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

Explode Your Plant Roots

Posted by Hugh on August 9th, 2011

Dead rootball

One of my gardening frustrations is watching a new plant linger and not grow. I dig a proper hole, deep and wide enough. I pour gallons of water on the plant to keep it alive during a dry hot summer. Four months later, the plant is the same size as last spring or it finally dies!

What went wrong? I dig it up. What I see is a root system which did not grow into good soil in the hole (photo). A friend asks, “did I explode the roots”. He has seen this problem many times at his nursery/ landscape business. He took action. His objective: “no plant, annual, perennial, shrub or tree, goes into a container or planting hole without exploding its root ball.

He uses a brick to bust apart the soil (media) around the root ball. His objective is two-fold: first, to break apart circling or potentially girdling roots; and secondly, to shake off as much soil that the plant is growing in. His goal is to coax new roots to venture out into the surrounding soil in the hole. Some landscape gardeners use a butcher’s knife to slice apart the root ball. He uses a brick.

When purchasing plants from late spring thru fall, assume that the nursery/greenhouse plants are leftovers that did not sell. Plants on sale likely need to be transplanted. The grower/garden center manager does not want to expend time and material to repot it. The grower is passing that chore along to you at a discount price.

‘Morning Calm’ Trumpet Vine

Posted by Hugh on August 5th, 2011

Campsis grandifolia 'Morning Calm'

Our native trumpet vine, aka trumpet creeper (Campis radicans), may instill fear in gardeners. A wild vine may climb a utility pole, 30- 40 feet in one year. The late horticulturist Dr. J. C. Raulston at NC State University in Raleigh recommended its tamer Chinese cousin (C. grandiflora) and the cultivar ‘Morning Calm’.

Trumpetvine climbs and supports itself by strong rootlets or “holdfasts”. Start one on a cedar pole, tying the shoots loosely with cotton cord. Within one year the vine bonds solidly to a wooden trellis, wire fence, or a coarse surfaced brick wall. The trellis should be structurally strong to support the vine’s incredible growth and weight.

The 7-9 leaflet glossy compound leaves are 6-12 inches in length. The vine blooms on new growth and the trumpet-like flowers are clustered in numbers from 6-12, sometimes more. The dark apricot colored flower (corolla) appears from late June thru mid- August. Each trumpet flower measures 3 inches in length when fully open.

Trumpet vine grows in average garden soil, is very heat and drought tolerant, and has few enemies. The vine should be pruned aggressively in late winter. Trumpet vine benefits from liquid feeding with Miracle-Gro™ or an equivalent fertilizer containing minor nutrients.

‘Morning Calm’ attracts numerous butterflies and hummingbirds and is often falsely marketed as “hummingbird vine”.

Hibiscus Sawfly Devastates Plant Foliage

Posted by Hugh on August 3rd, 2011

Hibiscus Sawfly Damage

The hibiscus (mallow) sawfly is a devastating pest of hibiscus (Hibiscus moscheutos) and hollyhock (Alcea rosea). The adult sawflies are small, barely a quarter inch long. They are mostly black, except for a yellowish brown spot on their thorax, and their smoky wings. The pale green larvae mature to 1/2 inch in length.

The larvae turn hibiscus foliage into lacy skeletons. The adult females lay eggs in the upper surfaces of leaves and, at first, produce blister-like bumps. The larvae hatch, move to the underside of the leaf, and begin to feed voraciously. Mature larvae pupate at the base of the plant. Hibiscus sawfly develops up to six generations from mid-spring until frost.

Select one of two control strategies:

foliar sprays of any one of the following insecticides: acephate, pyrethrins, synthetic pyrethroids (such as bifenthrin, permethrin, and cyfluthrin), and spinosad; spray every 7 -10 days or when leaf damage is observed.
soil drench with any insecticide product containing imidacloprid; only one application offers season long control.

Sawfly resistant cultivars may be in the future. Currently, there is no resistance in H. moscheutos, but some in swamp rose mallow (H. grandiflora), and in scarlet rose mallow (H. coccineus).

Related: Blog on ‘Fireball’ hibiscus published June 18, 2011

A Canna Lily Revival

Posted by Hugh on July 30th, 2011

'Bengal Tiger' Canna at Kingwood Center, Mansfield, Ohio

'Australia' Canna at Kingwood Center, Mansfield, Ohio

Depending on where you garden, Canna lily (Canna spp.) is a tropical-looking, herbaceous annual or perennial. Its colorful foliage and long blooming time leaves a huge visual impact. Canna is not reliably winter hardy in the Southern Appalachian region (USDA hardiness zones 6 and 7). Canna relishes moist soils. Container grown plants thrive submerged in a water garden.

