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

Bigroot Cranesbill

Posted by Hugh on September 10th, 2022

*Geranium macrorrhizum* ‘Bevan’s Variety’

Bigroot Cranesbill (Geranium macrorrhizum) is a favorite, easy to grow plant that forms a dense weed-resistant ground cover with attractive foliage and flowers. (USDA zones 4 – 8). This “cranesbill” is a true perennial geranium. It is a rhizomatous semi-evergreen perennial, native to southern Europe, typically grows to 12 inches tall and to 24 inches or more in spread. The rounded grayish-green leaves (4-8 inches long) have 5-7 deeply cut lobes. Leaves are strongly aromatic when crushed. Over the years this slow-growing cranesbill species develops into an attractive vegetative patch that asks for little maintenance.

Three varieties – ‘Ingwersen’s Variety’, ‘Bevan’s Variety’ and ‘Spessart’ – are commonly available at garden centers. ‘Bevan’s Variety’ grows to slightly more than a foot tall and bears magenta-pink flowers that are uniquely veined; ‘Ingwersen’s Variety’ bears pale pink flowers on dark red stems; ‘Spessart’ has white (soft pink) flowers on and off through the summer months. Blooms stand above the foliage, often with some re-blooming in late summer into autumn.

Bigroot cranesbills grow in full sun to partial shade and in average well-drained soil. Plants tolerate full sun in northerly cool areas; otherwise, they tolerate hot humid summers and dry shade better than most other cranesbill species. Plants do not need to be cut back or sheared after flowering. If you demand a tidy look, the taller flowering stems may be mowed back, leaving a rough appearance for maybe 7-10 days. Plants spread in the garden by rhizomes and occasionally self-seed. Clumps may be divided to expand the ground bed faster.

Site this low ground cover at the front of planting borders or edge large urns and planters utilizing this cranesbill and others. Deer and rabbits leave cranesbills alone and the bees work their small saucer-like blooms. Leaves acquire red tones in autumn and stand out more in unseasonably dry weather.

Worst Weed Ever Is Here?

Posted by Hugh on September 2nd, 2022

Mulberryweed (Fatoua villosa) is not related to mulberry trees but its leaves look a little like mulberry foliage. A native of eastern Asia, it was introduced into North America in the latter half of the 20^th century. Currently, it is seen in the Southeastern United States from Maryland to Florida, west to Texas and Oklahoma, north to the Ohio (zones 5-11).

Gardeners may argue whether it’s worse than nutsedge (Cyperus rotundus), creeping Charlie (aka ground ivy), crabgrass, or any other you wish to list. Even the U.S. nursery industry is concerned. It has gotten into growing (potting) media, and growers are warning their customers (garden centers and landscapers) to inspect shipped plants after purchase.

Mulberryweed is an erect, branched summer annual. Leaves are alternate, and roughly triangular in outline with toothed margins. Flowers are borne in feathery clusters in the leaf axils. Flower clusters are purple when young, fading to dark brown with age. Plants flower from late spring through early fall and die after frost.

If you mow over this weed, new growth branches and stays low and grows horizontally. It produces tons of seed and produces multi-generations over the growing season. New seedlings may flower and fruit within 12 days of reaching the 2-leaf growth stage. Learn to pull it out immediately. Individual flowers are inconspicuous, white to cream colored, and are not persistent. Seeds are forcefully expelled at least 4 feet.

Closeup of seed capsule (photos by Jane Conlon)

Seeds germinate from early spring through late fall, resulting in many generations per year. Consequently, although well managed by certain pre-emergence herbicides, populations may continue to build in the absence of aggressive sanitation programs. Herbicide efficacy rankings for this species are based on limited experimental data.

From personal experience, mulberryweed has really become a menace in our landscape. I’ve been sloppy pulling and leaving weeds in place to decompose – a big mistake. I am now carting all weed debris away.

Thanks to Mr. Jason Reeves, Horticulturist at the West TN AgResearch & Education Center in Jackson, TN, for initially identifying mulberryweed.

Salvias – Nature’s Last Hurrah

Posted by Hugh on September 1st, 2022

Salvias are native to central South America. Some species may surprising survive here in Tennessee/Virginia (zone 7) as tender perennials. In the early days of autumn, salvias seem to revitalize – vegetatively and flower numbers. Salvias are both reliable nectar and pollen sources for butterflies and hummingbirds and are seldom damaged by deer. Listed here are four star performers in late summer and autumn.

