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

Become Immersed In Swamp Hibiscus

Posted by Hugh on July 11th, 2014

Swamp Hibiscus (Hibiscus coccineus)

Swamp mallow, aka swamp hibiscus (Hibiscus coccineus) is native to marshes and swamps in South Carolina, Georgia, Alabama, and Florida (USDA hardiness Zones 6 to 9). Vibrant red flowers cover the tall 4–8-foot plant(s) from June through September. Space plants 3 feet wide apart. Deeply cut maple-like foliage presents a lush tropical look and the brightly colored blooms attract hummingbirds and numerous species of butterflies.

Flowers are supported on sturdy beet red and purplish woody stems. The 5-6 inch wide leaves are very hemp-like*, palmately compound, and dark green. Flowering period is long and the showy red flowers become more vibrant with the arrival of cooler weather in very late summer. Most flowering ends at the start of autumn.

It grows best in full to partial sunlight. Shade grown plants become weak and leggy with less flowering; they tend to require staking in shady areas. This native perennial thrives in average moist garden soils. Sunny, hot, wet warm weather revs up its growth rate. Submerge a large container in your water garden. The wetter the site, the taller it grows. A rain garden is another site possibility with backup irrigation called for.

In early summer (and no later), fertilize plants to spur growth and darken foliage. Swamp mallow is borderline winter hardy in Zone 6. Grow in a leeward protected area and protect the plant crown with a loose non-smothering organic mulch over the winter. Overcrowded plants are susceptible to a number of pest and disease problems. In areas plagued with hibiscus sawflies and Japanese beetles, be prepared to spray with carbaryl (Sevin®), malathion, or imidacloprid (Bayer Advanced Insecticide®). Deer tend to leave swamp mallow alone.

* explain to friends and neighbors that swamp mallow is not marijuana.

Mimosa Tree- Love It or Weed It

Posted by Hugh on July 8th, 2014

Mimosa (Albizia) tree in July in Washington DC

Mimosa (Albizia julibrissin) is essentially a 4-5 month ornamental tree indigenous from Iran to China (USDA hardiness zones 6-9). From late spring through summer, mimosa struts an attractive fine textured foliage and beautiful flowering. This small tree rarely leafs out until mid-May (in zone 6) and offers little in autumnal leaf color. Two seedling forms, either light to dark pink feathery blooms, are common. It blooms from late June thru July and the showy fragrant flowers attract numerous hummingbirds.

Mimosa grows 20-25 feet tall of equal to broader spread. It seems at home under full sun and grows in any soil that is adequately drained. It thrives in subpar soils, often dominating a vacant or abandoned urban lot or growing along a Southeast U.S. roadside fencerow. It likely was not intentionally planted on any of these sites. Yes, seedlings may quickly become a nasty weed invader.

‘Summer Chocolate’ is a recent introduction with stunning dark purple foliage. Chocolate Fountain™ is a soon to be released weeping purple leaf cultivar from Dr. Tom Ranney at NCSU in 2015. New cultivars are attracting new gardeners who like its lacy foliage texture, color and tropics-like foliage. I urge cutting mimosa in early fall to prevent seed dispersal. Gardeners may opt to grow the foliage and forego flowering.

The notion that mimosa is an exotic invasive is debatable. Trees are not long-lived, rarely more than 20 years old. They improve the soil’s tilth and nutrition, so that one day, an opportunist native species will shine in its place.

Late winter thru early summer (February-July) is the ideal planting time. Remove unwanted and dead branches at any time. Fertilizing mimosa trees is unnecessary as roots fix their own nitrogen.

Caveats Before Planting Planetrees (Sycamores)

Posted by Hugh on July 4th, 2014

American sycamore main trunk

American sycamore, aka planetree, (Platanus occidentalis) is a native tree planted over a large area of the United States (USDA hardiness zones 4-9). Its enormous size, often 70-90 feet in height, limits it to planting mostly on large landscapes such as parks, golf courses, and industrial parks. Northern U.S. cities have planted it extensively along major thoroughfares, wide avenues and boulevards. Sycamore is commonly utilized in reforestation work because it grows in a great variety of soils, wet or dry, and copes with most environmental situations including urban pollution.

Smooth white patchwork bark is its most identifiable winter feature. Chunks of bark, sometimes quite large, flake off to reveal a chalky white inner bark. Caveat: sycamore (planetree) is a messy tree. Chunks of fallen bark, gumball fruits, and numerous twigs, add up to a potential maintenance nightmare. Seedling trees are susceptible to spring leaf anthracnose, aphids, and lacebugs. Damaged leaves will litter lawn areas in mid-spring; the arrival of warm dry summer weather usually checks the disease and insect onslaught.

