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

American Elm Is Back

Posted by Hugh on November 2nd, 2012

American elm in woodsy landscape near Knoxville, TN

American elm (Ulmus americana) once lined America’s city streets until the deadly Dutch elm disease (DED) mostly eliminated it. DED is still present today. Outstanding disease resistant cultivars are truly making a difference, and American elm is on the comeback.

American elm is native to the eastern and central regions of the U. S. and southern Canada (USDA hardiness zones 3 to 9). American elm are related to hackberry (Celtis spp.) and zelkova (Zelkova spp.). There are many species of elm worldwide. Its arching vase shape branching habit is its trademark trait, and this large tree averages 60 to 80 feet in mature height and 25-30 feet in width.

Compared to other landscape trees, American elm is one of the earliest to flower, often in late winter in the Southern Appalachian region (USDA hardiness zones 6 and 7). By late May flowers have set small circular winged seeds (samaras) which float by wind over long distances. Seeds germinate rapidly under favorable conditions.

American elm grows in moist deep soils and full to partial sunlight. It copes with dry average soils, is mostly soil pH insensitive, and tolerates high soil salt levels better than most tree species. Elm withstands brief flooding episodes in spring and fall. Prune elm from mid-summer into fall when potential pest problems are minimal and the internal sap flow is low.

The first line of defense against Dutch elm disease is planting resistant cultivars. American elm is also susceptible to deadly phloem necrosis disease, with symptoms similar to Dutch elm. Elms are subject to numerous insect pests, but rarely threaten their long time survival.

Among the best resistant cultivars with true American elm bloodline, ‘New Harmony’, ‘Valley Forge’, ‘Washington’, and ‘Jefferson’ stand out. Among the Asian – American elm hybrids, ‘Morton’ (Accolade™) is a recommended choice. Accolade elm is also resistant to elm leaf beetle feeding.

Blue Mist (Caryopteris) Sparkles in Late Summer Garden

Posted by Hugh on October 31st, 2012

Caryopteris x clandodensis

Blue mist spirea or bluebeard (Caryopteris x clandodensis) is not commonly planted in U.S. landscapes. In mid- to late- summer, pale blue flowers open above the gray-green foliage. Leaves and stems are mildly aromatic to the touch. There are now several good hybrid forms, thanks to plant breeders’ efforts to improve garden performance.

Caryopteris (I prefer this name) grows in average soil, preferably slightly acidic, and wants very little extra care. Although moderately drought tolerant, don’t allow it to suffer through a prolonged dry spell without irrigation. Cold hardy to USDA hardiness zone 5 (perhaps 4 with some protection), branch tips may die back 30-40% over winter.

Some plant experts classify caryopteris as a hardy perennial and treat it as such. Shoot injury may become noticeable in early spring, necessitating pruning. The easiest solution is to severely prune back the entire shrub in late winter.

This shrub recovers rapidly from cutting back. The technique is simple, not time saving, and doesn’t require reading a pruning book. It results in a compact growing, space-saving shrub.

Caryopteris may open hundreds of blooms at any time over a 6-8 week period from late summer into fall. Caryopteris suffers from very few disease and pest problems, including deer feeding.

Its flowers and gray-green foliage (select varieties) are prized by florists who utilized them in fresh and dried flower arrangements. Fresh keeping quality often lasts 7 days and longer.

Many hybrid cultivars are available, including two favorites:

‘Worcester Gold’ – solid gold foliage and pale blue flowers.

‘Dark Knight’ – deep blue flowers on 3-4 foot compact plant.

Full Moon Japanese Maple Is Very Popular

Posted by Hugh on October 13th, 2012

Fall Color on Acer japonicum 'Acontifolium'

The term “full moon Japanese maple” may be confusing. There are actually three species and cultivars of Asian maples that are referred to as “full moon”. The most popular full moon cultivar planted in the Northeast and Southern Appalachian regions (USDA zones 5 thru 7) is Acer japonicum ‘Acontifolium’.

A. j. ‘Acontifolium’ is hardy as far north as Chicago, where it requires winter protection from nearby Lake Michigan (USDA hardiness zone 5). Winter protection is crucial in zone 5, and summer heat protection is key to successfully growing it in zone 7.

A. j. ‘Acontifolium’ grows as a small 15-30 foot tree or multi-stemmed large shrub. It exhibits a spreading or mounding form. During its early years you should stake up the leader to add greater plant height. Branches tend to nod slightly.