Blue anise sage (Salvia guaranitica) is a garden annual in northern areas of the U.S. (zone 7b-10). Deep purple flowers are produced from midsummer to fall. The 2-inch long, electric blue, two-lipped, tubular flowers contrast strikingly with the blackish stems. Two cultivars – ‘Black and Blue’ and ‘Black and Bloom’ – may survive a mild winter if plants are well-mulched. Plants develop an open shrubby appearance, to 3-5 feet tall (perennialized) and 2.5 to 3 feet tall (as an annual) in garden beds or large containers.

Mexican Bush Sage (Salvia leucantha) is prized for its dense, arching spikes and ability to produce an attractive late summer bloom of showy flowers (zones 7b-10). The plant feels soft and hairy to the touch, and the bi-color blooms include white corollas and purple calyces.

*S. leucantha* ‘Santa Barbara’ at NC Arboretum in Asheville, NC

Friendship Sage (Salvia x) is a showy violet-purple blooming sage. The cultivar ‘Armsted’ is an annual sage that overwinters in zone 7b.

Fuzzy Bolivian Sage (Salvia oxyphora), aka Bolivian Spearhead Sage, is fairly new in U.S. garden scene, but their bright, hot pink, fuzzy blossoms will surely make them a favorite (zones 8-10). The plant’s deep green tropical-like foliage is glossy green with clear, almost invisible hairs. Flowers appear in late June and plants continue blooming through the October frost, with terminal clusters of hairy rosy-pink tubes. It grows vigorously and can reach 4 feet in height by the end of summer.

**Fuzzy** **Bolivian** **Sage** (*Salvia oxyphora*) at Longwood Gardens

General Care: Plant any of these salvias in the flower garden or in containers in humus-rich, medium moist, well-drained soil and in full sun. Wait until the threat of spring frost has passed. Salvias become moderately drought tolerant 6-8 weeks after planting.

Why My Tree Turns Yellow in Summer

Posted by Hugh on August 27th, 2022

Leaves of some landscape trees turn yellowish- green color in the summer. The common cause for this malady is a lack of minor nutrients (“micronutrients”) that are essential for plant growth. These nutrients are available in the soil in very small quantities. Nutrient deficiencies are not common, except in the high pH soils, particularly the soils the central U.S. south to Texas.

Micronutrients include iron, manganese, zinc, copper, boron, silicon, and molybdenum. These are in contrast to macronutrients (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S), which are required in greater amounts and make up a larger portion of the plant tissue.

A bag of fertilizer (contains N, P, and K) and various forms of lime supply key macronutrients of (Ca) and (Mg). Soil pH plays a role in the availability of minor nutrients, particularly iron (Fe), manganese (Mn), and molybdenum (Mo). Micronutrient deficiencies also may occur when a plant’s root system is compromised, such as by injury, disease, poor site conditions, drought, or water-saturated soils.

Yellowing of the late spring or summer foliage is typically a symptom of a minor nutrient deficiency in specific landscape plants. As examples, look for mid-summer foliar yellowing (called “chlorosis”) on pin oak (Quercus palustris) and river birch (Betula nigra), and manganese deficiency on red and silver maples (Acer spp.).

Deficiency symptoms are marked by pale green or yellow leaves, with veins that remain green. As the deficiency is not corrected, new spring growth is stunted, branches may die back, and the leaf edges (margins) and interveinal areas of leaves may turn brown. In severe cases, the entire tree may decline over several years and die.

Iron deficiency on river birch (*Betula nigra*)

To avoid poor plant health caused by micronutrient deficiencies, test the soil before planting a tree and choose trees and shrubs that are tolerant of the high pH soil conditions. Foliar application of iron is a short-term treatment that can help trees appear more green and healthy in the current season, but must be applied later on when leaves have emerged. Repeated this fertilizer treatment annually.

Micronutrients injected into the trunk of the tree. These treatments help leaves to turn green within a week or two, and can last up to two years. Certified tree arborists can inject “liquid chelated iron” into holes drilled into the trunk of oaks and birch trees. Other products containing ferrous sulfate (iron / sulfur) may be fed directly into the soil around trees and shrubs also improves their foliar color.

