Category: Horticulture Highlight

Horticulture Highlight: American elm, Ulmus americana

April 2, 2019

Look, where the bluebird on the bough

Breaks into rapture even now!

He sings, tip-top, the tossing elm

As tho he would a world o’erwhelm.

Indifferent to the void he rides

Upon the wind’s eternal tides…

            -Edwin Markham

 “Don’t cry for me America. I never left you,” scattered locations within Mount Auburn seem to speak to us anthropomorphically. If not with these exact enunciated words, the continuing presence of the oft described canopies of American elms prove these much beloved arboreal sentinels never reached the comparable nadir of our American chestnuts. Nonetheless scores of millions of American elms have died over the last eight decades due to Dutch elm disease (DED).

Yet each April, we continue to count on one reliable phenological sign of New England’s spring, the American elm flowers, collectively tinting winter’s former stark canopies a light, purplish/red color. Weeks before other spring ornamental notables such as forsythia, cherries, magnolias, dogwoods, etc. and well before producing leaves, these flowers are commonly overlooked.Maya Angelou has stated,“Everything in the universe has a rhythm, everything dances.” Hence, after winds as well as early insects have danced through these flowers, cross-pollination fertilizes ovules which develop into elm seeds. These ½-inch, rounded samaras (winged, light-weight seeds) mature in May and can be blown considerable distances from the parent trees.       

Along about then, the middle of May,

I say to myself: “any day…”

And I guess up there in the tall elm trees

The leaves say something like “Listen, breeze:

It’s no good whispering stuff; just blow!

There’s a skyful of seed here set to go.”

And the breeze perks up

And the seeds fly loose-…

            –David McCord

Thomas J. Campanella has authored, Republic of Shade: New England and the American Elm, the definitive overview of this once popular shade tree dominating streets in towns and cities across the country, even designated the state tree of both Massachusetts and North Dakota. Then in the 1930’s, a vascular wilt disease (DED) was accidentally introduced to the U. S. likely on logs imported from Europe for use as veneer.

Great Elm on Boston Common 1810

DED is “Dutch” (actually Asian) because early researchers identifying the fungus were Dutch. DED was a problem in Europe 20 years before coming to our country. Causal organism was initially determined to be the fungus Ophiostoma ulmi (formerly Ceratocystis ulmi) with later an additional more aggressive Ophiostoma novo-ulmi. Compounding and exponentially exacerbating the pathogen virulence were European bark beetles. Transporting fungal spores from infected trees, they bored into the outer bark of elms, making tunnels (called galleries), mating and leaving their eggs under the bark.

Societal reaction to DED, slow at first, ramped eventually into literal overkill. Rachel Carson’s 1962 classic Silent Spring, recounts then contemporary efforts to control these bark beetles using DDT. “Spraying for [DED] began in a small way…soon it became evident that something was wrong…graveyard for most of the robins…at first…suspected some disease of the nervous system, but soon it became evident…robins were really dying of insecticidal poisoning…exhibited well-known symptoms…not so much by direct contact…indirectly by eating earthworms.” She reported on further published research, “killing directly not only the target…bark beetle, but other insects, including pollinating species…the poison forms a tenacious film over the leaves and bark. Rains do not wash it away. In the autumn the leaves fall to the ground…begin…becoming one with the soil…aided by…earthworms…also swallow the insecticide…concentrating in their bodies…become biological magnifiers of the poison…” Finally, “…even as the elm program is only one of the multitudinous spray programs that cover our land with poisons.”  So DED which many communities had mobilized to eradicate unanticipatedly expanded Carson’s grass-roots audience, hence influence, in contrast to assurances of the insecticide people that their sprays were “harmless to birds.” 

…Give me spots on my apples

But leave me the birds and the bees

Please…

            Joni Mitchell

After more than half-a century of research with numerous cultivar selections, no American elm has proven totally resistant to DED. Some however, are tolerant and recover after infection. While American elms will never regain their former prominence, their American tragic saga also provided urban forestry with the lesson to forever avoid the danger of monoculture plantings, as was often common, sometimes near ubiquitous, with American elms. This has led some advocates to consider as a guideline, a 10-20-30 goal. Plant no more than 10% of any one species, plant no more than 20% of any one genera, plant no more than 30% of any one family. The true goal being to ensure genetic diversity within all urban tree canopies.  

On a future visit to Mount Auburn look for some of our grandest mature straight species of American elms on Asclepias Path, Pond Road and Bluebell Path. Other fine examples are found on Arethusa Path, Bigelow Avenue, Harebell Path and Garden Avenue among other locations.

We also have cultivars of ‘Princeton’ on Fir Avenue, Heath Path, Honeysuckle Path, and cultivars of ‘Liberty’ on Fir Avenue, Field Road and Ailanthus Path.

The lovers disappeared into the wood.

