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

Pest Alert – Giant Hogweed

Posted by Hugh on June 29th, 2018

Giant Hogweed (Virginia Tech photo)

Leaves (Univ of Connecticut photo)

Giant hogweed plant (Heracleum mantegazzianum) is a large, invasive plant that can cause severe burns, blisters and rashes and vision loss in humans. As its name suggests, giant hogweed plant is enormous growing invasive species that originated from the Caucasus region of Eurasia. It produces large, towering purple stalks of white flower clusters. Don’t pick these flowers! Contact from its clear watery sap from all parts of giant hogweed (leaves, roots, stems, flowers, and seeds of the plant) results in blisters and rashes in humans. These serious reactions are called “phytophotodermatitis”).

The plant has been found in Canada, Northwestern U.S, New England and mid-Atlantic states, and North Carolina. It is listed among the most serious of invasive weeds. The plant may grow upwards of 15 feet high. Giant hogweed sap contains several photo-sensitizing compounds. Initial symptoms of skin injury after plant contact may not appear for several days. Sap can also burn and blind your eyes.

The sap from leaves and stems may also sensitize the skin so that it becomes easily sunburned. Children should be kept away from giant hogweed, wear protective clothing, and practice eye safety. If the skin has been exposed, wash the affected area(s) thoroughly with soap and water; and protected the exposed skin from the sun for 48 hours. If a rash develops or if eyes come in contact with sap, consult with a medical professional.

Control Options

Non-Chemical

Non-chemical controls may not be practical for large, dense stands of giant hogweed. Control options are best initiated when plants are small in size, preferably under 5 feet tall. Prevent plants from setting seed by removing flower heads; the seeds may remain viable in the soil for a number of years.

These controls are most effective when preventing seedling growth or when used in combination with a chemical control.

Digging is the most effective non-chemical control.

Mowing – repeated cutting back to the ground level. Protect skin and eyes from vegetation thrown from grass and string mowers.

Grazing – cattle, sheep and other livestock, unaffected by hogweed sap, can help control giant hogweed.

Chemical control

Hire a landscape professional pesticide applicator to apply an herbicide. Glyphosate and triclopyr, two common pesticide ingredients in herbicides, are labelled for control. Read and follow all label directions. Repeated applications will be necessary. Some states have set up a HELP hotline for people who came into contact with the plant and urged residents to report sightings.

Three July Blooming Trees (Other Than Crapemyrtles)

Posted by Hugh on June 25th, 2018

Vitex agnus castus

Chaste Tree (Vitex agnus-castus) is a 10-15 feet tall, vase-shaped, deciduous shrub or a small 15-20 foot tree. The species is native from southern Europe and Asia. Often mistaken as a purple-flowering crapemyrtle, vitex is grown where wintry weather is not severe (USDA hardiness zones 6-9). Its palmately compound grayish-green leaves, composed of 5-7 lance-shaped leaflets, are aromatic if you rub. Airy panicles composed of tiny, fragrant, lavender to pale violet flowers (to 12″ long) appear in early to late summer. Blooms attract numerous bees and butterflies.

Sourwood (Oxydendrum)

Sourwood (Oxydendrum arboreum), aka lily of the valley tree, is a deciduous understory tree that is native to the eastern U.S. from Pennsylvania south to Florida and Louisiana (USDA hardiness zones 5-9). A member of the Heath plant family, which includes azaleas, rhododendrons, and mountain laurels, plants prefer an acidic soil. This native tree (or multi-branched shrub) grows 20-25 feet tall (50 feet or more in the wild). Finely-toothed, 5-8 inch long, glossy green leaves produce one of showiest red fall hues. Terminal 4-8 inch long panicles of white lily-of-the-valley flowers drape off branch tips in early summer. Flowers are slightly fragrant. Long-lasting dried flower panicles are present through September, and attract many many bees and sourwood honey is a tasty result.

