5-10-5: Peter Zale, Curator of Plants and Plant Breeder at Longwood Gardens
Please introduce yourself.
Peter Zale, Ph.D. Plant breeder, horticulturist, and botanical explorer.
The arts or horticulture?
For me, horticulture, but I certainly appreciate the undeniable relationship between the two. At the time I became interested in plants, I was also very interested in drawing and would render botanical illustrations of the plants that interested me most. This soon changed after I began growing and propagating plants in my first garden, and my interest in drawing and the arts diminished as I became enthralled with the plant science. I have been on that path ever since.
Some people attribute their love of gardening to their parents or grandparents, others their neighbors or teachers. How did you initially become interested in plants?
As a freshman in high school, I was assigned a leaf collection project in a freshmen biology class. We were to identify, collect, press, and create herbarium specimens of native and cultivated trees of the greater Cleveland, Ohio region. The project was meant to teach us the fundamentals of taxonomy. Certain tree species, such as Franklin Tree (Franklinia alatamaha) and Pawpaw (Asimina triloba) were part of a large list of rare taxa considered difficult to find, and were worth extra credit if included in the final project. Finding these rare plants became something of an obsession for me, and my family supported my fledgling interest by taking me to places like Holden Arboretum and the numerous metroparks in the Cleveland area to search for these plants. In the end I found most, but not all, of them and for my final grade I received something like 300 points out a possible total of 100. Even after the project ended, I still wanted to find those that I couldn't find during the course of the assignment, and started going to nurseries, buying them, and planting them. It wasn’t long before my Mother’s yard was filled with these plants and many others. In many ways I am still working on this project!
You spent 6 years managing a large commercial nursery before deciding to enroll in higher education again. It is always hard for people to leave the workforce and become students again (needless to say, plenty of career changers have gone through this journey). Although one never stops learning during their jobs, how did you become motivated to devote yourself to the scientific discipline of horticulture and botany?
I had wanted to go to graduate school after completing my Bachelor’s, but I think one of the problems with graduate school is that most students tend to enroll right after finishing a bachelor’s degree. For purely academic disciplines, this is the best thing to do, but horticulture is different, and academia is just one facet of a huge array of opportunities that exist. I also had a chance to be part of an industry experience that I could not pass up, so I put grad school on hold and went to work.
My industry experience started while I was still an undergraduate at Ohio State. My college roommate’s father had been in the restaurant industry most of his life and was very successful at it, but had always wanted to start his own nursery. When I was two years away from graduating, he sold the restaurants, followed his passion, and decided to start the nursery. My experience was totally unique. From its inception, I was involved in every phase of the operation. I helped choose the land where the nursery was started, was involved in the planning and development phase, and ultimately managed operations on the entire farm. This was a tremendous experience, but over time I started to plateau in my daily routine, and I knew that some of things I wanted to do with my life, such as plant breeding and exploration were just not going to happen if I had stayed there. So I left the nursery to explore other opportunities. I was immediately offered another, similar job at the largest production nursery in the Cincinnati area, but during my senior year at Ohio State I did a study abroad trip to England, and made a good connection with the faculty advisor of the trip. He happened to be a well respected member of the OSU horticulture department, and told me at that time that if I ever wanted to enroll in graduate school, that there would be a place for me in his program. So, six years after he told me this, I went back and had a conversation with him and the place was still there for me. So, after much deliberation and many sleepless nights, I went back to school. Transitioning back to the student lifestyle wasn’t easy at first, and I specifically remember taking my first exam in grad school and having a mini-panic attack. I remember thinking to myself “what the hell am I doing here? I’m too old for this!” Ultimately, going back to school was one of the best decisions of my life, but for those in a similar situation, my advice is this. Go back to school with a well-defined plan for your future. Don’t go back with the thought that your future will just work itself out because you are a grad student and will ultimately have an advanced degree. Scientific discipline is no substitution for passion and enthusiasm, but it does help temper and direct it.
Plant breeding can be carefully controlled or spontaneous - surprises still can happen despite biotechnological strides. To what extend does control ends and nature's will begins in your work?
Personally, I think the breeding process begins with nature’s will, and becomes more controlled as advancements are made. I approach all of my breeding projects this way; collect as much raw germplasm as is possible, emphasizing wild collected material, and some key cultivars that might exhibit characteristics you are interested in, and go from there. This ultimately provides a broad template, but over time, the success and failures of certain germplasm accessions become evident and help shape different breeding avenues; this method does also provide a few surprises along the way! Not only does this method ensure that my breeding efforts remain novel and unduplicated by others, but it also allows me to refine the process in unique ways.
