Plant of the Month - May, 2006

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

Professor and Chair
Department of Horticulture
Iowa State University

Malus seiboldii
'Calocarpa'
(Redbud crabapple)

Crabapples have a polarizing effect on Midwestern gardeners. Don't believe me? Just trying dropping the "c" word at your next party and see what happens. Some will sing the praises of crabapples, preferring to focus on their raucous floral display and environmental toughness, while others choke on the word crabapple, referring to them instead as "those nasty little trees that litter the ground in the middle of summer with decomposing fruit and diseased leaves." Love them or hate them, there's no middle ground when it comes to crabapples.

Why then do so many gardeners and landscape professionals blanch at the mere mention of the word crabapple? After all, a family with upwards of 900 named selections is bound to produce a few, excuse the pun, "bad apples." Well, as much as we'd like to respect our elders, it seems many older crabapple cultivars ('Hopa' and 'Radiant' for example) originally embraced for their head-turning spring floral extravaganzas, now sadly, and maybe a bit unfairly, are remembered only for debilitating disease problems and objectionable fruit litter. And like those overbearing, attention-grabbing billboards along the interstate, a sufficiently large population of 'Hopa' and 'Radiant' can still be found in present day landscapes, reinforcing the wrong perception that all crabapples defoliate in July. But the vast majority of crabapples are excellent landscape plants, and Malus seiboldii 'Calocarpa' (redbud crabapple) is one of the very best

Malus seiboldii 'Calocarpa' (some still prefer the hybrid designation Malus x zumi 'Calocarpa') was introduced to the United States by the Arnold Arboretum. Apparently a chap named William S. Bigelow sent seed to the Arboretum from Japan in 1890, and one of those seedlings became the cultivar 'Calocarpa'. The common name (redbud crabapple) refers to the deep red flower buds that appear in late April. The effect is quite stunning but only lasts for a day or so. Fortunately, what follows is even better as the red buds give rise to pinkish-white and then all white flowers. And they're produced in abundance!

When grown in the open, most redbud crabapples develop a dense, rounded canopy (15' tall and wide), but very old specimens tend to become more spreading and picturesque. In fact, one of the most handsome specimens in Iowa resides at the southeast corner of the Visitor's Center & Library at the Bickelhaupt Arboretum.

In summer, redbud crabapple is green and that's a good thing for a crabapple. In other words, the tree demonstrates good resistance to fungal diseases that cause premature defoliation on lesser crabapple selections. And as summer turns to fall, redbud crabapple rewards us again with a dazzling display of small (1/2-inch in diameter), persistent, bright red fruit (in greek, 'Calocarpa' means "beautiful fruit") and in most years, yellow to apricot fall leaf color.

But don't just take my word for it. Get out to the Bickelhaupt Arboretum, have a seat on the lawn just downwind (the fragrance is delightful) from the venerable specimen that anchors the Visitor's Center, and simply enjoy being in the presence of one of our finest flowering crabapples. You might even bring a friend along who previously didn't have many good things to say about crabapples. The sight of Malus seiboldii 'Calocarpa' in full bloom will surely win them over.


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.