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

Causes of Sudden Leaf Scorch

Posted by Hugh on July 7th, 2017

Leaf scorch on full moon maple

Scorched sugar maple leaves

Leaf scorch or foliage burn is caused primarily by environmental stress factors such as drying winds, drought, mechanical root injury, and winter injury . Natural pathogens, such as viruses, fungi, or bacteria, can be secondary causes. Spraying the wrong pesticide or accidentally allowing spray to drift onto a nearby susceptible landscape plant can result in chemical foliar burn. Applying too much fertilizer may also injure roots and mimic drought- like symptoms.

If sun intensity gets too strong, leaves may turn brown, typically along the edges, or take on a bleached out appearance. Shallow-rooted trees like Japanese maples (Acer palmatum) are often troubled by leaf scorch. Drying winter winds may cause leaf burn on conifers if soils are frozen. Too much sunlight and lack of adequate soil moisture will result in brown-edged leaves or leaf tips.

Leaf scorch symptoms commonly show up on edges of leaf, leaf tips and/or between the veins. Yellowing becomes increasingly severe and tissue dies at leaf margins and between veins. Sudden changes in summer light intensity, such as from a loss of an adjacent large branch or an entire shade tree, may scorch the foliage of low-growing (understory) shrubs and small tree in spring and summer.

Deep watering of soil will enhance moisture uptake. Too much water, such as periodic flooding, can also be injurious. Do not fertilize most trees, shrubs and perennials after September 1^st. It stimulates shoot growth.at a time that plants should be going dormant. Leaf scorch symptoms may result.

If tree roots have been injured, prune off top growth to compensate for loss of roots. Stressed trees and shrubs should be mulched with an organic-based mulch to help conserve soil moisture.

Ground Cover Types Of Flowering Abelias

Posted by Hugh on July 4th, 2017

Abelia grandiflora ‘Confetti’ at UT Gardens, Knoxville, TN

Abelia Kaleidoscope’ (note aberrant shoots)

Flowering abelias (Abelia x grandiflora) come in all shapes and sizes (USDA hardiness zones 6-9). Over the past decade the ground cover types have become very popular. They’re also utilized as accent plants in large containers. In zones 7 -8, they are evergreen.

The term “ground cover” is used here to emphasize cultivars that grow low, mostly wider spreading than tall. From late spring to early fall, almost four months, white tubular flowers (pink in bud) are in bloom. Flowers attract a wonderful assortment of bees and butterflies to any landscape.

Abelias grow in average, well drained soil and in full to partial sunlight (6-hours minimum) for best flower numbers and leaf color expression. Plants are exceptionally heat and drought tolerant after 1st year. Feed 1-2 handfuls of 10-10-10 or equivalent granular fertilizer per plant in late winter or in spring. Mulching plants is recommended. Pruning is not a big chore. Remove unwanted and dead branches at any time and cut back aberrant leaders (suckers) to maintain uniform plant height.

Flower abelias have demonstrated very good resistance to drought, diseases and insects. Deer generally don’t bother them, but will eat them in a pinch.

Leading Variegated Leaf Forms:

‘Kaleidoscope’ is currently the most popular in the ground cover category. It grows 2 to 3 feet tall and 3 to 4 feet spreading. In the spring its new variegated foliage is vibrant green in the center and creamy yellow along the edges. Summer foliage is very golden-yellow and does not burn in the summer heat. In the fall foliage becomes a colorful blend of red, orange, green, and yellow.

‘Confetti’– offers finely textured medium green, variegated creamy white and pink foliage. Pale pink tubular flowers appear in summer into fall. This rounded, semi-evergreen shrub grows about 3 feet tall and 4 feet wide.

‘Mardi Gras’ – white to pale lavender flowers with pink tinge; dark green with creamy white edge that turns dark pink to red in fall; Leaves are mostly white, green centers, and edged in salmon-pink. Foliage takes on a golden tint in winter. Shrub grows to only 2.5 to 3 feet tall and 3-4 feet in spread.

‘Silver Anniversary’ – grows 3 feet tall and 3-4 feet in spread. It has highly glossy, creamy white-variegated grayish green leaves which develops an outstanding burgundy color in fall.

Agaves Like It Hot, Dry and Sunny

Posted by Hugh on July 1st, 2017

Agaves in Burbank, CA

Variegated agave in sidewalk planting in Burbank, CA

Agaves (Agave spp.) are long-leaved succulent landscape plants. These native perennial succulents grow in desert-like environments (USDA hardiness zones 8 and warmer). Plants grow in a rosette form with long their fleshy leaves frequently tipped with one or more sharp spines and a prominent bloom spike with cup shaped flowers. Most are native to the Southwest U.S. and Mexico.

