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

Japanese Larch Is Preferred In Northern U.S.

Posted by Hugh on November 10th, 2016

Larix kaempferi ‘Wolterdingen’ at Chicago Botanical Gardens

Larix decidua at Biltmore Estates, Asheville, NC

Larches (Larix spp.) are majestic deciduous conifers in their northern ranges of their habitat (USDA hardiness zone 4 to 7). However, trees do not prosper in hot and humid summers south of USDA Zone 7.

One of the best is Japanese larch (Larix kaempferi), but unfortunately, it is not commonly planted in U.S. landscapes. The tree averages 50-60 feet in height and 25-35 feet in width. Old specimen trees that are 70-90 feet tall are not difficult to find in botanical gardens in zones 5 and 6.

The tree grows rapidly with an open and pyramidal form and slender, pendulous branchlets. Its fine textured needles are soft to the touch. Bright green needles (to 1 ½ inches long) appear in brush-like clusters at the ends of spur-like shoots along the branches. In autumn needles turn golden yellow and dust the ground around the tree as fine mulch. Flowers appear in March, and the seed bearing cones ripen in October. Also, the 1 ½ inch long green cones feature reflexed bracts that turn brown at maturity.

Japanese larch prefers a fully open site. Soil should be mildly acidic and adequately drained. Larch is intolerant of poorly drained or dry soils, deep shade, and most urban pollutants. Japanese larch is preferred over European larch (L. decidua) because the latter is susceptible to numerous diseases and pests, particularly needle cast, needle rust, canker, and case borer.

Its enormous tree size makes it more suited for large properties such as parks and golf courses. Larch may be planted for reforestation, as a windbreak, or as an individual specimen.

Cultivars: ‘Pendula’ is a popular weeping form in the U.S. ‘Diana’ has contorted, twisted branches; it grows to 6-8 feet tall over the first 10 years, maturing to 20-25 feet high. ‘Wolterdingen’ is a slow growing dwarf shrub and very popular among dwarf conifer collectors.

American Witchhazel Blooms in Autumn

Posted by Hugh on November 7th, 2016

American witchhazel in late October

American witchhazel (Hamamelis virginiana) is the last native flowering plants to bloom in the calendar year. It is a deciduous shrub or small tree, native to woodlands, forest margins and stream banks in eastern North America (USDA hardiness zones 3-8). It typically grows 15-20 feet tall as a multi-stemmed shrub and 30 feet tall in tree form.

Beginning in late September (in Tennessee), branches are covered with tiny clusters of bright yellow flowers. Each flower is composed of 4 strap-like yellow petals. In some years flowers appear before leaf drop and some flowers go unnoticed.

The fertilized flowers form greenish seed capsules that mature to light brown almost a full year later. Seed capsules split open next fall, nearly a year later, and blast (dehisce) seeds 10-20 feet away. Obovate (oval) witchhazel leaves are dark green and average 6 inches in length. Foliage may turn many shades of yellow in fall.

American witchhazel grows in an average, moist, well-drained, mildly acidic soil and in full sun to partial shade. Growing preference is light shade to partial sun and in sandy loam soil. More flowers are produced in full sun than shade. It tolerates compacted and clay soil, but tends to sucker freely to eventually form thickets or colonies; remove suckers to maintain a tidy appearance. Otherwise, little pruning is necessary other than to limit plant height and spread. Pruning is best scheduled for early spring.

Witchhazels have no serious insect or disease problems. Occasional Japanese beetles may damage leaves over a short time, but rarely needs spraying. Deer will browse on the foliage, but cause little serious damage.

Cultivars: There are only a few known selections of American witchhazel. In a trial of various witchhazel clones, Dr. Andrew Bell at the Chicago Botanical Gardens, singled out ‘Little Suzie’ and ‘Harvest Moon’. Both are compact growers and produce abundant flowers. Little Suzie is more dwarf in stature. Harvest Moon drops its foliage early to show off its lemony yellow flowers.

Deerproofing

Posted by Hugh on November 4th, 2016

Deer Enclosure in Waynesboro, VA property

Blueberry planting in separate enclosure (cage)

Deer love to eat most of the flowers, plants and trees in your garden. To discourage deer from eating your garden, you basically have three (3) options.

