The rise and fall of the Bradford pear

Once upon a time the Bradford pear (Pyrus calleryana ‘Bradford’) was the darling of the nursery industry. Since its debut on the cover of American Nurseryman magazine on April 15, 1963, Bradford pear’s popularity soared as a street-tough tree that offered beauty and durability. In early spring Bradford pear trees erupted into bloom, these giant ovate snowballs of bright white flowers that were best admired from a distance because of their rotting fish aroma. The flowers, favored by honeybees, bumblebees and other pollinators oblivious to the stench, gave rise to leathery, dark glossy green leaves that “present[ed] a pleasing picture, particularly as they stir in the breeze and their wavy edges catch and reflect the sun’s rays,”  according to the authors of the 1963 American Nurseryman article “Bradford ornamental pear—a promising shade tree.” In the fall the longlasting leaves exploded into shades of orange, red, and purple. The beauty of Bradford pear was matched by its unparalleled toughness: tolerance to drought, pollution, and pests, notably to fire blight, a devastating bacterial disease that injures and kills edible pears.

Bradford pear appeared to be the perfect ornamental street tree, but like kryptonite and Superman, Bradford pear’s Achille’s heel was its production of closely spaced upright branches. As these poorly attached branches grew and expanded in girth, the crown to split apart, often during snow-, ice-, and windstorms. It often happened to unpruned or poorly pruned trees when they reached 15 to 20 years of age.

In the past I counseled anyone who purchased a Bradford pear to buy a pruning saw as well. As described in the 1963 American Nurseryman article, the limbs of young trees must be selectively removed to produce branches with wider angles and stronger unions to develop a strong canopy.

To overcome this structural flaw, cultivars were developed that offered improved branching habits, such as ‘Aristocrat’ and ‘Chanticleer’, a 2005 Urban Tree of the Year by the Society of Municipal Arborists. Other cultivars were developed with narrower forms, such as ‘Capital‘, a U. S. National Arboretum release, that embodied the aesthetic and urban-tolerant traits of Bradford but offered applications in tight, confined locations.

This profusion of callery pear cultivars eventually led to another problem that had ecological consequences. In the past, Bradford pear rarely produced viable fruit because it’s self-infertile and cannot pollinate itself.  With the widespread planting of cultivars that were differed slightly genetically, the barrier to fertility and subequent fruit production was overcome. In some cases the callery pear understock of a Bradford pear would sprout, flower, and provide pollen. The fruits were consumed and dispersed by starlings, robins, and other animals to open, disturbed habitats where the progeny formed dense thickets.

Callery pears mature early—flowering at 3 years of age–and is one of the first trees to bloom in early spring. It’s also one of the last trees to lose its leaves. Callery pears are resistant to insects and diseases and their thorny stems and branches discourage deer-browsing. Interestingly, the “Survivor Tree” at the 9/11 Memorial is a callery pear that survived the September 11, 2001 terror attacks at the World Trade Center. In the context of the Memorial, it serves as a symbol of survival, recovery, and resilience.

Some states in the mid-Atlantic, southeast and midwest regions have declared callery pear an invasive, self-sustaining species that dominates and disrupts native flora. In South Carolina callery pear (and Bradford pear) is considered an invasive species by the  Southeast Exotic Pest Plant Council (SE-EPPC).

In the past I encouraged Bradford pear owners in our state to selectively prune the branches. Now that I witnessed large tracts of land throughout our state covered like a white fog in early spring, I encourage them to prune their trees at soil level.

The glorification and eventual demonization of  Bradford pear is the result of our unwillingness to foster biodiversity in our urban environments. While we make our communities more livable for people, we don’t do the same for trees. We disregard decades of arboricultural research and practices and continue to shoe-horn trees into unsustainable 4 square ft. tree pits that are better suited for traffic lights, signs, and streetlights than trees. It’s the survival of the fittest, and only a handful of tree species can exist in these inhospitable conditions. Bradford pear is one of them. This monocultural approach that relies on a single or limited number of species or cultivars had already led to catastrophic losses in our urban forests as witnessed by the demise of American elms to Dutch elm disease and ashes to emerald ash borer. However, we continue to rely on a handful of nearly indestructible species and cultivars that thrive in wretched conditions. Crapemyrtle (Lagerstroemia indica cultivars and hybrids), Chinese elm (Ulmus parvifolia), sawtooth oak (Quercus acutissima), and Chinese pistache (Pistacia chinensis) have supplanted Bradford pear as street-tough urban warriors.