This seems to be the opposite of what many (or most!) commercial breeders do. They often begin with a limited genepool, and a ridiculously narrow range of genetic variation, and rely on advanced breeding techniques to generate new variants. Sometimes this works, sometimes not. Hence, you get 100’s of new introductions every year that are basically the same as their competitors.
For example, there are many people starting to breed Phlox right now, but basically all of them use plants that are available in the trade as the basis of their breeding programs. Before I even began hybridize phlox, I developed a large (probably the largest in the world) germplasm collection of Phlox by collecting new forms of widely cultivated species, and poorly known, rarely cultivated species. I also brought at least 3 species into cultivation. By doing this I was able to see a cross section of the total variation in the genus, and make informed decisions about where to begin the breeding process. It also allowed me to differentiate my efforts from those of everyone else breeding Phlox. Many of these hybrids are based on taxa that have never been cultivated to a large extent, but I would never have known this if I did not initially seek to understand the breadth of variation in the genus. Because these initial hybrids are immediately different from what is being done, we are starting to employ some of the cutting-edge breeding tools that can further advance breeding lines, and further contribute to a unique, adaptable, and reliable product.
Do you see or liken plant breeding to an artistic process? Certain colors and shapes must be preferable over others, and plant breeders do seem to develop a particular style.
I think it depends on the breeding objectives and personal interests of the breeder. In something like phlox, many people want to breed for resistance to disease. In this case breeding may be more pragmatic and defined by rigorous scientific objectives and protocols rather than flower color, plant form, or novelty. However, the artistic license may come later after the initial goals are met.
However I do think there is an artistic side to breeding, and that this is closely tied to passion for certain plant groups, especially for those that work in genera that are “off the radar” of the typical plant consumer. One genus of great interest to me, that exemplifies this, is Trillium. I personally find them to be among the most simplistically elegant and distinctive of all plants. Although they have tremendous importance as native plant species in the U.S., I also see tremendous opportunity for breeding and enhancement, especially given the diversity seen in wild species. Most people don't realize the range of flower colors, leaf variegation patterns, and breadth of plant sizes and habits that exists here; new species are still being described from the southeastern U.S. I am not the only one to think this; In New Zealand, there is a small, dedicated group of Trillium growers and hybridizers that have begun to develop this variation and some of the results are astounding. There is even a small business there that breeds and sells Trillium stems for the cut-flower industry! So yes, there is definitely an artistic side to the breeding process, but like my breeding philosophy, it starts with the plants.
Your M.S. dissertation 'Studies on the Optimization and Breeding Potential of Magnolia virginiana L.' beautifully bridged the ecology and horticulture on one of our beautiful native North American flowering trees. How did the topic come about and what did the subsequent research discover?
When I talked with my advisor about coming back to graduate school, he mentioned numerous projects that I could work on. I knew I wanted to get involved in plant breeding and botanical exploration, and the only project that fit this category was a project involving the enhancement of Magnolia virginiana for increased landscape usage. This project was also new to his research repertoire, so it also gave me the opportunity to help develop a research project, rather than just plug-in to a more established, ongoing project.
The most important part of this research, in my opinion, was what I didn't publish in my thesis! From 2007-2009 I designed and performed collection expeditions to study M. virginiana in the wild and obtain germplasm. During that time I was able to collect seeds from throughout the range of the species and develop one of the most comprehensive germplasm collections of this species in the world. This work taught me the value of collecting, not only for plant breeding, but also conservation. Most of the M. virginiana cultivars on the market are similar to one another, but when we started growing these wild collected accessions, I started to see horticulturally useful variation that could lead to real breakthroughs in the breeding and selection of this species, but also the uniqueness of certain populations that might one day garner conservation priority. Some of these unique collections have been passed on to the U.S. National Arboretum and have become part of their collection.
Native plants became the focus again when you tackled your doctoral dissertation 'Germplasm Collection, Characterization, and Enhancement of Eastern Phlox Species'. It is always interesting to leaf through old horticultural books and find Phlox paniculata popularized by Europeans when other Phlox species have tremendous future in gardens. We are finally seeing selections of these species, such as Phlox stolonifera 'Sherwood Purple' and Phlox divaricata 'Blue Moon', established in gardens. Anything interesting in the pipeline from your doctoral research?
