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

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.

‘Sunburst’ Golden St. John’s Wort

Posted by Hugh on July 16th, 2012

'Sunburst' hypericum at Arnold Arboretum in Boston

Our native golden St. John’s wort (Hypericum frondosum) deserves more planting space in U. S. gardens (USDA hardiness zones 5-8). ‘Sunburst’ is the leading cultivar and exhibits superior traits over the species.

Golden St. John’s wort forms a small, dense growing deciduous shrub, noted for its showy golden yellow flowers and attractive blue-green foliage. Sunburst grows more compact at 2-3 feet tall and wide, and rarely requires pruning. Leaves are 2 ½ to 3 inches long.

‘Sunburst’ sports slightly larger 2- inch wide flowers which blooms over 3-4 weeks starting in late June. Each bright yellow, 5-petaled flower possesses numerous pincushion-like stamens in the center. Flowers are borne on new wood, and are not threatened by sudden cold temperature snaps in the spring.

Autumn leaves turn an average yellow before dropping and tend to be evergreen in warmer climes. After two years in the garden, Sunburst demonstrates good heat and drought tolerances in the Southern Appalachian region (USDA zones 6 and 7).

In the autumn small reddish brown fruit capsules form that persist well into winter. Stems exhibit cinnamon colored exfoliating bark in winter.

Disease and insect problems are minimal if properly sited in well-drained soil under full sun (north of zone 7) and in partial shade further south. It grows well in slightly alkaline limestone-based soils.

‘Brigadoon’ Hypericum Wakes Up a Garden Bed

Posted by Hugh on July 13th, 2012

Chartreuse foliage of 'Brigadoon' hypericum

The bright chartreuse (almost golden) foliage Brigadoon St. John’s wort (Hypericum calycinum ‘Brigadoon’) can brighten up almost any dull garden spot. This Euro-Asian ground cover thrives in any well-drained soil under full to partial sunlight (USDA zones 4-7). Full sun may burn the summer foliage in zone 7.

‘Brigadoon’ grows 12 to 16 inches tall and spreads quickly to about two feet in width. Space plants 16-18 inches apart. In the sun, the small oval-shaped leaves turn a dazzling orange-gold. It blooms heaviest in full sun.

The bright gold two inch wide flowers form in June and July with clusters of pincushion-like stamens in the center. Often, the flowers do not visually stand out because of the golden foliage.

Brigadoon is easy to grow and maintain. Foliage often remains evergreen in the Southern Appalachian region (USDA hardiness zones 6 and 7), but dies back when left exposed to extreme cold in snowless winters. As a ground cover, it is best sheared back with a sharp lawn mower set at 5-6 inches high to encourage vigorous re-growth in early spring.

Use Brigadoon to edge the front border of a foundation, around tall trees and shrubs, or in a rock gardens St. John’s wort is an excellent vigorous groundcover, but be warned that its underground stoloniferous rootsystem may grow aggressively. Its rapid growth and deep rootsystem will stabilize steep embankments.

Brigadoon is bothered by few insect or disease problems. St. John’s Wort (Hypericum) has been utilized since medieval times in the treatment of wounds and to ward off evil spirits.

Selecting The Right Ivy For Your Garden

Posted by Hugh on July 5th, 2012

A trailing English ivy starts to climb shrub

Have you taken the “No Ivy Pledge”? I have not. In an effort to slow defections from growing ivy, the American Ivy Society has developed a list of non-invasive cultivars. It includes several dwarf English ivy cultivars (Hedera spp.). Add a little water and fertilizer and these mini-ivies do not miss a beat.

Mini- ivies are excellent performers in shaded areas and tolerate poor soils if well cared for with water and fertilizer in their first year in the garden. Their slow growth mode keeps them under control by most average gardeners. They tend to grow 1-3 inches per year and are little threat of becoming invasiveness.

According to the American Ivy Society, some of the best mini-ivies include: ‘Buttercup’, ‘Glacier’, ‘Golden Curl’, ‘Golden Ingot’, ‘Golden Starlight’, ‘Goldheart’, ‘Henriette’, ‘Ingrid’, ‘Itsy Bitsy’, ‘Jubilee’, ‘Lady Francis’, ‘Spetchley’, ‘Teardrop’, and ‘Willie’.

Ivy’s invasive stage starts when you allow the vegetative (juvenile) plant to flower and produce seeds (adulthood). Many ivy cultivars do not flower or seed when held in the juvenile vining stage on the ground, especially those growing in shade.

Adult ivy tends to flower only in bright sun. The vine becomes more shrub-like. Flowers form and subsequently berries, which are eaten by birds. The seeds are dispersed into woodlands, gardens, etc. This begins the invasive nature of ivy which can be avoided by keeping ivies growing on the ground and not in trees and shrubs.

