Bloom Date Project
This page provides links to various formats of the 2012 Bloom Sequence data set. This data combines the data from Reverend Miller, the Heartland Peony Society and more recent data collected by Michael Denny.
The links to Alphabetic Sort and Bloom Sequence Sort will take you to web pages with the data listed in either alphabetical order or by bloom sequence.
All bloom times are listed with respect to Red Charm. Red Charm is said to bloom at time zero and the bloom time of all other peonies is given relative to this time. This is the number contained in the offset column.
For example, the entry for Alexander Woollcott shows that from the 17 observations recorded (#obs = 17), Alexander Woollcott blooms 4 days (offset = 4) after Red Charm (offset = 0).
The data should be used as a guide in considering when a cultivar will bloom. There is a danger that the offset will seem too precise and consequentialy will mis-lead. Annual weather variations will change the exact number of days that a cultivar will bloom before or after Red Charm. Caution is particularly needed for cultivars with only one observation. As we obtain more observations we will update and improve the data in the current tables.
Note: The following tables are large and may take some time to download.
Data by Alphabetic Cultivar/Species Name
Data by Bloom Sequence
A .csv file is also available via the following link for anyone who wishes to import the data into a spreadsheet application such as Excel.
Download .csv file
Bloom Date Project
Seven Weeks of Bloom
As an alternative to poring over the actual peony bloom time data, some summary information is presented here without all of the details. The article is organized around the idea that the peony enthusiast can have seven weeks of bloom. Not many of us will choose to plant for all seven weeks but it is very easy to obtain four or five weeks of bloom.
Table 1 provides information on the distribution of cultivars by the weeks in which they first bloom. I took all the cultivars in the bloom data and asked what percent start to bloom in week one, week two etc. The answer is in the Table below.
Our data does not contain every cultivar but I believe that the distribution of blooming time shown in Table 1 is a reasonable approximation to the cultivars that are currently commercially available. I have no way to prove that my belief is correct and you should keep this limitation in mind. If one considers the set of all named cultivars (whether in commerce or not), my belief would change.
There are many more older lactifloras that are not currently available and this would change the distribution. The percentages in Weeks Five and Six, and perhaps Seven would be even larger. The percentages in the other weeks would fall although the pattern, a slow increase across the early weeks, would not change.
There is a huge peak in Week Five when almost one-half of the cultivars start to bloom. In addition, there are many cultivars that begin to bloom in the week preceding and the week after the Peak Week. These three weeks, Weeks Four, Five and Six, contain about 85% of the cultivars and represent the common blooming period that we are all used to enjoying.
If one wants a very long peony season, one has to select the early blooming varieties. There are three weeks of possible bloom before Week Four and only one week after Week Six. It is the long early bloom period that is attractive to peony enthusiasts.
In Southern Ontario, where I live, the peak, Week Five, would be about June 4th to 10th. These dates will vary with your location. Colder locations will have to wait a little longer and warmer location will see the peak earlier. Week Two will begin here about mid-May.
For each of the seven weeks, I will provide some examples of the cultivars that bloom during this period. The selections are biassed towards cultivars that are available and that perform well.
Table 2 provides examples for the first three weeks. Week One belongs to the species. These are not as widely available in Canada as in Europe but can be found. At the very end of this week, the Fernleaf peony and its hybrids, e.g. 'Little Red Gem' will begin to bloom.. A small number of Saunders' hybrids, such as 'Nova' will also bloom in Week One
|P. caucasica||Starlight||Claire de Lune|
|P. peregrina||Early Scout||Illini Belle|
|Little Red Gem||Laddie||Early Glow|
|P. tenuifolia||Yachiyo-tsubaki (TP)||Hana Kisoi (TP)|
Week Two continues with further hybrids of the Fernleaf peony, for example, 'Early Scout' and 'Laddie', P. Officinalis and its hybrids also begin to bloom in this week along with more of Saunders Hybrids.
Although our information on bloom dates for tree peonies is very limited, some tree peonies will begin to bloom in Week Two and one example is given in Table 2.
The bulk of the tree peonies will bloom in Weeks Three and Four with a few starting in Week Five. Because our data is so limited, we will not discuss tree peonies in any detail.
The volume of hybrid cultivars increases substantially in Week Three. There are now more gorgeous semi-doubles to accompany the singles. There are still no lactifloras but there are many hybrid varieties from which to choose. A few examples are shown in Table 2.
In Table 3, we provide a few examples of the cultivars that begin to bloom in Weeks Four and Five. The hybrids continue to dominate in Week Four although the earliest lactifloras will start to bloom by the end of this week.
|Scarlet O'Hara||M. Jules Elie||Coral Charm|
|Moonrise||Diana Parks||Festiva Maxima|
|Red Charm||Miss America||Red Grace|
|Richard Carvel||Sea Shell||Mother's Choice|
|Mme de Verneville||Mrs. F.D. Roosevelt||Gardenia|
The choice of cultivars is very large in Week Four and even larger in Week Five. Almost one in six cultivars begins to bloom in Week Four and almost one in two in Week Five. In Table 3, I have used two columns for Week Five to increase the number of examples. These twelve cultivars are only a tiny portion of the more than 300 cultivars in our data that will begin their blooming in Week Five.