Because cities are responsible for 70% of the world’s greenhouse-gas emissions but comprise only 2% of the world’s land mass (Time; Dec. 26, 2016/Jan. 2, 2017), we rely on trees to assume a greater role as ecological engineers in our urban communities. It’s important that communities create growing conditions that support a diverse population of native and noninvasive adapted tree species that provide environmental services and not ecological messes.

Bob Polomski  © 2017


Follow this Rx for your Spring fever

Despite “season creep,” Nature reminded me today that Spring has not officially arrived yet. At 7:26 a.m. it’s 38 degrees F and snowing. Despite this wintry mix, I still have Spring fever. It reminds me of the ”More Cowbell” Saturday Night Live sketch with “famed producer Bruce Dickinson” played by Christopher Walken. I find myself saying: “I got a fever! And the only prescription…is to get outside and garden.”

Fill your prescription for Spring fever after this unexpected unpleasantness passes with this short “to do” list of gardening activities.


  • Buy seed potatoes and cut them into egg-sized pieces containing one or two eyes. Allow the cuts to dry and callous for a day or two beHyssop seedlings in flat 3_2_2016fore planting. Plant them when the soil temperature remains above 50o
  • Set out transplants of broccoli, cabbage, and cauliflower as well, up to four weeks before the last spring freeze.
  • Sow seeds of carrots, lettuce (leaf and head), garden peas, mustard, radishes, rutabaga, and spinach.
  • Sow warm-season vegetables in flats or trays—try eggplant, New Zealand spinach (a heat-tolerant substitute for spinach), pepper, and tomato.
  • Vegetables that resent any root disturbance, such as cucumber, muskmelon, summer squash, and watermelon, should be sown in individual pots or peat pellets.
  • Sweet potatoes are started from “slips”—shoots that sprouted from last year’s crop. Purchase them as transplants or start your own by placing a sweet potato in a glass half-filled with water. Place it in bright light. Detach the plants from the mother root when they are 6 to 8 inches long, pot them up, and then plant them in the garden about three weeks after the last freeze.
  • Sow parsley and dill. To encourage parsley seeds to sprout more rapidly, soften the seeds by soaking them overnight in warm water. Refer to the Planting Chart — Dates to Plant in SC for more information (


  • After flowering, the leaves of your spring-flowering bulbs will turn an unsightly yellow. Temper your urge to remove the leaves, or braid them into attractive ponytails. The bulbs need the leaves to harvest energy that’s channeled to the bulb for next year’s flowers.

Perennials and Ornamental Grasses

  • Dig up, divide, and replant established perennials if they’ve become too crowded and flowering has been sparse. Some fast-growing perennials need to be divided between one and three years after planting—these include aster, astilbe, beebalm, boltonia, garden mum, garden phlox, rudbeckia, Shasta daisy, and many others. To avoid interrupting flowering, dig up summer- and fall-blooming perennials when the new growth is a few inches high.
  • Divide ornamental grasses before new growth emerges. Cut back the old culms to within 4 to 6 inches of the ground and use a sharp shovel or large knife to slice one or more wedges out of the crown. Immediately plant them elsewhere.


  • Dense shrubs should not be planted close to the foundation or siding, or in front of foundation vents because they can obstruct air flow around and beneath your home, which can lead to moisture problems. Prune these shrubs or move them to another area in the landscape. If you move them to south- or west-facing walls to insulate your house from summer’s heat, keep them away from foundation vents and at least 4 feet from the foundation.
  • Keep shrubs away from the compressor on your split-system air conditioner. While the shade cast by the shrubs can reduce energy consumption, they should be planted far enough away so they won’t obstruct air flow or service.

Bob Polomski © 2017



Engage your neighbors with Harry Lauder’s walking stick.

Some shrubs and trees that have shed their leaves look forlorn and miserable in winter. However, there is an exception: Harry Lauder’s walking stick (Corylus avellana  ‘Contorta’). This bizarre-looking small tree or large thicket-forming shrub looks its best after it sheds it leaves. Harry Lauder’s walking stick produces an assortment of twisted, curly twigs and dangling male flowers called catkins that creates a spectacular come-outside-and-look sight. This living sculpture becomes even more sublime with every passing year.