Construct a Barrier or Fence.
Make your garden unpleasant for deer.
Choose plants that deer don’t like.

Deer Barriers and Fences

Deer can jump an 8 foot fence, but in most cases this height is adequate. Fencing is made from woven wire and polypropylene products. Shorter fences serve as as deterrents and usually effective if deer populations are not starving. Additional deterrents should be considered (read-on). Fences are your costly option and limit your enjoyment of your home landscape. Create a natural barrier such as planting 1-2 rows of thorny shrubs or tall-growing hedges to discourage deer .

Scent Proofing

Commercial sprays are available at garden centers that keep deer away for short periods, 1-3 months. These are strange odors that deer are not accustomed to. Others include Tabasco sauce, mustard, garlic, cayenne pepper, fragrant bar soap, shampoo, et al. Additional short-term remedies are to edge your garden include human hair (ask your barber or stylist for sweepings), fresh garlic, rotten eggs, onions, and mothballs.

Some herbal plants give off a scent that deer usually dislike. They include mint, cloves, sage, yarrow, oregano, citrus, among others.Plant these herbs on the outer edges of your garden to discourage deer.

Deer Proof Plants

Check with your local Extension office for a list of deer-resistant trees, shrubs, and perennials. Plant lists abound in books and on the Internet. However, what may work best in one locale may not in another place. Deer in different parts of the same state may not have similar plant palates. If deer populations are extraordinarily high, they will feed or browse on any plant, some that are not their favorites.

Longwood’s Chrysanthemum Festival

Posted by Hugh on November 2nd, 2016

Ozukuri Mum Display at Longwood Gardens

Mum Display at Longwood Conservatory

As fall mums are finishing up in our gardens, Longwood Gardens in Kennett Square, PA has debut their annual chrysanthemum display in the Conservatory. More than 17,000 chrysanthemums were nurtured and trained, some for more than a year by their talented horticultural staff to resemble balls, spirals, columns, pagodas, and more. It is the largest display of exhibition chrysanthemums in the United States.

The star of the show, the Thousand Bloom Mum or (called “Ozukuri” in Japan), boasts more than 1,500 perfectly arranged yellow flowers on one plant and is the largest grown outside of Asia. Horticulturists grow a single mum plant containing hundreds of perfectly spaced blooms. The Ozukuri display serves as the centerpiece of their annual Chrysanthemum Festival. Visitors will see thousands of mums in 13 different classes and 70 different forms.

The thousand-bloom mum is massive: 12.5 feet wide and almost 8 feet tall. It takes 18 months to grow. They use an heirloom variety from Japan called ‘Susono-no-Hikari’.

Longwood Gardens brags that it’s the largest Ozukuri ever grown outside of Asia. Each year Longwood’s talented staff has increased the bud count: In 2011 — 1,167 flowers, in 2013 — 1,416, in 2015 — 1,509, and 1523 in 2016.

The 2016 festival runs October 15 through November 20. Peak bloom is from November 5-20. Don’t miss this and all the wonderful sights at this year-round Garden Wonderland. Next up is the annual “A Longwood Christmas” from November 24 – January 8, 2017.

Photo by Jane Conlon

Growing Amaryllis

Posted by Hugh on November 1st, 2016

Potted Amaryllis

Amaryllis is a tropical bulb that blooms indoors usually in winter (USDA hardiness zones 9-11). It is one of the easiest flowering plants to grow. Everything you need to enjoy a bouquet of big, beautiful flowers is inside the bulb. Simply plant the pre-chilled bulb in a container and add water.

There are many varieties to choose. Purchase large size bulb (over 30 cm) that produce more bloom stalks and greater numbers of flowers. Local garden centers stock bulbs starting in early fall and offer some already potted. Amaryllis bulbs should be planted immediately or can be stored over several months in a cool (40-50°F) dark dry place prior to potting.

Select a pot with a wide base, large enough to accommodate the new bulb. Fill the bottom of the container with soilless growing media and set the bulb on top. Finish filling and packing the soil-less media within 1 inch of the top. Leave the shoulders and neck of the bulb exposed. Thoroughly water the potting media to settle the bulb. The newly purchased bulb has been pre-chilled and is ready to sprout within 3-4 weeks. Place the pot in a cool (60-70°F) location and in bright light indoors or one-half day morning sunlight outdoors.

