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

Zone 6 Hardy Camellias – Plant Now!

Posted by Hugh on September 1st, 2019

More and more people gardening in zones 6 and 7 have discovered that they can successfully grow camellias. Once considered an exclusively Southern plant, many camellia varieties are very cold hardy where winter temps drop to 0 to 5°F. Their floral buds burst open with bright whites, pink and red shades, and spotted color blends.

Camellias offer beautiful garden color through the mid-South (Kentucky, Tennessee, North Carolina, and northern areas of Alabama and Georgia) and warm sections of the middle Atlantic States (Delaware, Maryland, Virginia. Planting zone 6 camellias from spring thru early September allows the root systems to grow out before the cold weather arrives.

For example, if air temperatures were to drop suddenly and plant roots were shallow in November, some flower and leaf buds will abort prematurely. A deeply-rooted evergreen camellia, one that is also adequately mulched, will succeed in a frigid winter.

Camellias grow well in partially shaded garden area where the plant(s) are sheltered from direct sun and wind. The planting site should be well-drained with an acidic, compost-rich soil. These plants prefer a moist soil, but do not over-water camellias. Add a 2-3 inches of an organic mulch around the base of each plant. Feed camellias lightly with a water soluble acidic fertilizer such as Miracle-Grow™ at planting time in late summer. Clip off any dead or broken branches.

Ten reliable zone 6 hardy camellia varieties are:

‘April Remembered’ blooming in mid-April

Spring Bloomers — ‘Pink Icicle’, ‘April Dawn’, ‘Artic Rose’, ‘April Remembered’, and ‘April Tryst’.

Fall Bloomers — ‘Winter’s Snowman’, ‘Winter’s Star’, ‘Snow Flurry’, ‘Long Island Pink’, and ‘Londontown Blush’.

Camellias are relatively deer-resistant. Most garden diseases and pests do not trouble camellias when plants are properly sited and cared for.

Wood’s White Aster Are Woodland Favorites

Posted by Hugh on August 26th, 2019

It’s late August and across the Southern Appalachian region White Wood Aster (Eurybia divaricata) are blooming. Their small daisy flowers are often seen blooming in shady woodlands in late summer. They start blooming a week or two later in the New England states and Canada (USDA hardiness zones 3-8).

In a natural woodland Wood’s Aster grows 1 ½ feet to 2 feet tall (2-3 feet in gardens). You can also identify them for their maroon (blackish) sprawling stems. The tiny long-petioled leaves are heart shaped and toothed. The smallish but plentiful white flowers measure 3/4-1 inches wide.

This trouble-free woodland aster grows in average, dry to medium, well-drained soil in part-sun, part-shade, or shade. Established plants are tolerant of dry shade. Good air circulation and an hour or two of morning sun help reduce any outbreaks of foliar diseases. Their numerous flowers attract bees and butterflies and deer don’t appear to bother white wood aster.

Wood’s white aster is available from nurseries selling native plants. Try them in rock and woodland gardens, containers and in flower beds. To increase flower numbers pinch (or mow) back plants 1-2 times in late spring to early summer to develop a compact plant habit.

This woodland aster blooms in summer’s heat and humidity and is highly tolerant to disease and pest problems. In cultivation it tends to self-sow and may become weedy.

Once established, white wood’s aster handles difficult landscape sites including clay soils and dry shade under trees and shrubs or on shaded slopes.

Editor’s note: not to be confused with Wood’s Purple Aster, aka New York aster (Symphyotrichum novi-belgii ‘Wood’s Purple’) which bears 1 to 1 ¼ inch medium violet flowers from mid-late September and grows 14-16 inch high plants.

Rose Of Sharon ‘Pillar’ Series –Floral And Architectural Splendor

Posted by Hugh on August 21st, 2019

RRose of Sharon (Hibiscus syriacus), aka althea, is a popular summer flowering shrub and small tree (USDA hardiness zones ((4)5-8). In northerly areas of the U.S., rose of Sharon may also be cultivated as a sun-loving perennial. The species grows 8-12 feet high and 6 -10 feet wide in full sun and in average garden soil. Shrubs, native from China to India, are drought tolerant once established for one year.