Growing Rain Lilies

Posted by Hugh on August 22nd, 2022

Rain lilies (Zephyranthes), aka Zephyr lily, Atamasco lily, fairy lily, et al. are small perennial bulbs that are native to the southeastern United States, Central and South America (USDA hardiness zones 7-10). In the U.S., these bulbous members of the Amaryllis Family (Amaryllidaceae) grow in shady woodlands and wet meadows where they peek out along the edges of a garden.

Rain lilies crave wet to rainy summer weather and perform poorly in droughty soils. Dormant bulbs wake up during periods when rainfall is plentiful in summer and early autumn. Plant (sow) them in the front of the border, in a rock garden, or even in a rain garden. Plantings get more notice by sowing multiples of rain lilies together.

Flower colors range from yellow, white or pink. Butterflies and honeybees are all over these late summer-fall blooming bulbs. Plants have grass-like foliage and their heights range from 2 to 12 inches (5 – 30 cm.) depending on species.

Rain lilies bloom from spring to autumn (species dependent). Sow bulbs at a depth of 3 inches (8 cm), and a spacing of 4-6 inches (10 -15 cm) apart following the last frost of spring. Plant them @ 8-10 bulbs per sq. ft. The top of the bulb should be about an inch under the soil surface and 2-4 inches apart in containers as they look best when crowded and slightly pot-bound.
They multiply rapidly.

Plants grow in partially shaded or sunny parts of the garden that have well-drained, moist, humus-rich, mildly acidic soil. Rain lilies benefit from fertilizing at planting time and annually. In northern gardeners grow these non-hardy bulbs in containers as annuals or overwinter the pots in a cool dry location.

Rain lilies are both pest resistant and critter proof. Bulbs and all parts of the plants contain toxic alkaloids that can cause vomiting, convulsions, and death if ingested.

Four Gold Leaf Landscape Trees

Posted by Hugh on August 17th, 2022

*Liquidambar styraciflua* ‘Gold Beacon’ (photo by Jason Reeves)

Deciduous trees that flaunt gold foliage in the spring and summer months are a rare sight in U.S. landscapes. Listed below are four tree species/cultivars that possess bright gold foliage, particularly when sited in full sun. Under partial shade, leaf color may eventually turn lime green to chartreuse. All four species are winter hardy in USDA hardiness zones 5 to 8.

Eastern Redbud (Cercis canadensis) is represented here by two gold-leaf cultivars: The Rising Sun™ and ‘Hearts of Gold’. Both varieties grow to 20-25 feet in height. Clusters of tiny, reddish-purple, pea-like flowers bloom for 2-3 weeks in early spring. After flowering, young leaves emerge with deep apricot leaves; by late summer leaves have aged to lime green. Hearts of Gold redbud was the first gold-leaf cultivar introduced. The Rising Sun is an improved form in that its leaf color better holds up to summer heat and dry weather and rarely burns compared to Hearts of Gold.

Golden Sweetgum (Liquidambar styraciflua ‘Golden Beacon’) emerges in mid-spring with light green foliage that quickly changes to a golden hue that does not fade over the summer months. Autumn foliage varies from red and orange. Be patient as this sweetgum variety tends to start off slow but may reach 40 feet high by 30 feet wide in 20 years. Grow in full sun for best leaf color retention.

Golden Locust (Robinia pseudoacacia ‘Frisia’) is a reliable form of black locust that flaunts bright lemon-yellow leaves in full sun in the spring and summer months. Each compound pinnate leaf is up to 12 inches long and composed of up to 23 oval leaflets. In June (or early summer), it produces hanging clusters of fragrant pea-like white flowers. The tree grows in average soil with adequate drainage. Established trees, 2 years and older, copes with prolonged dry spells.

Claim Jumper™ Katsura (Cercidophyllum japonicum) is a fine 25-30 feet tall by 20 feet wide tree. Young trees exhibit a strong upright branching habit. New spring leaves emerge with a pink blush and unfurl to a soft, golden-yellow. It retains its gold foliage color through most of the summer although some shade leaves may turn pale green. Katsura’s sweet cotton candy fragrance and buttery golden leaf color is revealed in the fall.