Goldenrain Tree (Koelreuteria paniculata) is a medium-sized, open-branched, deciduous tree with a rounded crown (USDA hardiness zones 5-9). Native to China, it grows 30-40 feet tall and almost as wide. Its pinnate or bipinnate compound leaves, up to 18 inches across, are comprised of 7-17 irregularly lobed leaflets. The bright green, blemish -free summer foliage turns yellow in fall. Bright yellow flowers (each 1/2 inch wide) appear in early July as part of terminal 12-15 inch panicles. Flowers give way to brown lantern-like, papery seed capsules in fall. Caution: many seedlings may arise and become troublesome.

Goldenrain tree flower panicle

General care recommendations: all three trees prefer a moisture, mildly acidic, well-drained soil and full sun. Sourwood prefers a more acidic pH soil. Vitex is best planted in sheltered sites in zones 6. In colder zone 5 winters, vitex can be grown as a 3-5 foot herbaceous flowering perennial. New compact vitex shrub forms are coming to garden centers.

‘Herbstsonne’ Rudbeckias Fill Their Spot

Posted by Hugh on June 20th, 2018

Rudbeckia lacinata Herbstsonne’

Rudbeckia ‘Herbstonne’ at Biltmore Estates

For an old fashion plant ‘Herbstsonne’ (Rudbeckia laciniata) still pops up in many modern day gardens. It is a tall upright growing, clump-forming perennial black-eyed Susan (USDA hardiness zones 5 to 9). This vigorous North American perennial grows 4-7+ feet tall and 2-3 feet wide. ‘Herbstsonne’ is also synonymous with the cultivar ‘Autumn Sun’. Formerly cataloged as Rudbeckia nitida, many plant experts believe that it is a hybrid between the two species.

Large daisy-like flowers, 3-4 inches across, with drooping sulphur yellow rays petals stand out in the late summer – autumn landscape. Flower centers have elongated bright green long “nubbins” or cone centers. Flowers bloom singly atop slender branching stems. Bright green cutleaf leaves vary in size from 3-6 inches in length and are coarsely toothed. Flowers attract numerous butterflies and winter feeding birds relish their nutritious seeds.

Herbstonne prefers a rich, moist, well-drained soil and mostly full sun. This aggressive perennial tolerates hot and humid summers and exhibits above average drought resistant after its first year in the garden. Tall growing plants, particularly those grown in partially shaded areas, may require staking. Deadheading old spent flowers encourages additional re-bloom. Herbstonne (aka Autumn Sun) has no serious disease and pests and is deer proof.

Herbstonne spreads slowly by rhizomes. Propagate by seed, division or terminal cuttings. They’re outstanding for inclusion into mass plantings on large properties such as public parks, golf courses, and industrial sites. Include them in border plantings, meadows, prairies, and in rain and cutting gardens. In rain gardens plants cope in average soils and seasonal moisture extremes. Cut flowers will fill vases in your home and friends.

Personal note: Clumps of this aggressive growing rudbeckia are long-lived. I’ve fallen in love with old plantings near the conservatory at Biltmore Estates in Asheville, NC and at Chanticleer Gardens in Wayne, PA. Give ’em lots of room as plants eat up lots of garden space.

Stunningly Beautiful Three-Flowered Maple

Posted by Hugh on June 16th, 2018

Acer triflorum on NYC Hi-Line

Leaf color change in late October

Three flower maple (Acer triflorum), often called trifoliate maple, is native to eastern Asia (USDA hardiness zones 4-7). The latter pseudonym is misleading as A. triflorum is actually one of many compound-leafed maples identified as “trifoliate maples”. This small deciduous understory maple typically grows 2o-25 feet tall with a densely-branched, rounded crown. Specimens often grow to 35-40 feet in height range.

The tree’s outstanding features include its attractive shape, exfoliating tan brown bark, and fall leaf color. The young fully expanded spring leaves show off a fine pubescence. As autumn approaches, the medium green trifoliate leaves (leaflets to 3 inch long) take on vibrant shades of orange to red in autumn.

Tan brown bark exfoliates in vertical strips to reveal orange-brown inner bark. Greenish-yellow flowers appear in April in clusters of three, hence the species and common names. As with most maples, the flowers are not showy. Fruits are double winged samaras (1-1.25 inches long). Some individuals may confuse the tree with paperbark maple, Acer griseum, another beautiful trifoliate maple.

