JARS v46n2 - The Biggest Test Garden

The Biggest Test Garden
Mass. Chapter Keeps Long-term Record
Joe B. Parks
Dover, New Hampshire

For almost a decade, Massachusetts Chapter members have been collecting and reporting performance data on their rhododendrons. Now for perhaps the first time in the history of any chapter in the Society, a long-term record is being created on rhododendron performance. Up until now reports on plant performance have been mostly anecdotal; and in the telling, too often the true information becomes a bit twisted or is even lost.
This makes the Massachusetts Chapter the biggest rhododendron test garden anywhere. Instead of a planting in some artificial situation where plants are "tested" every member who reports makes his garden a part of a New England wide "test garden". Thus we have test records based on how rhododendrons perform in real gardens under real conditions. Thus this testing involves not only the effects of the weather but most importantly how rhododendrons perform under the care and attention given by ordinary folk.
Moreover, it also provides a test bed with an incredible range of plant selections - running from the most common to the bizarre; from the hardiest to the tenderest; and woven throughout is that urge of every rhodoholic to grow something that no one else can grow. No formal test garden could ever dream of achieving such variety and diversity.

Needed A System
In 1982 after discussions with a number of chapter members, I designed a system for collecting data on rhododendron performance. The major problem in development of the system was deciding the results desired. The second biggest problem was to design one that would provide usable results even though reporting was, as it was bound to be, uneven and erratic. Everyone agreed that we needed more information on hardiness; but after that, agreement became more difficult. Therefore I arbitrarily took it upon myself to make the final decisions. Any shortcomings in the system can be blamed on my errors or lack of vision. The report as finally designed provides for an annual evaluation of plant appearance, performance and flowering. Interested members check off the condition of each of their plants on a multiple choice form, record the weather extremes they experienced and send the form in for compilation.
True, such evaluations made without rigid standards are subjective. But if you accept that the more conscientious are the most likely to report, then a summary of all the reports is likely to be a reasonably accurate representation of plant performance. Over time, there can be no question but that a written reporting system will be far more accurate than the word of mouth system we now have.

Aim Is Objectivity
The report itself is designed to provide for as many objective answers as possible and to provide cross-checks wherever practicable. Thus plant "General Performance" is broken into four components: 1. "Dead", 2. "Badly Winter Damaged", 3. "Some Winter Damage" and 4. "Good, No Visible Damage". The first and last items are obviously objective evaluations and the other two are fairly easy to separate and thus unlikely to overlap in most peoples' minds.
By including an analysis of leaf condition, performance is further defined (and the evaluation of "General Performance" sharpened). The thinking here is that leaves are by far the most significant part of the plant from the viewpoint of esthetics as well as the general health of the plant. "Leaf Condition" is broken into three components: 1. "Substantial Winter Damage", 2. "Minor Injury" and 3. "No Visible Damage". Again the categories are designed so that most people would agree on what is being seen and recorded. Incidentally a category to clearly cover deciduous plants will be included on the 1992 form.
Flowers are of course the "raison d'etre" for growing rhododendrons. While I don't agree that flowers are the only important reason we should have rhododendrons in the landscape, I certainly agree that flowering is the peak of their performance. Beginning in 1987, "Bloom" was evaluated under four, instead of five categories. This reduction from the five of previous years proved to be a mistake and will be corrected on the 1992 form. The five categories for evaluating "bloom" are: 1. "None, No Buds on Plant" (this is the one mistakenly dropped), 2. "None, All Winter Killed", 3. "Some Winter Damage", 4. "Blooms Frost Damaged" and 5. "Normal Bloom." Provision is also made for indicating whether a plant grew in an exposed or protected situation and whether it performed well only under Snow cover. In addition "Peak Bloom Date" is reported. This should give us a Good picture of what to expect, flower-wise, from our plants.