The Rose of Sharon (Althea) Pillar® series represents two unique columnar shrubs. Both cultivars, White Pillar® (white flowers) and ‘Purple Pillar® (lavender flowers), grow 10-16 feet tall and only 2-3 feet wide.

The Pillar althea series develop few to no side branches with little or no pruning needed. As the shrubs age, some minor spring pruning may be needed to maintain the narrow columnar form. During seasons of excessive rainfall, rose of Sharon may grow too vigorously and splay open. You may opt to clip off to hold the narrow look.

Plant in multiples of 3 or more for a formal front entrance. A lone plant standing by itself may serve as a landscape focal point. Plant in containers and grow on a sunny deck or patio. Perhaps you wish to conceal an unsightly utility box or create a short hedge or living privacy fence between you and your neighbor. Pillar altheas don’t take up lots of space width wise, perfect for a small urban garden or narrow planting spaces.

Rose of Sharon bloom on current season’s wood from late June thru August. Young plants start to bloom early. Its light purple blossoms of Purple Pillar feature deep red centers that really stand out in the garden and are stellar additions to cut flower arrangements. White Pillar bears snowy white blooms.

Their colorful flowers attract bees, butterflies, other pollinators, and an occasional hummingbird. This tough cold hardy shrub plant holds up well to heat and dry weather and deer don’t bother these shrubs. In some areas of the U.S., Japanese beetles may be an occasional pest.

Six Perennials To Include In Your Garden

Posted by Hugh on August 16th, 2019

I continue to report to you on plants that perform. I am quick to eliminate plants that don’t live up to expectations.Here are six topnotch perennials you will enjoy in your garden for many years.

Arkansas bluestar (Amsonia hubrichtii) grows into a 2-3 feet tall arching clump of soft, feathery green leaves. Blue starry flowers appear in late April into May (in Tennessee). This sun-loving plant is long-lived. Light green fine needle-like summer foliage turns an exceptional bright golden color in fall. 2011 Perennial Plant of the Year. (Z 6-8).

‘Gold Standard’ coreopsis (C. tripteris ‘Gold Standard’) is an unusually tall growing 5 – 7 feet high coreopsis. Starting in late July, multitudes of sunshine yellow flowers stand tall on sturdy wiry branches The bright floral display stands out over 2-3 months. ‘Gold Standard’ has a rhizomatous spreading habit, about 2 feet over 3 years. (Z 3-8)

‘American Gold Rush‘ blackeye Susan (Rudbeckia x ‘American Gold Rush’) is a compact hybrid cultivar, only 24 inches high compared to taller ‘Goldsturm’. Its narrow 2-inch wide hairy leaves are highly resistant to Septoria leaf spot disease. Bright, yellow-gold flowers cover the plant from July to September and attract lots of pollinators. Z 3-8

‘Glamour Girl’ Summer Phlox (Phlox paniculata ‘Glamour Girl’) bears large panicles of hot coral pink flowers that attract butterflies and hummingbirds. Flower heads are supported on strong 30 – 36 inch dark purple stems. This standout cultivar exhibits bright green foliage with good mildew resistance all season long. Z 4-8

Allium ‘Millenium’ is rhizomatous clumping onion with globe-shaped floral heads full of tiny rosy-purple florets. Compared to bulbous alliums, Millenium does not self-seed readily and is a lot less weedy. Flowers grow 16 – 18 inches tall and blooms are particularly attractive to butterflies. 2018 Perennial Plant of the Year. (Z 5-8).

White Cloud muhly grass (Muhlenbergia capillaris ‘White Cloud’) is a native ornamental grass that delivers quite a show in early fall. White billowy flower heads (inflorescences) stands tall on sturdy erect 4 feet tall stems along with blue-green foliage. Its bloom period begins a few days after pink muhly grass (M. capillaris). (Z 6-10).

Katsura Trees For Urban Plantings

Posted by Hugh on August 11th, 2019

Hooray! American gardeners are finally becoming savvy about Katsura tree (Cercidiphyllum japonicum) as one of the finest landscape trees. This medium to tall growing tree (height depending on cultivar) possesses four-season appeal. Numerous varieties are now available. Small growing cultivars will be featured here.

