Tuesday, December 23, 2014

Foliage Habits of Daylilies

Foliage Habits of Daylilies

Brian Reeder

Foliage habit is an interesting subject that I often spend a lot of time thinking about at this time of the year. I am in my garden every day, regardless of the cold or weather, as I have to feed and water my birds and that allows me to make observations of foliage type throughout the winter months.

An evergreen cultivar on the left and a true dormant cultivar on the right from my garden on 12/18/2014

To start this article, let’s look at how the AHS defines the foliage categories. From the AHS FAQ page we find the following:

What are the foliage traits of daylilies?

Foliage traits of daylilies include color, size, habit, and cold-hardiness and heat-tolerance.

The foliage of daylilies can be blue-green to yellow-green or any shade in between.

Daylily leaves vary considerably from slender and grass-like to husky, wide, and nearly corn-like. The leaves may arch, or may stand nearly erect. The length of daylily leaves ranges from as little as 6 inches to 36 inches or more.

The winter behavior of the daylily foliage is called "the foliage habit." For registration purposes, the foliage habit is loosely categorized as dormant, evergreen, and semi-evergreen.

  • Dormant. The leaves of these daylilies die completely back as winter approaches. They stop growing and form resting buds at the crown, and the foliage dies down naturally and gradually. In the spring, the resting buds have a distinctive spear-like appearance as they emerge.
  • Evergreen. These daylilies retain their leaves throughout the year. They do not form resting buds. Instead, they continually produce new leaves unless cold weather prevents growth. In mild climates, the leaves of evergreens remain green all winter. In the coldest climates, the foliage of evergreens nearly always is frozen back, but the crown survives if it is hardy (or well mulched).
  • Semi-Evergreen. Today, the term semi-evergreen is used to describe any foliage behavior that is not readily classed as simple evergreen or dormant. Originally, the term semi-evergreen (or conversely, semi-dormant) was used to describe those daylilies that retained many of its leaves and appeared somewhat evergreen when grown in the South, but lost all its leaves and went dormant when grown in the North.

Cold-Hardiness and Heat-Tolerance
The cold-hardiness of daylilies is quite variable. Some are ironclad hardy. Others are extremely tender. Cold-hardiness is not determined by the foliage habit. Evergreen, dormant, and semi-evergreen can be anything from extremely cold hardy to extremely tender. To avoid risk of losing a cultivar, choose daylilies that others have already grown successfully in your climate.
I think this is a very good description of the three foliage habit registration categories. I agree with the definition of dormant and evergreen and I think the description of semi-evergreen is particularly good in that it acknowledges this category as basically a catchall for anything that is not a true dormant or extreme evergreen. Further, the difference between foliage type and cold hardiness is defined.

It is a common habit of humans to generalize, and so we often hear generalizations such as ‘all evergreens are tender’ or ‘all dormants are cold hardy’, but these generalizations are not always true. There are cold hardy evergreens and tender dormants. It is important to remember this. At this point, the genes of the original species are so blended and recombined that almost any combination is possible.

I would also point out that in truth the semi-evergreen category is something of a generalization. There really is no such thing as a ‘semi-evergreen’ speaking from a genetic standpoint, though I don’t blame the AHS for using the category. It is a convenient generalization that is useful for registry and can encompass all the in-betweens in one classification. The only problem I see with the classification is that a lot of people seem to think it is a real thing that is absolutely definable, rather than a broad category with a lot of variation.

On the left is a clump of Ancient Elf, a true, hard dormant photographed in my garden on 12/18/14. It almost appears that there is nothing there and if you dig through it, the resting buds are almost completely underground. On the right is the same clump in bloom summer 2014.

In truth, there are only two foliage habits - dormant or evergreen. Anything that does not go completely dormant in the winter is an evergreen, technically speaking, though the 'evergreen' range is very variable. However, as daylily cultivars are hybrids of several wild species of daylily, the genes of those species are recombined into unique combinations in the hybrids and expressions that are not seen in the species can occur.

Those cultivars that we call semi-evergreen are likely the expression of both evergreen and dormant genes interacting within the one genome. It is highly unlikely that single genes control all foliage habits amongst the species and so there are probably major genes and minor genes (or modifier genes) at work to create the foliage habit expressions we see in the species and their hybrid descendants. It is generally accepted that evergreen foliage habit is dominant to dormant foliage habit (likely the action of some of  the ‘major’ genes).