Humor Too
The individual reports are interesting. One person who reported, who obviously has a wry sense of humor, gave an evaluation of a plant that grew in his greenhouse! This plant, along with others that members indicated with a "P" as being grown in a protected situation, is included in the summary with an indication ("PRO") that it grew in a protected situation. Snow is of course the ultimate protector, so plants that were undamaged only below the snow line or bloomed only under snow cover are marked "S" on the individual reports and include the word "Snow" in the evaluation. Most of us also have plants that grow in exposed situations where they really take a beating. These are shown by an "E" on the individual reports and indicated by "EXP" in the summary.
Combined with the performance evaluation is a weather report. Without it, performance analysis of the plants would of course be relatively meaningless. This section on weather covers four factors: 1. "maximum temperature the previous summer (°F.)", 2. "the minimum temperature during the winter", 3. "annual degree days" and 4. "abnormal days" and "cooling degree days". This would provide an evaluation of both summer and winter; perhaps not too important in New England but very important if the system were used in warmer climes.
For those who do not use oil heat and may not recognize it, a "degree day" is a figure based on the difference between the mean temperature of a given day and 65°F. For example, on cold winter day, a maximum of +20°F and a minimum of - 10°F would yield a mean of +5°. Subtracting this from 65° gives a figure of 60 degree days. This is a figure calculated and recorded daily by oil dealers. They use it to determine when to make "automatic" fuel delivery to their customers. For most dealers the "degree year" runs from July 1st to the following June 30th. Using a different date does not make a significant difference in the figure. There is some reason to believe that since degree year is related directly to the amount of cold (or hot) weather rather than a single maximum or minimum temperature, it can be useful in evaluating rhododendron performance. I have never seen a reference to its use for this purpose so this may be a fanciful concept on my part. Hopefully the figure will be reported more frequently in the future so that its usefulness (or lack thereof) can be better evaluated.

A Sample of the Rhododendron Evaluation Report
Massachusetts Chapter, American Rhododendron Society
Year Max Min Zone D. Day Grow General Condition Lea
Bloom Condition Site Peak Bloom
yedoense var. poukhanense {Evergr. Az.
1984 +92 -17 5B 0 Bro Badly Damaged Some Damage 28-May-84
1984 Bor Good Some Damage Normal 26-May-84
Acadia {Rhodo
1984 +96 -27 5A 0 Par Good Good No Buds Snow
1985 +90 -18 4B 0 Bar Good Good Normal
Accomplishment {Rhodo
1987 +95 -08 6A 0 Fal Good Good Normal Snow 23-May-87
Album Elegans {Rhodo
1984 +96 -27 5A 0 Par Good Good Normal 09-Jun-84
1985 +94 -13 5A 0 Par Good Good Normal 10-Jun-85
1985 +?? -05 5B 6780 Bro Good Good Normal 01-Jun-85
1984 +96 -27 5A 0 Par Good Good Normal 03-Jun-87
Alice Swift {Rhodo
1985 +90 -18 4B 0 Bar Good Good Some Damage
America {Rhodo
1983 +98 -15 5A 0 Par Good Good Normal 10-Jun-83
1984 +90 -27 5A 0 Par Good Good Frost Damage 09-Jun-84
1985 +97 -05 6A 0 Fal Good Good Normal 24-May-85
1985 +94 -13 5A 0 Par Good Good Normal 10-Jun-85
1985 +?? -05 5B 6780 Bro Good Good Normal 03-Jun-85
1987 +95 -08 6A 0 Fal Good Good Normal Snow 25-May-87
1987 +?? -?? 5B 0 Bro Good Good Normal 01-Jun-87
1991 +92 -13 5A 5288 Par Good Good Normal 25-May-91
Anna Baldsiefen {Rhodo
1983 +98 -05 6B 0 Mag Good Good Normal 10-May-83
1984 +92 -17 5B 0 Bro Good Good Normal 10-May-84
1984 Car Badly Damaged Badly Damaged Some Damage Snow 22-May-84
1985 +90 -14 5A 0 Car Badly Damaged Badly Damaged Some Damage Snow 05-May-85
1985 +?? -05 5B 6780 Bro Good Some Damage Some Damage 12-May-85
1985 +92 -05 6B 0 Mag Badly Damaged Badly Damaged No Buds
1987 +?? -?? 5B 0 Bro Some Damage Badly Damaged Normal 09-May-87
Anna H. Hall {Rhodo
1982 +92 -?? 5B 0 Bro Good Good Normal 22-May-82
1984 +92 -17 5B 0 Bro Good Good Normal 26-May-84
1984 Car Good Good Normal 01-Jun-84
1985 +90 -14 5A 0 Car Good Good Normal 24-May-85
1985 +?? -05 5B 6780 Bro Good Good Normal 20-May-85
1986 Hyi Good Good Normal
1987 +95 -08 6A 0 Fal Good Good Normal 18-May-87
1987 +?? -?? 5B 0 Bro Good Good Normal 24-May-87
Apple Blossom {Rhodo
1985 +97 -05 6A 0 Fal Good Good Some Damage 20-May-85
1987 +95 -08 6A 0 Fal Good Good Normal Snow 23-May-87