I sat among the boughs of the fallen elm

That strewed an angle of the fallow…

            -Edward Thomas

‘Jelena’ Witch Hazel, Hamamelis xintermedia ‘Jelena’

March 4, 2019

My garden will never make me famous

I’m a horticultural ignoramus

I can’t tell a string bean from a soybean

Or even a girl bean from a boy bean

            -Ogden Nash

Questions of bean gender aside, there are occasional, horticultural, true-love stories within our ongoing pastime of “who does your garden grow?” Prime example this time is our late-winter, blooming beauty, ‘Jelena’ Witch Hazel, Hamamelis xintermedia ‘Jelena’ (pronounced Ya-lay-na). This love story commenced in what is today the Kalmthout Arboretum, outside of Antwerp, Belgium, in the mid-1950’s. A century earlier the site began as a plant nursery, passing through two different lengthy ownerships before World War I and the ensuing economic collapse finally closed the business. In 1952 Robert de Belder (1921-1995) and his brother Georges bought the then overgrown, weed covered land/estate. In a raison d’etre echo to Mount Auburn’s and Longwood Gardens’ beginnings, the de Belders, local diamond traders, bought the site to preserve the mature and even rare trees from a proposed housing development.

On a separate life path, heading towards convergence, we introduce Jelena Kovacic (1925-2003), born in what is now Croatia, with a 1951 agronomy degree from the University of Zagreb. With a rare travel permit abroad, this botanist/horticulturist was in 1953/54 studying nurseries and horticultural sites in Denmark, Germany, the Netherlands and ultimately Belgium. Hearing about mature, rare Stewartias along with other ancient trees brought her to the de Belder’s new work-in-progress. A romance quickly developed with Robert, and these plant aficionados were married within three months.

Jelena joined the de Belder brothers, working to restore, replant, re-design and enlarge the long fallow property using a naturalistic style. The extensive plant diversity on the property included thickets with hybrids of witch hazels from the earlier nurseries. One attractive unnamed selection, shown at the Royal Horticultural Society in London, in 1954, was very popular. Robert named this Hamamelis xintermedia ‘Jelena’ in honor of his new wife.

Hamamelis, a small genus with but four (five) species worldwide, produce spider-shaped yellow or orange flowers, each with four, one-half-inch-long, narrow, strap-shaped petals. The two Asian species and their hybrids (crosses of Chinese and Japanese witch hazel) curiously produce their flowers during February and March. ‘Jelena’ in bloom, at first glance has a warm coppery-orange color. Look closer at the flowers to often see petals with reddish bases, orange centers and yellow tips.

Our ‘Jelena’ Witch Hazels on Snowdrop Path, Buckthorn Path and Sparrow Path have shimmered in the otherwise sparse winter landscape after each of the modest February snowfalls we have had so far. The tiny petals protectively curl up during extreme cold and more serious snowstorms, which allows the flowers to last four to seven weeks. ‘Jelena’ additionally will provide attractive red-orange autumn colored leaves.

The de Belders achieved notoriety for breeding Hamamelis cultivars and another winning selection was ‘Diane’, a striking red-flowered cultivar. Hamamelis xintermedia ‘Diane’ was named to honor Jelena and Robert’s daughter. A fine specimen of ‘Diane’ may be found on the southern end of Indian Ridge Path. Both Hamamelis xintermedia ‘Jelena’ and Hamamelis xintermedia ‘Diane’ have received the Royal Horticultural Society’s Award of Garden Merit.

Look for these winter beauties along with other witch hazels as the calendar turns to March.

Let us whir with the golden spoke-wheels

Of the sun.

For tomorrow Winter drops into the waste-basket,

And the calendar calls it March.

                                Amy Lowell

Siebold Hemlock, Tsuga sieboldii

January 29, 2019

No white nor red was ever seen

So am’rous as this lovely green

            -Andrew Morrell

As leitmotif to last time’s “who does your garden grow,” we turn next to Siebold Hemlock, Tsuga sieboldii. The genus Tsuga is small with just nine to eleven species, depending on taxonomic analysis, compared with the much larger genus Pinus, or pines. All hemlocks are medium-sized to large, evergreen trees, native to North America and Asia. Previously we have reviewed Canadian hemlock, by far the most prevalent species growing at Mount Auburn.

Siebold Hemlock, Tsuga sieboldii. also referred to as Southern Japanese hemlock may reach heights of 100-feet in the wild, but more often half that tall in landscape use. They have single, flattened, needle-like leaves, each about ½-inch-long, with smooth edges and a tiny notch on the tip. The undersides have two white stomatal bands. The seed cones when ripe are pale brown, one-inch-long. (more…)

Golden larch, Pseudolarix amabilis

October 30, 2018

From yellow leaves a blue jay calls

Grandmothers walk out in their shawls

And chipmunks run the old stone walls

When fall comes to New England

-Cheryl Wheeler

Autumn within Mount Auburn presents an arboreal cornucopia of multiple colors. A sampling includes the reds of dogwood, maple, tupelo, Virginia sweetspire, oakleaf hydrangea, interplanted with the yellow of hickory, ginkgo, Korean mountain ash and larch among many others. One lesser known golden-yellow, which sometimes exhibit bright orange-bronze instead, is provided by the Golden larch, Pseudolarix amabilis. This native to China which grows 30-50 (100)-feet in height is one of four deciduous conifers that grow here, the others are bald cypress, dawn redwood and European larch. (more…)