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

Swamp Milkweed Is Monarch Butterfly’s Favorite

Posted by Hugh on August 29th, 2014

Swamp Milkweed at Chicago Botanical Gardens

Swamp milkweed (Asclepias incarnata) is an erect, clump-forming, U.S. native plant indigenous to swamps, bottomlands and wet meadows (USDA hardiness zones 3 to 6). Obviously, it prefers moist soils but grows equally well in average, well-drained garden soils. Full sun is best, but copes with some light shade.

As its common name indicates, it makes a great choice for planting in moist spots such as in rain gardens and along stream/pond banks. No butterfly garden is complete without swamp milkweed. The flowers of swamp milkweed attract several species of butterflies including Monarchs. Monarch larvae (caterpillars) prefer swamp milkweed foliage for a nourishing food source over butterfly weed (A. tuberosa).

New plants emerge slowly in late spring. It develops a deep tap rootsystem which is best left undisturbed once established. Swamp milkweed grows 3 to 4 feet tall (sometimes to 5 feet) and 2 to 3 feet wide on branching stems. Narrow, willow-like leaves are 3-6 inches long with a tapered point. Stems exude a toxic milky sap when cut.

The clustered flowers are very attractive and fragrant. Small individual ¼-inch wide blooms are a pink to light lavender color; tight clusters (umbels) of five reflexed petals sit atop tall stems in July and/or August. Flowers are followed by attractive 2-4 inch long seed pods.

Swamp milkweed is short-lived, often 2-3 years, but it frequently re-seeds itself. In the fall the mature pods split open to release silky-haired seeds that are carried away on a blustery autumn day.

Swamp milkweed has no serious insect or disease problems. Aphids may be a significant pest. Deer generally leave milkweeds (Asclepias spp.) alone.

English Oak Demands A Moist Well-drained Soil

Posted by Hugh on August 27th, 2014

Leaves of Quercus robur ‘Skyrocket’

Thinking about English oak (Quercus robur) brings to mind Robin Hood and Sherwood Forest. This majestic oak forms a broad spreading crown supported by a short sturdy trunk with a medium-brown, deeply-fissured bark (USDA hardiness zones 4-8). A young tree exhibits a pyramidal form. In a city park or golf course, it typically grows 50-70 feet tall and 40-50 feet spread. Wild specimens across Europe have been measured over 100 feet tall and hundreds of years old.

English oak has small 3-5 inch long deciduous leaves with 3-7 pairs of rounded lobes and very short petioles. Its deep green foliage color holds long into the fall before turning brown and persisting on the tree most of the winter. In early spring strings of hanging catkins flowers emerge shortly before the leaves.

English oak is a member of the “white oak group”. Its rounded leaf lobes appear similar to white oak (Q. alba), a U.S. native which has ear-like basal lobes and very short petioles. Small 1-inch oval acorns form in the fall. English oak may take up to 25-30 years to bear its first crop of acorns that are an important source of food for wildlife. Acorns (nuts) are edible after poisonous tannins are boiled or leached out. Keep acorns away from grazing animals (horses, cattle, etc.).

English oak wants full sun and a moist well-drained, acidic or alkaline (pH 5.8-7.5) soil. This oak does not tolerate extended droughts. A balled and burlap (b&b) tree should best planted from late winter through spring. Young trees tend to grow slowly – 12 to 15 inches annually. Few disease and pest problems trouble it. In some years aphids, several species of caterpillars, and leaf miners feed on the leaves, rarely damaging the tree. Powdery mildew can become serious in hot, humid climates such as in the Midwest and Southeastern U.S.

There are many selections of English oak, as well as hybrids with other oak species.’Skyrocket’ has erect branches and a narrow pyramidal form. ‘Pendula’ has a weeping habit. ‘Crimschmidt’ (Crimson Spire™), a hybrid between English oak and white oak, exhibits a fastigiate habit and leaves turn reddish in autumn.