Sycamore grows very rapidly in either full or part sun (6 hours preferred). The roots of older trees tend raise up sidewalks and clog water, sewer and septic lines. Despite numerous pest and disease issues, American sycamore grows very aggressively,gaining in size and stature. Do not crowd trees close together to allow good air movement and less disease outbreaks.

London Planetree (P. x acerifolia) is a cross between Oriental planetree (P. orientalis) and American sycamore. Its disease resistance has made it the better choice and one of the most popular large trees in urban Mid-Atlantic and Midwest states (USDA hardiness zones 4-9). Good disease resistant cultivars of hybrid planetrees include ‘Columbia’, ‘Liberty’, ‘Yarwood’, and Exclamation™.

Japanese Pagoda Tree Becoming Popular In U.S. Cities

Posted by Hugh on July 1st, 2014

Japanese Pagoda Tree in Raleigh, NC

"String of Pearls" Fruits

U.S. east coast cities are finally planting Japanese Pagodatree (Styphnolobium japonicum). This medium-sized tree grows to 50 feet high, but 75 feet is not uncommon in the southeastern U.S. Pagodatree is native to eastern Asia (USDA hardiness zones 4 –8) where it is more known as Scholar tree. In the early 20th century it was frequently seen planted around schools and Buddhist temples in Japan.

Pagodatree grows in full to partial sun (6-hours minimum) and in a moist well-drained, slightly acidic soil. Pagodatree tolerates urban drought, air pollution, and moderate salinity around coastal areas. The tree has no serious disease or insect problems. A small number of cultivars, including weeping and upright (columnar) forms, are listed.

‘Regent’ is the most popular cultivar, high valued as a vigorous grower and lustrous green foliage. A newly planted tree blooms earlier and exhibits superior disease resistance than the species. Annual growth rate ranges from 18 to 24 inches. Summer foliage is comprised of 8-10 inch long, pinnately compound leaflets numbering 7 to 17. In some years its golden fall color can be spectacular.

What really makes pagodatree special is its July-August flowering time, when few landscape trees are blooming. Its pea-like, creamy-white flowers are showy and fragrant. Flower clusters, 12 inches long and wide, drape from branch tips. Another unique feature is the 3 to 8 inches long green “string of pearls” fruits which form in late summer and persist way into fall. Birds don’t appear drawn to the berries which shrivel to black and linger through the winter. By spring the tree has self-pruned many of the twiggy fruit rachises.

A young pagoda tree exhibits a semi-upright, vase shape habit and develops a full rounded canopy as the tree ages. A mature tree exhibits a lovely grayish-brown furrowed bark. Pagodatree is related to Mescal Bean tree (Calia secundiflora), native to Southern Texas into Mexico (Zones 8-10).

Blazing Star– Electric Summer Flowering Perennial

Posted by Hugh on June 27th, 2014

Blazing star (liatris)

Blazing star (Liatris spp.) is a popular summer flowering perennial. Also called gayfeather, it belongs in the aster family. This tall, upright, clump-forming perennial is found in moist meadows and at the edge of a marsh. (USDA hardiness zones 3-9). Liatris makes an excellent addition to a rain garden.

Its distinctively reddish-purple flower spikes win over a lot of gardeners. Individual flowers, each only ¾ inches across, comprise the floral head which open from the top down to the base. White blooming forms are also available. Multiple stalks rise from the crown, cloth in narrow, grass-like, medium-green leaves. Stem leaves are long and gradually decrease in size near the top. L. spicata ‘Kobold’ is an outstanding compact cultivar that has become the standard bearer in most gardens.

Blazing star grows 2 to 5 feet tall, depending on the fertility of the garden soil. Space plants 12 to 18 inches apart. Once established, plants require very little care. They thrive in their garden space upwards of 3 years, then should be divided, or replaced with new plants.

Blazing star grows in average well-drained soils in full sun. This prairie species is not tolerant of poor drained soils, particularly soggy soils in winter. It excels in moist, fertile soils. Other Liatris species demonstrate better drought tolerance. It’s tolerant of summer heat and humidity. They can be grown from seed, but some are slow to establish. Kobold may spread from seed in its garden spot.

The brightly colored blooms attract numerous birds, butterflies, and unfortunately rabbits. Deadheading will spur re-bloom within 4-5 weeks. A mid-summer fertilizer is advised. Blazing star suffers from no serious insect or disease problems. Taller plants may require staking or other support; ‘Kobold’ rarely requires staking. Flowers make excellent fresh and dried cutflowers.

