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

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.

Rose of Sharon – A Summer Delight

Posted by Hugh on July 16th, 2022

Rose of Sharon (Hibiscus syriacus), aka althea, is a vigorous, upright, vase-shaped, multi-stemmed, deciduous shrub that typically grows 8-12 feet tall with some exceptions. Altheas may also be trained as small trees or espalier. Showy 5-petaled flowers appear over a long summer period and sometimes into early fall. The center of each flower has prominent single staminal column (except where noted). The palmately-veined, coarsely toothed leaves are medium green leaves measure 2-4 inches in length but fall color is non-existent.

Hibiscus Pollypetite® (photo courtesy of PW)

Altheas are highly dependable landscape shrubs and among the easiest to maintain. They grow in average, medium moisture, well-drained soils and in full sun to part shade. Flowering is best in full sun and in moist, humus-rich soils. Established shrubs exhibit good summer drought tolerance. Prune to shape in spring. Old altheas may be cut back to the ground in late winter. Altheas are easily propagated by stem cuttings.

Disease and insect problems cause little overall injury to altheas and new aftergrowth covers up most damage. Feeding of Japanese beetles in June may injure foliage; Neem Oil or Sevin® dust will destroy beetles, Do not use insecticides when altheas are starting to bloom to protect bee pollinators. Altheas are rated deer resistant, meaning deer rather prefer other shrubs.

Altheas may be planted in groups for hedging or singly used as a specimen. Utilize them for foundations and shrub borders.

Chiffon® Series is an outstanding series from Proven Winners. Flowers are mostly sterile, meaning they may produce only a small amount of seed. Shrubs grow 8-12 feet tall and 6-10 feet wide. Currently, there are 5 color choices in the series: Blue Chiffon®, Dark Lavender Chiffon®, Magenta Chiffon, Pink Chiffon®, and White Chiffon®.

Pillar™ Series are planted as space-saving shrubs that grow 10-16 feet high and 2-3 feet wide. Now available in three color choices: Purple Pillar®, White Pillar®, and Red Pillar®.

Pollypetite® (H. paramutablis x H. syriacus) is a dwarf hybrid form. This rounded shrub grows 3-4 feet tall and wide with large rounded pure lavender purple flowers with soft ruffled edges and no center eye. Leaves are very dark green.

Paraplu Adorned® (NEW) has leaves that flush bright yellow in spring and are everchanging thru the season. It grows 10 feet tall and 4 feet wide with an upright, vase-shaped, spreading habit that can be trained as a small specimen tree or group several into a privacy screen.

Sugar Tip® is a double-flower seedless form that grows 6-8 feet high and 4-6 feet wide, bright cream and bluish-green variegated foliage and large clear pink double blooms.

Several other varieties are available at garden centers. The varieties listed above are among the best.

Beware: altheas can self-seed aggressively and become a weedy nightmare. Seedless forms are becoming more available.

A Late Season Blooming Tree

Posted by Hugh on July 10th, 2022

Seven Son Flower (Heptacodium miconioides) is a large, multi-stemmed, deciduous shrub that grows 15-20 feet tall and 10-12 feet wide at maturity. This rare unique specimen is catching on in the U.S. because of its year-round appeal (USDA hardiness zones 5-9). It is an excellent choice for a lawn specimen or plant several in a row to create a tall shrub border. It may also be trained as a single- or multi- trunk deciduous tree.

Starting in late summer into early autumn, terminal panicles of fragrant, creamy-white jasmine-like flowers arise. Flowers are flattened clusters of stalkless blooms (six in number). Flowers are followed in fall by small, purplish-red fruits (½” long drupes) crowned by very showy, rose-pink calyces which elongate after bloom and last into late fall. Floral display of white-petalled flowers last several weeks. Petals fall and ruby red sepals expand, giving the appearance of twice blooming from August to October.

Of winter interest the tan-brown bark exfoliates to reveal its attractive brown inner bark. The medium green leaves are narrow, shiny, and ovate-oblong in shape. A nursery-grown container plant transplants easily. This tree/shrub is becoming more available at on-line nurseries but is still difficult to find at independent garden centers.

This moderately fast-growing tree performs best in full sun and in good landscape soils that exhibit good drainage and retain enough moisture to survive dry periods. Light spring pruning is needed following harsh wintry weather.

Butterflies, other pollinating insects, and hummingbirds frequent the nectar-filled blooms late in the season. Serious insect or diseases are rare with this plant if the plant is properly sited and maintained. Seven son is the recipient of a number of Regional Plant Awards in the U.S. and Great Britain.

Cultivars:
Tianshan® is new selection for smaller gardens, grows 8-12 feet high by 5-7 feet wide.