Katsura tree is indigenous to Japan and China where some may reach an incredible 100 feet tall (USDA hardiness zones 4-8). In the U.S., it is a long-lived majestic 40-60 foot high tree. It exhibits a pyramidal form in its early years. Some aged specimens at some American botanical gardens are easily 75 feet tall.

The species is dioecious, e.g. separate male and female trees. The tiny flowers are mostly inconspicuous and small pods with numerous winged seeds are dispersed from female trees in late fall. Katsura tree is not invasive.

Its beautiful heart-shaped soft green summer foliage transforms to purple and gold shades in autumn. After the leaves shed in the fall the tree’s lovely symmetrical branching and scaly/shaggy bark is exposed. Often, the fall air holds a cinnamon scent reminiscent of cotton candy or a sugar-cookie.

‘Red Fox’ Katsura at Atlanta Botanical Gardens

Katsura Cultivars for Small Urban Landscapes:

‘Red Fox’ (‘Rotfuchs’) – exhibits new red spring foliage that becomes dark purple-green in summer.

‘Claim Jumper’ – a relatively new gold-leaved variety that grows 25-30 feet (8-10 m) and 20 feet wide. Leaves emerge with a pink blush and unfurl to soft, golden-yellow. Gold leaf color is lost by late summer.

‘Heronswood Globe’ – a small 15 to 20 feet tree with a rounded canopy, a good fit in a small urban landscape.

‘Raspberry’ – small 14 feet tall x 7 feet wide in 10 year; foliage turns a rich raspberry red fall color.

‘Tidal Wave’ – small weeping form that eventually grows to 20 feet and slightly wider

Katsura tree prefers a moist well-drained soil and full sun to part-shade. Its growth rate is equal to sugar or red maples. Seasonal soil moisture is most important. Newly planted 1-2 year old trees are particularly prone to leaf scorch in dry soils. Over the first 2-3 years following planting, supplemental irrigation should be provided.

Katsura are rarely troubled by serious pests or disease problems. Katsura tree and cultivars should be available at full-service garden centers, but sharp early shoppers are likely to buy up the inventory. Rare or new cultivars, some that are listed here, are sold by on-line specialty nurseries.

New Inkberry Varieties Substitute For Boxwoods

Posted by Hugh on August 6th, 2019

Inkberry holly (Ilex glabra) is a slow-growing evergreen shrub (USDA hardiness zones 5-9). This U.S. native hale from coastal Canada south to Florida, and west to Louisiana. Commonly, inkberry (the species) grows to 5-8 feet tall. It is at home in sandy woodlands and the edges of swamps and bogs where they form colonies via root suckers.

Two new varieties from Proven Winners® and Spring Meadow Nursery are Strongbox® and miniature Gem Box® , both growing only (24 – 36 inches tall and wide). Ideal for container planters! Strongbox shape is abit squat at the top than Gem Box. Utilize both as boxwood substitutes if you’re concerned about boxwood blight disease. Both varieties are densely branched with a low compact growth habit; they may lightly root sucker.

Inkberry hollies are undemanding., growing in average, medium to wet, acidic soils, and in full sun to part shade (4 hours minimum). It is one of few hollies that tolerates wet soils. Inkberries are dioecious, either male or female tiny white flowers. Black drupe (berry-like) fruits develop in the fall and persist through winter unless consumed by birds and other wildlife.

Inkberry hollies are popular hedging shrubs. Prune in early spring before new growth begins. Gem Box and Strongbox cultivars rarely need much pruning. Remove root suckers if undesired.

Inkberry is highly resistant to insect or disease problems, and winter burn. Leaf spotting occurs in wet summers. Spider mites may appear, especially during dry weather.

Fertilize in spring with an acidic water soluble fertilizer such as Holly-Tone® or Miracle-Gro® In high pH (alkaline) soils, foliar chlorosis (yellowing) may occur. Spider mites may appear, especially in dry conditions.

