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

Annual Geraniums Make Garden Comeback

Posted by Hugh on May 6th, 2019

‘Calliope Dark Red’

Geranium basket

Once popular annual geraniums (Pelargonium x) are making a comeback with U.S. gardeners. Geraniums are also planted in window boxes or hanging baskets. Three types of geraniums are sold at garden centers: zonal or bedding geraniums (P. x hortorum), ivy-leaf geraniums (P. peltatum), and Martha Washington geraniums (P. x domesticum). Color choices include red, pink, rose, salmon, orange, lavender, violet, or white.

Of the 3 types, zonal geraniums are the most widely planted. Ivy-leafed geraniums (Pelargonium peltatum) have a trailing habit with ivy-shaped foliage. They are principally planted in hanging baskets and window boxes. Martha Washington geraniums (P. x domesticum) are primarily sold by florists as flowering pot plants and do not perform well outdoors.

High summer heat is challenging for all types of geraniums. Some types of geraniums stop blooming completely and perk up when cool temps return. Over the past quarter century plant breeders have given gardeners more heat-tolerant types, such as the Americana™, Eclipse™, Rocky Mountain™ cutting series; Maverick™, and Orbit™ seed series; and the interspecific hybrids trademarked as Caliente and Calliope.

Plant geraniums outdoors after all threat of frost has passed. Depending on the geranium type and variety, plants are spaced about 8 to 12 inches apart and around the same depth as their original planting pots. Mulch around plants to retain soil moisture and suppress weeds. Deadheading of spent blooms also encourages additional blooming. Avoid overhead irrigation, as this may bring on disease problems. Geranium cuttings root easily and held over as house plants.

Geraniums must have a moist well-drained soil and should be planted in a garden receiving at least 6 – 8 hours of sunlight. Let the soil go slightly dry between waterings. Do not overfertilize. Fertilize with a slow-release, granular product once in spring and/or with a water soluble fertilizer such as Miracle-Gro™ or Jacks™ 1-2 times over the summer. Remove old spent flowers to keep plants blooming. Ideal light exposure is in full morning sunlight and in light afternoon shade.

Russian Arborvitae For Cool Areas Of The U.S.

Posted by Hugh on May 1st, 2019

Russian arborvitae and Siberian cypress (Microbiota decussata) is an underutilize ground cover (USDA hardiness zones 3-7). This tough juniper-like evergreen hails from Siberia and demonstrates exceptional cold hardiness to -40 ° F. In extreme northerly sites, the lacy evergreen foliage may turn complete brown in the dead of winter and re-sprout in spring.

In the cool temps of zones 5 and 6 microbiota really prospers. It struggles (melts down) in zone 7 unless cozied up under afternoon shade. Its soft feathery green foliage develops a purple to russet cast where winters are abnormally harsh. An early spring warm-up quickly restores its cool medium green hue.

Growth rate is slow to medium. Feed, if needed, in early spring with a general purpose granular fertilizer such as 10-10-10 or equivalent. Pruning is rarely necessary except to check its spread or to remove any broken branches.

The flat sprays of low growing microbiota range between 8-15 inches in height and 6-8 feet in width over several years. Microbiota is a great alternative to some disease plagued ground cover junipers. It is tolerant of dry shade. Deer and most disease and insect pests don’t bother it. It wants good soil drainage and cool summer temperatures.

Adjacent to my driveway I use microbiota to cascade over a low retaining wall. Foliage tolerates windy exposed sites once it becomes fully established in 2 years.

I am seeing more independent garden centers selling this terrific ground cover. E-commerce specialty nurseries also sell it. Plant container grown nursery stock in late winter thru spring.

Varieties: Celtic Pride™ – an exceptional cold hardy form.

Enjoy Two Kinds Of Stachys In Your Summer Garden

Posted by Hugh on April 26th, 2019

S. monieri ‘Hummelo’ (photo provided by North Creek Nurseries, Landenberg, PA)

Stachys ‘Countess Helene Von Stein’

Many gardeners are acquainted with the wooly leaf perennial called lambs ears (Stachys byzantina). But the genus Stachys is also home to betony (S. officinalis) / (S. monieri). Alpine betony (Stachys monieri) is native to Europe and Asia (USDA hardiness zones 4-8).

‘Hummelo’ betony is very different in appearance from its gray velvety leaf relative called lamb’s ears (e.g., Stachys byzantina). Instead of silvery foliage, Hummelo betony’s foliage is dark green and glabrous (hairless). In Southern climes the foliage is evergreen. This colorful and compact growing plant makes an excellent addition to the full sun perennial border. Wiry stems make for a great cut flower as well.