The tree grows in average, medium moist, mildly acidic (5.5-6.5 pH), well-drained soil and planted in full sun to part shade location. Keep in mind that three flowered maple is an understory species. In its southerly zone 7 range, full-day sunlight may be too harsh. Good soil fertility, moisture and drainage are keys to growing these small maple species.

A newly planted tree should be adequately irrigated the first two years after planting. Feed annually (in late winter or early spring) with a slow release fertilizer such as Osmocote® or Nutricote®. according to package directions. Maintain a 3-4 inch deep, weed-free, organic-mulched zone around the tree.

Disease and insect issues are rare if tree(s) are properly well cared for. Leaves may turn chlorotic (yellowed) if soil acidity climbs above 6.8 pH. In most years little annual pruning is necessary.

American Basswood Tree

Posted by Hugh on June 12th, 2018

Large American linden

Summer foliage and winged seed

American basswood (Tilia americana) is a common deciduous native tree in midwestern and eastern U.S. forests (USDA hardiness zones 2-11). This large majestic tree is remarkably fast-growing but not weak wooded. Basswood is planted as a large residential shade tree, street tree along wide avenues, or tall privacy screen. A mature specimen may grow 50 – 80 feet tall and 30 – 40 feet wide although individual trees 90 – 100 feet tall are not unusual. Basswood may be either single or multiple trunk.

Sweetly fragrant pale yellow flowers opened in June and attract numerous insects, including butterflies, nocturnal moths, bees and flies. Basswood honey is highly prized for its sweet honey. Early colonists knew to identify trees because where you saw basswoods, bee hives (and honey) were nearby.

The large, showy cream-colored bracts persist well into fall. Bobwhites, squirrels, chipmunks, and deer feed on the nutlets. Its large growth buds are very noticeable in late winter. Basswood’s dark green heart shaped leaves are large (to 6 inches long), serrated along the margin, and sharply pointed at the tip. Leaf undersides are silvery in spring and less so later in the summer.

Basswood grows in average, medium moisture, well-drained soils in full sun to part shade. Young trees are drought susceptible, but older established trees are highly drought tolerant. Generally, basswood is intolerant of air pollution and urban conditions.

No serious insect or disease problems trouble basswood trees. Aphid and lacebug feedings on leaf surfaces are evident by early summer; Japanese beetles may also mar foliage. Newly planted trees should be sprayed for 1-3 years, but after 3 years, the tree’s growth rate makes pesticide spraying unnecessary. Powdery mildew, leaf spots and stem cankers may occur but pesticide spraying is not practical. Spider mites can also cause significant damage, particularly over hot, dry summers.

Multi-Use Bowles’ Golden Sedge

Posted by Hugh on June 8th, 2018

Bowles’ Golden Sedge With Hosta in Vancouver, BC

'Bowles Golden' Sedge at Kingwood Center in Mansfield, Ohio

‘Bowles Golden’ Sedge in part shade at Kingwood Center in Mansfield, Ohio

Bowles’ golden sedge (Carex elata ‘Aurea’) is an easy to grow sedge (USDA hardiness zones 5-8). Golden sedge was introduced by English plantsman and garden writer E.A. Bowles who discovered it growing in eastern England.

Bowles’ Golden sedge grows 1 ½ to nearly 3 feet high (in flower) and 2-3 feet wide. It features bright lemon- yellow leaves with dark green margins. Its fine-textured foliage turns lime-green in heavy shade. In late May (in zone 6), tiny brownish-colored flowers appear, but are mostly insignificant. You may opt to clip them off and put all energy into growing the plant.

Bowles’ Golden can be utilized for erosion control along stream banks. It freely naturalizes and eventually may dominate its wet surroundings. Clumps 3 years and older can be easily divided and/or transplanted in late winter or early spring before new growth begins. Fertilize the planting with a slow release organic fertilizer in early spring or feed with a water soluble product such as Miracle-Gro™ or Peters™.

Grow it in a moist loamy acidic soil and in partial shade. Bowles’ Golden will tolerate moderately dry soils in a shady garden spot. Plant it on the edge of a pond or water garden submersed in 1-2 inches of water. It can be planted in full sun under frequent irrigation where its golden color will shine. Golden sedge may also be planted in containers among other moisture-loving plants. You may substitute with other gold leaf favorites like golden sweet flag (Acorus gramineus ‘Ogon’) or Aureola hakone grass (Hakonechloa macra ‘Aureola’).

