Plant of the Month - April, 2006

ARBORETUM PLANT OF THE MONTH FEATURE
by Jeff Iles
Arboretum Board Member

Professor and Chair
Department of Horticulture
Iowa State University

Magnolia x loebneri
'Merrill'

Let's face it. Our part of the Midwest is not prime magnolia country. Yes, there are plenty of "winter hardy" selections tough enough to survive in USDA hardiness zones 4 and 5, but if you're like me, you want the plants (magnolias) chosen for your yard to do more than simply survive, particularly when they've been selected specifically for their flowering attributes. But unfortunately, many of our most popular magnolias flower in April with an all too familiar result.

Imagine your prized magnolia has just unfurled its colorful flowers and the air is heavy with that unmistakable fragrance, but after a cold front sneaks into the region and drops early morning temperatures into the 20° range, every flower turns limp and brown, each sadly resembling a used teabag. Not a good look for any plant, but particularly embarrassing for the refined and gentile magnolia. So we respectfully avert our eyes from our unfortunate frost-bitten friend, and wishfully begin counting the days until next spring when we'll once again cross our fingers and hope for favorable April weather.

So answer me this? Why, after relating this tale of woe to you did I just return from the garden center with, of all things, a brand new Magnolia x loebneri 'Merrill' in tow? Am I a glutton for punishment? Was I hoodwinked by a clever salesperson? Have I lost my mind? Actually, none of the above is true. You see, even though 'Merrill' is not immune to the deleterious effects of frost, its blooms have proven slightly more resilient to low temperature than several other commonly planted magnolias, including the ever-popular star magnolia. Besides, there's just something special about magnolias and the cultivar 'Merrill' in particular, that allows me to accept a spring or two when the coveted bloom period might be cut short or come up missing altogether.

We thank Max Loebner, garden inspector at the Bonn Botanic Garden, Germany for the species Magnolia x loebneri. Shortly before the beginning of World War I, he made a cross between two Japanese magnolias, Magnolia kobus (Kobus magnolia) and Magnolia stellata (star magnolia) with the result being a tree intermediate in size between the parents (20-30' tall with an equal or greater spread) with spectacular white flowers. The cultivar 'Merrill' was a M. x loebneri seedling selection made in 1939 by Karl Sax, soon-to-be Director of the Arnold Arboretum (Boston, MA), but it wasn't until 1952 that this wonderful plant received the name 'Merrill,' given to honor botanist and another former Director of the Arnold, Elmer Drew Merrill (1876-1956).

If you've ever seen 'Merrill' magnolia in full bloom, you understand why the plant receives such universal acclaim. Each flower has between 10-17 white tepals (colorful, sterile, petal-like parts of a flower) with just a hint of pink at their base, and from a distance, the tree is a blizzard of white. Begin looking for the 'Merrill' magnolia at the Bickelhaupt Arboretum to flower sometime in mid-April. You'll find it nestled amongst several other magnolia species on the west side of Rock Creek.

In general, magnolias perform best when situated in full sun or very light shade, but planting them on southern or western exposures seems to invite trouble since these warmer, sunnier sites promote earlier than "normal" flowering, thereby increasing the chance of injury from a late spring frost. Magnolias are tolerant of many soil type and pH conditions, but fine-textured (clay) and chronically wet soils will reduce their vigor and overall health. If you're cursed with a poorly-drained soil, success with magnolias is still possible, but you must plant them "high" or use them on berms.

Chances are, once you've seen 'Merrill' in flower, you'll want to know if other M. x loebneri cultivars are worthy of your attention and investment. And in my opinion several are, including 'Ballerina', 'Leonard Messel', and 'Spring Snow'.

I'll be heading back to the garden center now. I've just thought of the perfect spot in my yard for a 'Leonard Messel'. By the way, have you heard the long-range weather forecast for April? Never mind, it really doesn't matter.


About the author: Dr. Jeffery Iles presently serves as Professor and Chair of the Department of Horticulture at Iowa State University in Ames, Iowa. He holds advanced degrees from Penn State University and Iowa State University. Among many awards and honors, Dr. Iles is an Honorary Lifetime Member of the Iowa Nursery and Landscape Association. He has authored or co-authored more than twenty journal articles in such journals as HortTechnology, Journal of Environmental Horticulture, Journal of Arboriculture, and HortScience. Research projects Dr. Iles is currently involved in include Landscape Plant Evaluation, Invasive Landscape Plants, and Landscape Plant Usage. The Bickelhaupt Arboretum is fortunate to have Dr. Iles on its Board of Directors.