Hummelo exhibits an upright plant form @ 18 to 20 inches tall and wide. Pollinators can’t resist the striking lavender-rose flower spikes in late June thru July, emerging above basal glossy green foliage mounds. The bright flowers can be easily mistaken for salvias.

In comparison, lamb’s ear (S. byzantina) forms a dense mat of woolly silver-gray leaves. Plants grow 12 -15 inches high and 18 – 20 inches wide. Spikes of purplish pink flowers appear on tall stems in early summer that detract from the foliage and, in my opinion, should be pruned off. Bloom stalks often re-develop and necessitate more pruning. Seedlings from this weedy species will spread to other parts of the garden.

The cultivar ‘Countess Helene von Stein’, aka ‘Big Ears’, is the preferred choice among landscapers. It exhibits showier velvet (hairy silver) foliage, better heat and humidity tolerances, and best of all, it rarely flowers and seeds-in. Over time Big Ears develops a wider vegetative mound than the species.

Both types of Stachys are easily grown in moist well-drained soils and full to part day sun (6 hours or more recommended). Soils should be kept evenly moist, but established plants have some drought tolerance. Plants spread by underground stolons. Set multiple plants 12-18 inches apart as a ground cover. Feed in early spring at planting time with granular 10-10-10 or equivalent fertilizer.

No serious disease or insect pests trouble either species. Pollinators can’t resist the striking midsummer colorful floral spikes. Deer and rabbits generally stay away. Snails and slugs may be troublesome in wet summers.

The Perennial Plant Association has selected Stachys monieri ‘Hummelo’ as 2019 Perennial Plant of the Year.

Planting Small Trees Under Power Lines

Posted by Hugh on April 20th, 2019

Three flower maple in mid-October at NYC Hi-Line

Look Up before you plant. From city streets to country roadside are a myriad of power (utility) lines, e.g. electric, telephone, and cable TV wires. Utility companies have a “right of away” clearance to operate their lines. In most municipalities, mature trees growing into their lines can be cut down or all offending branches removed. Large trees often end up massacred.

The mature heights of the following species rarely exceed 25 feet and eliminate tree/utility line issues. Most tolerant of a wide variety of soils, urban growing conditions and hardiness rating. Disease and pest resistant, drought tolerant, require minimal maintenance. This list includes a few large shrubs that can be trained into small trees such as smoketree, American witchhazel, and fringetree. All are hardy in USDA plant hardiness zones 5-9 except where noted.

Trident Maple (Acer buergerianum)

Hedge Maple (Acer campestre)

Flame Amur Maple (Acer ginnala ‘Flame’)

Japanese Maple (Acer palmatum) – lots of great choices; however many are not tree forms

Three Flowered Maple (Acer triflorum)

Shantung Maple (Acer truncatum)

Red buckeye (Aesculus pavia)

Autumn Brilliance® Serviceberry (Amelanchier × grandiflora ‘Autumn Brilliance’)

Princess Diana Serviceberry (Amelanchier grandiflora ‘Princess Diana’)

Snowcloud Serviceberry (Amelanchier laevis ‘Snowcloud’)

Pawpaw (Asimina triloba)

American Hornbeam (Carpinus caroliniana)

Redbud (Cercis canadensis)

American Fringetree (Chionanthus virginicus)

Smoketree (Cotinus coggygria)

Flowering dogwood (Cornus florida)

Chinese Dogwood (Cornus kousa)

Kousa dogwood in May

Cornelian Cherry (Cornus mas)

Winter King Hawthorn (Crataegus viridis ‘Winter King’)

Sweetheart Tree (Euscaphus japonicus)

Carolina Silverbell (Halesia tetraptera)

American witchhazel (Hamamelis virginiana)

Crape Myrtle (Lagerstroemia x) (zones 6-10)

Amur Maackia (Maackia amurensis)

Little Girl series of Magnolias (Magnolia x liliflora) – cvs. ‘Ann’, ‘Betty’, ‘Jane’, or ‘Susan’

Saucer Magnolia (M. soulangeana)

Star Magnolia (Magnolia stellata)

Select Crabapples (Malus ‘Adirondack’, ‘Prairifire’, ‘Sugartyme’, M. sargentii, M. floribunda)

Ruby Vase® Parrotia (Parrotia persica ‘Inge’s Ruby Vase’)

Crimson Pointe™ Plum (Prunus cerasifera ‘Cripoizam’)

Thundercloud Plum (Prunus cerasifera ‘Thundercloud’)