Surprise Lilies

Posted by Hugh on August 8th, 2022

Add a bit of unexpected beauty to your garden in late summer with surprise lilies (Lycoris spp.), aka spider lilies, resurrection lilies, magic lilies, and naked ladies. (Zones 4-9). Along coastal areas of the southern U.S., they are called “hurricane lilies”. The most popular is red spider lily (L. radiata), a long-lived heirloom flower in Southern gardens, often seen growing in old gardens and cemeteries.

These bulbous plants are in the amaryllis family (Amaryllidaceae) and have been cultivated for centuries in Japan. In some years, if Southern winters are unusually mild winters, bloom stalks may not pop-up. But be patient -blooms should return the following year.

Surprise lilies thrive in full sun to light shade and most soils. Keep the soil somewhat dry when the bulbs are dormant. They require no fertilization and are not troubled by pests. Anytime, in August or early September, surprise lilies come into bloom.

Plant 10 to 12 bulbs scattered over at least 5 linear feet of bed area. Culturally, surprise lilies behave like other late season bloomers like fall crocus and colchicum. They send up strap-like leaves in spring. The leaves create energy for the bulb and should not be disturbed, allowed to naturally die back to the ground by late May.

Three easily found species:

L. radiata – the most common form with bright red spidery blooms.

L. sprengeri – mixed shades of blue and pink that change as petals age.

L. squamigera – 5-7 pink, four-inch-long trumpet blooms stand atop 2-foot-tall stems.

Celebrate Summer Growing Colorful Perennial Hibiscus

Posted by Hugh on August 3rd, 2022

Summerific® Spinderella (Photo courtesy of Walters Gardens, Inc

Perennial hibiscus (Hibiscus moscheutos) is commonly known as rose mallow or dinner plate size hibiscus. Blooms measure a huge 7-9 inches across. Plants are exceptionally hardy, and can withstand winters as cold as zone 4 (-20°F to -30°F) in Minnesota (zone 4) and the heat of zone 9 (20°F -30°F) in Florida. Each flower lasts only one day.

Summerific® rose mallows are a huge improvement. Older varieties tended to produce flower buds only at the tips of the branches and bloomed for just a few weeks. Plants produced fewer flower buds.

Newer varieties in the Summerific series produce flower buds all up and down the stems, including the top. Newer Summerific varieties are bred to bloom for months, 3 times longer than older varieties.

Rose mallows need water and lots of it. Plants can actually grow in standing water. Grow them within reach of a hose or sprinklers and irrigate on a regular schedule. Whether you are growing in average soil or in a good garden loam, do not allow plants to wilt and dry out. Badly wilted plants may drop their lower leaves and flower buds.

Hibiscus ‘Evening Rose’ (photo courtesy of Walters Gardens)

Give them room to grow. Rose mallows are very robust growers that fill their space in the garden. Read the plant label about variety spacing. Dwarf varieties grow at least 3 feet tall and wide, and standard-sized rose mallows grow 4-6 feet tall and wide.

Bring on the sun. Full sun (6+ hours) is imperative. Dark leaf varieties develop a more intense dark purple foliage color in a sunny garden. Full sun equals more flowers. In partial shade, plants produce fewer flowers and dark leaf varieties appear more greenish.

Summerific® French Vanilla (photo courtesy of Walters Gardens, Inc)

Spring-Summer Perennial Hibiscus Care Tips:

Cut back rose mallow in the spring. Cut down the dormant woody stems to about 6 inches tall. Rose mallows tend to be one of the last plants to emerge, sometimes as late as early June in northern areas. Newly emerging shoots will grow rapidly, about an inch a day.
Once spring growth arises, sprinkle slow-release plant food such as Espoma™ Plant-tone^® or an equivalent slow-release organic fertilizer around the root zone (according to package directions. In early summer, follow-up with a water-soluble plant food like Miracle-Gro™ or Jacks™ just as flower buds are beginning to form.

Mini Reblooming Smooth Hydrangeas

Posted by Hugh on July 31st, 2022

‘Invincibelle Wee White’ hydrangea at Kingwood Center, Mansfield Ohio

Smooth hydrangeas (Hydrangea arborescens) generally grow 6 -7 feet high, and some wild forms upwards of 10 feet (USDA hardiness zones 3-9). The exceedingly popular Invincibelle® series grow 5-6 feet high. Three recently introduced mini-types (listed below) are perfect for a small garden or in a large container. Shrubs in the series reach full size in only 2-3 years with proper care.