English oak is native to Europe, western Asia and northern Africa. It is widely planted across Europe, Canada, and the northeastern U.S. as a landscape shade tree and as a tall privacy hedge. For centuries its hard wood has been utilized in the construction of sailing ships.

Mexican Sunflowers Thrive In A Hot Summer

Posted by Hugh on August 24th, 2014

Tithonia + swallowtail (photo by Joy Stewart, Bristol, TN

Mexican sunflower (Tithonia rotundiloba) is a fast growing annual that produces vivid orange-red zinnia-like flowers from early summer to autumn frost. It is native to Mexico and Central America. Dark green leaves remain blemish-free all summer long. Snails and slugs are occasional pests during wet summers or when irrigated overhead.

Plants grow 3-4 feet tall and 2 feet wide by the end of summer, and may reach 5-6 feet high. Its brightly colored summer flowers are supported on strong stemmed plants. Blooms make excellent cutflowers.

As its name hints, Mexican sunflower (tithonia) thrives in hot sunny location and languishes where summer is relatively cool. In the spring do not rush to plant; wait until all dangers of frost has past in your area. Plant in well-drained, moderately fertile soil. Mulch and feed the flower bed with a slow release fertilizer such as Osmocote™ or Nutricote™ at planting time. Staking may be needed if set in a part sun and/or windy location. Those growing in containers may also need some support.

Flowers are butterfly magnets, particularly swallowtails. Monarchs, bees, hummingbirds, and other pollinators visit the blooms for nectar. Generally, deer leave tithonia alone.

Leading cultivars include old-time favorite ‘Fiesta Del Sol’ and ‘Torch’ (series includes orange and yellow cultivars). Established plants, usually after 6-8 weeks in the garden, demonstrate exceptional drought resistance.

Mexican sunflower in late summer

Reawaken Your Garden This Fall

Posted by Hugh on August 21st, 2014

Fall flowering colchicum at Kingwood Center, Mansfield, Ohio

In many areas of the U.S., Labor Day traditionally signals return to school, the start of the football season, and an end to gardening for the year. Mother Nature surely did not schedule it this way.
Here are ten plants (plus an extra) that are blooming in late August thru the coming weeks:

Stonecrops or Sedums (Sedum x spectabile) – ‘Autumn Joy’, ‘Matrona’, ‘Autumn Fire’, ‘Brilliant’, many others.

Goldenrod (Solidago spp.) – S. rugosa ‘Fireworks’, S. sphacelata ‘Golden Fleece’, others.

Toadlilies (Tricyrtis spp.) – catching on with shade gardeners searching for fall bloom.

Fall anemones (Anemone x hybrida) – favorites include ‘Honorine Jolbert’, ‘Queen Charlotte’, ‘September Charm’.

Fall mums (Dendranthemum x grandiflorum) – select old-fashioned perennial types such as ‘Ryan Gainey’, ‘Clara Curtis’, ‘Sheffield Pink’.

Fall sunflowers (Helianthus spp.) – plants grow tall (4 to 7 feet) covered with showy yellow flowers.

Fall blooming asters (Symphyotrichum spp.)- ‘October Skies’, ‘Raydon’s Favorite’, ‘Purple Dome’ are three of the best to try.

Encore azaleas: ‘Autumn Ruby’, ‘Autumn Amethyst’, ‘Autumn Lilac’, and another 16 cultivars are hardy in zone 6. A number of the new Bloomathon™ azalea series are also zone 6 hardy.

Brassicas include the flowering cabbages and kales. For best results, plant mid-August and net plants to fend off cabbage butterflies. You may also spray weekly with Dipel® biological insecticide.

Collection of Flowering Kale at Dallas Arboretum in Winter 2013

Flowering Kale Collection at Dallas Arboretum in winter 2013

Pansies and violas– autumn is a revival for these cool-loving bedding plants. Change out those tired summer annuals with fresh pansies and violas. Pansies are actually violas. Viola blooms are petite and a rave with gardeners these days. Yes, you need to purchase more violas to fill the garden space. Violas bloom more in frigid January and February than pansies. Maximize winter bloom by completing planting before October 1 in zone 5 and before October 15 in zone 6.

