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

Success With Blue/Pink Mophead Hydrangeas

Posted by Hugh on October 1st, 2012

Mophead Type hydrangea in Jonesborough, TN garden

Mophead hydrangeas (Hydrangea macrophylla), the blue/pink flowering species, have been the gardening rage since the early 1990’s. Endless Summer® hydrangea started a wave of new repeat blooming (remontant) cultivars. They bloom on both new season’s as well as old wood from the previous year. These hardier cultivars extended the flowering time by 8 to 10 more weeks and bloomed in cooler climates formerly unable to grow mopheads.

To add to your success, here are additional tips on growing mopheads:

“The Right Plant In The Right Location” rule strongly applies to mopheads. The farther north you grow mopheads, the more sunlight they can handle. In USDA hardiness zones 4 thru 5-a, plant in a sunny location which receives a minimum of 6 hours of sunlight. Reduce to 4-5 hours of mostly morning sunlight in zones 6 and 7, and grow in high shade in zone 7-b to 9.

Protect Against Severe Winter Temps and Spring Freezes: Hydrangea buds openvery early. Late spring freezes frequently destroy or injure flower buds and new growth. Keep the crown (plant base) heavily mulch to mid-May in northerly areas.

Feeding: Fertilize with a slow-release fertilizer such as 10-30-10 or equivalent in early spring. For example, the phosphorus (30% P) level should be 2-3 times greater than the nitrogen (10% N) or potassium (10% K) levels. Container plants may need an extra bi-monthly feedings of a water soluble fertilizer. Over-feeding hydrangeas may result in dark green leaves (a good thing) and fewer flowers (not so good). In USDA zones 4 and 5, do not fertilize past August 15th, as it may lead to winter injury.

Watering: Mophead hydrangeas have large fleshy green leaves and insist on growing rapidly. Overwatering may lead to few or no flowers at all. On hot summer days, it is normal for mopheads to wilt for a short period in mid-day. It’s best to irrigate thoroughly once weekly, usually 1 ½ inches of water, than to water a little bit every day.

Pruning: Mopheads should not be cutback in the fall like other hydrangea species. Flower buds are borne on old wood for late spring flowering. Remember: the remontant type of hydrangeas bloom on both old and new wood.

Stunning Fall Color of Golden Larch

Posted by Hugh on September 29th, 2012

Golden Larch at NC Arboretum in Asheville, NC

Golden larch (Pseudolarix amabilis) is a rare find in U.S. landscapes. This deciduous conifer is native to eastern China. It is not a true larch (Larix spp.) and is relatively under-planted in the U.S. Golden larch appears to prosper in warm humid areas and should flourish in the southeast U.S. (USDA hardiness zone 6).

Golden larch may be planted in full sun to light shade. It thrives in organically rich moist soils which are well drained. A mature tree grows 50 to 60 feet in height and 30 to 40 feet in spread. A new tree starts out slowly, and growth becomes more moderately paced after 2 years. Tree shape is weakly pyramidal with open horizontal branches.

New spring foliage is light green, turns medium green in summer, and golden yellow in early fall before dropping. Golden larch earns its name for its spectacular golden yellow autumn leaf color, which ages to orangey-brown before falling in mid-October. Fall needle retention time is short compared to other deciduous conifers as larch (Larix spp.), bald cypress (Taxodium spp.) and dawn redwood (Metasequoia glyptostroboides). Needles range from 1 ½ to 2 ½ inches in length and are slightly curved.

Cones are 2 to 3 inches in length, 1 ½ to 2 ½ inches wide, green during the summer, maturing to golden brown in autumn. Young trees exhibit a reddish brown bark which age to grayish brown with some ridges and furrows.

Golden larch ages to a large majestic tree. Utilize it as a specimen tree on large properties such as golf courses, public parks, and college campuses. Disease and pest problems are as rare as finding this tree in U.S. commerce. Availability is from a few specialty nurseries selling on-line.

Autumn Clematis – Be Careful What You Ask For

Posted by Hugh on September 25th, 2012

Sweet Autumn Clematis on fence

SA Clematis over Holly

Autumn clematis (Clematis terniflora) is a late summer flowering twining vine with dark green foliage. The sweetly fragrant white flowers bloom for 4-5 weeks. The four petal (sepal) blossom is 1 inch across, borne in clusters, and mature into puffy plume-like seed heads. Its deciduous foliage is leathery in feel and remains mostly blemish free through the summer months.

