The Winter That Was, Part I
Truncated bundles of forsythia blossoms stood like regimental Hobbits in yellow dress uniforms while willowy branches ascended from the plants in embarrassed nakedness. Nearby specimen size rhododendrons of the PJM Group, Rhododendron mucronulatum, and R. dauricum bravely fizzled forth a wisp of an isolated bloom here and there attempting to encourage the spring's arrival. Tentatively shaking to shed their winter overcoats, Magnolia grandiflora became "magnolia sansaflora" and M. soulangeana died to the ground. However, M. 'Dr. Merrill' and Dr. August Kehr's M. x 'Sundance' weathered well.
| Forsythia was truncated by temperatures down to -25°F, and
blooms in the spring were restricted to snowline level.
Photo by the Max Byrkit
The miasmic winter of 1993-94 had interfaced with the spring and the horticultural "killing fields" resulted. In the nearby city of Hagerstown, Md., at an official weather reporting station the Jan. 21 temperature fell to a low of -21°F, relegating many previous records to obscurity. The more rural setting of my garden (usually 4 degrees colder) was measured at -25°F, and local farmers bragged their temperatures down to -30°F. On the following day, Mother Nature chose to adjust the thermostat and the official temperature rose to a near balmy 40°F with 90 percent sunshine - a 60 degree change in less than 35 hours. Twelve to 16 inches of snow cover saved many small plants and preserved some bloom. (Hybridizing this year required considerable lying down on the job!) January 1994, invigorated with up to 50 mph winds, produced the sixth coldest winter ever recorded.
Following many less severe winters and the lulling fantasy of growing those sumptuous but not hardy western yellows, reality had struck. Approximately 350 plants, species and hybrids, were examined and rated as to degree of plant damage and, secondarily, to floral display. Azaleas were not included because of lack of time, space and energy, although some comments are included.1 Observations and comments are just that, namely observations and comments, and friendly disagreement is invited and encouraged.
Species with Undercoats
Those indumented clans of rhododendrons which I grow, in general, seem reasonably hardy. Rhododendron bureavii survived minus flowers as did R. adenopodum (except for one plant which died).
Rhododendron degronianum ssp. heptamerum (syn. metternichii) grown here and R. yakushimanum survived. However, not all yaks are created equal. The Exbury form, 'Yaku Angel', some H.L Larson forms (but not the tall form) and one of my own clones experienced some dieback. 'Ken Janeck' and 'Mist Maiden' showed no plant damage but bloomed only under the snow line. Rhododendron makinoi and hybrids with 'Yaku Angel' showed no plant damage. Hybridization with R. yakushimanum produced "children" of varying degrees of winter hardiness as would be expected. An unhappy plant of R. caucasicum expired without my mourning.
| This plant of R. fortunei succumbed to the 1993-94 freeze, along
with nearly 50 percent of the plants of this species.
Photo by the Max Byrkit
"Fortunei Family" and Friends
Of 53 plants of R. fortunei (mostly Lu Shan seedlings over 6-7 feet), nearly 50 percent were killed. Those that survived showed considerable damage except for a few of suspect ancestry whose flowers were of darker color or devoid of scent. Known hybrids of R. fortunei demonstrated wide variation and degree of damage. From the undamaged 'Merley Cream' to the adjacent 6-foot plant of 'Dorothy Russell', which was nearly destroyed, the spectrum of injury was complete and well represented. Joe Gable's "hardy" R. decorum wasn't hardy enough and joined the long list of the deceased. The suspected "frigaphobics" R. hemsleyanum and R. fortunei ssp. discolor Houlstonii Group both managed survival only under the snow line with total loss of flower buds. Rhododendron fortunei, while normally a good source of relative hardiness and flower size, cannot be a reliable genetic source for hardiness in the more extreme climates.
| 'Merley Cream', in rear, survived undamaged, but
'Dorothy Russell' almost dies in the winter of 1993-94.
Photo by the Max Byrkit
Native American scaly hybrids, i.e., hybrids of R. minus, Gable scaly hybrids, PJM Group, and species R. dauricum and R. mucronulatum and their relatives were essentially undamaged. Rhododendron micranthum did not even sneeze and poured forth a few courageous trusses of flowers. Rhododendron myrtifolium showed her usual leaf burn, while the R. keiskei group managed much variation in damage. Surprisingly, Gable's R. fletcherianum survived with only moderate damage.
Azaleas Great and Small
'Corsage' and 'Louise' showed little damage, while 'Stewartstonian' and 'Caroline Gable' got hit. Hershey hybrids and Glenn Dales in general showed significant damage, while 'Silver Sword' survived with only flower bud damage. The Satsuki hybrids hunkered down under the snow and were spared damage. Rhododendron schlippenbachii was uninjured but naked of bloom. While the deciduous azaleas fared well as a group, R. atlanticum survived with few blooms as did R. calendulaceum.
Max and Cat
The friends of hardiness came through handily, but even these suffered extensive bud damage and occasional dieback. Hybrids of both R. catawbiense and R. maximum have produced children of wide ranging hardiness. A personal prejudice of mine was that R. maximum was hardier than R. catawbiense, but the low temperatures seemed to affect both equally. The hybrid 'Maxecat'* did well as a plant but suffered from bud loss.
Surprise Losers and Winners
Of the losers, most noteworthy were 'Bosutch', a very early bloomer, which took considerable damage as did the old hybrid 'Direcktör E. Hjelm'. Rhododendron hyperythrum plants all were damaged and one died completely, contrary to my long held belief of more substantial hardiness. 'Mrs. T.H. Lowinsky', in spite of parentage, did poorly, and R. pseudochrysanthum was devastated in spite of its reputation for some hardiness.
Of winners, I was surprised by the plant hardiness of R. anwheiense and its hybrid 'Blewbury'. Both had little plant damage but bloomed only below the snow line. Rhododendron brachycarpum was hardy enough, but its hybrids showed considerable variation. 'Queen Anne's', a double white, stood well and had a modicum of bloom, while David Leach's 'Rio' bloomed well on rather small plants.
In summary, this abnormally cold winter became an educator to me and reinforced the need for hardiness as a prime ingredient for plants to be grown in this area. It also caused some rethinking of my hybridizing goals and the means to achieve them. Hopefully, the data1, crude though it is, may be useful to others.
A caveat: my findings should not be used as a sole guide to determine hardiness or the lack thereof but only as one observation, which should be confirmed by others. Cultural idiosyncrasies, species variation, and disease or insect damage also are factors in the vigor and hardiness of any plant evaluation and are hard to evaluate and reduce to tabular data. A well chosen and well grown rhododendron is its own reward!
Dr. Max Byrkit is a member of the Potomac Valley Chapter.
1 Data on 333 plants, which includes plant height, health, damage on a scale from 1 to 4, site exposure, time since transplanting and bloom in spring 1994, will appear in Part II of "The Winter That Was" in the winter 1996 issue of the Journal.