Autumn crocus and colchicum are two bulbs that are planted in the cool fall (by late September in zone 5 and mid-October in zone 6). They will bloom next fall and many years thereafter.

Start A New Fescue Lawn In The Fall

Posted by Hugh on August 18th, 2014

Sodding Is An Option

Likely, summer heat and drought have taken their toll on your home lawn. Late summer and fall are opportune times to start a new home lawn. Rainfall is usually plentiful and cooler day-night temperatures should spur a rapid grass recovery.

If your home lawn is mostly weeds, including unwanted bermuda grass, think about starting over. First, you should kill off all existing vegetation without injuring nearby trees and shrubs. Herbicides containing glyphosate (Roundup™ is a popular brand) should be applied with a second follow-up application 2-3 weeks later.

You should test your soil at the local county Extension office to accurate amounts of lime and fertilizer to add. General recommendation: Apply granular fertilizer such as 10-10-10 or equivalent @ 20 -25 lbs per 1000 sq. ft. of ground. You can substitute 19-19-19 @ 10-12 lbs. per 1000 square ft. Rototill the fertilizer into the top 6 to 8 inches of soil and rake the ground smooth.

In USDA hardiness zones 4-7, cool season grasses such as tall fescue, ryegrass, and bluegrass are the preferred lawn grasses. Red or chewings fescue are best for cool shady areas. Bermuda, centipede, zoysia, or St. Augustine grasses are sprigged in late spring thru summer in warm climes (zones 7-10). See package directions for proper seeding rate in your area of the country.

Gently rake the seeds into the top quarter inch of soil and cover with 1-2 bales of straw (not hay). Keep the soil surface moist until seeds have germinated. If you have laid sod, spritz (lightly irrigate) daily until the sod has rooted into the soil, usually within 2-3 weeks.

Fertilize your lawn with a high nitrogen-based fertilizer that also contains lesser amounts of phosphorus (P) and potassium (K). The application rate is written on the bag directions. Fertilizing will not injure young seedlings or newly laid sod. Cool weather and adequate natural rainfall (or irrigation) adds to success.

Depending where you live, mid- to late- October is the deadline to seed a new lawn.

Avoiding Crape Myrtle Hardiness Problems

Posted by Hugh on August 15th, 2014

‘Acoma’ crapemyrtle on a street in Charlotte, NC

Late summer (September 1st) is your deadline to plant crape myrtles (Lagerstroemia spp.) in USDA hardiness zone 6. Your primary objective should be to grow deep plant roots. Crape myrtles are classified as perennials in northerly areas of zone 6. In many years their woody branches die back after a cruel cold winter. The hardy rootsystem recovers and the shrub will bloom later in thee summer.

Fall planting, particularly in northerly U.S. areas (zone 6 and cold zone 7), is often a mistake. Plant in full sun, in well-drained slightly acidic soil, and add 2-3 inches of an organic mulch. Crapemyrtles grow vigorously and flower best where summers are warm; they bloom poorly where summer temperatures are cool or where full day sunlight is lacking.

Purchase hybrid crape myrtles introduced by the U.S. National Arboretum (USNA). Most cultivars are hybrids of L. indica and L. fauriei . USNA cultivars are named after Indian tribes. Those with L. fauriei bloodline are hardier than L. indica alone.

In northerly areas avoid excessive watering, pruning, and fertilizing in the fall; these practices force new growth that does not adequately harden off and likely will be injured over winter. Two-year established crapemyrtles survive harsh winters better than first year plants because of their thicker trunk diameter and lesser tendency to grow luxuriantly in late summer.

Never fertilize newly planted crape myrtles in late summer or fall. In early spring apply a slow release fertilizer such as Osmocote™ or Nutricote™ to all crape myrtles, newly planted or not, according to recommended package directions.

In the fall garden centers sell crape myrtles at hugely discounted prices to reduce inventories. Consider Labor Day as the cutoff planting date for planting crapemyrtles.

