Japan (USDA hardiness zones 5-9). As with the native U.S. species (C. virginicus), this plant is noted for its fragrant white flowers. Gardeners first fall in love with this large, multi-stemmed, deciduous large multi-branched shrub. Some nurseries are also offering the Chinese form as a promising 20-30 feet tall, low-branched, (single or multi-trunked), lawn tree.

Fringetrees are primarily dioecious (separate male and female plants), but some perfect flowers do occur. Male flowers are slightly larger and showier. Female flowers (if fertilized) give way to clusters of olive-like fruits (each to 1/2” long) which ripen to a dark bluish black in late summer/fall and are a good food source for birds and wildlife.

Lustrous, leathery leaves are ovate to elliptic and 4” long. Leaves on young plants have serrate margins. Leaves are bright green above and downy whitish green beneath. Leaves turn yellow in fall (reportedly more attractive in northern areas). Exfoliating gray-brown bark is attractive in winter.

Chinese fringetrees require little special attention. Best flowering happens with 4-5 hours of sun. Site the tree in average, medium moisture, mildly acidic, well-drained soil. Young 1–2-year-old trees should be irrigated during dry spells lasting 10 days of more. Pruning is rarely needed. Leaves are tolerant of air pollution and adapts well to urban settings.

No serious disease and insect problems trouble Chinese fringetree. Occasionally, damage from mites, scales and borers have been reported, usually observed during stressful hot dry summers. Leaf spots, canker and powdery mildew diseases may occur as signs of over-irrigation or wet summer weather.

Fringetrees, both the U.S. native and Chinese forms, are rarely sold at local garden centers, but are available in limited numbers at online nurseries. They’re spectacular in full bloom and early evening fragrance is so worth it.

Noted cultivar – ‘Tokyo Tower’ is a narrow upright branched small tree. It grows 12 – 15 feet tall and 4 – 6 feet wide. In the spring (early May), its narrow stature standouts abundant clusters of billowy white flowers followed by blue berry (drupe) fruits ripening after mid-August; dark green foliage turns yellow in autumn. Fall color is variable from one year to the next.

Rough Bark at Biltmore Estates, Asheville, NC

10 Drought Tolerant Perennials

Posted by Hugh on May 1st, 2022

Once established, these ten drought-tolerant plants can cope with hot sun and humidity with low amounts of supplemental water. If you garden in a drought-prone area, or growing in fast-draining raised beds, these drought-resistant plants are a great choice for your garden. Perhaps you wish
to reduce your water bills. Plan to keep plantings adequately mulched during the season.

Purple coneflowers (Echinacea purpurea) are tough and pretty. Purple is the most common flower color, but white, orange, red and yellow varieties are available. New series such as Sombrero®, Artisan™, PowWow®, and Cheyenne Spirit® grow only 16 to 30 inches tall with non-stop blooming from June to September. Leave the dead flower cones to be visited by goldfinches or other birds over winter. (Z 4-9)

Butterfly weed (Asclepias tuberosa) – the iconic, bright orange beauty that’s a staple in every butterfly garden. This showy native wildflower is easy to grow, cold hardy, and does well in poor, dry soil

Yarrow (Achillea millefolium)- dazzling red-violet highlight into your pollinator garden. Compact fern-like foliage softens sturdy upright stems. var. Sassy Summer™series

Lavender (Lavandula x intermedia)- forms a compact shrub with aromatic silvery gray-green narrow leaves with long flowering stems are topped by 5 inch spikes of sweet scented bright violet-blue flowers. Often repeat blooms in late summer or fall. var. Phenomenal™ and ‘Provence’.

English Lavender (Lavandula angustifolia) – compact English Lavender like the varieties ‘Hidcote’, ‘Munstead’, or ‘Superblue’ grows 12-24 inches tall, with highly fragrant, deep purple-blue flowers; best planted for edging walkways and in patio containers.

Red Hot Poker (Kniphofia) – fiery colored flower spikes will lighten up your garden. Red-orange- mango-yellow buds, depending on variety, open from bottom to top. Cutoff spent floral stalks and it reblooms in 4-6 weeks. Try ‘Popsicle™ or ‘Pyromania™ series

Russian Sage (Perovskia atriplicifolia) – dwarf varieties like ‘Little Spire’ and ‘Denim N’ Lace’ tall, airy spires of lavender-blue color on highly-textured silver-gray foliage all summer long. low-maintenance, great choice for xeriscaping. Deadhead for continuous bloom.

Anise Hyssop (Agastache foeniculum) – very long blooming perennial (zones 6-10). var. ‘Blue fortune’, ‘Peachy Keen’, Kudo™ and Poquito ™ series

Feather Reed Grass (Calamagrostis) – creates a dramatic garden accent, with tall, slender, vertical growth and feathery plumes of shifting bronze color that stay in place year-round. var. ‘Karl Foerster’, ‘Avalanche’, ‘Overdam’.