For additional information on growing ivies, refer to the American Ivy Society website at: http/www.americanivysociety.com

Promising Hemlock Adelgid Research

Posted by Hugh on July 2nd, 2012

Hemlock woolly adelgid

Proper care of hemlock trees is important for their survival. Hot dry summer weather appears to slow population growth. During periods of severe drought, shallow rooted hemlock trees should be irrigated. Prune dead and dying branches from trees to promote new growth. Also, limit the amount of nitrogen fertilizers to hemlock(s), as it promotes heavier woolly adelgid populations.

Cultural practices may reduce numbers of adelgids in hemlocks. Pets, as well as birds, squirrels and deer, may transport adelgids from infested to healthy hemlocks. Refrain from moving infested plants, logs, firewood or bark chips onto an uninfested property. Clean your auto and camping tents after returning from woodlands and recreational areas. Wash off pruning equipment after working in infested trees.

Two Japanese and two western North American hemlock species are much more resistant to hemlock woolly adelgid than are their eastern North American counterparts. Of these four resistant species, the western hemlock (T. heterophylla) is most similar to eastern hemlock in appearance, growth form, and utility. Although adelgids do infest these resistant species, they seldom reach densities high enough to cause injury.

Entomologists are also releasing predator insects which hopefully may add hemlock woolly adelgids to their diet.

Credit: Special thank you for information supplied by NC State University Extension.

Pest Update – More Pesticide Options Available Against Hemlock Adelgid

Posted by Hugh on June 29th, 2012

Cottony masses of hemlock adelgids (photo by Dr. Alan Windham, UT Extension)

You may be able to prevent or save tree and shrub hemlock(s) from woolly adelgid. This serious pest has two generations per year. The first generation hatches in March and April from overwintering adults (as many as 300 eggs per adult) in white cottony masses on the small twigs. The crawlers (nymphs) hatch and feed in April and May. The spring generation ends by mid- June. A second crawler generation emerges in July and feeds until mid- October.

Loss of a hemlock tree or shrub hedge does not over 1-2 years. It may take a buildup of 3-4 years before serious damage occurs. Inspect hemlock(s) several times of the year for white adelgid masses on the underside of twigs and needles.

Imidacloprid is the most popular insecticide of choice. It acts systemically. The pesticide must be watered into the soil within 24-36 hours, to carry it down the hemlock roots to be absorbed. Imidacloprid and other pesticides appear to be effective over two and more years.

Read and understand the pesticide label! Do not use around streams or ponds or in rocky soils. Pesticide rates will vary according to the size of the tree trunk or the height of the hedge. Most soil drenches contain imidacloprid, including Bayer Advance Garden Tree and Shrub Insect Control™, Merit 75 WP, Malice 75 WSP, Zenith 75 WSP. Safari 20 SG (dinotefuran) has slightly faster uptake by the tree. Safari may be used as soil drench or bark spray.

Most pesticides may be purchased from garden centers, home hardware, and farm supply stores.

Credit: Special thanks for information and photos supplied by NC State University and University of Tennessee Extension.

Vintage ‘Strawberry Candy’ A Sensational Daylily Performer

Posted by Hugh on June 26th, 2012

'Strawberry Candy' daylily

Some vintage daylily varieties are timeless performers. Strawberry Candy daylily (Hemerocallis x ‘Strawberry Candy’) is a daylily classic, one of the first to open in June in Southern Appalachian gardens (USDA hardiness zones 6 and 7). Its grass-like foliage is semi-evergreen here.

The 4- inch diameter flowers open strawberry pink with a prominent rose red eye and golden green throat. Its 24-26 inch height and spread make it a good fit in almost any landscape situation. Plant it in the front border of the flower bed, grow it in a container, or as a ground cover.

Flowers bloom almost all day long, from the early morning to late evening. It’s also a re-bloomer, returning in September – October for another brief bloom cycle. For Strawberry Candy to re-bloom, plant(s) must be fertilized and irrigated through summer’s heat and dry spells.

Daylilies thrive in full to partial sunlight (6- hours minimum sun). They grow in any well-drained garden ground, but thrive in moist compost-rich soil. One-year old established plants exhibit good drought and heat tolerance. Strawberry Candy clumps should be divided every 3-5 years in late winter or in early autumn.

Strawberry Candy is a strong grower and relatively disease and pest resistant. It was introduced in 1989, the creation of daylily breeders Pat and Grace Stamile. It was awarded the prestigious Stout Silver Medal in 1998.