So a semi-evergreen may be a heterozygote for both types of major genes with evergreen habit predominating but not fully expressing (this could also be due to a dosage effect), or we may see some instances where a homozygote for evergreen also has one or more modifier genes coming from dormant ancestors and thus don’t express the evergreen genes fully. There are also likely combinations of both examples. As well, there are undoubtedly homozygous dormant cultivars that have some evergreen modifiers and so are something of a ’semi-dormant’, being far closer to a dormant than anything else, but not a real, true, hard dormant. These frequently (though not always) get registered as ‘dormant’.

A true evergreen seedling (Substantial Evidence x Kaleidoscopic Intrigue) in my garden photographed on 12/18/2014

However, to fully understand the foliage habit of daylilies, it is important to give some consideration to the species from which they all derive. There are dormant and evergreen species amongst the Hemerocallis genus. The dormant species are mainly true dormants that perfectly fit the description for dormant as per the AHS. An example of this type is H. dumortieri.

The evergreens however, are a different matter. They are much more variable, ranging from the tender and fully evergreen H. aurantiaca and its clone Major to the group that I would consider ‘conditional evergreens’ such as the many clones of H. fulva, H. citrina. In these later species the foliage is usually evergreen in warm winter climates while going dormant in cold winter climates. It is also interesting to note the AHS description of semi-evergreen says this type of habit was the old definition of semi-evergreen. A few clones of some of the species can actually maintain evergreen foliage while forming a resting bud in cold climates. The fulva clone Chengtu is an example. 

Even in Stout's day, when they were only dealing with species and the very earliest diploid hybrids, it was noted that some of the evergreen species could not survive in the north, or did very poorly.

From Daylilies by A. B. Stout 1934, regarding Winter Injury on page 99 of the 1986 edition - "In the northern part of the United States and further north daylilies which have evergreen habit of growth usually suffer to some extent from winter injury...In the region about New York there is usually a protection of snow for only a small part of the winter and there is an alternation of freezing and thawing temperatures. When spring arrives many of the exposed leaves have been killed and some buds may be dead... The H. aurantiaca clone Major suffers so severely from winter injury that is usually does not survive the winter throughout the northern United States. Many seedlings obtained by hybridizing H aurantiaca and (its clone) Major with more hardy daylilies are not fully hardy."

On page 100 in the section 'In semi-tropical and tropical countries', he states, "In the southern states the types and varieties which are evergreen or nearly so, are said to be most satisfactory."

So from the very beginning, there was a noticeable difference in the most hardy, dormant species and the most tender of the evergreen species, with some evergreen species being impossible or nearly impossible to grown in the north. This is just a fact of the evolution of the species in their native ranges in Asia. We can't expect that all evergreen cultivars, descending from those semi-tropical evergreen species, are going to suddenly 'get hardy'. Some evergreen cultivars are very hardy, and probably due to cold hardy dormant species deep in their ancestries or from the presence of hardy types of evergreens such as H. fulva or H. citrina in their background. Others are not hardy and that has a lot to do with the genes they have inherited from tender evergreen species in their backgrounds.

Because there are different variations of evergreen foliage habit amongst the species, as well as the true dormants, and crossing these species widely made the hybrid cultivars, we have an even wider array of foliage habit expression in the hybrids than we do in the species. Some of our cultivars perform exactly as the species do in regards to foliage habit, but some fall in-between their species ancestors.

Foliage habit, in and of itself, does not touch directly on the subject of cold hardiness, as the AHS text above points out very well. Cold hardiness seems to be determined by genes other than those that determine the foliage habit, though those genes would also derive from the wild species in the ancestry of the hybrids. While it is true that there are hardy evergreen cultivars, it is also true that some evergreen cultivars will not perform at their maximum capacity in areas of cold weather due to the stress they must endure through the cold months of winter, even though they survive from year to year and bloom. An example of such suppressed performance would be reduced branching and bud counts or scape heights. There are however some evergreen cultivars that simply won’t survive in northern climates.