Mass or group several inkberry hollies as a shrub border or as a low foundation planting. Species inkberries will naturalize in moist woodland gardens or near streams or ponds.

Tall Stonecrops (Sedums)

Posted by Hugh on August 1st, 2019

Sedum ‘Autumn Joy’

Sedum ‘Matrona’ at NC Arboretum, Asheville, NC

Stonecrops (Hylotelephium spectabile) are tall clumping sedums. They are frequent seen in their habitat growing on rocks or stony ledges. Also written as Sedum spectabile, many varieties grow 1.5 to 2 feet high. Approximately 33 species of these drought-tolerant herbaceous perennials are found to Asia, Europe and North America (USDA hardiness zones 3-9).

Stonecrop make excellent plants for the late summer – fall garden. Their late season flowers attract butterflies and other pollinators. Foliage and spent floral heads persist well into the winter providing some architectural interest.

Stonecrops like it “mean and lean”; set plants in average well-drained soils and under full sun. Plants thrive in sandy to gravelly soils under moderate to low fertility. Under light shade or in rich organic soils, stonecrops produce weak floppy shoots. Also, they decline in wet soppy soils.

They are easy to propagate by divisions in spring or from stem cuttings in early summer. To build up a large collection cheaply, detached leaves can be rooted in coarse sand that eventually form new plants. Plants may be cut back in late spring to control height.

Generally, serious insect or disease problems are rare. Slugs, scales, mealybugs, nematodes, and aphids are occasional pests.

Sedums provide winter interest and food for birds. Plant them in front garden borders, containers, and rock gardens. Mass several together for a colorful show.

Popular varieties:

‘Autumn Joy’ (‘Herstfreude’) – a very popular variety; blooms emerge pink, gradually change to deep rose-red and finish coppery-rust. Flowers are variable in size, 3-6 inches across, flattened heads (cymes), typically 1.5 to 2 feet tall.

‘Autumn Fire’ – an improved ‘Autumn Joy’, slightly taller and sturdier, less floppy stems.

‘Brilliant’ – tiny, star-like, carmine flowers, 3-6 inch flattened blooms atop grayish-green stems; plants form upright to slightly spreading clumps to 18 inches in height.

‘Matrona’ – strong, shiny red stems hold large, pale pink flower heads which last well into the fall season; noted for its deeper gray foliage and strong, erect purple stems.

‘Neon’ – (perhaps a sport of ‘Brilliant’) typically grows in upright to slightly spreading clumps to 15-20 inches tall. It grows slightly shorter than Brilliant with more steadfast magenta flower color and slightly larger bloom heads.

July Blooming Plumleaf Azalea

Posted by Hugh on July 28th, 2019

Plumleaf azalea (Rhododendron prunifolium), a deciduous azalea native to Georgia and Alabama, is a particular summer favorite (USDA hardiness zones 6-9). It’s hardy even in Boston, NY City, and Philadelphia. Its bright orange-red blooms surprise in late July to early August. Compared to many fragrant spring blooming native species, flowers emit no scent. Its autumnal leaf color is uneventful.

New red blooming form (Photo by V. Abney)

This 5-8 feet tall and wide shrub is best protected from summer ‘s harsh afternoon sun. Planting on a north or east facing site and in mildly acidic, well-drained, compost rich soil is ideal. Plumleaf azalea appears to prospers calcareous clay soils found in the Eastern Tennessee and Western NC without pH correction.

Irrigate plants the first two years of establishment. Set the shrub into a wide, shallowly dug hole which has been generously amended with compost and/or peat; maintain 2-3 inches of a bark chip type mulch around the shrub base.

Plumleaf azaleas are generally sold at native plant on-line nurseries. Purchase and plant by late summer so that the fine shallow roots get deeply knitted into the soil before winter arrives.

Plumleaf azalea is the signature plant of Callaway Gardens in Pine Mountain, Georgia where I initially purchased the plant which has prospered in my northeast Tennessee garden the past 28 years ago. A new red flower form is becoming more available (see photo).

Plumleaf azaleas bloom on new current season’s wood. Prune this summer bloomer anytime after flowering to maintain desired height and spread.