Agaves are exceptionally drought tolerant and ideal for xeric gardens. Temperature hardiness, sunlight, and soil drainage are the three key components to successfully growing agaves. Agave have a large tap root and do not transplant well, so carefully select an appropriate site where to plant. The majority of the roots are surface roots and do not require a deep hole if planted when young.

Porous, well-drained soil is an absolute must! When planting in clay soils, deeply amend bed or container soil with coarse sand or pea gravel in a 50:50 ratio. Water the plant diligently the first week after planting and gradually wean it back to 2-3 times monthly in containers, all depending on season of the year and outdoor air temps.

Never overwater agaves! They are famous for their low water use. In early spring apply a slow release fertilizer such as Osmocote™ or Nutrikote™. This should supply nutrient needs for the entire year.

Most agaves naturally dieback after blooming. They form new plants (“pups” or offshoots) at the base of the “mother” plant. Many gardeners opt to remove the spent floral spike with long handle lopper pruners to avoid their sharp spines. Agaves should be re-potted every year, usually in the spring in new media. Prune off old lower leaves if they detract from the plant’s beauty.

Non-hardy types are moved indoors or in an unheated garage where temps drop below 37°F and grown in an east facing window. Over the winter months reduce frequency of watering intervals and do not fertilize.

Agaves are deer-resistant. The tall bloom stalks attract hummingbirds.

Agave parryi var.

Four popular agaves:

Century plant (Agave americana) – a lovely flower (inflorescence) and leaves have a white stripe running along the center.

Parry’s or Mescal agave (Agave parryi) – an attractive slow growing compact form that measures 2-3 feet across. Leaves are grey green tipped with a spine (zone 7 hardy).

Ocahui Century Plant (Agave ocahui ) (zone 7b -10) – this 2-3 feet wide ball-shaped agave has attractive rigid dark green leaf blades with attractive red margins and sharp flexible spines. Bloom spike will eventually reach nearly 15 feet tall with yellow-green flowers.

Black spine agave (Agave macroacantha) – a medium sized rosette form and 1 ½ feet long thick grey green leaves, each tipped with a 1-inch long sharp black spine. Small grey and red flowers form on sturdy 7-10 feet high stems.

Firebush Is One Tough Texas Flowering Plant

Posted by Hugh on June 28th, 2017

‘Lime Sizzler’ firebush

Hamelia patens (photo from Texas Ag Extension website)

Firebush. aka scarlet bush (Hamelia patens), is indigenous from Mexico to Central America (USDA hardiness 10-11). Treat it as a tempermental perennial in zone 9, and an annual everywhere else it is not hardy. This fast growing plant blooms through most of summer into fall with showy clusters of tubular red buds and flowers. Firebush thrives in Texas heat from July to September where it finishes as a 4- to 5-foot mound. In the Tropical South, established plants may grow 10 to 12 feet high.

Once established, Firebush is highly drought tolerant and thrives in any average soil that is drains well. Full sunlight is preferable; shoots grow off weak and spindly in 1/2 day shade with reduced flowering. Leaves appear in whorls of between 3 and 7 at the nodes of the stems, and are about 6 inches long and lightly haired. Firebush leaves vary by species, individual plants, and seasonal growing conditions locally. Most often leaves are light to dark green but sometimes purplish or red depending on cultivar. In fall foliage often turns bright red.

Firebush is also called “hummingbird bush” because hummingbirds are attracted to its tubular red flowers. Flowers are in cymes; the terminal and axillary inflorescences are widely forked and showy. Flower buds last longer than the actual flowers themselves. These inflorescences are 2 to 4 inches long and almost as wide. Flower buds emerge yellow, becoming orange. Occasional shearing keeps plants in a nearly perpetual state of bloom.

New in the Southern Living Plant Collection in 2017 is Lime Sizzler™ Firebush which features green and yellow variegated foliage with sizzling red-orange flowers from late spring through fall. Performs well in the landscape or in a container. The cultivar ‘Firefly’ has leaves and flowers about half normal size.

