PLANT OF THE MONTH
January, 2009
Plant of the Month Feature
by Jeff Rathje
Bickelhaupt Arboretum
Roots Board Member
Pinus strobus x Pinus ayacahuite
Pine Hybrid
My story of a spectacular large growing pine that seems wrapped in obscurity started around 7-8 years ago. Local members of the American Conifer Society, ACS (a self-help group of conifer addicts) were strolling through the arboretum Heartland Conifer Collection. We were marveling at all the soft-textured "five needled pines" such at Pinus koraiensis (Korean Pine), Pinus cembra (Swiss Stone Pine,) Pinus flexillis (Limber Pine,) and Pinus parviflora (Japanese White Pine.) Most cultivars of these pines belong in the ACS size classification intermediate or semi-dwarf, 6-12" annual growth and 6-12' tall in 10-15 years, and are very desirable in today's smaller landscapes.
This day we were drawn to a larger pine with long blue green needles and a handsome tight shape. It resembled a "souped-up" Pinus strobus (White Pine) but was denser with bluer needles. The heavy resin deposits on the cones looked like they had been frosted. We agreed this may be the finest large (ACS size classification over 12' in 10-15 years) conifer in the collection. I found the tag and read it, ACS legend Joe Stupka's method for identifying plants. It was Pinus strobus x Pinus ayacahuite.
Pinus strobus (Eastern White Pine) is very common in Iowa with native stands nearby in White Pines State Park, Muscatine, Iowa. Cultivars of White Pine include many dwarf, weeping, variegated, columnar, and "gold in the cold" forms, but this ayacahuite business threw me for a loop and I realized I didn't know a Pinus ayacahuite (Mexican White Pine) from a kick in the keister. It's probably unfamiliar to many because it's a zone 7 plant native to Mexico.
Being inquisitive, I searched for a source of this exciting new (to me) pine. Fortunately, Meadowcroft Farm in Oregon City, Oregon had some availability. As for growth rate, in the fall of 2004, I incorporated 3 of these pines into a screening grouping with Picea pungens, Colorado Spruce and Picea abies 'Aurea' a gold-tinged Norway Spruce on the west edge of Eldridge, Iowa at the corner of LeClaire Rd and South Thombergs. They are now about 7' tall. The plant in the collection is listed as about 20 years old and appears to be around 20' tall. In both cases, with dissimilar locations and soils the plants appear to average about one foot of growth per year. As a contrast, straight species White Pine in my yard averaged every bit of twice that.
According to the ACS website, Pinus strobus x Pinus ayacahuite was originally selected from hybrids developed at the Yale University Forest Research Center in the 1960's by ACS member Rich Jaynes and Earl Cully of Heritage® Trees in Jacksonville, Illinois who is well known for developing the Heritage River Birch and Shawnee Brave Bald Cypress. In speaking to Jaynes from Hamden, Connecticut, he stated that events surrounding this selection are a little fuzzy after 50 or so years... He did recall that there were many assorted hybrids in the plot at Lichtfield, Connecticut but only one chosen for cuttings. When I asked him if he was there specifically to look for plants with commercial appeal, he said no. He deferred to Earl Cully for more details saying that Earl was quite revved up about the discovery of this pine. Unfortunately, Earl was unavailable for comment. Regardless, the thinking is that all current plants can be traced back to the cuttings taken by these gentlemen with obvious good taste in plants.
Roy Klehm of Beaver Creek Nursery in Poplar Grove, IL put this plant in production 12-15 years ago and gave it a more manageable name, Pinus x 'Forest Sky'. Dave Wanninger of Beaver Creek stated it is his favorite large pine they grow. They have experienced minor winter burning in harsh winters, but less burn than on straight White Pine. This same plant was named 'Domingo' by John Risserger of Auroa, OR.
In short, Pinus strobus x Pinus ayacahuite is what a hybrid should be: the best of both parents. Evidently, it gets its hardiness from Pinus strobus and its beautiful foliage from ayacahuite. A plant like this deserves to move to the front and belongs in residential, commercial, and park-like landscapes. In light of serious problems with Pinus nigra (Austrian Pine) infected by Diplodia tip blight and Pinus sylvestris, (Scotch Pine) succumbing to Pine wilt, alternatives like this special large pine become even more attractive. Stop by the Heartland Conifer Collection at Bickelhaupt Arboretum to see why.
About the author: Jeff Rathje has been the owner of Lasting Beauty Landscape in McCausland, Iowa since 1989, which is a small contracting business that is open for retail by appointment only. He has a degree in horticulture from Kirkwood Community College and a true passion for rare and unusual conifers. His other major interests are catfishing on the Wapsipinicon River, woodcutting, and sports. Jeff is a valued Roots Advisory Board member. The Bickelhaupt Arboretum is fortunate to have him on the Roots Board.