Yes! I have about 20 or so selections, of both species and hybrids that are being trialed for introduction. That may seem like a lot, but because I dealt primarily with species and germplasm accessions that had not been previously used for breeding, there is quite a bit of novelty among these selections. I have had numerous plant breeding companies look at these plants and they have all been blown away by the results. This is very exciting and I hope to continue with this work as I move into the next phase of my career.
I imagine that your work takes you to unique ecosystems. What are some of your favorite natural areas in North American to explore? You seem very partial towards the pine savannahs and bogs.
I designed and executed 16 different collection expeditions throughout the eastern U.S., and while I do love the pine savannahs and pitcher plant bogs of the coastal plain, there are a couple of other areas that I favor slightly more. First would be the state of Kentucky. I suppose that may sound strange, but Kentucky is a state of extraordinary physiographic diversity, this in turn translates into often overwhelming plant diversity within a small geographic region. While I did not cover the entire state, some of my best botanical discoveries happened there, primarily within the rugged hills of interior low plateaus of the central part of the state. This area has historically been poorly botanized, so the herbarium record is incomplete, so plant-hunting there is rife with new species and unknown variants of well-known species.
Another favorite was the shale barrens of the valley and ridge province on the borders of Virginia and West Virginia. This region in well-known for harboring rare, endemic plant species, but is also one of the most diverse plant species regions of the eastern U.S. Again, the extraordinary physiographic and geologic diversity in the area has contributed to this proliferation of species. This region also fulfills my love of being in the mountains, and is relatively remote, so it allows for a good escape from the city life in Columbus without having to drive too far.
Novelty drives the horticultural industry. Unfortunately the rush to fulfill the public's demand for novelty has led to disappointing duds and caused older selections or simply good garden plants to fall out of favor. We risk discouraging the public from gardening because the 'new plants' fail not to horticultural ignorance, but simply their poor performance outside of the greenhouse. How long do you trial your results before they are deemed ready for introduction?
I think any new introduction should be trialed for at least three years before introduction. More importantly, the trials should be held in a diversity of different climates, environments, and garden conditions to accurately gage the overall adaptability of a particular selection. Of course, by doing this, someone else might usurp your efforts, but I feel like what I’ve developed is unique enough to withstand the time needed for proper trials. I think it is also important to determine the ultimate market. For example, the Phlox introductions are likely to be on the mass-market, but a special form of a Trillium may just be distributed to plant collectors interested in amassing unique forms of a particular genus or species.
Some people might argue that the search for novelty does not need to involve exotic destinations overseas when our backyards can still provide interesting germplasm. For example, in an effort to safeguard its natural heritage, New Zealand has imposed strict legislation on importing exotic species, if not introducing stringent quarantine requirements, causing plant breeders there to lament the 'tighter lids'. Although your graduate research tackles native species in North America, exotic species overseas still draw your attention. What is your philosophy on developing a balance between protecting our natural biodiversity against introduced pests and allowing for plants of possible economic significance to be imported?
There are two parts to this. First, I have tried to focus in areas where there has been little previous collection in climates quite different from my own in central Ohio, and the majority of the eastern U.S. Most of what I have seen and collected there is not going to be hardy here, but might have value in to the industry when marketed as an annual or container crop etc. However, I have sent collections from these places to a few select friends in the Pacific Northwest, where many might be hardy. In this case, I collaborate with knowledgeable plant people that have a sense for what might be a good garden plant, and what could potentially be an invasive species. Serious plant people are uniquely attune to the dangers of invasive species, and just as much as I don't want to be responsible for introducing a potential problem plant, they don't want to be growing them either.
My overseas collecting efforts have been very targeted, and I have purposely avoided generalist collecting which might result in the introduction of a potentially invasive species. In Vietnam I specifically wanted to find the recently described Lilium eupetes, an epiphytic lily closely related to the rare Lilium arboricola, which was my target in Myanmar. These are rare plants with exacting cultural requirements that are not likely to be great garden plants, but they are botanically interesting and make good stories for botanical gardens or private growers that might succeed with them. Obviously these areas are rich in genera that have invasive potential such as Euonymus, Berberis, Lonicera, etc. While these plants are interesting and ornamental, I do not collect them because of their invasive potential. Other genera such as Quercus, are also quite common in these areas and have broad appeal, and although there is no previously described invasive potential, the opportunity for importing unknown pathogens is huge. The USDA still allows for the importation of acorns with some special treatments, but even with such precautions I think the risk is greater than the reward. As I watch all of the ash trees in Ohio die off, I cant help but think what would happen if the oaks were to become infected or afflicted by a new disease or insect pest. So as tempting as it is, I do not collected Quercus when abroad, and choose instead to focus on collecting and promoting our native species.