Small clusters of reddish purple flowers appear in early to mid- spring, followed by double-winged samaras (seeds). Palmate, almost fern-like green leaves are deeply divided into 9-11 toothed and cut lobes. The circular leaves turn orange to crimson red in the fall.

The soil should be moist and compost rich, planted in full sun in the North (zones 5 -6), and in partial shade in the South (zone 7). Protect against strong winds. Japanese maples are best pruned in summer and early autumn to reduce sap bleeding.

Fertilize in late winter before growth begins with granular 10-10-10 or equivalent. Irrigate shallow rooted Japanese maples during exceptionally long dry spells.

Seven-Son Flower Is Flowering Again

Posted by Hugh on October 10th, 2012

Fall Flowering on Seven Son Flower

Back in bloom for a second time in two months! This is my way of describing seven-son flower (Heptacodium miconioides), a small 15-20 foot tree or large shrub from China.

Seven-son’s creamy white petals open in late August and finish up in early September. By late September, the petals have fallen, and the small green sepals (calyces) have expanded and turned pinkish red. Blooms are lightly fragrant if your nose is a few inches from the cluster. Numerous species of butterflies and bees are attracted to their scent.

Fall leaf color is non-existent over the drab greenish yellow heart shaped leaves in late October and November. The grayish or tan colored bark peels off in narrow strips to reveal an off-white inner wood.

Seven-son appears happiest in the north, growing in northern Ohio (USDA zone 5) as far south as Nashville, TN (zone 7). The tree does not seem to handle the rollercoaster ups and downs in winter temperatures which we commonly experience in the Southern Appalachian region (USDA zones 6 and 7). By late winter, twigs and small diameter branches become heavily cankered, leading to serious dieback in the new spring growth.

Seven-son has a rambling growth habit from stem and root suckers which necessitates annual pruning. Otherwise, it makes a good patio tree so you may enjoy its twice flowering habit.

Plant in well drained soil and irrigate when summer drought period is severe.

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.

Apples Ready To Pick?

Posted by Hugh on August 27th, 2012

'Gravenstein' apples espalier trained to wall

This unusually hot summer has sped up the harvest time of your backyard apple crop. Here are five good indicators that the apples are ready to harvest.

Change in skin color is one of the easiest for gardeners to spot. The green skin pigment gradually matures to red, yellow or oft green, depending on variety. Photos in fruit nursery catalogs, many available on-line, are good resources for fruit color. Some varieties will develop red skin color before they’re fully ripened, so color should not be your only indicator of maturity. The bottom of the apple (calyx end) turns from green to light-yellow.

On some varieties fruit shape is another change. Red Delicious and many varietal sports form 4-5 nubbins (raised bumps) on the bottom. The nubbin formation is dictated by the region where the variety is grown. Red Delicious from the Northwest U.S. is most to type, while those produced in the warm southeastern states less so.

Next harvest tip is flavor. Bite into an apple and determine its taste. You may not know what kind of apple that you’re eating, but its flavor and sweetness may be what you like. Apples which are hard to bite into or have a sour or starchy flavor are not ready. The inside flesh color often changes from oft-green to white, sometimes to yellow.

The number of days (interval) from bloom period to harvest date can be a reliable guide. Extremely hot summer weather may move up the harvest interval by 7 to 10 days. The approximate picking intervals of popular varieties are: Gala and McIntosh @ 110-115; Empire, Jonagold, and Jonathan @135-140; Red Delicious and Golden Delicious @ 145-150; and Rome, Granny Smith, and Winesap @155-160 days.

Finally, if you harvest too early, apples will be of smaller size, but will ripen off the tree indoors.

Strong Vertical Presence of Serbian Spruce

Posted by Hugh on August 17th, 2012

Serbian spruce at Arnold Arboretum in Boston

Serbian spruce (Picea omorika) rises as a tall spire in the urban landscape. A mature tree may reach 50 to 60 feet high and it creates a narrow footprint of 15 to 25 feet wide. Lateral branches uniquely bend downward while the growing tips sweep gracefully upward.

Annual growth rate is slow at 12-15 inches. Two-thirds of the short dark green needles lay flat. Needles are lustrous on the upper surface with two prominent white bands on the underside. Oval-shaped 2 ½ inches long cones hang downward, bluish-black early and light cinnamon at maturity.

Serbian spruce is highly adaptable. It grows well in full or partial sunlight (6 hours recommended) and rooted in moist well-drained soils with a wide pH range. A 3-year and older established tree handles summer dry spells and rough urban environs. A nursery-grown tree transplants well in the early fall or late winter periods from container or balled and burlapped (B&B) stock. It is northern hardy to USDA hardiness zone 4 and with good heat tolerance to zone 7-a. It becomes heat challenged past this point.