Sweet autumn clematis grows vigorously in full to partial sunlight, easily 20 to 30 feet per year once established after its first year. It is not fussy as to soil type and does not require fertilizing ever. Irrigate only in the first year to get the vine established.

Autumn clematis comes into a garden uninvited and is capable of self-seeding and may become invasive. It can climb up and blanket a small tree or shrub as its arbor. You may thin out the vine in the spring and summer months, so the tree or shrub can access sunlight, allowing both to co-exist.

Autumn clematis has no serious disease and pest problems when properly sited in a garden. It flowers on new wood. Its vigorous growth rate suggests that you cut this clematis back hard before the start of spring. Some additional pruning may be necessary to corral its rampant growth leading up to late August flowering.

Decorate With Fall Mums

Posted by Hugh on September 21st, 2012

Beautifully Grown Fall Mum

Dendranthemums (mums) are favorite plants for outdoor decorating in the autumn season. Fall mums come in a variety of colors from white, yellow, pink, orange, red, bronze, and purple. Blooms attract numerous bees and butterflies.

Plant heights vary, depending on the degree that the greenhouse grower has sheared or sprayed (with growth retardants) the mums. As perennials, mums are reliably hardy to zone 6 (see exceptions below). Plant sizes vary from short pixies at 8 inches to tall 48 inch well-branched plants. Plant widths measure 12-36 inches across.

If you are growing mums, plants may be purchased in early spring and nurtured through the summer months. Plant them in full sun and in moist well-drained soil. Avoid planting them in areas where street and house lights will shine on them at night. Mums bloom poorly without a full night of darkness.

Feed once at spring planting time with a slow-release fertilizer. As an alternative, feed with a water-soluble fertilizer such as Miracle-Gro®, Daniels®, or Jack’s Classic® twice monthly until buds form or through the end of August.

From late spring until mid-July, pinch growing tips back 2-3 inches every two weeks. This will create well-branched plants full of blooms. Do not allow mums to bloom early in the summer, usually a reaction to severe heat or dry soil. Mums should be irrigated during dry spring – summer periods.

To perennialize fall-purchased plants, remove them from the pot and set them in the garden soil by mid-September for their pot-bound roots to knit into the soil. Mulching also helps to protect them overwinter. Do not fertilize fall-planted mums.

After a freeze has killed top growth, don’t cut back plants. Wait until late winter when buds are sprouting near the soil line. At this time you may dig up and divide the tiny plants. Discard the woody center of the crown.

Heirloom or “old-fashioned” mum varieties are back! These tend to bloom very late in the fall and are hardy in zone 5. Some of the best are:

‘Clara Curtis’ – deep pink, daisylike blooms

‘Mary Stoker’- peachy yellow blooms

‘Sheffield’ (aka ‘Sheffield Pink’) – light pink

‘Ryan’s Pink’ – bright pink daisy blooms with yellow centers.

Mums are good garden companions with fall asters and fall sunflowers (Helianthus spp.). These companion perennials require the same care, although they differ in plant heights and widths.

Emerald Spreader® Yew Exciting New Ground Cover

Posted by Hugh on September 16th, 2012

Emerald Spreader® Japanese Yew

Emerald Spreader® (Taxus x media ‘Monloo’) is a short wide-spreading Japanese yew. Emerald Spreader grows slowly, and may reach 2 ½ feet in height and 8 to 10 feet in spread over 20 years. The short 5/8 inch long, fine textured needles retain their rich dark green color through the winter months in USDA hardiness zones 6 and 7. Foliage may discolor from cold wintery winds in zones 4 and 5, unless protected.

Yews are classified as conifers and are separate sexes (“dioecious”). Female yew varieties bear green fleshy fruits called “arils” instead of cones. In early fall the green aril fruits ripen to bright red and are quite ornate in the fall-winter landscape.

Yews grow in average landscape soils and in full sun to partial shade. Good soil drainage is absolutely essential for yews. Provide adequate soil moisture during the first growing season to develop an extensive root system. Before new spring growth begins, feed with a general purpose fertilizer, such as 10-10-10.