In my own experience with around 800 cultivars, I have only lost a tiny handful of evergreen cultivars outright to cold. What I see more frequently is suppressed performance, occasional loss of a few fans, reduced branching, bud counts and scape height. Because I am in an area that can be very cold or very warm in the winter, each year can be variable. However, my area almost never has the snow cover that more northern areas benefit from and so some evergreen cultivars are hardier both further north and further south than they are in my Kentucky garden. This can come as quite a surprise to folks not familiar with our variable winter weather and late, often devastating frosts.

A particularly bad combination here is cultivars that are evergreen and are early-early blooming. We frequently have late frosts, but we may get very warm as early as March and have full growth very early with scapes beginning to form on the earliest flowering cultivars by the beginning of May. When those late April and early to mid May hard frosts occur, this causes considerable damage to those early blooming evergreens and the entire first round of scapes may be completely destroyed or severally damaged. When those cultivars are also rebloomers, then the later bloom scapes will be fine, but for those first ones these late frosts are a disaster. There are very few years when we don’t have an episode of late frosts, so this damage is something I see almost every year. I do want to stress though that this does not mean these are ‘bad’ plants. I fully understand why the early-early evergreen cultivars are very desirable in more southern settings. They just aren’t the most suitable cultivars for my climate. In spite of that, I am still using some of these, especially strong rebloomers, in my breeding program. I am just careful about what I cross them with.

With that said, though, I want to stress that I buy and grow evergreens, usually bred in the deep south, making them a part of my breeding program and fully intend to keep growing them and breeding from them. While I personally prefer hard dormant cultivars, I want to produce plants that can be grown successfully in climates other than my own, both north and south. Another thing I keep in the back of my mind is that one can never tell how the climate may change over time and should we become warmer and warmer, hard dormants may start to be less viable here than the more evergreen cultivars. No one can know what will happen, and I certainly don’t claim to know, but I like to be prepared for all eventualities. Another thing that I take into consideration is that there is generally more information on the rust resistance of plants bred in the south than there is for plants bred in the north.

In my own garden there are very successful evergreens. I have grown Nivia Guest, for example, for over twenty years and it has never shown any problems. I would also point out that it is not a very early blooming cultivar, so I think this helps make it more successful as a garden flower, but the plant never reduces in fan count here in even the coldest winters. Other evergreens don’t do as well, and a few do really poorly, decreasing every year and showing infrequent bloom scapes only after the very mildest winters. However, some of these are still a part of my breeding program, even if only in a very limited way.

There are many reasons to use these cultivars. The southern breeders can go through their generations much faster than most of us in the north can (except perhaps where greenhouses are used in the north), and so the southern breeders are almost always ahead of everyone else in terms of flower trait advancements. Those advanced flower genetics are reason enough alone, but there are also other reasons. For me, the known rust resistance of some cultivars from the south is a huge necessity, as most northern growers can’t test for rust resistance so the results of their programs are far too often an unknown quantity. Finally, using the southern evergreens over northern dormants can often produce both foliage types, as well as the in-betweens so plants can be produced that may flourish in the south or in the north, and sometimes you get lucky and get a plant that flourishes in both extremes. Using the southern evergreens over northern dormants is a long-practiced, tried-and-true method. Just look to Curt Hanson’s amazing program if you need an example.

I have some evergreens here that survive (though certainly don’t flourish) and set seeds well, but their seedlings have very poor survivability through the winter in my environment. Those few that make it through though are often well worth the effort and usually continue to show hardiness. A technique I have found that is giving me some success is to use the pollen of these more tender evergreens on hard dormants that are very cold hardy to produce seedlings that seem to survive more frequently. Often all the seedlings are somewhere in the semi-evergreen category, but they may be more hardy and can often throw dormant offspring when backcrossed to other dormants.

I have no peer reviewed proof on this technique, and so far this is only my anecdotal experience, but it seems that when I take one of these more tender cultivar's pollen over a very hardy dormant as pod parent, I get better survival rates in the seedlings than I do if I make the reverse (reciprocal) cross. This may not prove to be true in all cases, but so far, this seems to be the most successful route in getting hardier seedlings from these more tender cultivars in my breeding program.

Now I want to turn to another aspect of foliage type. It is important to remember, especially for beginners, that all plants registered as a given foliage type may not always be that foliage type. Sometimes it is that a cultivar performs differently in your garden than it did in the hybridizer’s garden. Sometimes a seedling gets labeled wrong or information gets mixed up in the registration process. I don’t like to think that anyone is intentionally falsifying foliage habit for whatever advantage they may assume they get from doing that, but it is not outside the realm of possibility I suppose. I never assume that is the case though as I always give people the benefit of the doubt.

