Progress report: Evaluating new plants

Editor’s note: This is part two of Michael Dirr’s latest treatise on plant genetics. Part one focused on hydrangea and other flowering shrubs. Read it in our February issue.

Broadleaf evergreens

There are never enough great ones and with Buxus in turmoil, what are the options? In truth, not many but extraordinary research and breeding by private and government agencies have improved the boxwood situation. NewGen boxwood from Saunders Brothers, Virginia, and Better Boxwood (Babylon Beauty, Heritage, Renaissance and Skylight) from PDSI show promise. Freedom, Independence, and Liberty Bell (newest) are the current NewGen introductions. Freedom has performed well at the UGA Horticulture farm and along with Independence is rated highly for blight and leaf miner resistance. The U.S. National Arboretum is breeding for blight resistance. To my knowledge nothing has been released but several hybrids were highly resistant to blight. Anyone interested in Buxus blight and leaf miner resistant species/cultivars should read J. Environ. Hort. 40(4):129-142. 2022 and Plant Health Progress 24:298-302. 2023.

Distylium- Breeding started at UGA. Now one of the most popular broadleaf evergreens for zones 7 to 9. Hoping/working for zone 6 adaptability. Twenty years of breeding resulted in 10/12 commercial cultivars. Emerald Heights is the hardiest. PII has several new selections, one with compact-rounded habit, boxwood size, lustrous dark green leaves (3), a dense columnar form with small dark green leaves (1), variegated leaf selection (2).

Ilex glabra, inkberry, has always been popular, especially in the Northeast, but a common fault is lower leaf shedding. Forever Emerald (‘Peggy’s Cove’) is the first legitimate compact cultivar that maintains foliage to the base. A previous NM article described the origin of the cultivar. (Nursery Management, January 2023).

Nandina and Mahonia have received attention from breeders. I have representatives of both in the garden but fail to get overly excited. Nursery producers requested increased cold hardy Mahonia Soft Caress. Soft Caress was killed to the ground in the Dirr garden at 6°F. I enjoy Ozzie Johnson’s Mahonia Marvel with terminal spined, lustrous dark green leaves. The plant is now 8 feet high and produces fragrant, bright yellow flowers atop the rigid shoots in early January.

 

Flowering trees

Amelanchier- Is there anything new in serviceberries? Great native. Leaf spot (Entomosporium sp.) is a huge issue in the south. A selection from UGA with high resistance, pumpkin-orange fall color, is in production. Numerous ‘Ballerina’ seedlings are under evaluation at PII, all with brilliant orange-red fall color and no leaf spot in 2023. Amelanchier × grandiflora ‘Autumn Brilliance’ is the most popular cultivar in commerce. Purchased ‘Ballerina’ seed from F. W. Schumacher, Sandwich, Massachusetts. Required 3 months cold/2 months warm stratification before germinating.

Cercis canadensis- Remarkable array of new cultivars from North Carolina State and Ray Jackson. Dirr favorites include Black Pearl, Flame Thrower, and Hearts-A-Fire. ‘Floating Clouds’ is a green-white variegated foliage cultivar that breeds true to type from seed. Numerous self-sown seedlings in the Dirr garden display degrees of marble cake variegation from 70 to 80% white to green and the reverse.

Styrax japonicus- Minimal enthusiasm for the species. Not sure why although ambrosia beetles will infest. ‘Evening Light’ (compact small tree, purple leaf, white flowers), Nightfall (weeping, purple leaf, white flowers) and APrystine Spire (columnar habit, leathery lustrous dark green foliage, white flowers) are unique. I have healthy vigorous seedling trees throughout the garden. Aprystine Spire and ‘Evening Light’ were planted along Oconee County’s four lane connector and, five years later, are thriving. Dwayne Moon of Moon Tree Farm in Washington, Georgia, who introduced APrystine Spire, recently told me the tree is “catching on.”

Noble trees

Nyssa sylvatica- Great enthusiasm for this native species. Continually searching for improved traits. In the southeast, leaf spot (Mycosphaerella nyssacola) is devastating. Afterburner is the most susceptible. Red Rage and ‘Wildfire’ the most resistant. New columnar selection from Mount Vernon is being propagated. Nyssa sylvatica continues to gain commercial traction and Mike Hayman, Louisville, Kentucky, has assembled the most diverse collection of selections/cultivars. Mike rates Red Rage one of the best performers for brilliant fall color and leaf spot resistance but believes the quest continues for the perfect tupelo.

Needle evergreens

Disease may catch up with ‘Green Giant’ as it did with Leyland cypress. Our industry needs more screening needle evergreens. Several sports of ‘Green Giant’ have been introduced including Everyst, ‘Junior Giant’, and Virginian.

Cryptomeria japonica Kashyma- Compact tree selection with grass green needles and to date no branch dieback/interior browning. From Zeke Harvey, former student, Chappell Mill Trees, Milner, GA.

Thuja Everyst- Tight, pyramidal-columnar sport of ‘Green Giant’. Thick dark green foliage. This has commercial legs. Moon Nursery introduction, Washington, Georgia.

Thuja koraiensis- Korean arborvitae. Only five species of Thuja worldwide. This is little known. Extremely variable in habit, often shrubby. Great opportunity exists for a blue needled form. They exist in Europe. Tested in Georgia and heat tolerant. Considered zones 5 to 8. ‘Glauca Pendula’ with arching blue green branches makes an elegant accent/specimen plant.

Thujopsis dolabrata- Hiba arborvitae. Closely related to Thuja and needs to be hybridized with it. Waxy dark green needles above, silver markings below. Artistic conifer. Beautiful specimens in the University’s botanical garden. ‘Nana’, a compact, rounded form, has prospered in the Dirr garden for 15 years. Tolerates considerable shade. Zones 5 to 7(8).

Tsuga hybrids- U.S. National Arboretum bred adelgid resistant hemlocks over a 20 to 30 year period. Slow to release with ‘Crossroad’ (T. caroliniana × T. chinensis) and ‘Traveler’ (T. chinensis × T. caroliniana) now available. ‘Traveler’ was patented (PP32,784). Great potential but largely unknown. ‘Traveler’ is more graceful; the habit reminiscent of T. canadensis. They are listed as zones 6 to 7. See HortScience 58(3):289-290 2023 for specifics.

Herbaceous perennials

What a way to ruin a woody reputation. At PII we dabbled with a few, particularly Amsonia, Baptisia and Penstemon.

Baptisia- Always loved this native genus. Great pollinator plant. Grew up with B. australis. Started to dabble with breeding in 2010 and initiated a pollinator garden in 2017. Decadence series dominates the commercial market. Katie and I have a Baptisia video on YouTube titled Plant America with Baptisia that has garnered 6,200 views and many positive comments. I believe the genus is not sufficiently well known or presented (i.e., container appeal) in commerce. Plants at retail often have a few stems and no flowers. Difficult to ask $25 for herbaceous perennials with no eye-candy appeal. I penned a Baptisia article in Nursery Management, January 2022 issue.

The future

People! Industry requires people with moxie, passion, work ethic, curiosity and critical thinking ability. Starting in August 2022, I mentored a local high school senior, John Reid Foell. Taught him breeding, propagation, general nursery work, and he continues to work with me at PII and the garden. I tutored his FFA nursery landscape judging team. They won the state and traveled to the nationals in Indianapolis in October 2023. The team placed eighth out of 50. John is now majoring in Horticulture at UGA. Another team member is majoring in Horticulture at Auburn. One more plant will not change our industry. One more talented employee may.

Opinions expressed are those of the author and do not necessarily reflect the view of Nursery Management or GIE Media.