Emerald Spreader is planted in low front borders such as home foundations or along walkways. At times branches may look rigid or stiff. Shearing 1-2 times during the growing season will soften their appearance. Do not prune yews during cold dry wintry intervals as to injure branches and needles.

Yews suffer from few insect or disease problems when properly sited. Root rots and plant deaths are common in poorly-drained soils. Yew foliage is poisonous and should not be planted if livestock are in close proximity. The seeds inside the aril fruits are also poisonous. Birds eat the fruits, but do not digest the seed. Deer and rabbits keep their distance from yews.

Muhly Grass Pink Color Emblazens The Autumn Season

Posted by Hugh on September 12th, 2012

Muhly grass in November at NC Arboretum in Asheville

For most of the season Muhly grass (Muhlenbergia capillaris) grows pretty much unnoticed. Muhly exhibits a semi- erect growth habit, 3-4 feet in height and 3-4 feet in spread.

Walking past a pink billowy inflorescences of Muhly on a brisk sunny October morning is nothing short of “wow”. For 10- 12 weeks, from early September thru late November, a pink haze arises 12 inches or more above the narrow bladed green foliage. Muhly stands up well to rainfall and early frost. By late autumn the vibrant purple to pink hues gradually fade to beige.

Muhly grows best in full or partial sunlight (6- hour minimum) in average moist well-drained soil. Its native range extends from southern New England to southern Florida, west to Texas. Mulhy prospers in dry, gravely, often poor soils. Muhly stalls out in wet soggy winter soils.

Selecting a hardy seed source is very important. Muhly is marginally hardy in zone 6. Buy plants or seeds from a nursery which has checked on seed provenance. Foliage is semi-evergreen in parts of zone 7 and further south. Old growth should be cut back to 5-6 inches above ground in late winter.

Plant Muhly as a single specimen or group several for a larger display in a garden border or meadow setting. Muhly does not aggressively spread to other areas of the garden.

Three cultivars: Pink Cloud™ (shorter 2 ft. height, pink inflorescence); White Cloud ™ (4-5 ft. tall, more upright habit, and white inflorescence); and Regal Mist™ (3-4 ft. height, dusky pink inflorescence)

Leyland Cypress For Fast Growing Evergreen Privacy

Posted by Hugh on September 9th, 2012

: Leyland Cypress

Leyland cypress (xCupressocyparis x leylandii) is winter hardy in the Southern Appalachian region (USDA zones 6 and 7). It is frequently regarded as “the” conifer for Southern states. Its growth rate, compared to other evergreen conifers, is horrendously fast, with young established plants growing 3 feet or more annually. A young 2-3 foot specimen may reach 25 to 30 feet tall in only ten years. A 50 to 60 foot tall Leyland screen is a common sight.

At planting time Leyland should be spaced 16 to 18 feet apart and no closer. An alternative design is to plant each 8 foot apart and eliminate (or transplant) every other Leyland within 3-4 years.

Plant Leyland in full day sun and in fertile well-drained soil. A new planting should start off irrigated the first two summers. Backup irrigation during severe summer dry periods is highly advised to prevent disease flareups.

What attracts gardeners to plant Leylands is the soft green sprays of evergreen foliage. Numerous cultivars are available, and three commonly planted include: ‘Haggerston Grey’ (green needles with slight gray cast), ‘Leighton Green’ (rich green), and ‘Gold Rider’ (yellow with green tips).

Crowded and/or shaded plants are susceptible to any of three serious fungal diseases: Cercospora needle blight, Botryosphaeria canker, and Seiridium canker. Occasionally, bagworms populations may ravage Leyland foliage in late spring. Fungicide and pest spraying are mostly ineffective due to the enormous size of Leyland cypress.

Leyland is now commercially grown as a Christmas tree in the deep South, where fraser fir trees do not thrive. Leyland’s foliage displays exceptional sea salt tolerance, making it a good wind barrier around coastal areas.

This Korean Maple Deserves To Be Planted More

Posted by Hugh on September 4th, 2012

Acer pseudosieboldianum ‘Takeshimense’

Ullung-do Island Korean maple (Acer pseudosieboldianum ‘Takeshimense’) is a small deciduous tree which will grow to be 20 -25 feet tall tree, with a spread of 15-18 feet. It tends to branch low to the ground. It originates from the Ullung-do Island in the sea of China.