Leaves wrap spirally around the main stem(s). Most cultivars have emerald-green foliage, either a waxy (glaucous) or dull (matted) leaf surface. Some exhibit colorful andvariegated foliage. New canna leaves unfurl at night.

Canna flowers from midsummer up to first frost. Cultivar heights range from 5 to 15 feet (and more), depending on the cultivar and its care. Removal of spent flowers stimulates formation of new floral heads. Flower choices range from oft-white, yellow, orange, red, and a mosaic of many colors. Canna flowers are visited by bees, hummingbirds, and butterflies.

Three favorites in the colorful foliage category are ‘Australia’ (purple leaf, red flower); ‘Bengal Tiger’ aka ‘Pretoria’ (yellow/green striped leaf, orange flower); ‘Tropicana’ aka ‘Phaison’ (green, red, purple, gold striped leaf, salmon orange flower).

A serious problem of cannas is virus diseases, which cause leaves to distort or mar the colorful foliage. Leaf roller insects may also build up and become a serious pest in some gardens.

In late fall canna rhizomes are lifted from garden beds and stored in dry peat moss above freezing over winter.

More about “Winter Care of Tropicals” in a late October blog.

Native Plumleaf Azalea Blooms In The Heat Of Summer

Posted by Hugh on July 28th, 2011

: Plumleaf Azalea (Rhododendron prunifolium)

From my garden here is a look today (July 28th) at plumleaf azalea (Rhododendron prunifolium). Plumleaf is an Alabama native, and its orangey red flowers has been growing in my east Tennessee garden for the past 15+ years.

It is hardy to zone 5-b (- 15°F) which includes most of the mid-Atlantic and southern New England states. Plumleaf handles Southern clay and mid-6.0 pH soils quite well. Flowering time is nearly two weeks long, mostly in morning sunlight. A red and pinkish-red flowering selections are now available.

Annual care is minimal, including little pruning, nutrition and watering chores. There have been no disease or insect problems over the years. I admit to irrigating established shrubs during severe dry spells.

Plumleaf azalea may be purchased from most native plant vendors in the Southeastern U.S., several within reasonably close drive of your home or on-line. I purchased my plant, seems like a long time ago, at Callaway Gardens in Pine Mountain, GA .

Move Over AJ, Here Comes T-Rex

Posted by Hugh on July 26th, 2011

'T-Rex' Sedum (photo credit-www.PerennialResource.com)

For nearly half a century, ‘Autumn Joy’ has been the leading “stonecrop” or “live forever” sedum cultivar planted. More than once I’ve heard this saying: “if Autumn Joy won’t grow in your garden, you should try another hobby. ‘T-Rex’ is a terrific new hybrid and ‘Autumn Joy’ is one of its parents. ‘T Rex’ has better resistance to stem rot than many veteran sedum cultivars, including ‘Autumn Joy’.

Compact growing T-Rex barely reaches over two feet in height and its stout sturdy stems support the massive flower heads. The serrated blue-green foliage of T-Rex is another plus.

By mid-July across the Southern Appalachian region (USDA zones 6 and 7), cream colored floral buds have formed, open to light rose pink flowers in late summer, and finish reddish pink in mid-autumn. If left standing, the seed heads provide winter interest and food for birds. Sedums flowers attract copious numbers of bees and butterflies.

T-Rex thrives in any average well-drained garden soil in full to partial (minimum 6 hours) sunlight. It requires no trimming, no deadheading, and no pinching. Very little, if any, watering is required once plants become established. Stonecrop sedums behave very shrub-like and are one of the easiest low maintenance choices.

Torch Lily Has Long Bloom Life

Posted by Hugh on July 23rd, 2011

Torch Lily (Kniphofia spp.)

Torch lily (Kniphofia spp.), aka “red hot poker”, is an easy to grow long-lived perennial from South Africa. Its colorful floral spike (and a little imagination) resembles a fiery torch or sizzling poker, visited often by hummingbirds, bees and butterflies.

New cultivars are mostly hybrids and vary in plant height and flower color. Starting in May one or more floral spikes arise 18 inches to 4 feet in height, depending on the cultivar(s) planted. Color choices include off-whites, yellows, oranges, reds, and blends of two or more tints. From the months of June thru October additional re-blooming follows soon after the spent floral scapes are pruned off.