Serbian spruce deserves a more prominent place in commercial and residential landscapes. Few diseases and pests trouble this staturesque tree. You can group several together as a windbreak or privacy screen or plant a single specimen, where ground space may not be plentiful.

If you are searching for an alternative to the oft-used Norway and Colorado spruces, try Serbian spruce. Dwarf and weeping cultivars are also available through e-commerce specialty conifer nurseries on-line.

Yellow Nutsedge Control Is In Your Hands

Posted by Hugh on July 21st, 2012

Yellow nutsedge

Yellow nutsedge, aka “nutgrass” (Cyperus esculentus) is a nasty weed found in lawn and garden areas. It is a sedge, and not a grass, and methods of eliminating it vary. Yellow nutsedge is easily identified by its yellow to light green glossy leaves and the triangular shape of the stem. It grows most actively during the warm spring and summer months.

Yellow nutsedge is a perennial which reproduces primarily by small underground tubers or nutlets. It also spreads by rhizomes (underground stems). The nutlets often spread from contaminated soil which you have transported into your garden.

Maintaining a healthy dense growing lawn or garden bed is best way to avoid yellow nutsedge infestations. For small infestations, judicious hand pulling will eliminate it. This may take several weeks as the underground nutlets may re-sprout.

Mid-spring thru early summer is the ideal time to control yellow nutsedge in the Southern Appalachian region (USDA hardiness zones 6 and 7). The plant is young, actively growing, and the nutlets have not matured. By late summer the seedheads have formed and is very difficult to control at this time.

For treating large infested areas, use of chemical weed killers (herbicides) may be your best option. Available to homeowners are herbicide products containing the ingredient MSMA (methanearsonate). MSMA is packaged under several product brand names. The herbicide works better if the lawn or garden area is irrigated a day or two prior to application. Continue to repeat herbicide applications until all nutsedge plants are eliminated.

For selective control of nutsedge in lawn areas, without injuring the lawn grass, Basagran™ (bentazon) and Manage® (halosulfuron) are available. However, these two products are not available to homeowners and are applied solely by certified landscape professionals only.

Hollyhock Rust Prevention Tips

Posted by Hugh on July 19th, 2012

Hollyhock (Alcea)

Hollyhocks (Alcea rosea) are old-fashioned perennials (and biennials) which are currently finding a new audience. There are numerous cultivars differing in plant height from 5 to 9 feet and spread of 1 to 3 feet. Flowers come in single and double forms and in many color shades. Hollyhocks are hardy to USDA hardiness zone 4.

Hollyhocks are short-lived perennials and want full sun and moist, rich, well drained soil. Sow the seeds outside about a week before last frost. If you are planting seedlings outdoors, wait until 1-2 weeks after the last expected spring frost. Hollyhock seeds only need to be sown shallow, no more than 1/4 of an inch deep. Hollyhock transplants should be set 3 feet apart.

Hollyhock rust is a destructive leaf disease common in Southern Appalachian and Northeast U.S. gardens (USDA zones 5 -7). Symptoms of hollyhock rust are orange-brown spots on foliage and stems. The orange-red spores are splashed by rain or overhead watering or blown by wind to nearby leaves, starting new infections all spring and summer long. In severe cases infected leaves turn brown and shrivel up.

Tips on reducing hollyhock rust include: 1. Purchase only healthy disease-free plants; 2. Prune back all plant debris to the ground in the autumn to reduce overwintering of the disease spores; 3. Remove any weeds related to the mallows; 4. Space plants 3 or more feet apart in a sunny location; 5. Water and fertilize to maximize plant growth. Avoid overhead watering and remove all rust-spotted leaves.

Rust can be severe in a wet growing year. Daconil 2787 (chlorothalonil), mancozeb (e.g. Fore, Dithane, or Penncozeb), trifloxystrobin (Compass®), or myclobutanil (Systhane®) can prevent severe hollyhock rust outbreaks. Fungicides can protect but not cure leaves with rust symptoms.

A final tip comes from Allen Bush with Jelitto Seed in Louisville, KY. He recommends cutting back the newly emerged hollyhock plants (back to the ground) in late April. Healthy hollyhocks will rapidly re-grow in the drier warm weather in late spring and summer. Hollyhock is one of the first garden perennials to emerge in the spring when the weather is generally wet and cool when the threat of rust is most severe.