Crimson evergreen

When I arrived in Georgia in 1979, redtip photinia, P. × fraseri ‘Birmingham’ (P. glabra × P. serratifolia) was ubiquitous. Primarily used for hedges, screens, barriers and groupings, the brilliant red emerging foliage was spring’s siren song. At that time, redtip was grown by the millions in the Southeast. It has declined precipitously in popularity because of leaf spot (Entomosporium maculatum/E. mespili). The disease is especially virulent in cool, moist humid springs, partially to fully defoliating plants, affecting young and mature foliage.

I knew little about the genus, except for P. villosa, a white flowered, red fruited, brilliant yellow orange fall colored shrub/tree, which unfortunately is fire blight susceptible. This species has developed reliable fall color in the Dirr garden for 15 years. Taxonomic revisions have separated the original ~30 Photinia species into seven or eight genera. Photiniavillosa is now Pourthiaea villosa. The three species discussed herein, Photinia × fraseri, P. glabra and P. serratifolia remain with Photinia. See www.ars-grin.gov for the current changes.

The University of Georgia (UGA) campus was rife with P. × fraseri, large P. serratifolia, and a few P. glabra. In my woody plant courses, the three species were taught, their virtues and liabilities shared. Photinia glabra is the most susceptible to disease, followed by P. × fraseri, and the resistant P. serratifolia. I thought screening seedling populations of P. × fraseri for red leaf color and disease resistance was realistic, because of the hybrid’s P. serratifolia parentage. Working with the U.S. National Arboretum, a single leaf screening process was developed that correlated with disease observations of landscape plants (J. Environ. Hort. 14(3):154-157. 1996). Young leaves of the species were two (P. glabra) to nine (P. × fraseri) times more susceptible than mature foliage; ‘Birmingham’ the most susceptible with 23% necrotic young leaves; P. serratifolia with 2.2% necrosis on young leaves and only 0.2% on mature. Photinia × fraseri ‘Kentucky’, a resistant clone that was sent to me from Jellico, Tennessee, developed one-third the necrosis compared to ‘Birmingham’. Occasionally, a lone plant in a hedge has little/no leaf spot. Is this resistance or simply luck? Unfortunately, we never proceeded with large scale screening of seedling populations. In the paper, we suggested crossing P. serratifolia × ‘Birmingham’ to develop seedlings with greater disease resistance. Had this been accomplished, the single leaf screening process would have made short work of selection.

This work was published in 1996 and most nursery growers/retailers and gardeners were resolute about other options, although it is still utilized in drier parts of the country and throughout the world. In July 2023, I noticed an abundance of redtip in English gardens and retail centers. The Royal Horticultural Society’s Plant Finder (2023) listed ~38 cultivars of P. × fraseri. Star Roses and Plants offered Dynamo Red (‘Parsur’ PP19,390) in its 2023 online catalog. One would think there are measures of resistance among the many cultivars. An Oklahoma State University Extension report stated all cultivars were susceptible. The introduction of Loropetalum chinense var. rubrum and the red leaf cultivars in the 1990s helped to push redtip to benchwarmer status in the Southeast.

P. serratifolia with inherent leaf spot resistance offers an avenue for new introductions. Venerable, ancient specimens on the UGA campus and Athens area attest to high resistance. In the early 1990s, I selected a clone from campus and named it ‘Green Giant’. The original plant was 30 feet high and 30 feet wide. It was shared with nurseries, and John Barbour from Bold Spring Nursery (Hawkinsville, Georgia) continues to produce field grown material. New foliage emerges apple green followed by unpleasant smelling, large white inflorescences which give way to red fruits in fall/winter. The species may reach 50 feet in height and is adaptable in Zones 6 to 9. ‘Green Giant’ was the most leaf spot resistant taxon in the screening study.

Four cultivars were listed in RHS Plant Finder, 2023, with none available in U.S. commerce or with red growth. In W. J. Bean’s, Trees and Shrubs Hardy in the British Isles, the species is exalted as “the most beautiful of broadleaf evergreens. Wherever it thrives, this is undoubtedly one of the finest evergreens ever introduced.”

Species characteristics:

Habit: Low branched, single stemmed tree or large shrub, densely clothed with large evergreen leaves. Can be trained/staked to develop a single trunk specimen.

Leaves: Large, leathery, 4 to 8 inches long, 1½ to 3 inches wide, petiole 1 to 1½ inches long, clothed with whitish hairs, emerging leaves green, bronze, copper, or red, maturing lustrous dark green, older leaves often turning red before abscising in fall-winter; young foliage may be injured by spring freezes. I have searched for brilliant new red growth on self-sown seedlings in Athens and have found none.

Flower: The white, malodorous flowers arrive with the expanding leaves in March-April (Athens), in 4 to 6 inches diameter corymbs. The red fruits persist into fall/winter. Birds eat the fruits and stray seedlings are frequent in understory habitats. Vigorous seedling foliage resembles the prickly/spiny leaves of holly.

Adaptability: The species grows in full sun and moderate shade. It is heat, drought tolerant, prospers in well-drained soil, is easy to produce in containers and the field. Tolerates heavy pruning.

Epilogue: Is there nursery/landscape potential for new P. serratifolia selections? On March 27, 2023, Stewart Winslow, horticulturist at Wofford College, (Spartanburg, South Carolina) sent photos of a brilliant ruby red foliage seedling discovered in the woods near Anderson, S.C. The color is so vibrant it makes the original redtip appear blasé. Stewart brought rag-tag woody cuttings on April 7 to Premier Introductions Inc., which were treated with Clonex (0.31% IBA) plus Dyna-Gro Root Gel (0.216% IBA + 0.027% NAA),and placed under mist with 75°F bottom heat. Cuttings rooted by May 2, and transplanted to 3-gallon containers on May 24, fertilized with Harrell’s 8-9 month 15-6-11; the tallest plants now 4 feet. The ruby red new color persisted into November. Plants watered overhead with no evidence of leaf spot.

Does this selection have wiggle room in the future marketplace? The species is the hardiest of the three discussed herein, Zone 6 to 9(10). At Leu Gardens in Orlando, Florida, there was a 50-foot high tree, indicating a low chilling requirement to satisfy dormancy. Timing is everything as Winslow mentioned the original plant was lost when the woods were bulldozed for new construction.

Opinions expressed are those of the author and do not necessarily represent the views of GIE Media, Inc.

For more than 40 years, horticulturist, breeder and author Michael A. Dirr has impacted the green industry through research, teaching, books and plant introductions. michirr@aol.com