Torch lily excels when planted in an average well-drained soil. Full to partial (6 hours minimum) sunlight is ideal. Most, but not all, cultivars are cold hardy in the Southern Appalachian region (USDA zones 6 and7). The sharp edged grass-like foliage is evergreen, but tends to take a beating in rough winters. Prune back the entire plant near the soil line in late winter for a fresh start.

A 2-year and older plant clump is both heat and drought tolerant. Every 3-4 years rhizomes are dug and divided either in early fall or late winter. Torch lily has few serious disease and insect problems. Root rot may become a significant problem when planted in a poorly drained soil.

To Grow Crocosmia Or Not?

Posted by Hugh on July 19th, 2011

'Lucifer' Crocosmia at Kingwood Center, Mansfield, Ohio

This South African native, also called ‘montbretia”, thrives in full sun in well-drained average garden soil. A richly composted soil tends to boost foliage size and bloom count, but often weakens bloom stems, requiring some staking. Crocosmia may struggle in a wet soggy wintry soil. Established plants are exceptionally summer heat and drought tolerant.

Brightly colored flowers rise on wiry stems above the sword-like leaves in early July in the Southern Appalachian region (USDA zones 6 and 7). The foliage closely resembles gladiolus. Most cultivars are hybrids and vary in flower color, height and plant vigor.

Flower stalks arise from fast-multiplying underground bulbs (they’re really corms) in red, orange, yellow and mixed colors. The most popular cultivar is ‘Lucifer’, a Blooms of Bressingham introduction. ‘Lucifer’ produces vivid red flowers on 4-5 foot arching wiry stems. Crocosmias make excellent cut flowers.

Corms are planted 3 to 4 inches deep in fall or early spring. In northerly zone 5, either plant corms 6 inches deep or lift and store them by late fall. Container-grown plants are also sold at most garden shops.

Many low growing forms (not ‘Lucifer’) tend to start slow their first year, but wind up as long-lived perennials. Over the years crocosmia may become a nuisance (perhaps invasive?) as corms spread to other garden areas. Mites may draw sap (stipple) leaves in a dry summer.

Panicled Raintree Promises Showy Lantern Pods

Posted by Hugh on July 15th, 2011

Chinese Flametree With Autumn Lantern Seed Pods

Chinese flametree (Koelreuteria bipinnata) is also called bougainvillea raintree. This rare tree, available primarily from internet nursery commerce, deserves to be planted more. It has performed well in the Southern Appalachian region (USDA zones 6-b and 7) and is questionably hardy further north.

Flametree is less popular in Southeastern landscapes than goldenrain tree (K.paniculata). Low branching and broad canopy limits its landscape use to a small 25-30 foot tall specimen tree. Very showy dense terminal panicles of small fragrant yellow flowers appear in mid- to late summer, nearly 3-4 weeks after goldenrain tree (K.paniculata).

Large clusters of two-inch-long showy rose-colored “Chinese lanterns” form quickly after flowering which persist to mid-October. The papery thin seed husks retain their pink color indoors in dry flower arrangements. The bark on Chinese Flame-Tree is smooth and light brown when young, becoming more ridged or furrowed as the tree matures.

Flametree’s dark green summer compound leaves, each 1-2 feet long, turn yellow for a short autumn interlude before falling. Later, numerous fertile seeds drop, which potentially, may raise invasive issues for this species.

(See also blog on Goldenrain tree (K. paniculata) published 7-1 -11)

Galinsoga -The Gardener’s Weed

Posted by Hugh on July 13th, 2011

The dreaded galinsoga

Thirty plus years ago a gardening friend passed along this tidbit: “galinsoga (Galinsoga parviflora) is the gardener’s weed”. Galinsoga grows only in cultivated soils such as in your vegetable and/or flower garden from part shade to full sun. It prefers moist soil but grows almost anywhere, even between cracks in a sidewalk. Its thin leaves may wilt in the hot midday summer sun, but recover by nightfall.

The rule is to never allow galinsoga to bloom. It produces abundant seed and those seeds frequently germinate within days, potentially producing multiple generations in one growing season. The seeds overwinter in the soil and become a bigger nuisance in subsequent years.

The hairy leaves and stems grow rapidly to 18-24 inches in height and begin blooming when plants are only 6 inches tall. Tiny 5-petalled white ray flowers surround a yellow disk center. Flowers are less than ½ inches wide.

Hand pulling or hoeing, followed up by mulching, is most effective control measure. Remove galinsoga before it flowers. Seeds already in the soil continue to germinate throughout spring and summer. Pine straw, grass clippings or compost serve as excellent mulches.

Preen® (trifluralin) is a pre-emergent herbicide for garden use. Read and understand the label before using.