Harry Lauder’s walking stick was discovered by Victorian gardener Canon Ellacombe growing in a hedgerow around 1863 near Frocester, in Gloucester, England. Apparently it was a “sport” or mutation of the European filbert (C. avellana), which is cultivated for its delicious nuts.

The twisted, misshapen twigs were not named after a famous contortionist, as you would assume, but in honor of the Scottish entertainer, Harry Lauder (1870-1950). Actually, it was named after Sir Lauder’s twisted walking stick, his companion on stage as this Scottish baritone sang ballads and comic songs.

Despite its English roots, Harry Lauder’s walking stick performs well in the Carolinas. Expect it to grow 10 ft. high and wide. Because ‘Harry Lauder’ is almost always grafted on European filbert understock, it suckers heavily. The suckers should be promptly removed at the base to prevent the slower-growing scion from being crowded out by the more vigorous understock.

Although Harry Lauder does not bear any edible nuts, it acts like a magnet to attract inquisitive neighbors and passersby. Harry Lauder’s walking stick will get people talking.

Bob Polomski © 2017

Beware of the importance of American Holly now and next year

While the Christmas tree takes front-and-center stage during this holiday season, supported by a cast of poinsettias, cyclamens, kalanchoes, Christmas  cactuses, and amaryllises, hollies often find themselves relegated to wreaths, garlands, and candle adornments. Years ago, as I learned from Fred Galle’s tome, Hollies: The Genus Ilex (Timber Press, OR 1997), hollies were quintessential Christmas symbols extensively used for centuries in holiday wreaths and Christmas decorations. Galle wrote that in London in 1851, 250,000 bunches of hollies were sold and adorned houses, churches, street corners, and market places.

Ilex opaca 12_2_2014

Use American holly for decorating indoors and outdoors for feeding grouse, quail, wild turkeys, and other songbirds.

If you decorated your home with holly this year and happen to be superstitious, don’t remove the holly from your home tonight unless you wish to experience dire consequences. In some parts of England residents retained the holly sprigs until the following year to protect their homes from lightning strikes. In Louisiana, residents saved holly berries at Christmastime to receive good luck throughout the year.

I consider our American holly (Ilex opaca)–not the English holly (Ilex aquifolium)–our signature holly of Christmas. It can be found growing wild from Massachusetts south to Florida and west to Texas and Missouri and north to Tennessee and Indiana. It’s commonly found as an understory tree growing in mixed hardwood forests in a variety of habitats that include dry woodlands, stream and creek banks, and even swamps.

American holly grows slowly, which is unfortunate for nursery producers and consumers. Nevertheless, it was introduced into the trade in 1744 and presently there are more than 1,000 cultivars. Some cultivars will exceed 50 ft. in height, while others, such as ‘Maryland Dwarf’, grows 3 to 5 ft. high and 8 ft. wide. The fruit on female American hollies is commonly red, but some cultivars bear orange or yellow berries. American holly, like many evergreen hollies that include the yaupon, Japanese, inkberry, and lusterleaf are dioecious–separate male and female plants. The males produce pollen and the females produce berries. So, if you’re wondering why you’ve never seen fruit on your American holly, it could be a male that will never produce fruit. There’s also a chance that it’s a female that had not been fertilized by a male. Holly flowers are insect- or wind-pollinated, so it’s important that the separate sexes are within 30 to 40 feet of each other for fertilization and subsequent berry set to occur. To improve your chances at berry set, bring the pollen source closer by selectively removing flowering shoots from the males and placing them in a bucket of water at the foot of the female hollies.

In the past, people in Germany and England called the prickly holly varieties “he-hollies” and the smooth-leaved kinds “she-hollies.” (Interestingly, English hollies produce out-of-reach, smooth-margined adult leaves at the top of mature trees.) The type of leaf brought indoors determined who was to dominate the home in the upcoming year. If the holly leaf had a smooth margin, the wife was in charge. (She should be if she was able to reach the spineless leaves in the uppermost reaches of the

tree). If the holly was prickly, the husband ruled the roost for the year. Obviously you can’t tell the difference between male and female hollies by examining their leaves; you have to examine the flowers that emerge in May. Male hollies tend to produce a prolific number of flowers. These many-branched cymes emanate from the leaf axils-the points where the leaf attaches to the stem. Each flower has four stamens sticking up between the petals. When the anthers ripen and split open, sticky yellow pollen appears. Generally, female hollies produce fewer blooms, and these solitary flowers occur in the leaf axils.  A green pealike pistil, which develops into the berry, rests in the center of each flower and is surrounded by four nonfunctional stamens.