Testing Real Conditions
The chapter has made a terrific beginning; we should soon have enough information to provide a good idea as to how particular rhododendrons are likely to perform in various New England areas. We all recognize of course that every planting situation includes indefinable conditions such as micro-climes, soil conditions, etc., that affect performance. But on the other hand, even these problems are far more controllable than the weather - and they are real conditions in real gardens. Thus our information should be more indicative of real life than a "test garden". Regardless of how well planned and cared for, a test garden is bound to be artificial - and it can only provide data on plants growing at that particular site. The idea behind this evaluation program is to enable us to select those rhododendrons that are the most likely to perform well in ordinary gardens cared for by ordinary people.
Several members first reported on their plants in 1982 and thus started what is hoped will long continue to be a chapter project. Over the years some members reported only once, some did not report all the requested data and others reported fully nearly every year. Though regular, complete reports are the most valuable, irregular reporting does not of itself create a problem since all data, if good, adds to the data base. Thus even if skimpy, the more data we have on a particular cultivar or species the better the picture over a period of time of how it performs under varying conditions. Lack of a particular bit of information on an individual report merely means that it will take us longer to get a good overall picture of how that particular cultivar (or species) performs under given conditions.

Peak Bloom Analysis
A very interesting aspect of the evaluation is the peak bloom analysis. Reading the flowering dates gives an uncanny sense of spring moving north across New England. Thus plants of the same variety tend to bloom 10 to 14 days later here in New Hampshire than they do on Cape Cod. It also shows the warming trend of our recent winters. All across New England flowering has moved up a week or more earlier than it used to be; for me it's more like two weeks. "Annual degree days" data should help us to better analyze this situation. Though you may wish to draw your own conclusion, this seems to me to settle the argument sometimes heard as to what is the major determinant of bloom date. To me it seems clear it is winter temperature.
All in all we now have some 1400+ reports on over 500 different species and cultivars. For some we of course have reports for only a single location for a single year. On the other hand for others we already have enough data to begin to see a pattern.
To me, the real surprise is the number of cultivars and species that are grown by only one reporting member - over 300 out of the 530 reported on. On reflection, though, this wide variety should be expected. Clearly it reflects the wide area - weatherwise covered by the chapter plus the wide diversity of interests among the members. From Zone 7 on the south to Zone 4A in the north is a truly wide range weatherwise - without doubt a far greater range than that experienced by most chapters.
Not too surprisingly, no matter how warm or how cold the area in which members live, nearly everyone seems to try to grow something that is just not quite hardy there. Thus we are collecting data on that marginal hardiness of many plants even in the warmest of winters. I suspect that if more members were to report we'd have even more marginal performance data (and an even greater diversity) than the report now shows.