Aphids can be a nuisance on new spring leaves. Caterpillars, lubber grasshoppers, scales, mealybugs and mites may cause damage. Firebush demands little special care after its first year in the garden Irrigate periodically during first year. Lightly shear the plant a couple of times during the growing season to promote the heaviest flowering

Check Out These Four Plant Select® Picks

Posted by Hugh on June 26th, 2017

Salvia ‘Furman’s Red’ in east Tennessee landscape in mid-August

If you’re search for top performing plants, especially very drought tolerant, take a look at the picks from Plant Select^®. This is a nonprofit collaboration of Colorado State University, Denver Botanic Gardens and professional horticulturists. Their mission is to seek out and distribute the very best plants for landscapes and gardens from the intermountain region to the high plains and beyond. Plants chosen for program exhibit these eight attributes:

Red Yucca (Hesperaloe) in Mount Carmel, TN

Flourish with less water
Thrive in a broad range of conditions
Habitat-friendly
Tough and resilient in challenging climates
One of a kind/unique
Resist disease & insects
Long-lasting beauty
Non-invasive

Here are four Plant Select® picks that prosper across most areas of Tennessee:

‘Furman’s Red’ Salvia (Salvia greggii ‘Furman’s Red’)

This hardy selection of a southwestern ever-blooming sage grows 18-24 inches high and wide (USDA hardiness zones 5b-10). Crimson to scarlet flowers form in repeated flushes from late spring, summer and autumn. It is deer resistant and drought tolerant; provide good soil drainage and does poorly in soggy winter soils. Wait to cut old plant back in spring.

Red Rocks® Penstemon (Penstemon x mexicali Red Rocks®)

This hybrid penstemon forms a bushy clump, 14-18 inches high and 12-14 inches wide of narrow green leaves (zones 4b-8). Short spikes of bright rose-pink trumpet flowers bloom, on and off, through most of the summer and attract butterflies and hummingbirds. Narrow, dark green leaves form an attractive mound. It sports a constant succession of bright rose flowers all summer. Red Rocks thrives in a wide range of sites and soils.

‘Standing Ovation’ Little Bluestem (Schizachyrium scoparium ‘Standing Ovation’)

This warm season ornamental grass grows 24-36 inches high and 15-18 inches wide (zones 3-8). It performs well in poor, dry soils. It holds its tight upright growing habit all 4-seasons. Spikey bluish-green leaves transition to a brilliant display of red shades, changing to deep purple from August into October. Seed heads stand upright through winter and provide winter interest and food for birds. It can be utilized in mass plantings or meadow designs.

Red yucca (Hesperaloe parviflora)

This shrub native to Mexico and Texas grows 3-4 feet tall and 1.5 to 2 feet wide (zones 5-10). Tall spikes of brilliant coral-pink, yellow-throated tubular blossoms curve skyward and attract hummingbirds from early summer to autumn. It prefers a porous loam soil and avoid frequent irrigation. Tidy up plant by pruning off brown foliage and seedheads in late winter. Deer resistant.

Ice Plants (Delosperma)

Posted by Hugh on June 23rd, 2017

Delosperma cooperi at Atlanta Botanical Garden

Delasperma

Ice plants (Delosperma spp.) are perennial evergreen succulents from South Africa. Two species are most popular in U.S. gardens starting with hardy ice plant (D. cooperi) (zones 6b – 9) and yellow ice plant (D. nubigenum) (zone 4 – 10). There are also many hybrid cultivars sold at garden centers and on-line.

North of zone 7, hardy ice plants (D. cooperi) are semi-evergreen and needs winter protection. This succulent mat-forming plant typically grows to 3 – 6 inches tall and spreads quickly to 24 or more inches in width. High gloss, bright red-purple, daisy-like flowers (up to 2 inches or 5 cm across) cover the plant from June to September. Bloom colors are iridescent. The succulent foliage is generally medium green.

Yellow ice plants (D. nubigenum) form a low mat of succulent, evergreen leaves, bearing loads of small starry yellow flowers starting in late spring. Plants grow 2 – 4 inches tall, and form a tight attractive mat. Foliage take on vibrant pinkish tint over winter.

Ice plants are best grown in dry, sharply-drained soils in full sun. Plants fail (die) in almost any kind of soil that is not adequately drained. Sandy and gravelly soils are the best. Ice plants are especially responsive in reduce reflected heat and glare when planted in areas covered with gravel mulch. Plants are exceptionally heat and drought tolerant. Feed only once annually with a very dilute fertilizer solution and water sparingly.

Ice plants are trouble free with regard to insect or disease problems. Aphids and mealybugs are occasional pests.

Garden uses: Ice plants grow well in containers or in the garden in a sunny area including rock gardens, rock walls, border fronts as edging or on slopes.

Depending on species and cultivars, plant and flower size varies; dwarf selections hug the ground. Here are four recommended selections from Plant Selects™:

Red Mountain® – large flowered blazing orange-red color and attractive growing habit (zones 4-9).