So, while some of you are contemplating the gender of the hollies in your landscape or neighborhood, I am heading outside to remove a few of the lower branches of my American hollies in the backyard. It’s not too late to deck the halls with boughs of prickly he-holly sprigs.

Copyright © 2016 Bob Polomski

During dry spells, prioritizing is the key to a successful garden

The scant rainfall and torrid weather has taken a toll on a number of my landscape plants. Because I value potable water, I prioritize its use. Edibles and newly planted shrubs and trees, which are highly vulnerable to drought stress, earn the right to receive water from my spigot. When plants become established, meaning that they’ve regenerated enough roots to sustain themselves without supplemental irrigation, they’re watered only when the need arises.

I follow this rule regarding tree establishment: for every inch of trunk caliper (trunk diameter measured six inches above the ground), it takes at least 6 months before a tree becomes established. During the establishment period, I apply 2 to 3 gallons of water per inch trunk diameter (for example, 2 to 6 gallons for a 2-inch tree) over the root ball. After a few months of frequent irrigation, I water weekly until the plants are established.

After experiencing several dry summers that spanned more than a quarter century, I know that even established shrubs and trees may succumb to hot, dry summers, which means that you need to visit your landscape often and be on the lookout for the initial signs of water stress:  curling or crinkling leaves, yellowing or off-colored, du

Scorched magnolia

Newly planted trees, such as this southern magnolia, will experience “scorching” or browning of leaves during dry spells.

ll-looking leaves, and brown or scorched areas along the leaf margins. Obviously when you see azalea leaves that look like brown potato chips or Florida anise leaves that look like wilted leaf lettuce, the damage is already done. More severe signs of water stress include leaf drop and branch dieback. These aboveground signs are only a reflection of the unseen damage belowground, particularly to the fine, water- and mineral-absorbing roots.

Despite my hardline approach to avoid watering established plants—or at best, only when absolutely necessary, I did lose some treasured specimens this summer. Less than a week ago I cut down a seven-foot tall Atlantic white-cedar (Chamacyparis thyoides) that I planted in 2012 from a 3-gallon container. Atlantic white-cedar, native to swamps and low lying areas along the coast from Maine to Florida, was a gift from the horticulturists at Moore Farms Botanic Garden in Lake City. A photo of this conifer accompanied my July 24, 2015 post on bagworms. Sadly, I never appreciated its bright green needles and natural pyramidal habit until it turned completely brown.

Pinus pinea 7_8_2016

Italian stone pine (Pinus pinea)

While it was difficult to lose this treasured specimen and a few others, I am comforted by the gain in planting space. I have about 30 replacements that need a permanent home. In a 20-square foot area beneath a small trio of northern red, Shumard, and overcup oaks, I have a variety of potted species and cultivars that I started from seed, rooted from cuttings, or received as passalong plants. I can only hope they’ll be amendable to my tough love approach to watering.

One tree that has survived for the past four years without any supplemental irrigation is an Italian Stone pine (Pinus pinea). I purchased it in a one-gallon decorative pot right after the Christmas holiday season. This Colorado blue spruce lookalike was on the discounted table surrounded by poinsettias and rosemaries sheared into miniature Christmas trees. After two bitterly c

Pinus pinea1

New shoot growth of Pinus pinea.

old winters where temperatures dropped to 8 degrees F, this Mediterranean native is now three-and-a-half feet tall and thriving. It morphed from the cute, short-needled blue conifer into a shaggy-looking green-needled attention-getting specimen. Unlike other plants that have stopped blooming and growing, my Italian stone pine has 3 to 4 inch long expanding new shoots studded with short blue needles. I can’t wait for it to reach reproductive maturity so I can harvest its delectable pignolia or pine nuts for pesto.