Why My Hydrangeas Are Not Blooming

Posted by Hugh on July 23rd, 2019

Thankfully, this is not a very common problem that few gardeners run into. U.S. gardeners grow four (4) species of hydrangeas: smooth hydrangea (Hydrangea arborescens), oakleaf hydrangea (H. quercifolia), bigleaf hydrangea (H. macrophylla), and panicle hydrangea (H. paniculata).

There are five reasons why some hydrangeas don’t bloom:

1. Type of hydrangea… Bigleaf hydrangeas, those that produce blue or pink flowers, are the most troublesome. Lots of cultivars are available, some that are very winter hardy and others not so much. If winter temps in your region are extremely low, plants may die back to the snow line or to the ground. Bigleaf hydrangeas bloom on both old (last year’s) and new (current season) wood. Loss of the old wood results in your hydrangea blooming only in late summer on current season’s wood. No flowers may mean that the variety that is not reliably hardy in your zone.

2. Not enough sunlight… The site should receive 3-6 hours of direct sun daily. Panicle hydrangeas require the most sunlight and oakleaf hydrangeas and smooth hydrangeas as little as 2 and 3 hours daily respectively. As a rule, more sunlight means more flowers.

3. Pruning at the wrong time… Generally, hydrangeas don’t need pruning other than to control plant size and to remove dead wood. Pruning time is most important. H. macrophylla and H. quercifolia plants are pruned in early summer or in late winter; H. arborescens and H. paniculata are pruned in late winter to early spring before new growth begins. Don’t cut plants back too far. If your hydrangea won’t bloom, skip pruning any time. You may be overpruning.

4. Too much fertilizer… Overfeeding your hydrangeas particularly with too much nitrogen (N) or not enough phosphorus (P) in the soil. High nitrogen levels produce lush green growth, but little to no blooms. Phosphorus is responsible for the flowering and fruiting in most plants.

5. Deer… If you live in an area with deer, their feeding may prevent your hydrangeas from blooming. One solution is to construct a 6 foot (or higher) fence around your garden.

Five Shrubs Make Wonderful Small Trees

Posted by Hugh on July 18th, 2019

Multi-trunk rose of Sharon tree

With some aggressively growing shrubs, it frequently comes down to you (and your pruners) versus the plant.

Technique: a sharp pair of hand pruners along with 3-4 times annually to train a large unruly shrub into a behaved small tree.

Here is a list of 5 great shrub candidate that may become a great small tree:

Harlequin glorybower (Clerodendrum trichotomum) frequently grows as an unwieldy shrub that is 10 – 15 feet in height and spread and lacks symmetry. Through judicious pruning, you can create a beautiful 10-12 foot specimen tree that blooms in September. (USDA hardiness zones 6b-10).

Ninebark (Physocarpus opulifolius ‘Diabolo’ is a vigorous ninebark cultivar with deep burgundy maple-like foliage and an upright, spreading habit. ‘Diablo’ninebark also boasts pink-tinged, 2- inch wide white flower clusters in late May or June. (USDA hardiness zone (3-7).

Rose of Sharon (Hibiscus syriacus) is an old-fashioned summer flowering shrub which is easily converts into a small single or multi-trunk lawn tree. Flower colors range from snow white, pink, red and purples. (zones 5-8).

PG hydrangea (Hydrangea paniculata ‘Grandiflora’) is an old-fashioned shrub that bears lacy creamy white flowers starting in late July. Its dark green foliage is highly disease and insect resistant. (zones 3-9).

Shoal’s Creek chaste tree (Vitex agnus-castus ‘Shoal Creek’) is a southern favorite that blooms reliably from late June into August. Many cultivars are available; mid-size 12 foot ‘Shoal Creek’ has proven landscape reliability. (Zones 6-9).

Some basic tips: All 5 plants perform well in average well-drained acidic soils and in full to partial sun. All bloom best in full sun. Major pruning should be done in late winter after the severity of the winter weather has been evaluated. Secondary cuts, including root suckers, can be performed in any season to develop and maintain its tree form. Trees may also be maintained in large containers.