A new term, “climate resiliency,” is making a mark to describe the character of urban trees and shrubs we should be planting in the landscapes of Texas. Everyone has seen the predictions of melting ice, rising seas and violent storms punctuated by long stretches of punishing heats and droughts never seen before. In the Pineywoods, it’s apparent that we need more drought and heat tolerance as well as more salt and alkalinity tolerance in the plants we use. And, judging from recent events, we should accept that our urban landscapes need to tolerate low temperatures we’ve never seen before.
Urban landscapes need a redo. Plants in the urban landscape need to be resilient. I like the 80:20 rule, which is to plant 80% of the landscape, the backbone, to proven performers — those plants that will deal with it all. Save the 20% for plants you might suspect are a bit edgy. Bananas as the backbone in your Dallas garden is probably a poor idea.
I wrote an article for Texas Gardener (“Ice Ice Baby,” July/August 2021) that described our first impressions of winter storm Uri. In 2023, that record-breaking event can be seen as one of three mega-climate challenges we’ve endured in the last two years. I call the situation a triple whammy. For Nacogdoches, we can describe our challenges this way:
First was the February 16, 2021, never-seen-before -4° F record low. Winter storm Uri in East Texas was a weeklong event accompanied by ice-and-snow loads that devastated many Texas urban landscapes. Every county in Texas saw temperatures below freezing. Landscapes were devastated, and brown became the dominating landscape color. In Nacogdoches, ice-and-snow load meant limbs falling from above. Many of these trees had to be removed, and debris removal from that event is still on our agenda. The urban landscape was devastated.
Second was the record-breaking heat in summer 2022, with 36 days over 100° F, a high temperature of 42° C and 10 weeks of drought. Records indicate it was the second-hottest summer in Texas since 1883. While 2011 is considered the hottest, driest summer on record, 2022 was a year to remember. The average summer (June 1 through August 31) temperature was 88.8° F degrees compared to 89.5° F in 2011. While East Texas received some welcome August rains, my friends in Central Texas did not, and it is there that many counties experienced the all-time record.
Third was the Dec 23, 2022, 9° F winter-storm Elliott event, which can best be described as a bomb-cyclone. It was preceded by a mild dry fall. Plants weren’t acclimated. The entire state fell under a freeze alert. The storm stretched 2,000 miles from the Great Lakes near Canada to the Rio Grande along the Mexico border. The temperatures ranged from freezing along the U.S.-Mexico border in McAllen to as low as 8° F in parts of the Panhandle. Elliott downed powerlines, littered highways with accidents and led to record plane-flight cancellations. The Southwest Airlines fan club took a hit. Gusty winds made it feel even colder, with wind chills ranging from 23° F to -10° F.
Most gardeners across the state experienced these same three events in lesser or greater fashion. Because of the extensive diversity in the SFA Gardens, a project was implemented in the summer 2021 to document the extent of damage to woody ornamental taxa. Taxa is a taxonomic group of any rank, such as genus, species, variety or genotype. A 1-6 damage-rating scale was employed (with 1 representing no damage and 6 representing dead), and other data was collected, including plant height, appearance and comments. Below are the results of our observations of various taxa commonly used in urban Texas landscapes.
Abelia — 16 varieties, no damage; A. chinensis, no damage.
Berberis — barberries, mostly B. thunbergii varieties, minor damage; plants recovered.
Callicarpa — beautyberry varieties and genotypes of C. americana suffered no damage; C. rubella and C. dichotoma showed damaged trunks and branches; C. salicifolia and C. longissima froze to ground in 2021, recovered and froze to ground again in December 2022.
Camellia — 300 plus cultivars ranked with a wide range of damage ratings. Most survived, though many badly damaged. ‘Frank Hauser’, a favorite here, was killed outright in a number of locations. ‘Yuletide’ branches and tops died back on some, lesion on others. For many camellia species, it was common to have the top alive with unthrifty new growth and with considerable sprouting from base and lower trunk and branches. Many straight Asian species died to near ground. C. yuhsienensis fared well.
Gardenia — wide collection of varieties froze to ground or near ground and recovered. However, we can now report that we do have one genotype, a robust gardenia with double flowers, that survived both freezes in fine form and flowered well in 2021 and 2022. That clone is being multiplied for further evaluation and for sharing with cooperators.
Hydrangea — H. quercifolia (oakleaf) and H. paniculata were unaffected. While all H. macrophylla varieties froze to ground — as they often do here — they returned vigorously. Dichroa survived from under snow cover.
Ilex — a large holly collection, unaffected for the most part. I. rotunda damaged. I. vietnamensis froze back. I. decidua, I. vomitoria and I. opaca, all natives, were untouched by both the 2021 and 2022 freezes.