Temple Of Bloom®, introduced in 2019 by Proven Winners (PW), grows 10 feet tall and wide.

Rhizomatous Alliums

Posted by Hugh on July 1st, 2022

Alliums are a members of the lily family, containing 1100 species, including the edible kinds that you add to your burgers and salads. In the ornamental flower world include spring- blooming bulbs, culinary herbs and durable foliage and bountiful summer flowers.

Whether your summer garden is located in a challenging part of the U.S. such as Texas or Oklahoma or a moist humus-rich ground in New York or Virginia, take a peek at the perennial gems in the onion family (genus Allium). Recently, Richard Hawke, Director of Ornamental Plant Research at the Chicago Botanical Gardens CBG), published the top-rated rhizomatous alliums in the Midwest region (see below).

Rhizomatous alliums just ask for sun and well-drained soil. All are all drought resistant and thrive on dry sites. They are all highly drought tolerant, especially after plants have established themselves their first season. Pest and disease issues are usually rare. Watch for occasional leaf spots, molds, thrips, and onion flies. Allium plantings are busy with beneficial insect life, covered by numerous bees and butterfly species. And deer don’t dig onions or chives.

I have a number of favorites, many of them on the “CBG’s Best Of” listing which appears in the August ‘22 Fine Gardening Issue. Let me start with A. ‘Millenium’, Perennial Plant of the Year winner in 2018. It produces masses of 2.5″ rosy-purple flowers above the dark green foliage in midsummer.

A. ‘Windy City’- thin dark-green leaves provide a dramatic backdrop for 2″ lavender-purple flower clusters on strong, dark stems. Spent flowers persist for winter interest, and are near-sterile, meaning very little seed. This compact variety is perfect for small spaces such as in a rock garden.

A. tanguticum ‘Summer Beauty’ – long-blooming ornamental onion that produces showy, globe-shape 2” lavender-pink blooms in mid-summer and shiny deep green throughout the season.

In the CBG evaluation, three rhizomatous alliums were highly mentioned but not rated:

A. ‘Serendipity’ – sport of ‘Millenium’ great stuts attractive blue green foliage. Globe-like, 2.5” rosy-purple blooms that flower abundantly in mid to late summer.

A. ‘Big Beauty’- soft pink 3” flowers with gray-green foliage in early to mid-summer.

A. ‘Lavander Bubbles’ – blooms a month later than ‘Millenium’ with darker shade of 3″ purple floral globes above attractive glaucous blue-green foliage.

Read the full CBG report in Fine Gardening magazine (August 2022 issue).

New Annual Vincas ‘Kawaii Soiree’ Series

Posted by Hugh on June 26th, 2022

Sun-loving vincas (Catharanthus) are annual periwinkles. This may confuse gardeners who also grow perennial periwinkles (Vinca spp.) that are grow in shady groundcovers.

New from Proven Winners (PW)!! Soiree Kawaii® series of vincas (C. roseus) are bred by Suntory and entered the market around three years ago. I highly recommend that you include them to your list of summer flowering bedding plant.

The name Soiree Ka·wa·i·i means “cute” in Japanese to describe the adorable flower size and shape. Compared to most vincas, petals are dissected and offer a finer floral texture in garden beds and containers. Their bright, attractive flower petals are irresistible to pollinators, especially hummingbirds and butterflies. These micro-blooming vincas grow compact and spreading, and are exceptionally floriferous.

Look for plants to arrive in mid-South garden centers in late April. Plant them into your garden after garden soil temps have risen above 55 °F and the frost danger has passed. Enjoy continuous bloom thru the early non-killing frosts in autumn. Don’t wait a day. Plant them in garden beds and landscape containers and watch flower numbers explode almost within the first week.

Soiree Kawaii vincas perform best in well-drained, humus-rich garden soils and in containers. One caveat: vinca plants despise soggy wet cool soils. Fertilize plantings every 4-6 weeks with a water-soluble product like Miracle Gro® or Peters®. Mulch beds and irrigate over long dry spells. Plants bloom non-stop during the hot humid days of summer.

Soiree Kawaii vincas are valued for their neat mound-like form (6-10 inches tall / 12-18 inches wide). Their glossy dark green leaves make flower colors pop. Even more impressive is how nicely the plants fill out beds and containers, including window boxes and hanging baskets. Pinching is rarely needed.

Currently, six colorful varieties in these compact growing vincas are available. Soiree Kawaii come in white, pink, coral, lavender, peppermint, and red shades. My personal favorites so far are Peppermint® and Blueberry Kiss®.

Modern day vincas exhibit improved disease resistance compared to olden varieties that your mother once grew.