Interestingly, I’ve read comments from a variety of “experts” on the internet who nearly dissuaded me from growing this Italian stone pine, which is widely planted in California and not expected to thrive east of the Mississippi, let alone in the southeast. Fortunately, Italian stone pines can’t read.

Copyright © 2016 Bob Polomski

Green or brown: the choice is yours

I am not concerned that my bermudagrass lawn has turned a paler shade of brown. I know that warm-season lawns, such as bermuda-, centipede-, and zoysiagrass, whose optimum growing temperature is between 80 and 95 degrees F, have the ability to escape the dry conditions by going dormant. These grasses possess buds in their crowns and rhizomes (underground stems) that may remain alive and grow when more favorable conditions return. Tall fescue is a different matter. This cool-season grass, whose favorable growing temperatures are between 60 and 75 degrees F, cannot escape. Three or more weeks of no rain in the summer can injure or kill tall fescue.

Lawn owners who choose to have a green, lush lawn in summer must water their lawns during hot, dry spells. If you choose to water your lawn with potable water, then please use this precious resource properly.

Apply the correct amount of water:  one-inch of water per week, which wets most clay soils to a depth of 6 to 8 inches. (It takes 640 gallons of water to irrigate 1,000 square feet of lawn, and the average household in SC uses 120 to 150 gallons of water per person per day.) If you cannot apply this amount all at once because water runs off the lawn or puddles up, then apply one-half inch at a time. Allow the water to soak in before you continue irrigating. If you use a portable sprinkler, move it frequently to avoid runoff. Use a screwdriver to determine if you applied the right amount of water. About 2 to 4 hours after watering, insert the screwdriver into the ground; it’s easier to push the screwdriver into moist soil and much harder in dry soil.


Know how much water you’re applying to your lawn by calibrating your automatic sprinkler system.

For homeowners with an in-ground irrigation system, calibrate it so you know how much water you’re applying at each irrigation event. Here’s how:

  1. Place several equally-sized coffee cans or other straight-sided, flat-bottomed containers randomly throughout the area to be irrigated. For above-ground, portable, hose-end sprinklers, containers should be arranged in a straight line away from the sprinklers to the edge of the water pattern.
  2. Turn the irrigation on for 15 minutes.
  3. Turn the water off, collect the cans and pour all of the water into one of the cans used.
  4. Measure the depth of water you collected.
  5. Calculate the average depth of water by dividing the total amount of water in inches by the number of cans. For instance, if the total depth was three inches, and you used six containers, then the average depth would be 3/6, or 0.5 inches.  Multiply the average depth by four to determine the application rate in inches per hour. For example, one-half inch multiplied by four equals two inches per hour.  If you run the system for one hour, it will apply two inches of water; run it for half an hour, and it will apply one inch.  If, while the system is running, water runs off the lawn, note the time, stop the system, and let it soak in. Then turn it on again and run it until you apply the full amount of 1 inch of water.

When you operate your in-ground system, evaluate its coverage. If you’re watering the street, sidewalk, or perhaps creating a small pond in your lawn because of excessive overlap, make adjustments to ensure head-to-head coverage and an even distribution of water.

Finally, water late at night or early in the morning when dew has already formed. Use a timer to program the system to run between 11 p.m. and 2 a.m. If possible, avoid running your automatic sprinkler system between 4 a.m. and 7 a.m. out of respect for the rest of the residents of your community who like to have adequate water pressure when showering and bathing in the morning. One more thing: add a rain sensor so your neighbors won’t be talking about you when they see you watering your lawn during a frog-choking rain.

Keep in mind that watering your lawn in the summer will keep it green, but it comes with consequences. Besides having to mow that lush new growth on a regular basis, watering may encourage weed growth, stimulate disease outbreaks, and raise your water bill.

Bob Polomski © 2016     




Seek out hydrangeas for summer-flowering shrubs

Many believe that “hydrangea hysteria” erupted in 2004 with the debut of the reblooming bigleaf hydrangea, ‘Bailmer,’ known by its trade name of Endless Summer™. Since this mophead hydrangea cultivar entered the marketplace, the interest in mophead and lacecap hydrangeas skyrocketed, especially remontant or reblooming types. This frenzy to produce bigger-flowered, smaller-statured, more floriferous hydrangeas caused the number of Hydrangea macrophylla cultivars to swell to more than 300 and counting.

