Fothergilla spp. has shot to the rank of superstar in a few decades, but there are more exciting improvements in the pipeline.
Michael A. Dirr
Who would have thought Fothergilla would become a mainstream nursery flowering shrub? Better question: 30 years ago, who knew anything about the two species, F. gardenii and F. major? The genus was not mentioned in my Ohio State horticulture classes (circa 1962-66). My first serious introduction occurred in the early 1970s when the late Henry Ross, owner of Gardenview Horticulture Park in Strongsville, Ohio, showed me the plants in his garden. He shared one, which I carried to the University of Illinois in Urbana, where it was planted in our garden around 1974. While teaching at the University of Illinois (1972-79), I scheduled three-day field trips in late April to early May to Cincinnati, visiting Mt. Airy, Rowe, and Spring Grove Arboreta. At Mt. Airy, a beautiful fothergilla in full flower coincided with the yearly trips. Fast forward to the late 1980s when I was verifying the Mt. Airy collections. I was given cuttings of this magnificent shrub, and named it ‘Mt. Airy.’ For 30 years it has gained a national and international reputation for superior 2-inch long, fragrant, white bottlebrush flowers; rich bluish green summer foliage, and kaleidoscopic yellow, orange and red fall color. The drivers in its commercial acceptance have been the relative ease of cutting propagation and ease of container culture.
Initially, I categorized ‘Mt. Airy’ as a F. major selection, but cytological studies by Dr. Tom Ranney et al., HortScience 42:470-473 (2007), showed it to unequivocally be a hybrid between F. gardenii and F. major, now correctly F. × intermedia ‘Mt. Airy.’ It is a pentapolid (5x), the result of 4x F. gardenii × 6x F. major. I have never observed fruit/seed production on ‘Mt. Airy’ and speculate sterility due to 5x ploidy, much like sterility associated with triploids (3x).
Mark Griffith, Jeff Beasley and I wanted to breed Fothergilla, but could never locate seeds. I queried Rich Lewandowski, who with Ron Miller, collected both species throughout the native range (more on this later). Rick told me that in his numerous experiences collecting in the wild, fruit was rarely found. Quoting Rick, “Once, at the base of Shortoff Mountain in North Carolina, we hit the jackpot and found copious amounts of fruit with viable seed.” This would have been F. major.
The logical question to pose is how to improve/integrate new traits into a genus when viable seed production is a treasure hunt. Since most of the cultivars are F. × intermedia (5x), they must have arisen in cultivation from seed collected in arboreta/botanical gardens. Rick reported earlier this year of seeing F. gardeniiand F. major wild populations, less than 20 miles apart in North Carolina, but not overlapping. In Dr. Ranney’s research, ‘Blue Shadow,’ ‘Eastern Form,’ Beaver Creek, Red Monarch, May Bouquet, ‘Mt. Airy,’ ‘Red Licorice,’ ‘Sea Spray,’ and ‘Windy City’ were F. x intermedia. ‘Appalachia,’ ‘Bill’s True Dwarf,’ ‘Blue Mist,’ ‘Harold Epstein,’ and ‘Jane Platt’ were true F. gardenii(4x). ‘Arkansas Beauty’ and Mystic Harbor were true F. major (6x).
So, where are the diploids (2x)? In Ranney’s study there were none, but subsequent collections by Lewandowski et al. showed diploid (2x) F. gardenii occurred and were “geographically aligned with the southern Gulf Coast and there were absolutely no tetraploid (4x) populations until the Georgia-South Carolina border in Effingham County, Ga.” A diploid F. gardenii collected in Baldwin County, Ala., and named ‘Redneck Nation’ was given to me by Bobby Green, of Fairhope, Ala. The leaves are blue-green, soft-pubescent, turning orange-red in autumn. Container-grown plants show good vigor, density, and pretty foliage color. Heat tolerance should be high, but I do not know northern limits. I have grown all the 4x F. gardenii clones listed above and none are superior to this diploid form (2x). Tetraploid plants are theoretically more adaptable than diploids, but not so in this situation. Incidentally, a photo of ‘Redneck Nation’ reflected a 4-foot by 4-foot plant at Bobby’s nursery in Fairhope. It was growing in full sun.
From a breeding standpoint, does the fact the ploidy levels are known portend improved fothergillas? Take 2N, 4N, and 6N, mix the genotypes, and perhaps 3N, 4N, 5N might result. Beyond cytogenetics, the new wild collections from Rick Lewandowski et al. add phenotypically superior traits that I have yet to experience in current fothergilla. The USDA National Germplasm Resources Laboratory in Beltsville, Md., shared 11 of 26 wild-collected types. Curator Kevin Conrad allowed me to target/select the best of the best. They were shifted to 3-gallon containers and are currently housed at Griffith Propagation Nursery in Watkinsville, Ga. We have taken cuttings and continue to evaluate for flower, fall color, etc. Mark, Jeff, and I are hopeful that viable seed will be produced as fruits are present on several plants. Dr. Ranney has made crosses with the above germplasm and got modest seed set. The F. gardenii2x germplasm may constitute a new species.