If the pine savannahs and bogs of Southeast US exposed an interesting flora for you in our backyard, the lure to traverse across oceans for different plant life was still irresistible. How did your overseas expeditions fit with your graduate research?
Lilium was one of the priority genera for the OSU/USDA Ornamental Plant Germplasm Center where I did my PhD work. Even though I did not work on Lilium for my dissertation research, it is a genus I am personally interested in, and I often collected native species when I was in the field collecting Phlox. As I developed these projects and a comprehensive native Lilium collection, they culminated in presentations and publications. A British friend suggested that I travel to Vietnam to study the recently described L. eupetes in the wild. Even better was the fact that he offered to pay for it! So off I went. Not only did I find L. eupetes, I found more of it than had ever been found previously. Riding this momentum, I wrote a grant to the North American Lily Society and they funded an expedition to Myanmar the next year. While these experiences didn’t directly benefit my dissertation work, they complimented my domestic plant hunting experiences and have helped me gain greater perspective in plant collecting and diversity. Understanding plant diversity is like understanding cooking; you need to travel and experience different climates and ecosystems to gain a complete appreciation of the greater picture.
Due to its political repression and hermit reputation, Burma (Myanmar) is relatively unexplored for its biodiversity awaiting to be tapped and catalogued before modernization sweeps into the country. Earlier plant explorers Frank Kingdon Ward and Richard Schultes did manage to document some of the botanical riches there, and modern plant explorer Dan Hinkley has made a few forays there, giving us horticulturists a glimpse of its floral potential. Of the world's bio hotspots, you chose to travel to Burma. What led to that choice?
Myanmar was not a place I had ever really thought of going to until I started to focus more on Lilium. Truth be told, I had never even thought of traveling to Myanmar, but when I returned from Vietnam in 2013, I was hungry for more international exploration. My experience gave me some “street cred” among the world’s comparatively few plant collectors and I was invited by a contingent of British plant explorers to explore the region. In a way the opportunity just kind of fell into my lap, but it gave me the opportunity to search for the long lost Lilium arboricola, so I went.
The cloud and subtropical forests must yield endless plants, such as gingers. orchids, magnolias, and bladderworts. What are some of the promising plants you saw in Myanmar?
One of the most beautiful and promising plants encountered was an impatiens, tentatively identified as Impatiens aff. stenantha. Everyone who sees the photos wants it!
Another group of plants I think is worth more interest from horticulturists are the vining gentians in the sister genera Tripterospermum and Crawfurdia. On both of my trips to Southeast Asia, I have seen them in flower and fruit at all elevations and always think, “why aren’t these grown in gardens more than they are?
Quercus lamellosa was one of the most interesting trees found on the trip and the unique acorns that littered ground always amazed us at each encounter.
I went to Myanmar with the specific goal of finding the long lost Lilium arboricola. This epiphytic lily was originally found by Kingdon-Ward and described by Stearn. It flowered once in cultivation in 1962, promptly died, and has not been seen again since that time. Even before I left, I was doubtful about finding it, as it was the proverbial needle in a haystack. But, while hiking a narrow ridge through a pocket of cloud forest, I stopped to rest, and there it was. Without a doubt it was one of the finest botanical moments of my life.
There are so many others. How much space do you have?!
It is easy to glamorize plant hunting afar - the threats of landslides, unfriendly natives, inclement weather, and a subsistence diet on stale biscuits or unrecognizable cuisine never seem to loom largely in the public's conscious when murmurs of admiration and envy are elicited from audience members at seeing the pics of beautiful landscapes or plants. Any harrowing experiences or near-misses in your plant hunting exploits?
I am happy to report that I have not had any near misses while abroad, although the geographic isolation and rugged topography in these regions certainly sets the stage for it.