Smooth hydrangeas bloom in early summer (June-July). Flowers start out cream, open pure white, and age gracefully. As the season goes by, the flowers droop and fall away. Clip or not to Clip? The old dried floral heads remain attractive for off-season interest. No deadheading required!

Invincibelle hydrangeas are noted for their rapid growth. Their large flowers are prominently displayed above the foliage. Floral stems are strong and sturdy, not laying down on the ground. Plants can be utilized as garden borders. Flowers emit little scent from far away but the floral odor is delightful close up.

Bright green leaves appear in late spring. In autumn leaves gradually turn yellow and abscise.

‘Invincibelle Mini Mauvette’ (photo courtesy of PW)

General Care: For big abundant blooms, plant where they capture at least six hours of sun each day (warmer climates can get away with a bit less). A 3–4-inch layer of shredded bark mulch aids to minimize water loss. Prune back the entire shrub by about one-third its total height in early spring, just as new growth begins to emerge. Feed once in early spring, with 1-2 handfuls of 10-10-10 or equivalent fertilizer.

Introducing three mini-re-bloomers in the Invincibelle® series. They bloom from late June through frost with new flowers throughout. They re-bloom, again without need for deadheading. In hot southerly zones, plants grow best in afternoon shade.

Mini-Varieties:
‘Invincibelle Wee White’ grows just 1.0 – 2.5 feet tall and wide, forming a tidy, rounded mound. Each flower emerges soft, blush pink before changing to white. (zones 3-8).

‘Invincibelle Mini-Mauvette’ grows 2.5 – 3 feet tall. Beautiful and unique pink-mauve blooms stand upright and sturdy all season. Summer foliage is dark green. (zones 4-8).

‘Invincibelle Garnetta’ boasts a compact size (2.6 – 3.0 feet tall and wide), sturdy stems. This cultivar blooms a bit later than the rest of the Invincibelle series. Silvery-pink/ruby-red flowers add a different flair to the summer landscape. (zones 3-8).

Mimosa Tree – Love It Or Not

Posted by Hugh on July 21st, 2022

Over the hot spring and summer months, weedy Mimosa trees (Albizia julibrissin) stand beautiful along U.S roadsides. During the rest of the year, people pay very little attention to this arboreal Asian beauty that inhabit a vast area from Iran to China (USDA hardiness zones 6-9).

From late spring through summer, mimosa struts an attractive fine textured green foliage and lovely flowering. It leaves out as late as mid-May in its northern range. Wild seedlings produce pale pink to dark pink feathery blooms from late June thru July. The showy fragrant flowers attract numerous bees and hummingbirds. Fall leaf color changes is non-existent.

Mimosa grows 20-25 feet tall of equal and broader widths. Under cultivation, it may achieve 35-40 feet high. It grows best under full sun and in almost any adequately drained soil. It copes with subpar sites, often overpowering an abandoned urban lot or a roadside fencerow. Its seeds take flight from miles away.

The cultivar ‘Summer Chocolate’ exhibits fern-like dark purple foliage. The cultivar is rated hardy in USDA zones 7-10. Chocolate mimosa grows rapidly to 20 feet tall and wide; that is nearly half the size of a mature green leaf specimen.

Chocolate Fountain™ is a recently released weeping purple leaf cultivar from Dr. Tom Ranney at North Carolina State University (zones 7-10). Dramatic, deep purple, fern-like foliage graces the pendulous, weeping habit, enhanced by delicate pink flowers in summer. An elegant accent for smaller spaces or containers.

In general, mimosa trees tend to be short-lived, around 15- 20 years. However, trees tend to colonize, depositing loads of seeds that beget lots of seedlings. They improve the soil’s tilth and nutrition, so that one day, an opportunist native species may take over in its place.

Late winter thru early summer (February-July) is the ideal planting time. Remove unwanted and dead branches at any time. Over the first two years, water deeply during extreme heat and dry periods and the entire growing season those growing in containers. Fertilizing a mimosa tree is unnecessary as roots manufacture their own nitrogen.