An interesting example - the cultivar on the right is a registered dormant, while the cultivar in the center is a registered semi-evergreen and the cultivar on the left is a registered evergreen. Can you tell any significant difference between any of them? I can't either... To me, these are all three in the 'semi-evergreen' category, with none being true dormants or true evergreens in my garden.

It is important to remember that there are species that are evergreen in warm winters and dormant in cold winters, and there are cultivars that perform in the same manner. When this happens, it is usually a happy surprise for all concerned, as such a plant registered as dormant by a northern breeder may prove to be evergreen in the south and vice-versa. More often it occurs that plants registered as semi-evergreen or evergreen by a southern breeder may turn out to go dormant when grown in the north. Both Linda Sierra and Priscilla’s Rainbow are examples of semi-evergreen and evergreen cultivars that go dormant in the north.

Priscilla's Rainbow - a registered evergreen that, as you can clearly see, goes dormant in my garden. This one is well known to go dormant in cold climates, but remains evergreen in warm climates. It has very tight resting buds that are mostly underground throughout the winter.

Another registered evergreen that goes dormant in colder climates, Challenger is a Stout cultivar from 1949 that is a blending of H. altissima and H. fulva, both of which show this type of foliage habit being evergreen in warm climates and dormant in cold climates.

What can be less exciting and desirable is when you purchase a ‘dormant’ only to have it prove to be some form of evergreen/semi-evergreen in your garden, if you really wanted a dormant (and I can assume the opposite would be true if you wanted an evergreen, but got a dormant instead). I have heard discussion that there are two types of dormancy - one is alleged to be temperature-triggered dormancy and the other is alleged to be light-triggered dormancy. If this is the case (and there is no solid proof that I know of that it is), perhaps the triggers for dormancy are very different in various areas and so something that goes dormant in one area may not get the right trigger to go dormant in another area. I can’t say, but I don’t want to think people are too fast-and-loose with their observations of the foliage habits of their introductions.

A situation that does raise my eyebrows a bit is when I receive a ‘dormant’ from a breeder in a very similar climate or not too far from me, only to have it remain green here through the winter. Maybe I am just enough further south of the grower, enough warmer, to not trigger full dormancy? I hope that is all it is. I also suspect that some growers have looser definitions of what a dormant is than I do. For me, if there is any green foliage still present during winter, then I don’t consider it a true dormant. One grower sent me a ‘dormant’ that remained fully green all winter, with foliage identical throughout the winter to Great White (an evergreen), which grew directly beside it. That was ok as it was fully hardy and bloomed late enough not to have any problems. I asked the breeder about this and the reply was, “Oh, yes, it remains green, but its leaves don’t grow at all in the winter and it shows resting buds, so it is a dormant.” 

While it is true that the H. fulva clone Chengtu shows leaves that remain green through cold winters yet develops resting buds, the cultivar I am referring to did not show what I would call resting buds, any more than did Great White, growing beside it. If it was a dormant then so was Great White. None of the evergreens growing here in a normal or hard winter grow new leaves (unless we have an occasional warm spell out of season) and a great many of them don’t have nearly as much green foliage above ground as this ‘dormant’ did. Further, it doesn't match the AHS registration definition of a dormant. I don’t grow this one any more because it turned out to be extremely susceptible to rust, but the foliage habit would not have been any deterrent to me buying or using the plant.

Center - a registered 'dormant' that is one of the most evergreen cultivars I am currently growing...

Foliage habit seems to be a continuum, moving from the true, hard dormant all the way to the true evergreen, with a range of variations in-between. For me, and based on the AHS definition of a dormant, it is only those cultivars that go fully dormant that are true dormants. However, there are cultivars that are probably genetically dormant while also having some small amount of modifier genes from evergreen ancestors and are close to the true, hard dormant on the continuum, but don’t express as true, hard dormants in many (most?) environments. These may be what some refer to as ‘semi-dormant’ and to me should be registered as semi-evergreens, rather than dormants, but it seems these frequently get registered as ‘dormant’. When I walk through my garden in the winter, I observe a good many registered ‘dormants’ with a bit of foliage sticking up out of the dead leaves. These are not the resting buds of true dormants, but are small fans with obvious leaves, even though they may be quite small.

