Versatile Long-blooming Catmints

'Blue Wonder' Nepeta Growing At Kingwood Center, Mansfield, Ohio

Catmint (Nepeta spp.) is a favorite of cats who like to roll around in it, sometimes to the detriment of the plant(s) (USDA hardiness zones 3-8). There are several species of catmint. Most popular are the gray-green leafed N. x faassenii and hairy gray heart-shaped leafed N. racemosa. Depending on the cultivar selected, this versatile perennial grows 1 1/2 to 3 feet high and varying widths.

Catmint grows in average well-drained soil and in full to partial sun (6 hours minimum); shade-grown plants are floppy and flower poorly. One-year established catmints exhibit exceptional heat, drought, and humidity tolerance. Established plants prefer dry (not sopping wet), and low fertility soil.

Catmints bloom from late spring to early fall. Purple, blue, pink or white flowers (depending on species and cultivar) bloom over 3-4 weeks. Prune back plants by two-thirds in late June or July to stimulate August-September re-bloom. Catmints need to be divided every 3 – 4 years in early spring. Cutback old foliage in late winter rather than in the fall.

Plants are highly deer and rabbit resistant. Hummingbirds and numerous nectar gathering bees and butterflies visit the aromatic flowers. Foliage is seaside/salt resistant. The aromatic blooms make good cutflowers and are utilized in floral designs.

Catmint grows in flower gardens, rock and herb gardens, and in containers. Low-growing cultivars work as great edging plants in front borders and as a perennial ground cover.

Popular cultivars:
N. racemosa ‘Walker’s Low’ grows 24 to 30 inches high with blue violet sterile flowers and aromatic grey green foliage (2007 Perennial Plant Association Plant of the Year).
N. x faassenii ‘Six Hills Giant’ is a taller growing catmint (30 to 36 inches high) with dark green leaves and deep violet-purple blooms.
N. x faassenii ‘Blue Wonder’ is a compact grower (12 to 15 inch tall plant and greater spread), dark green leaves, and dark blue blooms. ‘White Wonder’ has white blooms.

Disease Resistant Crape Myrtle Cultivars

‘Apalachee’ crape myrtle trunk

'Sioux' crapemyrtle mildew resistant

‘Sioux’ crapemyrtle mildew & leaf spot resistant

Hybrid crape myrtles (Lagerstroemia indica x L. faurei) are popular landscape trees in the southeast and along the coastal areas of the U. S. Over the past decade plant pathologists in Louisiana (Louisiana State University), Alabama (Auburn University), South Carolina (Clemson University), and Georgia (University of Georgia) have tested the disease resistance of cultivars for powdery mildew and cercospora leaf spot resistance.

Only the cultivar releases from the U.S. National Arboretum are listed below. These are among the hardiest (USDA hardiness zone 6). Each is listed according to its mature plant height:

10 to 15 feet category:

Acoma – white flowers (weeping/cascading habit); light gray-brown bark; high powdery mildew and average leaf spot resistance.

Hopi – medium pink flowers; gray to brown bark; high mildew and average leaf spot resistance.

Sioux – vivid pink flowers; medium gray- brown bark; good powdery mildew and average leaf spot resistance.

Tonto – dark fuchsia flowers; light cream bark; high powdery mildew and leaf spot resistance.

16 to 20 feet category:

Apalachee – light lavender flowers; medium-brown bark; high in mildew and leaf spot resistance;

21-25 feet category

Tuscarora – coral pink flowers; light brown bark; high powdery mildew and leaf spot resistance.

Tuskegee – dark pink flowers; light gray to tan bark; high powdery mildew and average leaf spot resistance.

Over 25 feet category:

Muskogee – light lavender flowers; gray-brown bark; high resistance to powdery mildew average and leaf spot resistance.

Natchez – white flowers; dark cinnamon bark; high powdery mildew and good leaf spot resistance.

Designing With Crape Myrtle

'Dynamite' Crape Myrtle falls in 12-15 feet height category

‘Dynamite’ Crape Myrtle fits in 15-20 feet height category

Undeniably, crape myrtles (Lagerstroemia indica x L. faurei ) thrive in the southern U.S. (USDA hardiness zones 6-9). You see them planted on practically every street. Their showy summer flowers are spectacular. Many cultivars exhibit colorful autumn foliage, and their smooth patterned trunks and architecture grace the winter landscape.

“The right crape myrtle for the right site” is the golden rule here. Before visiting the garden center to make your purchase, measure the intended space where it will be planted. The plant tag will provide the flower color, as well as its height and spread. Is the cultivar hardy where you reside. Cultivars named after Indian tribes (there are 33 of them) are among the hardiest (several zone 6 hardy) and are resistant to some insects and diseases.

“Variety is the spice of life” and crape myrtles surely fit this adage. They serve a number of landscape uses. They make a large deciduous hedge or screen. Plant a single tree for accent or group several together for a formal hedge or screen. Will it be the right size for your site? Dwarf shrub forms as low as 3 feet and tall trees upwards of 30 feet are available.

The larger crape myrtles need room to grow. Stay a proper distance from buildings, power lines, or walkways. Medium-size types grow 10 to 15 feet tall and wide, perfect fits for small urban spaces. The dwarf selections are attractive in large containers or as part of your home foundation. Container plants will require winter protection.

Crape myrtles love sun and well-drained soil. Flower production is greatly declines in light shade and disease problems ramp up in shade. One-year established crape myrtles demonstrate above average drought tolerance.

Become Immersed In Swamp Hibiscus

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

Mimosa (Albizia) tree in July in Washington DC

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 anytime. Fertilizing mimosa trees is unnecessary as roots fix their own nitrogen.

Caveats Before Planting Planetrees (Sycamores)

American sycamore main trunk

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

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

Blazing star (liatris)

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

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

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

Glads in the summer garden

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.