In 2002, at Oregon’s Farwest Nursery Show, Gary Handy showed me a small segment of a blue foliage basal sport of ‘Mt. Airy.’ My first reaction was WOW, what beautiful silver-blue foliage color. The plant was patented (PP 15,490; January 25, 2005) and named ‘Blue Shadow;’ similar in most respects to ‘Mt. Airy,’ but not as fast growing. ‘Blue Shadow’ is described as reaching 10 feet by 10 feet in the patent description. For point of reference, I have never observed a ‘Mt. Airy’ that large. Few blue-foliage shrubs exist, so I thought ‘Blue Shadow’ would be a monumental advancement. Unfortunately, tissue culture was utilized to quickly increase numbers. Both green and blue foliage plants resulted and frustrated growers. Even established plants will produce green reversion shoots. When properly grown, there is no deciduous flowering shrub that rivals it for the rich silver-blue foliage. In USDA Hardiness Zone 8, the blue coloration is diminished in the heat of summer.
In Plantsman 7(1):10-17, Rick Darke presented an overview of “Fothergilla in Cultivation,” discussing species and cultivar characteristics. He mentioned ‘Mt. Airy’ as the seminal cultivar that propelled the genus to commerce. A major reason for acceptance beyond ornamental characteristics according to Darke was ease of propagation. He noted, “Paul Cappiello has observed that this plant is so easily rooted in the southeast U.S., the window for taking cuttings extends from May into September.” I take cuttings with firm, but not brown, basal tissue, still actively growing, treat with 0.3 percent KIBA, with rooting occurring in 6 to 8 weeks. Remove from mist, lightly fertilize, and growth flushes will soon follow. Woody (hard, brown stems) cuttings are difficult to root. At Griffith Propagation Nursery, Mark produces up to 20,000 liners per season, taking cuttings when just firming, 0.3 percent KIBA, with 80 to 90 percent success.
Worth the trouble
As far as newer or late-to-be-appreciated introductions beyond those listed in Darke’s article, the Dirr Manual of Woody Landscape Plants (2009), Dirr Encyclopedia of Trees and Shrubs (2011), and Hillier Manual of Trees and Shrubs (2014), little has emerged. I named what appears to be a F. × intermedia type ‘Suzanne,’ that is more compact than ‘Mt. Airy,’ with excellent fall color. Alan Jones of Manor View Farms in Monkton, Md., has always championed the plant.
Often, in nursery catalogs, fothergillas are offered as F. major or F. gardenii. Why roll the dice on unknown genetics when so many named and unpatented cultivars are available? It’s safe to surmise that most F. major or F. gardenii in the trade are actually F. × intermedia selections. The only named F. major selections are ‘Arkansas Beauty’ and Mystic Harbor, neither of which are overly impressive. The 2017 RHS Plant Finder (England) lists F. gardenii‘Glaucophylla’ and ‘Zundert’ and F. major ‘Bulkyard,’ neither of which I have observed.
F. major is more cold hardy than F. gardenii with F. × intermedia reliable in Zones 4-8. Cappiello reported F. gardeniiwas killed in Orono, Maine (Zone 4). The Minnesota Landscape Arboretum (Zone 4) has significant plantings of ‘Mt. Airy’ and ‘Blue Shadow.’ On the University of Georgia campus, ‘Mt. Airy’ is planted in large masses in full sun to partial shade. Dave Creech at Stephen F. Austin State University in Nacogdoches, Texas, told me with shade and moisture, fothergillas perform well.
Our industry could simply slam the door on fothergilla improvement, for the current offerings are quite impressive. However, the adage “Good is the enemy of great” might be the impetus to push forward with new selections. The wild-collected germplasm from Rick Lewandowski, Ron Miller, and Tom Ranney offers exciting opportunities for superior selections. These genetics bring new traits for breeding, unique foliage, flowering, and habit. In fact, the foliage of NA 81929-04 and NA 81972-05 is the thickest, most lustrous, dark green I have observed. Additionally, the new growth on NA 81972-05 is a pretty purple-bronze. These two accessions have set numerous flower buds. Habits are quite compact on the 3-gallon container plants. Hope springs eternal. Fothergilla may offer a new frontier in shrub breeding.