Newport Plum (Prunus ‘Newport’)

Okame Cherry (Prunus x ‘Okame’)

Japanese tree lilac (Syringa reticulata ‘Ivory Silk’)

Peve Minaret bald cypress (Taxodium distichum ‘Peve Minaret’)

City Sprite zelkova (Zelkova serrata City Sprite™)

Three New Summer Annuals You’ll Get Excited Over

Posted by Hugh on April 15th, 2019

Euphorbia ‘Diamond Mountain’

Senecio ‘Angel Wings’

Here are three new annuals which should delight:

Striking Senecio ‘Angel Wings’ has silky, silvery white foliage. Angel Wings senecio is beautiful to add to mixed containers or use it solitary on patio or deck planters. Warning: you can’t resist touching the long, broad velvety leaves.

Angel Wings grows 10-12 inches high and about as wide. Plant Angel Wings in full sun in an acidic, neutral or alkaline soil. This fast growing Senecio candicans is drought and salt tolerant.

Diamond Mountain® euphorbia explodes clouds of airy white flowers from spring to fall frost. Plants are low maintenance and demonstrate exceptional heat- and drought-tolerance. Diamond Mountain produces larger plants than Diamond Frost^® with a great garden presence; plant in large size containers. It grows 24 – 36 inches tall and wide. It performs at its best in part to full sun.

Diamond Mountain might look delicate and frilly but is much tough as nails. It needs little to no irrigation after initial 6 week establishment period and is extremely heat tolerant in the summer. No floral deadheading is necessary.

Angelface® Perfectly Pink

Angelface® Perfectly Pink is a new angelonia for your summer garden. Plants grow vigorously, 18-30 inches high and 12-18 inches wide. Plants sap up sun and humidity where they bloom at their best. Plant as soon as soil temperatures warm up. Angelonias are moderately drought tolerant within 6 weeks after planting. Plants ask for little additional care including no deadheading. Angelface series produce great long lasting cut flowers with a slight grape soda fragrance. Try some in a flower arrangements.

Feed all three annuals the same. At planting time apply granular fertilizer such as 10-10-10 (or equivalent) to nourish them up to mid-summer. At that time feed additionally with a water soluble fertilizer such as Miracle-Gro™ or Jacks™. Add compost on garden beds at planting time and regular fertilization of plants in containers will help ensure the best possible performance.

Select List Of The Better Kousa Dogwood Varieties

Posted by Hugh on April 10th, 2019

Cornus kousa ‘Wolfeyes’ at UT Arboretum, Oak Ridge, TN

C. kousa ‘Lustgarten Weeping’ at Rutgers University, NJ

There are over 100 named varieties (cultivars) of kousa (Chinese) dogwoods (Cornus kousa) in nursery trade (USDA hardiness zone 5-8). Most cultivars grow 20-30 feet high with some exceptions. Kousa dogwood blooms 2-3 weeks after U.S. native flowering dogwood (C. florida). Most grow shrub-like and tree forms require extensive training at the nursery.

Flowers are 2-4 inches wide with either white or pink tapered bracts. Flowers appear after the leaves emerge. Fleshy pinkish-red to red fruits ripen in late summer. Flowers and foliage are highly resistant to anthracnose disease and deer tend to stay away.

Several cultivars are very new and others are not well known. Dogwood researchers, such as at the University of Tennessee, continue to evaluate the best cultivars for the Southeastern U.S. Key characteristics they search for include drought tolerance, heat resistance and better tree forms.

Some cultivars that show great promise include:

‘Blue Shadow’– exceptional dark green foliage; blooms at an early age.

‘Gold Cup’ – dark green foliage marked with a prominent golden yellow streak in the leaf center and small white blooms

‘Gold Star’ – slow growing tree; green leaves with butter-yellow center blotch.

Heart Throb® (’Schmred’) – red-colored bracts do not fade out in southeast U.S. heat as do many red flowering varieties.

Fruits of C. kousa

‘Lustgarten Weeping’ – strong weeping form but is reportedly disease prone.

‘Milky Way’ – popular “generic” variety that flowers early and prolifically; flowering tends to be biennial, heavy one year and light the next.

‘National’ – vigorous, vase-shaped tree and dark green foliage

‘Scarlet Fire’ Kousa dogwood

Scarlet Fire® -new! 2018 introduction from Rutgers University with fade-proof red (dark pink) bracts.

‘Summer Stars’ – heavy-blooming; good drought tolerance.