Starburst® – (D. floribundum) produces bright pink shimmering flowers with white centers (zone 5-9).

Mesa Verde® – (D. cooperi) short growing salmon-pink-flowers (zones 4-9).

Lavender Ice® – iridescent lavender blooms with dark eye; foliage turns purplish in winter (zones 4-9).

Less Invasive Butterfly Bush Identified

Posted by Hugh on June 20th, 2017

Buddleia ‘BlueChip’ at J C Raulston Arboretum, Raleigh, NC

Butterfly bush (Buddleia) is a popular garden shrub in many areas of the U.S. Buddleia invasiveness is a serious issue in the Pacific Northwest. The Oregon Dept of Agriculture, Plant Division, has approved for sale these buddleia cultivars in the state. The approved varieties produce 2% or less viable seed, meeting Oregon’s standards for sterility.

The approved list includes: ‘Blue Chip’, ‘Asian Moon’, ‘Purple Haze’, ‘Flutterby Grande Blueberry Cobbler’, ‘Flutterby Grande Peach Cobbler’, ‘Flutterby Pink’, ‘Flutterby Petite Snow White’, ”Flutterby Grande Sweet Marmalade’, ‘Flutterby Grande Tangerine Dream’, and ‘Flutterby Grande Vanilla’. Add to the list the cultivars ‘Miss Molly’ and ‘Miss Ruby’ as personal non-invasive favorites.

Butterfly bush should be planted in full sun for sturdy stems and high floral count. Cultivars vary in size, some tall ones are placed in the rear bed, and dwarf cultivars in the front of the planting border. Flowers are sweetly fragrant upclose. Shrubs are drought tolerant once established and are tolerant of urban pollution.

New sterile hybrids are hardy to zone 5-9. They grow in average well-drained garden soil with pH range between 5.5 to 7.5. Keep plants well mulched in summer and add additional amounts in late fall for winter protection in northern areas. Shrubs are light constant feeders; choices include slow release fertilizers like Osmocote® and Nutrikote®, or monthly liquid feeding of Miracle-Gro™, Daniels™ or Espoma®.

Butterfly bushs require little pruning, but large flowering types weigh down the branches. Cut back plants to the ground in early spring as flowers are borne on new growth (wood). Pests seem to be problematic when shrub(s) are stressed out because of a poor garden site. Spider mite feedings appear to be most severe during extremely hot dry summers.

Summer Lawn Care Tips

Posted by Hugh on June 17th, 2017

Properly mowed lawn

“Summertime and the living is easy”. That’s a good adage to follow for home lawn care as well. Most lawn care chores, such as fertilizing, seeding, thatch management, and weed cleanup, should be delayed until late August through early October in most locales (USDA zones 4-7). During the heat of summer, proper mowing and irrigation are the only work necessary. Key to success is to raise the mowing height over the summer months.

Follow the one third rule. Remove no more than one-third of the grass height when mowing. Wait a few days to mow the lawn again. Scalping (close cutting) often results in a weak and weed infested lawn. If you miss a few scheduled mowings, don’t try to do it all at one time. Gradually reduce height of cut over several mowings. Don’t pick up the clippings as they contain nutrients that can be recycled as they decompose. Raked up clippings may be added them to the compost pile.

During the summer, mow cool season lawn grasses, such as Kentucky bluegrass, perennial ryegrass, and fine fescue, at heights around three inches or slightly higher. When in doubt, set the mower as high as it will go. Lawns maintained at higher heights usually develop deeper roots and dry out slower than closely mowed turf. Mulching mowers are a good investment as they are engineered to lift clippings and strike them several times before they are returned to the turf.

Cool-season lawn grasses naturally slow down and go dormant in the heat of summer. If you must irrigate, water lawns deeply at one time @ 1 to 1 1/2 inches per week. Water early in the day if at all possible. During periods of high stress, dormant lawns need only 1/4 to 1/2 inch of water every 2 to 3 weeks to keep root and crown tissue alive. Keep foot and vehicle traffic to a minimum if visible signs of drought are obvious.

Panicle Hydrangeas For Small Gardens And Containers

Posted by Hugh on June 13th, 2017

‘Bobo’ Hydrangea

‘Baby Lace’ hydrangea (Photo from Gardeners Confidence)

Panicle, PeeGee or PG hydrangeas (Hydrangea panculata) brighten up your July-August garden. They hail from China and Japan and grow almost anywhere in the U.S. (USDA hardiness zones 3 – 8). PG hydrangeas are far more reliable in northern areas (zones 3-5), than mophead hydrangeas (H. macrophylla). They flower at their best in full to partial day sunlight (6 hours or more).