Ground Hugging Sedums – a carpet of changing colors that grow only 4 to 6 inches tall and spreads to 24 inches wide. Popular examples: Sedum spurium ‘Dragon’s Blood’, S. ‘Cherry Tart’; S. reflexum ‘Blue Spruce’, S. ‘Neon’, S. rupestre ‘Angelina’. Leaves of some may take on red-orange-yellowish tones in autumn. Star-shaped yellow, ½ inch wide flowers in summer.

Caveat: this information is not relevant to perennials growing in containers.

Heartleaf Iceplant (Aptenia)

Posted by Hugh on April 26th, 2022

The world of succulents is a treasure trove for many cool garden plants that attract many collectors, including house plant enthusiastics. Heartleaf iceplant (Aptenia cordifolia), also called Baby sun rose, is a non-hardy succulent or evergreen ground cover.

This herbaceous subshrub is indigenous to South Africa and favors a Mediterranea- like climatic conditions (in USDA hardiness zones 9-12). Aptenia is closely related to hardy iceplant (Delasprema cooperi). Both genera are found in the botanical family Aizoaceae.

Heartleaf iceplant loves light, but you may need to shelter leaves from direct sun during extreme heat and dry periods. Keep it moderately watered can potentially harm the leaves. In temperate regions, it is beloved for its thick green foliage in spring-summer gardens and nurtured indoors as a houseplant in a well-lit room. Heartleaf iceplant tolerates to dry periods. Treat it as any other cactus or succulent and water this as you would water others in your home. Avoid extremes of overwatering and drought.

Heartleaf iceplant can be propagated from seeds and by cuttings. Seeds can be purchased online plant shops or snip 4-5-inch-long cuttings from garden plants in early fall before cold weather arrives. Pot rooted cuttings and seedlings in a well-drained soil-less media.

Aptenia creates a colorful foliage and flowering plant. In a garden container, utilize as a filler or a chiller to drape over the edges of containers. Flower colors include red, purple, pink, and white; flowers are comprised of strap-like multi petals.

Four Space-Saving Summer Blooming Shrubs

Posted by Hugh on April 21st, 2022

Miniaturation of many of our garden shrubs has been a trend for over 30 years. A common saying among gardeners has been they no making any more land making anymore or, in this case, garden planting space. In particular, urban gardeners continue to squeeze more color into limited spaces. Here are four flowering shrubs that are very successful.

Chaste tree (Vitex agnus-castus) is now available in shorter shrub forms. Standard Vitex growing to 15-25 feet. Spikelets of lavender-blue flowers appear in mid-summer. Thus far, varieties Blue Diddley® and Blue Puffball’™ are available, but many other varieties, including white and pink-flowering forms, are coming. ‘Blue Puffball’ grows only 3-4 feet tall and wide in a near perfect ball-shaped plant with deep blue, fragrant flowers from June through September. ‘Blue Diddley’ grows 5-6 feet tall. Flowers form on new growth. In the north (zones 5-6), Vitex performs as a perennial and dies back to the ground; it regrows and flowers much like a butterfly bush (buddleia). (Non-native)

Cherry Dazzle® or Berry Dazzle® Crapemyrtles (Lagerstroemia indica) have proven to bloom reliably from one year to the next in zone 6. Plants require minor cleanup pruning in early spring and a handful of 10-10-10 fertilizer. Bot cultivars grow 3 to 3.5 feet tall and are covered with red flowers in midsummer (late July-August). (Non-native)

Pugster® series of Buddleia x davidii) is a new compact plant, only 2 ft. tall and wide but with the full-size flowers on sturdy stems. The Pugster series bloom non-stop from early summer through frost with true-blue flowers, each with a tiny yellow-orange eye in the center. The Pugster® series is available in four colors: Pugster Blue, Pugster Periwinkle, Pugster Pink, and Pugster White. All cultivars offer vastly improved cold hardiness and winter survival over other types of dwarf butterfly bush (zones 5-9). (NonNative)

Wee White® Smooth hydrangeas (Hydrangea arborescens ‘Wee White’) is a dwarf ‘Annabelle’ like hydrangea, just 1-2.5 feet tall. The shrub develops into a tidy, rounded mound. Flowers emerge a soft, blush pink before changing to white on a sturdy stem. All new flowers develop from early summer to frost. (Native)

Bobo® Panicled hydrangeas (Hydrangea paniculata ‘Bobo’) grows only 3 feet tall, along with large creamy white summer flowers held upright on strong stems. Flowers finish with a pinkish hue in fall. (Non-native)