‘Wolf Eyes’ – slow growing compact (10-12 feet) shrub form; creamy white variegated foliage is scorch-resistant; small white flowers fade into foliage.

Spring Ephemerals

Posted by Hugh on April 6th, 2019

The cold dreary days of March have waned and many of our great Appalachian wildflowers have awakened. These plants are often referred to as “ephemerals” because they come up, bloom, and fade away in 6-9 weeks. They bloom in a shady woodland or garden environment before the deciduous tree canopy has completely leafed out.

Trout lilies and mayapples

Their appearance tells gardeners that spring is nearly here. We are heartened to see them popping their heads up. Virginia bluebells (Mertensia virginica), trout lilies (Erythronium americanum),
celandine poppies (Stylophorum diphyllum), spring beauties (Claytonia virginica), bloodroot (Sanguinaria canadensis), twin leaf (Jeffersonia diphylla), and toothwort (Dentaria diphylla) are blanketing woodland areas. By late spring or early summer, most will have died back to the ground preparing for the next year’s display.

In designing your own wildflower garden, these favorites associate with each other: foamflowers (Tiarella spp.), coral bells (Heuchera spp.), several ferns, yellowroot (Xanthorhiza simplicissima), woodland phlox (Phlox divaricata), and Jack in the pulpit (Arisaema triphyllum). They prosper well under deciduous trees and where the soil does not get bone dry.

Spring wildflowers do not demand moist, fertile soil. They gather nourishment from the soil organic matter. The chances of spring wildflowers to seed-in and naturalize in your landscape are greater in humus-rich ground. If their soil, light and water needs are met, these spring beauties tend to form small colonies.

Some young wildflowers may be difficult to identify from seed. For example, Virginia bluebells may take 5-6 years to reach full flowering-sized size. Be careful not to mistakenly weed out young bluebells that look like tiny clumps of bibb lettuce.

Numerous native plant nurseries sell these beloved late winter-spring wildflowers or ephermerals. A few favorites include Sunlight Gardens (www.sunlightgardens.com) in Andersonville, TN and Sunshine Farms (www.sunfarm.com) in Renick, WV.

Virginia bluebells
Bloodroot

Hybrid Wax Begonia Revolution

Posted by Hugh on April 1st, 2019

Whopper Rose with Green Leaf at Chicago Bot. Garden

Big begonias with coleus and lantana

Wax begonias (Begonia x semperflorens) are popular summer annuals in public and private gardens. Begonias are excellent for mass bedding, in mixed borders, and in large containers. Plants hold up to summer heat, humidity, and moderate dry spells. The foliage stays mostly pest and disease free.

A few years back, two series of interspecific hybrids (Begonia benariensis), were introduced by the Benary Seed Co. and trademarked as Big™ and Whopper™ begonias. These hybrids boast larger showier flowers than traditional wax begonias. Color choices in the Big series are red, rose and pink. Whopper series come in red and rose only. Whopper plants grow 20-25% larger than Big. This means fewer plants to plant for good garden coverage which will save you money.

Big™ begonias bloom non-stop for almost six months (mid-May thru October (USDA hardiness zones 6 thru 9). Big begonias are available in bronze-leaf (full sun) and green leaf (part sun) forms. Bronze-leaf types perform at their best (leaf color) in full sun, and green leaf cultivars prefer partial shade. Begonias need well-drained soils amended with lots of well-rotted compost.

In 2017 Pan American Seed released the Megawatt™ series. Current varieties include ‘Red Green Leaf’, ‘Pink Bronze Leaf’, ‘Rose Green Leaf’, ‘Red Bronze Leaf’ and ‘Rose Bronze Leaf’. Proven Winners (PW) has recently introduced Surefire™ Series with a red and a rose variety. Expect new color choices to be added over time.

All hybrid wax begonias grow robustly, 18 to 24 inches tall and 16-18 inches in spread, by the end of summer. Plants grow compact and are well-branched. Flower size varies from 2 to 3 inches across. The brightly colored blooms are visited by many kinds of butterflies over the long bloom season. Flowers are self-cleaning and require no deadheading. Space plants 15-18 inches apart depending on which series that you plant.

Begonias perform best with moderate fertility. At spring planting, feed with a slow-release fertilizer such as Osmocote™ 14-14-14 or Nutricote™ 13-13-13. One to two additional feedings in mid-summer with a water-soluble fertilizer (such as Miracle-Gro®, Schultz®, or Jacks®) are often needed in southern climates (zones 7-9). Add 2 to 3 inches of mulch to prevent weeds and to conserve soil moisture. Irrigate during extreme dry spells to maintain plant vigor and flowering.