Another problem is that in the far north, cultivars will go fully dormant that won’t even this far south, and may be full evergreen in the near tropical south. I always try to bear these many environmentally influenced variations in mind, as I don’t want to think badly of anyone or think anyone is being deceptive, and while that may make me have my head in the sand, it allows me to just shrug it off and move forward. After all, as a breeder, I can always work toward the foliage habit I want in my garden, in my own program.

Another thing that I sometimes hear, but have not observed personally, is there being any direct correlation between foliage habit and foliage quality. I have seen beautiful blue-green foliage on all foliage habits, and I have seen sickly, ugly foliage on all foliage habits. These variations in foliage color/quality seem to have nothing to do with foliage habit and are likely genes separate from the genes controlling foliage habit.

One final point that I want to touch on concerns foliage habit and rust resistance/susceptibility. I have been told by several northern breeders that their cultivars are ‘likely resistant, because they are good hard dormants”, the implication being that only evergreens are rust susceptible. This is absolutely false. There is absolutely no linkage what so ever between foliage habit and rust susceptibility/resistance. I have cultivars of all foliage types that show strong rust resistance, and I have cultivars of all foliage types that show rust susceptibility. I can assure you that foliage habit has nothing to do with this and neither does foliage color or cold-hardiness/tenderness. The genes of resistance/susceptibility are not the same genes as those that determine foliage traits.

I will say that I actually have more highly resistant evergreen and semi-evergreen cultivars than I do resistant dormant cultivars. Again, this has nothing to do with foliage habit. I suspect this is because breeders in the south have had to contend with rust now for over a decade and so they have been able to evaluate cultivars for resistance (so there is some information on these available) and some few breeders in the south have actually been breeding for rust resistance now for a good long while. Conversely, cultivars in the north are not being evaluated for rust resistance with any frequency nor is much selection for rust resistance being done in the north.

In defense of northern breeders, this is understandable, as they don’t have the conditions to evaluate for rust, but it does mean that northern cultivars are thus an unknown quantity in this regard. So my experience points to there possibly being more susceptibility amongst many hardy, northern dormant lines by default, than there is amongst some of the lineages (but certainly not all!) of southern-bred evergreens and semi-evergreens, but this has nothing to do with foliage habit and rather is caused by environmental constraints and chance.

In closing, I would like to encourage people to talk about the subject of foliage habit. I know some people get offended, but these things are just facts. We in colder climates don’t say that some evergreens do poorly, or don’t perform to their full potential, to offend people. Dormancy is not a marketing scam (I have actually been told that!), nor is it an attempt to vilify those breeding evergreens. Every foliage type is important and necessary. Not every plant will prosper in every garden. This is a simple fact of life. Sometimes that is related to their foliage type/cold hardiness, and sometimes it isn’t. When someone in the north relates that a given southern-bred cultivar has done poorly in his or her garden, being harmed or killed in the winter, this is not an attack on the breeder of that plant. If I introduce a hard dormant and a southern grower buys it and it dies, quickly or gradually, I know that many hard dormants often don’t survive in warm areas, so I can’t take that personally. Why should the reverse situation be any any different?

I fully understand why southern breeders focus on evergreen/semi-evergreen foliage and I understand why northerners tend to focus more toward dormants. I don’t in any way blame southern growers for growing and breeding the foliage that works best for them. Why on earth would they not? I grow and breed what works best in my garden, as should everyone else. Further, it seems intuitively obvious to me that no southern breeder can know beyond a shadow of a doubt how any of their introductions will behave in cold climates until they have actually been grown in cold climates in many parts of the continent, and they should be aware that there are instances where a plant is hardier in the far north with constant snow cover all winter than they might be in less cold areas where there is not a constant snow cover and where temperatures can fluctuate a great deal. Conversely, the same can be said for any plant bred in the north in regards to its ability to survive and flourish in the south.

It is only by exchanging information and our experiences that we can start to gather a broad base of information to help people in making proper cultivar choices for their area. I would think this would be important to all of us, because successful gardeners are probably going to stay with it longer than people who constantly have failures due to poor cultivar choices for their area. I hope that this post can help to generate a civil and friendly discussion and that we can share our information and experiences without hurt feelings or angry responses and through that sharing only improve our understanding of, and success with, our beloved daylilies.