Week Six continues to offer a very large range of choice of lactifloras. A few of these are shown in Table 4.
|Sarah Bernhardt||Marie Lemoine|
|Martha Bulloch||Marilla Beauty|
|Nick Shaylor||Myrtle Gentry|
|Shaylor's Sunburst||Glory Hallelujah|
Many of the best known Japanese form peonies will bloom in this week. If one wants to have some contrast in flower form, it will be these Japanese that offset the numerous doubles in bloom.
There may only be only six and one-half weeks of bloom. Very few cultivars reliably bloom in Week Seven. You may find, as I have, that cultivars listed in Week Six bloom later than some of those listed for Week Seven. The late blooming cultivars are all sensitive to the weather patterns in a given year. If summer heat arrives early, many of the cultivars in Weeks Five, Six and Seven may open very close together. With a gentler climate or a slow onset of summer many of us can enjoy a longer period of bloom as shown in Table 4.
There are distinct temporal patterns for the different flower forms, single, Japanese, double etc. During the peak Week Five almost all flower forms are widely available.
In our data, about 47 percent of the cultivars are Doubles, 25 percent Single, 14 percent are Japanese and 14 percent are Semi-Double.
Single blooms start the peony season and are very dominant in Weeks One and Two. Even in Week Three they are the most common bloom type.
At the other end of the season, there are no singles in Week Seven and very few in Week Six. This flower form is still widely available in Weeks Four and Five.
Just as the singles become rarer, the next form begins to bloom. The Japanese have perhaps the shortest or most compact bloom period.. There are no Japanese cultivars in the first three Weeks and only a few in Week Four, for example, 'Jewel'.
Japanese cultivars are concentrated in Weeks Five and Six. There are no very late blooming Japanese cultivars in Week Seven. Examples of the latest blooming Japanese cultivars are 'Barrington Belle', 'Shaylor's Sunburst' and 'Sword Dance'.
Semi-Double cultivars span a longer bloom period than the Japanese cultivars. There are many early hybrid Semi-Double cultivars whereas there are almost no Japanese hybrids - 'Jewel' and 'Walter Mains' are hybrid Japanese exceptions.
In Weeks One and Two, Semi-Double cultivars are rare but not unknown. It is the hybrid semi-doubles of Weeks Three and particularly Week Four that form the most important season for this bloom type. There are almost no Japanese hybrids and in contrast there are relatively few Semi-Double lactifloras. There are some, but Semi-Doubles are rare in Weeks Six and none bloom in Week Seven..
The most numerous flower type are Doubles. These are scarce during the first two weeks. The exceptions are 'P officinalis. A few more start to bloom in Week Three but these are uncommon cultivars that are not readily available.
The Doubles take over in Week Four and provide much of the bloom for the remainder of the season. In the last two weeks, the predominant forms will be the Japanese and the Doubles.
In my garden, I have the impression that the passage of time brings a change in the predominance of different bloom colours. This may reflect my choice of cultivars. I looked at the data to see if my impression could be supported by evidence. In general, the answer is no or that the evidence is quite limited.
Hybrids and Lactifloras
The term hybrid peony conjures up images of vivid colours and early blooming. As noted above, the hybrids (and species) dominate the season from Week One through Week Four. The lactifloras take over and carry most of the bloom for the last three weeks.
During Week Five, the hybrids continue to offer their vivid colours although numerically they are dominated by the lactifloras. During this week, most of the coral hybrids bloom as well as some Double and Japanese hybrids.
By Week Six, the hybrids are finished and the lactifloras carry on for the remainder of the season.
This brief summary can not convey the range of choice available. There is a definite bloom peak and if one grows very few peonies there are excellent choices at the peak times. As one grows more peonies, it is worth considering more of the early hybrids and species both for their vibrant colours and for the increase in the length of the peony season.
Bloom Date Project
This Bloom Date Project is an attempt to clarify what we know and more importantly, do not know about the blooming pattern of peonies. This is a long run project to which I hope many will contribute.
For the peony buyer, it would be better if nurseries had a common bloom period classification system. Currently, buyers will find the same cultivar classified as mid season in one catalogue and early in another. This problem carries over to peony books. If the author gathered information about bloom time from a number of sources, it is very likely that the different sources use different classification systems.
By collecting data over a long period of time and in several different locations, this project attempts to make available the information required to put in place a common bloom period classification system.
Bloom Date Project
In the past peony bloom dates have been collected by many people. To my knowledge, previous to this project, there have been two major attempts at collecting/consolidating and publishing data over a large number of cultivars. To this we can add the body of information published in nursery catalogues.
The Miller Data
Rev Floyd Miller collected bloom dates for 200 cultivars at Fergus Falls, Minnesota from 1963 to 1975. The location is 140 miles West and 80 miles North of Minneapolis.