Illicium — extensive collection of anise. All native-derived varieties seem to survive well, even the variegated and golden-foliage clones. Surprisingly, I. mexicanum was unaffected. I. anisatum damaged; I. verum killed.
Lagerstroemia — 136 varieties of crapemyrtles; good survival but some varieties showing dieback and unthrifty growth; final verdict not in.
Lauraceae — Laurels, a record large Cinnamomum chekiangensis was unaffected, a surprise. Young plants in one-gallon containers killed in December 2022 event, even under frost fabric. Phoebe sheareri killed; Phoebe chekiangensis froze to near ground.
Loropetalum — a surprise, with major damage on a wide range of varieties, most to ground. Major sprouting from base. Green-leaf less affected than dark-leaf forms.
Osmanthus — an extensive collection of O. fragrans. Most survived the Feb 2021 freeze well. ‘Fudingzhu’ and ‘Apricot Echo’ damaged, but ‘Aurantiacus’ was not. Three variegated forms damaged but recovered from low in the shrub. Osmanthus yunnanensis taken to ground. Note: The December 2022 freeze has created more damage than at first anticipated and the verdict is not yet in.
Parrotia persica and P. subaequalis (the Persian and Chinese witch-hazels) came through all three events in fine shape. Bullet-proof, noninvasive exotic plants for East Texas with bright-yellow and bright-red foliage in the fall.
Photinia — quite common in Texas, all red-tip varieties suffered varying degrees of damage. P. serrulata performed well. Potentially invasive in East Texas.
Pittosporum — about a dozen P. tobira varieties froze to ground but are returning. Both the green and variegated P. heterophyllum froze to ground, sprouting from base and from underground roots, an aggravation. Some rarely encountered Asian pittosporum species all froze to ground but have returned from the base.
Podocarpus — the collection of varieties at SFA Gardens varied from major damage to very little.
Raphiolepis — Indian hawthorn, mainly R. indica varieties, mostly froze to ground. Indian hawthorns are a commodity in Texas landscapes and were badly damaged or killed all the way into Houston. R. umbellata survived with minor damage. Those that survived 2021, died back to ground in the December 2022 event.
Rhododendron — 300 azalea varieties, selections or genotypes in the SFA Ruby Mize Gardens database. Sherry Randall and Barbara Stump, both with long-term involvement in the Azalea Society of America and the Texas chapter, made an on-the-ground evaluation in late spring. Several quick conclusions were evident. There was no damage on native deciduous azaleas, Aromi hybrids and other genetics in that arena. On R. indicas, the data were all over the map. Encores in general were slightly damaged. ‘Koromo shikibu’, a signature azalea at SFA Gardens, lost a few leaves but was generally unaffected. Badly damaged varieties were cut to a few feet above ground, fertilized and they have rebounded. Verdict on most recent freeze is not yet in.
Styrax — The snowbells and silverbells did well here. Styrax japonicus varieties took the cold in stride, as did other Asian species, many rarely encountered. For example, Styrax tonkinensis was unscathed. A very large Styrax formosanus var. formosanus was killed to ground but vigorously sprouted from low on the trunks and from the root system. A large six-inch diameter Huodendron tibeticum (never flowered but grew well) was killed outright.
Viburnum spp. — natives fared well except for V. obovatum, which is more Gulf South in its natural range. For the most part, Asian viburnums fared poorly.
With that in mind, we can make some preliminary conclusions.
1. Native species fared better (damage rating 1, rarely 2).
2. Freeze impact is a delayed response and subject to what follows.
3. Young plants suffered more than older.
4. Having multiples of a variety is useful and having them in several locations is better to arrive at solid conclusions. Making a judgment on hardiness based on one plant is problematic.
5. Nurserymen and landscapers might rethink several commodities as a part of their marketing and production mix. The fan club for Indian hawthorns needs a meeting.
6. There are surprises everywhere. There’s value to long-term trialing of woody ornamentals. SFA Gardens is looking forward to perhaps introducing a bone-hardy gardenia.
7. While most were damaged, green Loropetalum fared better than the dark-leaved varieties.
The woody ornamental data above and our conclusions represent mainly the impact of winter-storm Uri in February 2021 in Nacogdoches, Texas. It’s what we experienced in East Texas. Winter-storm Elliott in December 2022 is destined to jumble our data. Some woody ornamentals that were killed to near the ground by Uri in 2021 returned vigorously from the base; that vigorous growth was unprepared for the December 2022 winter-storm Elliott. Many are back to the ground again and some seem to have given up and gone to heaven. What that means is that a return to the landscape this summer is in order with our maps and databases in hand. Many of what 2021 knocked down, 2022 may have finished off. The final conclusions are still uncertain. Until later, let’s keep planting, but let’s be smarter about it.
Dr. David Creech
Director, SFA Gardens, Stephen F. Austin State University, Nacogdoches, Texas