Lovely Tall Stewartia Deserves Your Attention

Posted by Hugh on June 24th, 2014

June-flowering Tall Stewartia at Biltmore Estates, Asheville, NC

Not enough gardeners know about stewartias (Stewartia spp.). Six species are found under cultivation, 2 native to the U.S. and 4 of Asian origin. One of the rarest seen in U.S. gardens is tall stewartia (S. monadelpha) (USDA hardiness zones 5-8). Tall stewartia is a more site forgiving than Japanese stewartia (S. pseudocamellia), the most popular planted in U. S. gardens.

Tall stewartia develops into a 25 to 30 feet high shrub or small tree. The bark on the trunk and adjacent branches gradually ages to a lovely cinnamon tint. Spring/summer foliage is medium green, 3-inches long, and slightly glossy on the surface. Leaves turn red to burgundy red before abcising in late autumn. Numerous small white frilly petalled flowers with gold stamens appear in June. By early fall reddish brown fruits have fully developed and are of little ornamental value.

All stewartias are fussy in one respect. Their roots should be planted in a moderately acidic (pH 5.8 to 6.8), organically rich, and most important, in a well-drained soil. Just a hint of soggy ground might be enough to trigger an outbreak of root rot disease and their demise. Extreme summer drought is also punishing to stewartias. Planting on a slope is often a wise practice.

Tall stewartia exhibits better heat tolerance than other species. It is best protected from direct mid-day sun in zone 7 and further south. Most stewartias are meant to be viewed 12 months a year. Plant them in full morning sunlight nearby a patio or deck, or near a window where it may be viewed from inside your home. Install up-lighting to capture branching silhouette and lovely flaky cinnamon colored bark in the evening hours. Cinnamon bark coloration gets better as the tree ages.

Pests and other diseases are rarely problems except for Japanese beetles, which can skeltonize leaves over 3 to 4 week time span. Numerous pesticides, including short-lived pyrethrins or insecticidal soaps, are effective, but must be reapplied every 3-4 days until the bug onslaught has subsided.

Gladiolas Are Wonderful Cutflowers

Posted by Hugh on June 21st, 2014

Glad in the summer garden

Across most regions of the U.S., planting gladiola corms (they’re not really “bulbs”) begins a week before the probable frost-free date has passed in the spring. Stagger individual plantings every 2-3 weeks through mid- July. Many people opt to grow them as cutflowers for their homes.

Purchase large or premium sized corms that measure 1 1/4 to 1 1/2 inches across; quality corms produce tall floral scapes in wide color array. Floral scapes range from 18 to 36 inches high depending on variety. Bargain bulbs produce smaller sized individual flowers and shorter scapes.

Glads grow in full sun and in average well-drained soil. Compost-rich, slightly acidic soil is best. Roto-till the ground to at least a 6-inch depth. Add a slow-release fertilizer designated for flowering bulbs according to package directions.

Sow bulbs 4-6 inches deep and 6 inches apart, pointy side up. If rainfall is lacking, glads should be irrigated weekly at least 1 inch of water. Add a 2-3 inch layer of organic mulch to conserve soil moisture. Staking each row of glads as plants often become top heavy when floral scapes are heavily budded up. Place a heavy duty post or stake at opposite ends of the row and weave two sturdy cords through the glads about 2-3 weeks prior to bloom when scapes are beginning to form.

Thrips are a serious pest of glads. Thrips are very tiny and tend to congregate inside the flowers, reducing floral life. Several insecticides, including soaps, are labeled for managing heavy thrip populations.

In most areas of the U.S. where winter temperature dip below 25º F, treat gladiolas as annuals (USDA hardiness zone 7 and northward). Some gardeners dig, clean off soil, and divide the corms in the fall. Grade by size and throw away all rotted or poorly formed corms. Undersized corms, called “cormels”, are usually discarded or planted in a nursery bed next spring to grow and size up. During winter glads are stored in mesh bags and stored in a cool area (36-41º F) that does not freeze.

Expect Garden Visits From Pipevine Swallowtail

Posted by Hugh on June 18th, 2014

Pipevine swallowtail on thistle

Pipevine Swallowtail (Battus philenor) is a beautiful butterfly common over a large geographic area of North and Central America. Pipevine swallowtail can be sighted in open meadows, parks, along streams, and hopefully in your garden.

The butterfly larvae (caterpillars) feed on plant members of the pipevine family (Aristolochiaceae), particularly Dutchman’s pipevine (Aristolochia spp.), including Virginia snakeroot. This native vine, found in the Eastern United States, is a fast-growing perennial that can be easily trained to a fence or trellis. It may take 1-2 years for a pipevine to mature into a sizeable vine to become noticed.