Temperamental Big Leaf Hydrangeas

Posted by Hugh on March 25th, 2019

Hydrangea macrophylla

H. macrophylla ‘Summer Crush’

Get use to it… big leaf hydrangeas (Hydrangea macrophylla), also called hortensia hydrangeas, are temperamental (USDA hardiness zones 6-9). After a long winter of sub-freezing temperatures, these blue (or pink) flowering shrubs should be stunningly beautiful in spring. However, if the late winter- early spring temps flucuate wildly, grab your pruning shears.

Too most gardeners, myself included, find growing these hydrangeas totally frustrating. Bloom buds on the old wood are predictably injured two out of three springs in zone 6 eastern TN, Southwestern VA, and western NC (southern Appalachian region). Flower buds and stems are most susceptible to injury as the plants start to break dormancy in late winter, then get smacked by a sudden cold snap.

To protect against winter freeze damage: 1. site big leaf hydrangeas close to your house or a heated structure; 2. do not feed plants in the fall; 3. select better cold tolerant cultivars (varieties).

In northern climes, such as Midwest or New England states, cover big leaf hydrangeas with mulch or leaves. In late winter inspect the lower buds as the plants start to awaken. You don’t want to trap excessive moisture around the growing buds and invite diseases to the plant.

Hydrangea breeders (Bailey’s , Proven Winner’s and Spring Meadow Nurseries to list three) continue to introduce hardier bigleaf hydrangeas that bloom on both new and old wood. Old wood flowers are set on last year’s shoots and new flowers are made on current season’s growth. Do not prune hydrangeas late in the summer, as you may be removing flower buds the following spring.

Over a quarter century, Proven Winners Colorchoice™ and Bailey’s Nurseries (Endless Summer™, Bloomstruck™, and Summer Crush™ brands) have introduced new hydrangea genetics. Try short growing Let’s Dance™ series in small gardens. Also, grow a different hydrangea species such as mountain hydrangea (H. serrata). New from PW Colorchoice is the Tuff Stuff® series of mountain hydrangeas which display superior bud hardiness and re-bloom. Tuff Stuff Ah-Ha® re-blooms heavily and has large lacecap blooms with double sepals,that are either pink or blue depending on soil (media) pH.

Spike Winterhazels

Posted by Hugh on March 20th, 2019

I

Winterhazels (Corylopsis spp.), native to China and Japan, is a wonderful genus comprised of winter flowering shrubs of varying heights and widths (USDA hardiness zones 5 to 8). Few U.S. gardeners know of them. Their bright yellow flowers are a lot bigger and showier than the witchhazels (Hamamelis spp.) which are close botanical relatives. In my early March garden the winterhazels start blooming as the witchhazels are finishing up.

The winterhazels occupy partially shaded shrub borders or woodland areas. Eight species, sometimes more, are available from on-line nurseries. Spike winterhazel (C. spicata) and buttercup winterhazel (C. pauciflora) are low spreading forms that fit into smaller urban and suburban gardens. Their slightly fragrant flowers are lemony yellow with red-purple anthers.

Spike winterhazel grows to 4-8 feet tall and to 6-10 feet wide. Individual flowers, only 3/8 inches long, comprise small drooping clusters (racemes to 2 inches long); clusters hold 6-12 flowers. After bloom, 4-inch long circular (ovate to obovate) leaves unfold with a bronze-purple tint; within 2-3 weeks leaves take on a bluish-green color. Tiny hairs on the leaf surface give the leaves a dusty look by late summer. Fall leaf color is an yellowish-green. Fall seed capsules swell and hold two small seeds.

Winterhazels prefer a compost-rich, well-drained, acidic soil in full sun to part shade. They tolerate most garden soils except heavy clays. Plants favor shading from direct afternoon sun in southerly climate zones 7-8 as well as shelter from high winds. Flower buds/flowers are susceptible to cold injury if winter temperatures are severe.

After flowering or by late spring, prune winterhazels as needed to hold shrubs in check. Feed with 10-10-10 or equivalent granular fertilizer. No serious insect or disease problems trouble these low maintenance shrubs.

Significant cultivar: With its circular golden foliage, C. spicata ‘Aurea’ is an attention grabber from March through October. New spring foliage opens rosy-pink, turns golden yellow, and to bluish green by early summer. Nodding racemes of small, bell-shaped pale yellow flowers open in the late days of winter and last 2-3 weeks. Frigid nights in the mid- 20’s rarely trouble the blooms. Flower fragrance does not overwhelm.