Golden sedge has no serious pests and is deer resistant. The foliage on established clumps may brown or grow shorter during temporary dry spells and recovers as soil moisture is more plentiful.

Shredded Umbrella Plant For Woodland Gardens

Posted by Hugh on June 3rd, 2018

Shredded Umbrella Plant with Hostas At Kingwood Center, Mansfield, Ohio

Flower head of Syneilesis in mid-July

Shredded umbrella plant (Syneilesis aconitifolia) is native to China, Korea, and Japan (USDA hardiness zones 5-7). The plant is often misidentified as mayapple (Podophyllum). The foliage is exquisitely dissected, similar to a finely dissected Japanese maple leaf. The plant serves a wonderful addition to any shade garden.

In mid-spring exquisite umbrella-like foliage emerges covered with hairy silver hairs. Umbrella-like pubescent leaves are very dissected and coated with tiny hairs. They stand 18 -24 inches tall atop sturdy stems. As the plant ages, pubescent hairs disappear and leaves turn deep forest green. After a brief number of years small plant colonies arise from underground rhizomes (2 feet wide in 5-7 years).

Flowers are very insignificant. Pinkish-white florets (each to ¼ inch across) bloom in June-July in corymbs atop striated purple stems that rise 3 feet or more above the foliage. Individual flowers are very small, and not interesting up close.

Shredded umbrella plants tolerate full shade, but perform best in dappled morning shade. Plants grow best in sun-dappled woodland conditions with moderate moisture, but will tolerate short dry spells of 2-3 weeks once the plants have adapted to their site, usually after the first year. Ideal garden environment is a humus-rich soil that is mulched with leaf compost. Humus supplies much of the needed nutrients.

Over the years shredded umbrella plants will naturalize via rhizomes to form colonies which widen out slowly. Plants are rarely purchased at garden centers. Shop at on-line nurseries which specialize on shade or woodland plants such as Plant Delights Nursery in NC and Fairweather Gardens in NJ.

Build A Hotel To Invite Beneficial Insects

Posted by Hugh on May 29th, 2018

Insect hotel

Bee Hotel at NC Arboretum In Asheville, NC

Insect hotels are intended for most (not all) sorts of pollinators. They’re easy to construct from new or recycled materials. These structures should be weatherproof as they serve as year-round shelters for bees, wasps, ladybugs, and others that may hibernate over winter.

Insect hotels are essentially the same as “wildlife walls” as they invite multiple critters and different kinds of insects. They really don’t specialize in attracting bees although they do have some cells for bees. On a wildlife wall, the usual guideline is to build it and ignore it. It gets better use if left alone to age.

This is a wonderful opportunity to show off your artistic skills in efforts to rebuild our native bee populations and new different pollinating insects. There are lots of helpful tips on the internet about constructing an insect hotel or wildlife wall.

Here are some additional “good bugs” that you should encourage to move into your insect hotel:

Non-colonizing or solitary bees and wasps – they built their nests in the ground, tubing, cracks in pavement are perfect “invitees”. European honeybees are colonizing bugs and not suited here.

Parasitic Wasps – these tiny parasitic wasps lay their eggs in the bodies of numerous pests, and their larvae feed on tomato hornworms, cabbage worms and many other damaging pests.

Centipedes & Millipedes – prey on all sorts of soil-dwelling pests, like slugs and help break down organic matter. Please note that these become nuisance bugs when they find their way into your home.

Lacewing larvae also feed on aphids, mealybugs, scale insects and some caterpillars.

Ladybugs (several kinds) feed on aphids.

Ground Beetles are good bugs that feed on such garden pests as snails, slugs, aphids, and mites.

Sowbugs (Pillbugs) feed on decaying organic matter.

A tip from a blog reader: If you do include tunnels in wood or cardboard tubes with liners for bees, you should replace them every two years to prevent bee predators from moving in. The rest of the hotel can be left undisturbed.