Continue to water as needed after shoots and flower buds have emerged. Overwatering will cause amaryllis bulb rot. The large flowers may become top heavy; stake the flower stalk if necessary to support the floral stalk. Blooms last longer if you can keep them away from direct sunlight and dry heat. As the individual flowers fade, snip them off with a sharp knife. Eventually, cut back the entire bloom stalk to about an inch above the bulb. Bloom stalks cut flowers.

Bulb will grow in the same pot and bloom again for several years. When spring frost is over, move amaryllis outdoors to ½ day of morning sunlight and protect from drying winds. Continue to water and feed monthly with a water soluble fertilizer from spring to early fall. Bring the pot back indoors when night temperatures fall below 40°F.

Every 3-4 years in late summer, divide and repot your amaryllis bulbs that have become crowded and pot bound. Stop watering and allow 2-3 months for chilling temps and very low light. The old leaves will dry up and the bulb is dormant. Store the potted dormant bulb in a cool (40°F minimum) garage or storage area.

Amaryllis bulbs make great holiday gifts to garden friends. Brent and Becky’s Bulbs in Gloucester, VA list many colorful varieties in their on-line catalog.

Polar Express Sunbelt Rose Big Winner At 2016 Biltmore Gardens Rose Trial

Posted by Hugh on October 29th, 2016

Polar Express Sunbelt Floribunda (Photo: The Biltmore Company)

‘Honeymoon Arborose’ (photo: The Biltmore Company)

If you grow roses in the U.S. Mid-South region, the historic Biltmore Gardens in Asheville, NC is key source for discovering what varieties you should be growing.

Recently, a jury of world rose experts selected the winning roses in the 2016 Biltmore International Rose Trials. Since 2011, Biltmore’s historic Rose Garden has been home to the trials in which more than 150 varieties from growers and breeders worldwide have been planted and cared for by Biltmore’s horticultural team.

Polar Express Sunbelt, a fluffy white rose bred by Kordes, took the top award: the George and Edith Vanderbilt Award for Most Outstanding Rose of the Trials.

In addition to winning the Best in Show Award, Polar Express Sunbelt won the Edith Wharton Award for Best Floribunda, and the William Cecil Award for Best Growth Habit.

Additional winners this year were:

Honeymoon Arborose, bred by Kordes, won the Gilded Age Award for Best Climber and the Lord Burleigh Award for Most Disease Resistant
Double 10, bred by Ping Lim, won the Pauline Merrell Award for Best Hybrid Tea
The Lark Ascending, bred by David Austin Roses, won the Chauncey Beadle Award for Best Shrub

Each trial lasts two years and a permanent jury judges the roses four times per year. This year’s final round of competition started with 31 entries planted in 2014 from Canada, the U.S., France, Ireland, Great Britain and Germany. Competing roses are evaluated for overall health and rigor; fragrance; disease resistance; and ability to repeat bloom.

Biltmore’s Rose Garden receives Award of Garden Excellence
Biltmore’s rosarian Emily Wilson and past American Rose Society president Jolene Adams unveiled an award in honor of Biltmore’s historic Rose Garden: the World Federation of Rose Societies Award of Garden Excellence. Biltmore’s rose garden is one of only 10 gardens in the United States and 62 worldwide to receive this honor.

Conifers for Small Garden Spaces

Posted by Hugh on October 27th, 2016

Dwarf Blue Colorado spruce with other conifers

Abies koreana ‘Silberlocke’ at Atlanta Botanical Gardens

Some properties can not accommodate the enormous size of tall evergreen trees. In the world of conifers, a select number of genetically dwarf species and varieties are better fits for small spaces. Most evergreens are sun lovers and require a well-drained soil. Mulching around trees and shrubs also benefits to conserve soil moisture and keep roots cool.

Here is a collection of conifers that you should try in your landscape/garden. Mr. Duane Ridnour at Beaver Creek Nursery in Knoxville, TN and Michael Balogh, owner of Mountain Meadows Nursery in Weaverville, NC, assisted in developing this list. Any list is never complete and additional numbers of excellent dwarf conifers could be added.