Exclamation™ London Plane Tree Is A Game-Changer

Posted by Hugh on August 13th, 2014

Exclamation! Planetree (photo by Dr. Jim Ault, Chicago Botanical Gardens)

Exclamation! London Plane Tree (Platanus x acerifolia Exclamation!™) is probably one the most improved cultivars to date (USDA hardiness zones 4-8). Exclamation! was introduced by Dr. George Ware at the Morton Arboretum and released through the Chicagoland Grows® program.

Exclamation! develops a strong central leader, a uniform upright pyramidal shape (when young), a vigorous growth rate, and is highly resistant to both anthracnose and powdery mildew diseases. Mature height is thought to be approximately 60 feet tall and 45 feet broad. Under optimum conditions young trees may grow 3 feet annually and 1 1/2 feet after 8-10 years. The tree seems to take on a stovepipe form around its base as reaches maturity.

London planetrees resist the harsh environs associated with parking lot islands, median traffic strips, and urban street plantings. They stand up to urban air pollution, poor drainage, compacted soil, wet or droughty soils. Its medium green foliage color holds all summer long, turns yellow for a short interval in autumn before abscising. Numbers of gumball fruits are reportedly less than on other planetrees. Its exfoliating patchwork bark of white, tan, brown and green is absolutely exquisite and develops very early in the tree’s life.

In urban areas plant London Plane 35-40 feet apart. They become a massively large tree in a short time. Include a root barrier along the edge of the sidewalk and curb. Roots grow aggressively and can lift sidewalks and curbs, invade sewer pipes, and crack building foundations. London planetree may be pruned into hedges, screens, and arbors. Mature trees do holdup to extensive root pruning.

The Giant Or Jumbo Class Of Hostas

Posted by Hugh on August 10th, 2014

Row of ‘Sum and Substance’ Hosta at Chicago Botanical Gardens

The “Giant” class of hostas is aptly named. Cultivars in this class are novelties. Their enormous leaves and plant sizes (height and spread) definitely will make a bold statement in any garden.

To attain their glorious best in plant majesty and leaf size, each cultivar must have a compost-rich, moist, well-drained soil with pH between 5.5 and 7.5. Moderate shade to dappled sunlight is the rule. Morning sun (where tolerable) may help to intensify the leaf color(s) of some. Intense afternoon sun is usually harmful, particularly on powdery blue leaf types. Clumps should be regularly fertilized and irrigated according to soil moisture needs. Five of the most popular cultivars are listed below:

Sum and Substance- 3 feet tall and 6 feet wide
Komodo Dragon- 2 1/2 feet tall and 7 feet wide
Empress Wu- 4 feet tall and 7 feet wide
Titanic- 2 1/2 feet tall and 6 feet wide
Blue Mammoth- 3 feet tall and 5 feet wide

‘Sum and Substance’… struts glossy heavily-textured green-gold leaves; near-white lilac flowers stand 6 or more inches above the foliage in late July. Foliage turns brighter gold in full morning sun in USDA hardiness zone 6. (2004 Hosta of the Year).

‘Komoda Dragon’…forms a mound of dark green, heavily rippled leaves. Four feet tall floral scapes of lavender arise in midsummer.

‘Empress Wu’…this hybrid of ‘Big John’ features heavy-textured, quilted, heart-shaped leaves that are topped by lavender flowers in mid-summer.

‘Titanic’…displays thick, glossy, prominently veined, green-centered leaves edged by a wide chartreuse margin. Lavender flowers appear from late July into early August. It is a sport of H. ‘Sum and Substance’.

‘Blue Mammoth’…features very large chalky-blue leaves that are heavily quilted and proven slug resistance. White flowers emerge in July.

These hosta giants standout as nice single specimen by themselves or plantd behind smaller growing shade-loving plants in your garden.