Short Grasses For Small Places

Posted by Hugh on May 25th, 2018

Pennisetum orientale ‘Karley Rose’

Many gardeners have small sunny or partially shaded places where select ornamental grasses thrive, including using them as companion plants in containers. Enjoy their winter architecture. Perennial grasses should be cut back to 3- to 6 inches in late winter.

Here are an assortment of six of the very best along with several varieties that you should plant.

Fountain grasses (Pennisetum spp.) represent decorative ornamental annual grasses (zones 9-11). My favorites in the group are ‘Fireworks’, ‘Cherry Sparkler’, and ‘Rubrum’. ‘P. orientale ‘Karley Rose’ is a zone 6 hardy perennial form that has proven to be highly reliable over many years.

Hakone grasses (Hakonechloa macra) are short growing accent grasses from Japan. They thrive in shady garden areas as well as are included as accent plants in container designs. Three popular varieties are ‘Aureola’, ‘All Gold’ and the green species H. macra.

Carex oshimensis ‘Everillo

Feather reed grasses (Calamagrostis spp.) – grow 3-5 feet tall and 1 -2 feet wide. It has tight upright stance, and planted in multitudes to show off its erect architecture. The feathery plumes emerge in early summer and ripen to handsome wheat-colored seed heads in fall.

Japanese Sedges (Carex oshimensis) so many great ones to choose from-. Everest’ and ‘Everillo’ (chartreuse foliage) are two favorites in this group. Carex morrowii ‘Ice Ballet® and ‘Ice Dance’ are also favorites for moist well partially sunny areas.

*Little bluestem (Schizachyrium spp.) – ‘The Blues’ with stunning blue foliage, ‘Blaze’ for fall color, and ‘Standing Ovation’ (bluish-green, semi-erect habit) (zones 3-9).

*Sea oats (Chasmanthium latifolia) is a 2-5 feet tall clump-forming ornamental native grass. It is easily identified by their flat, drooping seed heads which hang in terminal clusters on arching stems. Seed heads flutter in the slightest of breezes. Seed heads emerge green but turn purplish bronze in late summer. Bright green leaves (5-9″ long) turn a coppery color after frost and eventually brown by winter. Excellent for dried flower arrangements.

*Warning: some grasses may seed in prolifically.

Sea oats (Chasmanthium latifolium) in fall

Two Native Cardinal Flowers Add Up To A Stunning Combination

Posted by Hugh on May 21st, 2018

Red cardinal flower (Lobelia cardinalis)

Blue lobelia (Photo by North Creek Nurseries, Landenberg, PA)

Great lobelia or blue cardinal flower (Lobelia siphilitica) is a native perennial USDA hardiness zones 4-8). They bloom about a month later than cardinal flower (Lobelia cardinalis). They’re part of the late summer perennial bloom season that includes turtlehead (Chelone obliqua), asters (Symphtrictum), ‘Henry Eilers’ black eyed Susan (Rudbeckia subtomentosa). and dahlias (Dahlia spp.). Add this clump-forming perennial to a perennial border or woodland garden.

The erect 2-3 feet, stems produce lavender-blue, tubular flowers crowded together on the upper stem. Showy, bright blue flowers are in the axils of leafy bracts and form an elongated cluster on a leafy stem. Each flower is split into two lips – the upper lip has two segments and the lower lip has three. Flowers form a dense terminal raceme atop stiff, unbranched leafy stalks, typically rising 2-3 feet tall. Finely-toothed, lance-shaped, light green 5-inch long leaves are attached to the flower stem.

In the wild you see both red cardinal flower and great lobelia growing in wet soils. A garden plant want a humus- rich, medium to wet soils and full sun to part shade. It is tolerant of acid to neutral (pH 5.2-7.0). They demand almost constant moisture, but great blue lobelia tolerates drier sites and more shade. Immerse them in your bog or water garden. Both tolerate full sun in cool, northern climates, but otherwise appreciates part shade in southern climes. In a wetland habitat plants may self-seed in optimum site and form attractive colonies.

Planting both species create a stunning show. Hummingbirds will come and visit.

Both plant species are generally short-lived. For longevity a 2-3 year old plant clump should be lifted and divided in the spring. No disease or insect problems trouble this native plant. Snails and slugs may damage the foliage.