‘Silberlocke’ Korean fir (Abies koreana) -best grafted on Abies firma rootstock in clay soils

Shrub selections of Deodar cedar (Cedrus deodara) -two selections: ‘Feelin’ Blue’ – spreading evergreen with bluish-green needles; ‘Divinely Blue’ -dense multi-stemmed evergreen shrub with a distinctive and refined pyramidal form. Zones 6 (with protection) – 9)

Shrub selections of Japanese cedar (Cryptomeria japonica) – ‘Gyokuri’ – 18 feet high intermediate form or ‘Elegans Nana’ (compact shrub form).

‘Sester’s Blue’ Colorado spruce (Picea pungens var. glauca) is a dense multi-stemmed evergreen shrub with a distinctive and refined pyramidal form; retains its silvery blue needle foliage color through the winter (zones 3-7).

Shrub selections of Bosnian pine (Pinus leucodermis), formerly P. heldreichi, comprises a number of excellent dwarf selections (USDA hardiness zones 4-8); thrives at home in dry limestone soils. Dwarf selections include ‘Compact Gem’, ‘Irish Bell’, and ‘Schmidtii’.

‘Bergman’ Japanese White Pine (Pinus parviflora ‘Bergman’) is a compact upright shrub or small tree with slightly twisted blue-green needles.

‘Thunderhead’ Japanese black pine (Pinus thunbergii ‘Thunderhead’) is an 8-10 feet high shrub with superior disease and insect resistance.

‘DeGroot Spire’ Eastern Arborvitae (Thuja occidentalis ‘DeGroot Spire’) grows about one-third the size of popular cultivar Emerald®.

‘Roger’s Aurea’ Western arborvitae (Thuja plicata ‘Rogers Aurea’) grows 4 to 6 feet tall and wide with bright golden foliage (zones 5-9).

‘Van den Akker’ Alaskan cedar (Xanthocyparis nootkatensis ‘Van den Akker’) is a narrow vertical form that grows less than half the height of the species.

Most conifers listed here are available for regional nurseries specializing in dwarf conifers. Many large west coast U.S. nurseries ship to independent garden centers across the country.

Eastern White Pine Losses Continue

Posted by Hugh on October 24th, 2016

Eastern White Pine (Pinus strobus)

Environmental and pathogenic problems continue to take their toll on Eastern White Pine (Pinus strobus). This valued landscape and lumber tree is native in the Eastern U.S. and Canada (USDA zones 3-8). Climate change is likely contributing to recent losses of white pines due a number of serious disease and pest problems that are reducing tree numbers.

Pests:

A decade ago, pine beetles devastated large populations of white pines in the Southeastern U.S. Injury symptoms closely mimicked drought injury. Beetles lay their eggs and larvae tunnel into the branch wood. Needles turn straw brown, often showing up at tops of trees. Summer droughts have made infestations more severe.

White Pine weevil is another serious pest. Weevil larvae feed on the sapwood and kill the top growth (leaders). A common symptom is presence of pearl white resin leakage on limbs.

Pine Sawfly larvae (caterpillars) can cause rapid defoliation of branches if left unchecked; they feed in groups on the needles.

Pine needle miner larvae feed inside needles causing them to turn yellow and dry up.

Two kinds of scale insects feed on needles: pine needle scale (white, elongated scale) and pine tortoise scale (brown colored). Horticultural light oils are very effective applied in late winter.

Diseases:

White Pine Blister Rust. In some areas of the U.S., farmers and home gardeners are prohibited by law to grow black currants, which are alternate hosts for this disease. Red currants should not be grown within 300 feet of white pines. Infected branches may be pruned off. Some varieties of white pine are resistant to this disease.

White Pine Decline describes the slow decline of pine trees. Needles turn pale green, shrivel, and ooze sap. The entire tree is usually affected and mimics a root system. Causes seem to be a combination of environmental stresses, and shows up worse in dry clay soils. Tree usually does not recover and dies within 4-6 weeks.

Additionally, white pines are susceptible to urban air pollutants including ozone and road salt. Limbs are susceptible to ice breakage.