Initially, young black or red caterpillars are not poisonous. They feed the poisonous leaves of pipevine and become toxic to predators, particularly birds; but the swallowtails are not harmed. The caterpillars generally eat for 10-15 days, grow, and mature. Full grown caterpillars are mostly black and covered with red spines. Other similarly colored swallowtail species try to mimic the pipevine swallowtail.

An adult butterfly develops quickly inside the green and brown chrysalis and emerges to fly, mate, and lay eggs over 7-10 days. Swallowtail wing span averages 3 to 3 ½ inches across. As autumn nears, pipevine swallowtail may remain in the chrysalis stage through the winter and emerge next spring. In areas with a long growing season, it may reproduce twice, but often the second generation overwinters in the chrysalis.

Pipevine swallowtail butterflies drink nectar from a large selection of flowers. Favorite nectar plants include milkweeds (Asclepias spp.), thistles, honeysuckles (Lonicera spp.), joe pye (Eupatorium spp.), lilac, anise hyssop (Agastache), phlox, purple coneflower, clover, beebalm (Monarda spp.), teasel, garden sage (Salvia), buttonbush, butterfly bush (Buddleia), azaleas, summersweet shrub (Clethra), and many others.

‘Going Bananas’ Daylily Blooms Continuously

Posted by Hugh on June 15th, 2014

Hemerocallis 'Going Bananas' Flowers Wide Open

‘Going Bananas’ is an extended-blooming daylily. This diploid cultivar flowers a three month long continuous blooming cycle (rather than stopping and starting again) from early summer into fall. Each bloom stays open longer, at least 16 hours per day. Each trumpet-shaped flower opens wider, a new genetic trait in daylilies.

Going Bananas features slightly fragrant, 4-inch wide clear lemon yellow blooms with ruffled edge. It is a hybrid between Hemerocallis ‘Happy Returns’ and H. ‘Brocaded Gown’. Flowers are lighter yellow and wider opened than its parents. It form a large number of scapes, each bearing 10-15 buds. Going Bananas is extremely vigorous and clumps should be divided every 4-5 years in the fall to maintain vigor.

Daylilies grow in average, medium moist, well-drained soil in full sun to part shade. Deadhead spent flowers daily for neatness and remove the woody scapes when completely bloomed out. Plants are tolerant of summer heat and humidity, but relish deep watering over dry spells to maintain foliage attractiveness.

Daylilies are popular sun perennials planted singly with other flowers in a garden or a container. Several can be massed together as a ground cover on steep slopes to retard soil erosion. When not in flower, the grass-like foliage is valued for color and texture. Daylilies are extremely adaptable perennials with no serious insect or disease problems.

‘Stella D’Oro’- First And Last Daylily To Bloom

Posted by Hugh on June 13th, 2014

‘Stella d’Oro’ daylily

For over a quarter of a century, wherever daylilies (Hemerocallus spp.) grow, you will find the very popular gold-flowered ‘Stella d’Oro’ daylily (USDA hardiness zones 2-9). It’s one of a few daylilies that blooms 3 out of 4 seasons. Its small size makes it an ideal choice as a ground cover.

This short clump growing daylily grows 10 to 15 inches tall and 15 to 18 inches spread with grass-like foliage. Blooms measure 3-inches across. Multiple uses include in rock gardens, front of beds or as edging, or planted in a container. Several plants grouped together make them stand out.

Stella d’Oro grows in an average soil that is adequately drained. Good loamy soil is preferred. Full to partial sun (6 hours minimum) is ideal for maximum flowering. Purchase daylily divisions that have 2 to 3 fans and spaced them 18 inches apart. Cut foliage back to 6 to 8 inches.

Every 5-6 years daylily clumps should be dug up and divided. Early fall is the best time to divide daylilies. Late winter is also a good replanting time. Mulching fall planted beds reduces problems with frost heaving and offers some winter protection.

Don’t allow daylilies to become overcrowded by surrounding shrubs, perennials, and weeds. Plants are highly disease and pest resistant. Stella d’Oro is moderately susceptible to daylily rust, a more serious problem in the southern U.S. Rabbits don’t bother daylilies.

Feed all daylilies in early spring with a slow release fertilizer such as Osmocote 14-14-14, Nutricote 13-13-13, or equivalent products. For reblooming varieties like Stella d’Oro, should be fed a second time in early July with a water soluble fertilizer such as MiracleGro™, Schultz™, Nature’s Source™, or Daniels™. Do not allow them to suffer through a summer drought.

Stella d’Oro has earned the Stout Medal, the American Hemerocallus Society’s highest award.