PG hydrangeas are vigorous growers. Branching is upright and their deciduous foliage is coarse textured. Depending on cultivar, PG hydrangeas grow 3-15 feet, and 20-25 feet tall in tree form. Multi-branched shoots are clothe with dark green, oval shaped leaves and are topped with upright, sharply-pointed, conical, 6-8 inch long terminal flower panicles. Flowers may be a mix of both fertile and sterile florets and bloom from mid-summer into fall. PG hydrangeas are pruned any time from late fall to mid-spring. They may also be trained into a tree form.

Most gardeners are well acquainted with the popular cultivar Limelight™, the standard for excellence in PG hydrangeas. Limelight grows 6-10 feet tall (depending on amount of annual pruning provided). Its sturdy upright branched are covered with 6-8 inch long, conical shaped white flowers. Blooms make beautiful fresh or cut flower arrangements.

‘Limelight’ at NC Arboretum, Asheville, NC

Four “new” panicle hydrangeas for planting in small gardens and in containers:

Baby Lace® – petite, lacy white blooms against dark green foliage. Its smaller size of 3 by 5 feet .

Bobo™ – grows very compact size, the perfect size in small gardens and containers; large white loose flowers appear from midsummer to early fall.

‘Bombshell’ – is dwarf (compact) form with abundant star-shaped sterile flowers with elliptic sepals, dense nearly round flower panicles, and free blooming habit. It blooms earlier and longer than most other panicle hydrangeas. Flowers emerge white and slowly turn rosy pink. Strong stiff stems hold the flower panicles upright with no drooping.

Little Quickfire® – is a shorter of Quickfire, growing 3-5 feet tall with creamy spikes that turn to deep pink with red highlights on bold, red stems.

Bacterial wilt, leaf spot, rust, and mildew diseases and aphids and mites are occasional disease and insect problems. Poor site selection often enhances problems with diseases and pests.

Tidy Up These Perennials After Blooming Is Finished

Posted by Hugh on June 10th, 2017

Alliums (rhizomatous types) not responsive to deadheading

Hostas Are Best Cleaned Up After Flowering

Deadheading, the practice of removing the old spent flowers from perennials, is a way to improve a garden’s appearance and reduce overcrowding. Secondarily, many (not all) will rebloom after deadheading.

Not all perennials respond to deadheading by reblooming. Most daylilies (Hemerocallis x.), coralbells (Heuchera spp.), and hostas (Hosta spp.) are prime examples of perennials that do not rebloom. Other examples include:

Bear’s breeches (Acanthus mollis)

Bluestar (Amsonia tabernaemontana)

Lady’s mantle (Alchemilla mollis)

Rhizomatous Onions (Allium spp.)

Artemisia, wormwood (Artemisia spp.)

Astilbe, false spirea (Astilbe spp.)

Baptisia, False indigo (Baptisia spp.)

Bergenia (Bergenia cordifolia)

Heartleaf brunnera (Brunnera macrophylla)

Montbretia (Crocosmia)

Joe Pye (Eupatorium spp.)

Most kinds of fall flowering sunflowers (Helianthus spp.)

Lenten Rose or hellebore (Helleborus x orientalis)

Bearsfoot hellebore (Helleborus foetidus)

Rose mallow (Hibiscus moscheutos)

Most kinds of Irises (Iris spp.)

Ligularias (Ligularia spp.)

Monkey grass (Liriope spicata)

Catmint (Nepeta × faassenii)

Herbaceous Peony (Paeonia spp.)

Woodland phlox (Phlox divaricata)

Obedient plant (Physostegia virginiana)

Lungwort (Pulmonaria spp.)

Lambs’ ears (Stachys byzantina)

Culver’s root (Veroncastrum virginatum)

To reinforce the benefits of deadheading, the perennial bed should be weeded, mulched, fertilized, and watered. Apply a water soluble fertilizer such as Miracle-Gro™ or Schultz™. Clean up the bed of weeds and apply additional amounts of an organic mulch. If soil is dry, irrigate the bed deeply over 3 – 4 hours of overhead irrigation (equivalent of 1 ½ inches of rainfall).

Removal of the old flowers also lessens the threat of seed dispersal and future hoeing of unwanted seedlings. Many one-time bloomers, such as columbine, fall anemone (Anemone x hybrida), and gaillardia will self-seed if spent flowers are not deadheaded.