Korean maple is one of the best maples for fall color in the Southern Appalachian region (USDA zones 6 and 7). For a short time, new spring foliage emerges with a reddish tinge. Its forest green foliage lasts all summer long and stays disease and pest free. Autumn leaf colors are exceptional with reds, oranges and yellows throughout the tree.

It features subtle clusters of creamy white flowers with purple bracts rising above the foliage in early spring before the leaves appear. The two winged samaras turn purple in mid-summer. The rough gray bark and brick red branches add an interesting dimension to the winter landscape.

Korean maple excels in full sun in northerly areas (USDA hardiness zones 4) where few Japanese maple (A. palmatum) cultivars, if any, will grow. In northerly areas Korean maple grows in full sunlight and a compost rich, well-drained, and slightly acidic soil. Further south (zones 6 and 7), partial day or full morning sunlight is the rule. The tree shouldn’t be permitted to dry out. Irrigate during extended dry periods and cover the ground with 2-3 inches of mulch.

This is a relatively low maintenance tree, and is best pruned in the summer after the leaves have fully developed. Korean Maple is an open multi-stemmed low canopy deciduous tree which makes it ideal for planting under power lines.

Availability of Korean maple is limited to e-commerce nurseries on-line.

Growing Full Moon Maple in the Southeast U.S.

Posted by Hugh on September 1st, 2012

Acer shirasawanum 'Aureum'

Simply put, golden full moon maple (Acer shirasawanum ‘Aureum’) is a stunner (USDA hardiness zones 5-7). It is a slow growing maple, eventually reaching 18-20 feet in height and spread at maturity. It tends to be a long-lived tree if properly cared for. Leaves are circular with 9-13 short pointed lobes. Each lobe does not cut deeply into the leaf. The circular gold leaf creates a “full moon” design.

Foliage color is changeable with the seasons. Spring foliage starts out bright yellow and darkens to lime green in the summer. Clusters of tiny delicate flowers emerge in April for a brief period. The golden foliage serves as a bright background for tiny reddish purple flower clusters. Leaves may be tinged red along the edges. In early autumn leaves display a mix of orange and red tints. Small double winged samara color up red against the lime green foliage in late summer.

Growth rate starts off moderately, but slows down after 8-10 years. Full moon maple has a long life span. Plant it in a compost rich, slightly acidic, well-drained soil. In the Southeast U.S. full moon maple prefers morning sunlight to avoid leaf scorching in the summer heat. Irrigating during excessive dry spells is also warranted. Leaves may turn green in heavy shade. Protect from strong winter winds which may desiccate the dormant growth buds.

Full moon maple is a relatively low maintenance small garden and patio tree. Pruning, when needed, is best performed anytime from mid-spring through the summer.

‘Northwind’ Switchgrass Is Environmentally Tough and Beautiful

Posted by Hugh on August 28th, 2012

: Young Clump of ‘Northwind’ Switchgrass

Northwind switchgrass (Panicum virgatum ‘Northwind’) is a medium sized 5 to 6 feet tall ornamental grass. This tall native prairie grass grows best in full sunlight for most of the day. Its tight narrow posture seems to fall apart in shade. There are many good switchgrass varieties. Northwind makes a strong vertical presence, perhaps the best of the lot.

Northwind grows tall and narrow, with steely blue foliage and a lacy inflorescence. Beginning in mid-summer the soft pinkish white inflorescence rises 1-2 feet above the foliage (USDA hardiness zones 5). By early autumn floral heads fade to a silvery gray tint and look great in floral arrangements. The narrow grass blades turn many shades of yellow in autumn.

Switchgrass prefers a moist fertile ground, but adapts to most soil types, and either wet or dry conditions. This tough prairie inhabitant is heat and drought tolerant and is disease or pest resistant. Vigorous overcrowded crowns should be divided every 4-5 years, which is no easy task. Overwintering clumps stand rigid like sentinels and provide shelter for birds and other wildlife.

Take advantage of its natural form and foliage color in residential and commercial properties. Northwind is attractive alone or mixed with other plants in containers, massed along a stream bank, or set on steep slopes or reclamation lands. Switch grass is utilized in dune stabilization along coastal beaches and tolerates high winds and salt spray. Incorporate switchgrass in highway median strips; the dense upright vegetation effectively blinds headlights from opposing traffic.