The Miller data has two strengths. The first is the use of 13 years of data. The second is the evidence on many older American lactiflora cultivars. It is unlikely that we will find new evidence on these older American cultivars. The Nichols Arboretum has many early American lactifloras but they do not have the staff to collect bloom data.
As presented on pages 191-2 of the APS, Best of 75 Years, the Miller data is a single date for each cultivar. The data is not a simple average of the actual observations but appears to be a median rather than a mean. A median date has an equal number of bloom dates before and after. It will differ from a mean, or simple average, date but probably not by more than one or two days.
The Heartland Peony Society Data
Leon Presnell compiled bloom sequence data and placed it on the Heartland Peony Society web site. This is the most comprehensive list of bloom dates available. There are about 440 cultivars and 1300 observations in the Pesnell data.
Nursery catalogues provide information on the bloom time for cultivars that they sell. They all do this using variants of a classification system that designates a cultivar as an early, middle or late bloomer. Many use a more complex system that includes very early, very late and some intermediate cases such as early-middle or mid-late. Don Hollingsworth of Hollingsworth Nursery has one of the more complex systems while Klehm's Song Sparrow has a relatively simple one.
I constructed some tables that compared the blooming period category given in catalogues from Klehm's Song Sparrow, Wilds, Hollingsworth Nursery and La Pivoinerie D'Aoust with the bloom data. It is not surprising that there is rough general agreement between the nurseries and the bloom data. There are however some definite disagreements which need further investigation.
Al Rogers in his book "Peonies" is very careful to exclude the bloom period for the cultivars in his longer lists because he recognizes that there is no common source of information.
Lindsay D'Aoust of La Pivoinerie D'Aoust and I have discussed trying to create a common classification system. Personally, I favour a system with five groups or categories, VE, E, M, L and VL. A new common classification system is important because it is not likely that nurseries will ever use a system such as the Red Charm relative dates. The basic weakness of any classification scheme is that some cultivars will bloom near the boundaries of the groups.
Recent Canadian and American Data
New bloom data has been collected and organized by myself, Michael Denny from observations in 1999 to 2003. This adds about 1200 new observations. Bloom data was collected by Brian Porter, Carlos Beca, Lindsay D'Aoust, Leo Smit, Julia Dicks, Val Ames and Irene Tolomeo. I added my own data and organized the information. Some of the data are for years prior to 1999. In particular, Julia and Brian had observations over a number of prior years.
I am hoping that everyone who contributed data in the past will continue to collect bloom dates in 2011 and beyond.
In our current data, we are measuring the bloom dates relative to the bloom dates of Red Charm. This is an attempt to adjust for different bloom dates for a given cultivar at the same location in different years and at different locations in the same and in different years. It is a relatively crude adjustment but will remain in use until we devise a better one.
Our objective is to provide reliable information on the bloom sequence of peonies. The simplest method would be to construct a ranked list of cultivars starting with the earliest bloomers and moving on to the later ones. Such a ranked list is simpler than our current methods because no information is provided about the period of time between the blooming of each cultivar.
We have evidence that even a ranked list is not totally reliable. We have data over a number of years from several gardens and the ranking by bloom time is not identical from one year to the next. This should not deter us from our task but it should warn us that the bloom sequence data that we create has to be used as a valuable guide and it should not be interpreted too literally.
Climate variations are likely the major source of variations in bloom dates. However there is a mystery because some cultivars seem to be affected to a different extent than others by the same weather variation. If this were not true, we would not see the rankings change in the same garden in different years. This is not a simple story of hybrids versus lactifloras but seems to occur for both groups.
Heat is probably the most important variable in explaining the variation in bloom time. In agriculture and the building industry, there has been wide- spread use of degree days. Degree days are a simple transformation of the average daily temperature. For example suppose we believe that it is the temperature above 40F that is important. Then the number of degree days for a day with an average of 60F is 20 ( = 60 - 40) degree days. There are many variants of degree days because one can choose the base temperature (40F in my example) to suit the problem of interest. We will probably want to create our own degree day measure from data on daily maximum and minimum temperature.
When this evidence is available, it would allow us to assess the influence of heat on the bloom sequence. One of the open questions is whether degree days is enough information to explain most of what is happening. If it is, there is less of a role for moisture and soil conditions. The latter may be important but I am hoping that it is temperature that is the major source of variations in the bloom dates.
What is Missing?
We have very limited information on the bloom times for tree peonies and for the peony species. In both cases, far fewer peony enthusiasts grow the plants. Over time, I hope that we can improve this situation.
For the lactifloras and hybrids the current data is more extensive. What we need is more years of observations from more locations and additional cultivars.
Finally, there are many common cultivars for which we have no bloom date observations.
Public Gardens that Grow Peonies
This is a list of public gardens that grow peonies (20 cultivars or more). This information would be valuable if you are traveling and would like to find a public garden to visit on your trip. You may also discover some new gardens not too far from where you live to visit. If you know of a botanical garden, arboretum, or public garden near you that grows a collection of peonies, please contact us so we can add it to our listing.