Many gardeners as well as hybridizers are really passionate about double daylilies. In fact, the additional petals as well as petaloids of double daylilies contribute to the sense of completeness and depth of the blooms, thereby creating an exquisiteness that has captured the hearts and imagination of flower lovers and breeders alike. Similar to the double flowers of other genera, this type of large and complete flower form gives a new dimension; in addition to an entirely new look to these flowers. However, double daylilies are in no way a new form of the flower. Plants belonging to the Hemerocallis species that are found growing naturally in China include H. fulva "Flore Pleno" and H. fulva var. kwanso - both double daylily varieties. Nevertheless, it is really unfortunate that these flowers are basically triploids. This means that these plants are sterile and, hence, cannot be used for developing modern hybrids. It is worth mentioning here that the hybrid double daylily was actually developed from single daylilies, which had double tissue at one time. These double daylilies, usually only partially-double, started in the form of flowers with narrow petals, but no ruffling. However, the hybridizers continued working on them to improve the form of the doubles. As a result, new flowers came into existence. These flowers not only have broader petals, but they are also ruffled. This gave the flowers a more complete look. Following several generations of double breeding, the flowers become further consistent and entirely double. The double tetraploid daylilies came into existence during the 1980s and 1990s. These flowers have relatively heavier substance and come in brighter and clearer hues. Similar to tetraploid singles, in the beginning the tetraploid double daylilies also did not exist that would enable breeders to work with. Therefore, the first task before them was to create tetraploid doubles. This took a lot of effort and was certainly a very slow and ardous work.
One does not need to have knowledge regarding the intricacies of the form of double daylilies to simple value their wonderful beauty. Nevertheless, one will be able to appreciate the double daylilies better when they have a perception regarding the manner in which they have been created. The double daylily flower is rather complex and changing all the times. Hence, it is certainly worthwhile to stop by for a few minutes and examine the nature of these blooms. Endeavours to understand as well as classify the forms of double daylilies are not something new. Over the years, dissimilar terms have been used by different people to describe the daylily varieties. In 1945, A. B. Stout brought out a catalogue in Herbertia describing the different forms of double daylilies that he observed alongside some suggested names for those double daylily forms. Although over half a century has passed since then, some of the terms suggested by Stout are still in use today. However, as of now, no standard means to classify double daylilies has been agreed upon. As discussed above, double daylilies have been developed from the single daylilies. A standard single daylily flower comes with three petals, three sepals, and six stamens. In fact, daylily flowers are composed of four layers or whorls - sepals, petals, stamens and the pistil. The perfect technique to develop a double daylily bloom is to add additional layers to the petal whorls, thereby creating several petal layers. Contrary to this, majority of the double daylilies have been developed by transforming the stamens of the single daylilies. Nearly all double daylilies are developed by means of petaloid formation. While they appear to be additional petals of a bloom, petaloids are actually stamens having additional tissue the length of their sides. There are some double daylily flowers that only add tissue on one plane of the stamen. These petaloids can be recognized easily as transformed stamens. On the other hand, there are flowers that add tissues to both the sides of the stamen. Petaloids of the second type of double daylily flowers have resemblance to true petals. However, one can recognize them as petaloids, as they usually continue to have the anther (also known as the pollen sac) on them. Occasionally, the anther is underdeveloped or even may not exist. In such cases, the petaloid has the appearance of a standard petal. As petaloids are developed from the tissue of the stamens and daylilies usually have just six stamens, the maximum number of petaloids a daylily can possess is also six. In case a daylily flower has fewer than six petaloids, the other stamens will be regular and the bloom will appear to be semi-double. In fact, double blooms of nearly all other genera comprise additional strata of true petals and not just modified stamens. In addition, they also have in excess of six additional petals. Therefore, we can see that daylilies are certainly different from the double flowers of most genera. While most double daylily flowers add additional tissue to the side of their stamens, there are a number of blooms of this species that add tissue to the petaloid's midrib. Usually, the midrib tissue develops outward and upward from the middle of the petaloid, thereby bearing resemblance to a butterfly's wings. Moreover, the form or shape of the midrib tissue can also be different in different flowers. While some petaloids