Just recently avid peony grower and Canadian Peony Society (CPS) member Michael Denny published the peony bloom time data he has been collecting and collating for the last few years. The data and a complete description of the project can be found at http://bloomdate.paeonia.com

If you grow a few peonies and know what variety they are, the bloom date project needs your help! All we need to know is the date the first flower appeared on each variety you grow. Michael can give you all the details, so if you are willing to donate a few dates to the project please contact him at mjdenny@sympatico.ca

This information in the following article should be of interest to anyone growing peonies who wants to extend the period of time peony flowers are in their garden. Michael maintains that by carefully selecting which peonies you grow (and with a little help from the weather), it is possible to have peonies in bloom for as long as seven weeks.

A fascinating article that will help any gardener trying to decide which peonies to grow!

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Seven Weeks of Bloom

by Michael Denny

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.

Table 1

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

TP = Tree peony

Table 2

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.

Table 3

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.

Table 4

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.

Variations in Bloom Times
Gardeners observe that the dates on which peonies bloom depend on the weather. If the spring is cooler than normal, the peonies will bloom later. If a sudden heat wave arrives then the peonies will rush into bloom.

How much variation occurs from year to year? In particular, how much variation is observed in at a single location. Table 5 below shows the the actual bloom dates for a group cultivars growing at La Pivoinerie D'Aoust in Hudson, Québec..

Table 5

The reader can see that in 2001 the bloom season began as in 2000 but due to unusually high temperatures at the beginning of June many cultivars bloomed as much as 10 days ahead of previous years. The bloom season was contracted by almost two weeks. In 2002 the actual bloom dates returned to the pattern of 2000.

Flower Form
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.

Colour
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.

Concluding Comment
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.

Michael Denny

mjdenny@sympatico.ca

Note:

The above article is a slightly edited reprint of the article Michael published in the CPS Newsletter "C to C" in May 2003.

The bloom date website can be found at http://bloomdate.paeonia.com

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