Hysterical hydrangea breeders diverted their attention to other species, notably the native, white-flowered smooth hydrangea (Hydrangea arborescens), which gave rise to the pink-flowered Invincibelle™ Spirit ‘NCHA1’ in 2010 and the new-and-improved Invincibelle™ Spirit II (‘NCHA2’) this past Spring.

Even the often maligned panicled hydrangea drew attention from plant breeders, who looked past its gawky, gangly stature (15 to 25 ft. high and 10 to 20 ft. wide) and homed in on its large mid-summer white panicles, preference for full sun, and tolerance to drought. Their breeding efforts led to a wide range of cultivars boasting a variety of shapes and sizes that include ‘Bulk’ (Quickfire™), ‘Phantom’, and ‘Tardiva’.

Despite these contenders, the beloved bigleaf hydrangea has no rivals. While visiting the hydrangea collection at the SC Botanic Garden this past week, I can see why. There are mopheads with cabbage-sized blooms and dainty, more refined-looking lacecaps with flattened, disk-shaped inflorescences. On many bigleaf hydrangea cultivars, their flowers are either blue or pink depending on the level of aluminum that’s available in the soil, which is dictated by the soil pH. For blue flowers on your mophead and lacecap or French hydrangeas, maintain a soil pH between 5 and 5.5. An acid soil increases the availability of aluminum, which turns the flowers blue. Apply sulfur to reduce the pH to this ideal range in late summer or when you see new growth emerging in the Spring.  To avoid having to adjust the pH, grow a blue-flowered hydrangea such as ‘All Summer Beauty’, ‘Blue Wave’, or ‘Nikko Blue’.

Pink flowers occur on bigleaf and lacecap hydrangeas with a soil pH between 6.0 and 6.5. In this pH range, aluminum becomes “tied up” or rendered unavailable in the soil and so is absent from the flowers. Use lime to increase the soil pH to this desirable range. To avoid having to maintain a particular pH, grow pink-flowering cultivars such as ‘Forever Pink’ and ‘Pia’.

Hydrangea macrophylla 'Goliath' SCBG 6_3_2016

The cultivar ‘Goliath’ is an old-timey bigleaf hydrangea from Germany that produces bouquet-sized blooms that range in color from deep pink to purplish-blue. June 8, 2015. SC Botanical Garden, Clemson, SC.

Some cultivars produce a kaleidoscope of colors, such as ‘Goliath’, which is perfect for people who aren’t sure if they want pink, blue, or blurple (a combination of pink and blue) hydrangea flowers.

If you have a landscape with high, filtered shade or a site that receives morning sun and afternoon shade, grow hydrangeas. Dr. Michael Dirr, renowned plantsman and author of Dirr’s Encyclopedia of Trees & Shrubs (Timber Press, 2011), evaluated over 250 cultivars of Hydrangea macrophylla in Athens, Georgia, and created two lists of favorites.  His “historical” favorites include ‘All Summer Beauty’ (mh = mophead), ‘Ami Pasquier (mh), ‘Blue Wave’ (lc = lace cap , Frillibet (mh), Generale Vicomtesse de Vibraye’ (mh), ‘Lanarth White’ (lc), ‘Lilacina’ (lc), ‘Mme. Emile Mouillere’ (mh), ‘Mousseline (mh), Nikko Blue’, (mh), ‘Veitchii (lc), and ‘White Wave’ (mh). His list of reblooming bigleaf hydrangeas include ‘Blushing Bride’ (mh), ‘David Ramsey (mh), ‘Decatur Blue’ (mh), Endless Summer® (mh), ‘Mini Penny’ (mh), ‘Oak Hill’ (mh), ‘Penny Mac’ (mh), and Twist-n-Shout™ (lc).

You don’t have to take his word for it. In the hydrangea collection at the SC Botanic Garden there are 39 cultivars of bigleaf hydrangeas in bloom right now, and more than 30 cultivars of mountain hydrangea, oakleaf hydrangea, smooth, and panicled hydrangea. This team of 5 hydrangeas will provide color in your garden from May to late September, and will always give you an excuse to go outside for a spell. If the heat and humidity is not to your liking, you can always enjoy them as cut flowers indoors.

Bob Polomski  © 2016