‘Midwinter Fire’ Dogwood Brightens Up The Winter Landscape

Posted by Hugh on October 21st, 2016

Cornus sanguinea ‘Midwinter Fire’ in November

Winter Scene at Biltmore Estates in Asheville, NC

Bloodtwig dogwood (Cornus sanguinea), indigenous to Europe and Asia, is an upright branched, round-topped, spreading deciduous shrub (USDA hardiness zones 5 to 7). In the wild the species matures to 8-15 feet in height and spread.

Its common name “bloodtwig” is misleading. Winter wood on 1-2 year old branches is not red. Instead, winter stems turn a striking orange-yellow at the base with reddish twigs on the tips. Fall leaf color is golden yellow some years and a blah red in others. The 3-inch long broad-elliptic to ovate leaves in spring and summer are dark green above and grayish, covered with tiny hairs underneath.

If your goal is to introduce more vibrant color into the winter landscape, select the cultivar ‘Midwinter Fire’. This compact form grows only 5 to 6 feet tall and wide after 3-4 years. It flourishes in any soil type that is well-drained and in full to partial sun. Brightest stem color occurs on young 1-2 year old wood. Annual pruning is an absolute! and take care of this chore in early spring. Every 3-4 years rein in the entire shrub by cutting back all stems to the ground in early spring (renewal pruning). Bloodtwig dogwood tends to ramble and you will want to remove root suckers to check spread of shrub.

Flat white 2-inch wide cyme flowers are not sensational but do attract numerous butterflies and other pollinators. Up close, flowers emit a stale fragrance in May to early June. In August-September blue-black fruits (1/4 inch wide drupes) form and later attract winter feeding birds. Fall color can be average yellow some years and bright orange-yellow in other years. Summer foliage is green and remains blemish-free.

Utilize as a specimen shrub or group 3-5 together for color impact in fall and winter as a hedge or short privacy barrier. Redtwig is a great choice for attracting wildlife, particularly to rain gardens. No disease or insect problems trouble bloodtwig dogwood and deer leave it alone.

Happidaze® Sweetgum Produces No Gumballs

Posted by Hugh on October 18th, 2016

‘Happidaze’ Sweetgum on Median Strip In Johnson City, TN

Sweet gum (Liquidambar styraciflua) is a low-maintenance deciduous shade tree. The species is native from Connecticut to Florida and west to Missouri and south to Texas and Mexico (USDA hardiness zones 5 – 9). A popular landscape shade tree, it typically grows to 60 to 80 feet tall with a straight central trunk. A young tree is pyramidal in outline, but an older tree gradually forms an oval to rounded canopy.

Most sweetgum cultivars is notorious for producing “gumball” fruits which are hard, spherical, bristly fruit clusters to 1 ½ inches in diameter. Happidaze® is a fruitless cultivar. The absence of messy fruits littering lawns and walkways all fall and winter long sets Happidaze apart from most sweetgum varieties.

Lustrous, long-petioled, deep green leaves (4-7 inches across) with toothed margins emit a sweet fragrance when bruised. Fall color is a rich red maroon. Yellow-green flowers appear in spherical clusters in April-May and offer no significant landscape value. Branchlets may have distinctive corky ridges.

Sweetgum is easily grown in moist, well-drained soils. The tree prospers in full sun and falters in shade. It prefers a slightly acidic soil pH between 5.8 – 6.5; leaves frequently turn chlorotic (yellow) in high alkaline pH soils. Feed in early spring with a slow-release fertilizer such as Osmocote® or Nutrikote®. Refresh the mulch cover around the tree every spring.

Sweetgum rarely succumbs to serious insect or disease problems. Leaf spot diseases, webworms, caterpillars, borers and scales may be occasional problems. Iron chlorosis, a lack of available nutrient iron, may occur in alkaline soils.

Sweetgum is excellent shade, lawn, park or street tree. Give this large tree room to grow and it will reward you with lots of cooling summer shade and glorious fall color for many decades.

Special note: Sweetgum cultivars ‘Rotundiloba’ (medium size tree) and tall narrow ‘Slender Silhouette’ are two other seedless (no gumballs) forms.