Tall Sedum – The New Mailbox Plant

Posted by Hugh on August 7th, 2014

Planting Of Tall Sedums Around Mailbox

Tall sedums (Sedum x spectabile) are a popular late summer blooming perennial often nicknamed “showy stonecrops” (USDA hardiness zones 3-9). Members of the succulent plant family, tall sedums have thick round leaves and are recognized for their drought resistance. Star shaped flowers are clustered in colors ranging from whites, pinks, and reds, depending on the cultivar. Bloom clusters attract bees and butterflies.

Sedums are best grown in full sun but can cope with half day or less of sun. Numbers of flower buds in clusters are less and stems tend to be floppy when planted in shady garden areas. They thrive in average well-drained soil with neutral to slightly alkaline pH. Old-timey cultivars tend to flop late in the summer and need staking. Avoid this problem by cutting plant(s) back by half in early June.

Sedums are best divided every 3 or 4 years. They are also easy to propagate from stem or leaf cuttings. Cuttings set in the summer root quickly in sand or perlite. Disease problems are rare and mealybugs, scales, slugs, and snails are occasional pests.

For decades ‘Autumn Joy’ (‘Herbstfreude’) has been the popular favorite. Here are six other tall sedums (hybrids of S. spectabile and S. telephium) to try:

‘Autumn Fire’- dusty-rose (August) to red (October) flowers on 18-24 inches tall on sturdy stems.
‘Brilliant’- compact 16-18 inch high plant and hot pink flowers.
‘Matrona’- bright pink flowers, purple stems on 24 inch high plant.
‘Neon’- dense flower clusters with deep rose color compared to ‘Brilliant’, a sister sibling.
‘Stardust’- plants 18 inches high, open to large silvery white flowers, aging to pinkish tinge.
‘T-Rex’- light rose pink aging to dark pink flowers atop 26-28 inches tall and 18 inches wide. Very upright branching and leaf edges sharply toothed.

Four Old Fashioned Hostas Continue To Delight

Posted by Hugh on August 4th, 2014

‘Krossa regal’ (blue-green) & ‘Piedmont Gold’ hostas at Kingwood Center, Mansfield, Ohio

'Sieboldii Elegans' hosta at Indianapolis Museum of Art gardens in Indianapolis, IN

‘Sieboldii Elegans’ hosta at Fine Art Museum gardens in Indianapolis, IN

During my annual summer travel to public gardens around the U.S., several clumps of old-timey hostas that were popular in the 1960’s and ’70’s caught my eye. These hosta beauties still own their garden place. Here are listed only four, but there are so many more.

‘Gold Standard’is an old-time favorite. In August multiple pink-lavender floral scapes up to 30 inches tall rise above a 22 inch wide plant mound. Flower fragrance is faint, never overwhelming. Summer foliage has a high gloss; yellow-gold leaf centers darken to a deep avocado shade circumvented by a medium green margin. Leaves average 8 inches in length and 6-8 inches in width. Leaf venation is average, not prominently displayed as on some cultivars.

‘Elegans’, a variety of Hosta sieboldiana, is an extra large hosta with powdery blue heart-shaped leaves. Early spring foliage is deeply textured with powdery wax coating. The white flowers peak through the July-August foliage. This large hosta measures up to 30 inches high and 48-60 inches in spread depending on its age and care.

‘Piedmont Gold’ is another large selection (20-25 inches high and 50-55 inches spread). It stands out with bright golden-yellow foliage with a dusty or powdery finish. The near-white flowers open in July. exhibits good slug resistance.

‘June’ is an medium-size hosta that sports beautiful golden yellow centered leaves streaked with a wide blue-green leaf rim. Pale lilac flowers appear in July. June has moderate slug resistant and is the most sun tolerant of the four.

Plant these cultivars in a full to moderately shady site and in moist well-drained soil. Feed hostas in early spring with a slow release fertilizer such as Osmocote™ or Nutricote™. Hostas are low care perennials ideal in shady, woodland settings, tubs and patio pots, or as a single specimen or in multiples for edging beds.

Hostas are commonly divided in either spring or fall, but these four may be left alone for years.