‘Red Volunteer’ – Outstanding Veteran Red-flowering Daylily

Posted by Hugh on June 24th, 2012

'Red Volunteer' daylily

In the gardening world new does not always mean better. Red Volunteer daylily (Hemerocallis x ‘Red Volunteer’) is not new, introduced by Oakes Daylily Nursery, near Knoxville, TN in 1984. Daylily catalogs describe it as a “candle red self with a golden yellow throat”. It is a mid-season bloomer and the foliage is semi-evergreen.

The 7- inch diameter blooms stand 30 inches tall, not hidden inside the grass-like daylily foliage as some varieties do. Its vivid red flowers are real standouts. The red color does not fade in the summer sun, as red at 5 p.m. as it was at 8 a.m. in the morning. The color of many red daylily varieties is washed out by noon

Red Volunteer is a good multiplier, a rapid clump producer. A 2-3 year old well-grown plant may form 8 or more floral scapes, each with a dozen buds. Red Volunteer does not need to be divided every 5 years.

Red Volunteer blooms in mid- to late June in the Southern Appalachian region (USDA hardiness zones 6 and 7). While preferring a moist, compost rich, well drained soil, it grows well in a heavy clay soil. Once established in a garden for one year, Red Volunteer exhibits exceptional summer heat and drought tolerance. Its long grass-like foliage stays green and lush when adequately watered and fertilized.

Daylilies are mostly disease and insect resistant. Aphids and thrips, as well as slugs and snails, may cause minor damage to the foliage.

Red Volunteer was awarded the AHS Award of Merit in 1994.

No Scorch ‘Verdoni’ Dwarf Hinoki Cypress

Posted by Hugh on June 22nd, 2012

'Verdon' Hinoki Cypress

For a small urban garden many dwarf evergreen conifers are a good fit. There are so many to choose from and Verdon hinoki cypress (Chamaecyparis obtusa ‘Verdoni’) is one of the finest. Its fan shaped gold-edged green foliage will light up almost any garden locale. It makes a great garden companion with short growing perennials, summer flowering annuals, and other dwarf conifers.

Verdon’s scale-like leaves hold their golden hue through all four seasons, and do not scorch in the summer sun or the frigid cold of winter once established for two years.

Grow Verdon in a well-drained, compost rich garden soil and keep properly mulched for adequate soil moisture. Its growth rate is very slow, just 2-3 inches per year. In ten years it may grow to 3 feet in height x 2 feet in width. It is rated as hardy to -30°F (USDA hardiness zones 4-7).

Verdon may grow slightly asymmetric. Give it a permanent spot in the garden or grow in a container for several years. Lightly fertilize with 10-10-10 or equivalent granular fertilizer in early spring or feed a water soluble fertilizer such as Hollytone®, Miracle-Gro® or equivalent 2-3 times from March through August.

Dwarf conifers ask for very little extra care and prosper for many years in a sunny to partially shaded garden spot or in a container on a deck or patio. They are rarely troubled by disease or insect pests.

‘Color Guard’ Yucca Hold Gold Variegation

Posted by Hugh on June 19th, 2012

Unidentified Yucca Cultivar

Architecturally, yucca (Yucca filamentosa), aka Adam’s needle or Spanish bayonet, makes a strong landscape statement. Yucca is often difficult to fit with with other shrubs, except perhaps other xerophytic plants. Yucca is frequently used in an arid-looking or in a courtyard setting in gravel mulch.

Yucca prospers in full sun and a well-drained soil. This evergreen rosette (no stem) shrub is native from South Carolina south to Florida and Mississippi, but is surprisingly hardy as far north as USDA hardiness zones 5 (zone 4 with additional winter protection).

Yucca’s foliage stands upright and arching. ‘Color Guard’ is a gold-centered variegated form. The sword-like foliage reaches 3 to 4 feet tall and wide. The spine-tipped leaves are 1-2 ½ feet long and 3- 4 inches wide with green margins and striking creamy gold centers. Long curly white threads are found along the leaf margins. Variegation is steadfast and is not lost over the years as experienced with some other variegated cultivars.

In cool weather, the creamy-gold hue in the midsummer foliage takes on a pinkish tint in the autumn and rosey in the winter. Its deer-resistant foliage is covered in hundreds of curly white hairs. Branched clusters of 3-6 feet tall bouquets of fragrant creamy white bell-shaped flowers open from mid-spring into summer depending on where you garden. Flowers open from the bottom upward, keeping the plant in fresh blooms for 3 or more weeks!

Wet soil is yucca’s nemesis. Amend heavy clay soils with coarse sand or gravel for excellent drainage. It doesn’t mind very long dry spells (once it’s established in the garden for two years). Color Guard tolerates wind, heat, and humidity nicely and has few serious insect or disease problems.

Wear heavy gloves when pruning off dead flower stalks, decaying or dead foliage. Over the years plants tend to colonize or become stoloniferous. They may be cut from the mother plant and allowed to create small colonies.