possess just a solitary wing, many of them have double wings. Sometimes, each separate wing may develop as two parallel tissue layers. When the daylilies add tissue to the midrib of their stamens, they seem to have many additional petals. This gives the bloom fullness, especially when the tissue turns out to be large as well as ruffled. Then again, a number of "apparently single" daylily blooms, which have just three petals, may also have additional tissue arising upward from the petals' midrib - something similar to the additional tissue on the petaloids. This type of formation has resulted in some sort of disagreements regarding whether these blooms ought to be classified as single daylilies or double daylilies. In any case, currently, flowers with this type of formation are known as "midrib doubles". Many people maintain that such type of daylilies is single, as they only contain three true petals. There are several others who assert that if it is possible to create doubles by developing petaloid tissue from the stamens, it is also possible to produce double daylilies by developing petaloid tissue from the petals. Hence, midrib double daylilies are basically blooms with just three true petals having additional tissues that have developed from or fused to the midrib of those three petals. Usually, this tissue develops from the centre of the regular petals at angles ranging from 45 degrees to 90 degrees, thereby bearing resemblance to the wings of a butterfly. In fact, the midrib tissue can develop on any of the three true petals of a single daylily flower or form on the petaloids' midrib. This is an indication of the fact that this aspect is a hereditary attribute in daylily flowers, which is potentially separate as well as distinct for the development of additional petals or petaloids derived from stamens. However, this is completely different from adding additional regular petals to form a double daylily flower. Blooms having additional true petals, which are referred to as supernumerary doubles or occasionally called "super-doubles", are actually very unusual in daylilies. In fact, supernumerary double daylilies are very different from the type of doubles we discussed above. These flowers pile on extra petal layers and also retain their regular stamens. Typically, supernumerary doubles comprise nine petals, six additional, together with the normal six stamens. As these doubles retain their regular stamens together, these flowers possess the potential of modifying their regular stamens into petaloids. In such instances, this type of daylily blooms will comprise nine petals, three in each layer, in addition to six petaloids. This makes them look magnificent, altogether having 15 colored sections. Different from petaloids, whose number never exceeds six, the number of additional true petals in a double daylily can actually be infinite. Hypothetically speaking, it is possible to have several petal layers stacked up to produce a double daylily bloom having the number of petals in a rose or camellia. In fact the sterile Hemerocallis fulva var. kwanso as well as the H. fulva "Flore Pleno" are both supernumerary daylilies each having several layers of true petals. However, majority of daylily enthusiasts are of the view that plants of this species do not posses the exquisite beauty of the contemporary hybrids. On the other hand, they do possess the form that is yet to be accomplished by hybridizers in the modern daylilies. Nevertheless, following several decades of hard work, hybridizers are now starting to create supernumerary double daylilies. This, in fact, is paving the path to an area for advanced daylily breeding. Classification of double daylilies can also be done as per the form of their additional petals or petaloids. The two main double daylily groups comprise the peony types and the hose-in-hose varieties. The second variety comprises flowers which have petals or petaloids that lie in horizontal layers, bearing resemblance to the appearance of extra regular petals. In fact, this form gives the double daylily a look that is akin to that of a completely opened rose or camellia. If the flower has any petaloids, generally they are full and not semi- or half petaloids. In addition, these petaloids do not have any midrib tissue formation. In other double daylilies, the petaloids usually emerge from the middle of the flower and point outwards similar to stamens. This particular form of petaloids is called cockatoo or peony. The petaloids in this form of doubles may either be full or half. In addition, such petaloids may or may not possess midrib tissue. However, it is advisable that your perception regarding double daylily forms should never be very rigid. In fact, the double daylily's form can differ from one day to another in a particular cultivar and also on a single plant. Precisely speaking, latest forms of double daylilies are emerging continuously. Moreover, there are several daylily cultivars that not only produce double blooms, but also bear single flowers, especially during the start of their flowering season. It has been found that the extent to which a particular cultivar can double largely depends of the temperature prevailing at the place where they are being grown. Several daylily cultivars bear single blooms when grown in cool weather, but produce double flowers very often when the weather warms up.