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Carlos collecting Quercus ×alentejana (Q. faginea × Q. pyrenaica) in northeastern Portugal for his PhD thesis © Carlos Vila-Viçosa
An interview with Portuguese oak conservationist Dr. Carlos...
Amy Byrne | Apr 19, 2024
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It was a great pleasure for me to be able to write about my...
Gert Fortgens | Feb 15, 2024

Plant Focus

Quercus crassipes acorns with inrolled cupule margin
One of the more well-known Mexican oaks in cultivation.

Frost Damage in Aiken, South Carolina on March 15, 2017

Following a very mild South Carolina winter, many species of plants had begun to break dormancy by mid-March, nearly a month ahead of schedule, setting the table for a potentially disastrous situation. On the night of March 15, overnight lows dipped to 17 ⁰F in the county and around 19 ⁰F in the City of Aiken. Many species of trees and shrubs had already begun pushing growth and some such as azaleas, rhododendrons, and oaks were already in flower. That temperature drop reduced many of those plants to droopy, blackened representations of their former selves, more closely resembling wilted lettuce than valuable landscape plants. Bob McCartney took a tour around the oak plantings in the Citywide Arboretum and relayed what he witnessed a couple of days later. In the interest of providing valuable information that others may use in their collections, we will list those species that were dormant and those that were hit especially hard, and describe how some of those plants came back after the damage.

The list of species that remained dormant and were largely unharmed include species like Quercus bicolor, but also includes a few species that may surprise readers:

Q. ×alentejana (pendant form) Q. buckleyi Q. hinckleyi hybrid Q. pungens
Q. ×comptoniae Q. calophylla Q. hypoleucoides Q. pyrenaica1
Q. ×heterophylla Q. castanea Q. ilex (Portugal) Q. ×warei
Q. ×leana Q. coccifera (Greece) Q. imbricaria Q. rotundifolia
Q. ×sternbergii Q. durata (Durango, Mexico) Q. invaginata Q. sadleriana
Q. ×turneri Q. ellipsoidalis Q. laeta (Mexico) Q. saltillensis
Q. ×undulata Q. engleriana Q. longispica (China) Q. senescens
Q. ×vilmoriniana Q. faginea (pendant form) Q. look Q. similis
Q. acerifolia Q. faginea subsp. alpestris Q. lusitanica Q. sinuata var. sinuata
Q. acherdophylla (Mexico) Q. geminata Q. michauxii Q. suber
Q. aliena (Vietnam) Q. gravesii 1 Q. montana Q. texana
Q. arizonica1 Q. grisea Q. nigra × myrtifolia Q. tomentella
Q. arkansana Q. greggii (La Siberica strain) Q. obtusata Q. tristis (Guatemala) 
Q. bicolor Q. havardii × stellata Q. palmeri Q. turbinella
Q. boyntonii Q. hinckleyi Q. prinoides Q. vacciniifolia

1 Swollen buds appeared to be unharmed

Unfortunately, there were many more species that had at least broken dormancy. Many of these had catkins and new growth ranging from 2 to 8 inches, which were completely killed back. The bright spot is that many also had a number of still dormant buds on older wood that might be the saving grace for these trees. These are the species that received the most damage:

Q. ×rosacea Q. dalechampii Q. john-tuckeri  Q. polymorpha (South Texas)
Q. acutifolia Q. dentata subsp. yunnanensis Q. laurifolia Q. pubescens
Q. acutissima Q. dolicholepis Q. laurina Q. pumila
Q. afares Q. emoryi 2 Q. libani Q. robur (Fastigiata Group)
Q. affinis (Central Mexico) Q. fabri Q. lobata Q. rotundifolia
Q. affinis (Northern Mexico) Q. fabri × dentata subsp. yunnanensis Q. macrolepis Q. rugosa (New Mexico)
Q. aliena – near full leaf Q. faginea subsp. broteroi Q. marilandica var. ashei  Q. rysophylla
Q. aliena (Vietnam) Q. frainetto ‘Trump’ Q. mexicana Q. sartorii (Northern Mexico)
Q. alnifolia 1 Q. franchetii  Q. mohriana × stellata Q. sartorii (Southern Mexico)
Q. canariensis Q. fusiformis Q. mongolica Q. similis
Q. canbyi Q. garryana Q. muehlenbergii (Mexico) Q. sinuata var. breviloba
Q. castaneifolia (full leaf) Q. georgiana Q. myrtifolia Q. trojana – small plant
Q. cerris (‘Wodan’ F2) Q. graciliformis 3 Q. pagoda Q. variabilis
Q. coccifera subsp. calliprinos Q. greggii 4 Q. parvula 3 Q. vaseyana
Q. cornelius-mulleri Q. griffithii Q. petraea Q. virgiliana (Q. pubescens)
Q. crassifolia Q. haas (Q. robur Haas Group) Q. petraea subsp. pinnatiloba  
Q. crassipes Q. ilicifolia Q. planipocula  

1 slight damage;2 swollen buds damaged; 3 swollen buds dead; 4 slight damage to stems

After giving these plants a few months to monitor how the dormant plants came out and how the plants that were frozen back regenerated growth, there were a few surprises.

The Q. dalechampii was killed to the ground and has not re-sprouted. This came as quite a shock considering it was a sizable tree of nearly 20 ft tall. Q. pubescens was likewise totally killed to the ground and Q. haas was severely weakened and is struggling to recover. The Q. acutifolia has also died, but Bob reports that it appears to have succumbed to the oak wilt fungus (a positive test has not yet been received). Fortunately, almost all of the rest have either recovered or are recovering nicely.

Not so fortunate is the acorn crop. Since most of the damaged species were in full flower during the freeze, species in the White Oak group will not have a crop this year. It appears the Red Oak species that had undeveloped acorns from last spring will have a decent crop, but they will not have a crop next season. Of the oaks that remained largely unharmed during the freeze, it appears many will have a crop, although it appears that the crop may be smaller than normal.

All in all, I am amazed at the resiliency of plants, oaks in particular, to endure such a setback and be able to outgrow the damage inflicted upon them (there’s a lesson for us in there somewhere). In a couple of years the great freeze of '17 will be all but forgotten in Aiken.