The strangest and most nerve-wracking experience I have encountered was in northwest Arkansas of all places. My traveling companion and I were following a gravel road and stopped briefly to admire one of the many turquoise-colored, spring fed rivers in the region when out of nowhere, an unmarked police vehicle drove up, slammed on its brakes, and came to a sliding stop behind our vehicle. Two plain-clothed police officers got out of the vehicle and immediately started harassing us about our intentions and repeatedly asked us if we were planning to drink beer and kayak down the river. When we started to explain the reason for our trip and started talking about plants they became immediately disinterested and eventually left us alone. We didn't even have kayaks with us and I wondered what prompted their investigation. Then I remembered the two large coolers in the backseat of the car! They probably thought they were filled with beer, but much to their dismay they were only filled with the plant germplasm we had collected. They had thought they were going to make a big bust, and were immediately disappointed when they realized we had a legitimate reason for the being where we were. Needless to say, we were mortified after the experience, but glad that it did not proceed any further.
Imagined that you've been shipwrecked, but permitted to select one plant to breed. What is your desert island plant?
How about one genus? Lilium. It has extraordinary diversity within and between species. I don't want to imagine being confined to a single species! This probably sounds rather conventional, but many lily species are rarely cultivated, and there exists such a great amount of diversity within and between species. There is enough room for experimentation for several lifetimes, even though there has already been a tremendous volume of work in the genus.
I always wonder what kind of garden plant breeders have. Is it a garden full of rare plants? Or gardening at home is restricted to vegetables and edibles? What kind of garden do you tend at home?
I am steadfastly dedicated to growing plant species of known provenance, and plant collecting is one of my life’s passions. Private gardens can serve as a tool for plant conservation, especially when there is a well-executed plan for collection, propagation, and dissemination. Currently, I cultivate a collection of about 2000 taxa, and most of these are my own collections or the collections of some of my plant hunter friends. When I come home at night, I don’t take off my “horticulturist hat” and switch to a different hobby, rather I switch genera! This collection also serves some of my personal plant breeding interests and endeavors.
Your career certainly puts you in touch with the international community of gardens and plantspeople. What gardens, private and public, have inspired you? Individuals?
As previously mentioned I did a study abroad trip to England for my last semester as an undergrad. During this time we visited many gardens, public and private, but two stand out in my memory and I still think about them with frequency. First is the Royal Botanic Garden of Edinburgh (RBGE) in Scotland. This place was an epiphany for me. With over 50,000 taxa in cultivation there, I couldn’t help but study every nook and cranny of the gardens. In fact, after the study abroad had ended, I was traveling with friends on the continent, but kept thinking about RBGE. So I left my friends and went back to Scotland and studied the garden for the few final days of my trip.
Also, while there I had the opportunity to visit a small public garden in Lake District called Holehird Gardens. This may be my all-time favorite garden. Nestled into a mountainside, there grew many of the plants I could only dream about in the Midwest: flowering Meconopsis, Pleione, Primula, etc. I hope to go back there someday.
I should also mention the gardens at Heronswood. I made five pilgrimages there in the early 2000’s over different seasons. I was amazed at how much the garden changed from season to season and the phenomenal complexity of the plantings. I’m glad to hear that it is open to visitors again as it sure to influence generations of horticulturists to come.
Four individuals that have vastly inspired my career are Jim Archibald, Edgar T. Wherry, Mary Gibson Henry, and my friend Dr. Warren Stoutamire. I will never forget the first Archibald seed list I ever received. It was a revelation. Although I had been earlier influenced by Dan Hinkley’s collecting forays into southeast Asia, Jim Archibald’s work was concentrated primarily in eastern Turkey and Iran. Collecting in those regions had never crossed my mind and the seed lists opened up the flora of an entire region to me. Traveling to and collecting in Iran is still one of my life goals.
Anyone who has studied Phlox knows the name Edgar Wherry is synonymous with the genus. What I admire most about him is his dedication to botanical clarity, persistence as an author, and indefatigable disposition. He mortgaged his life to study Phlox and wrote down seemingly every thought he encountered. He was also a gardener, which seems rare among modern day botanists and evolutionary biologists.
In my opinion, Mary Gibson Henry is one of the most under-looked and underrated American botanists. Despite her privileged life, she relished intensive fieldwork, described new species, and endeavored to create a world-class garden at the Henry foundation. She found and described one of my all-time favorite plants, the mythical Lilium iridollae - the pot-of-gold lily. I think part of the reason I cherish this species so much is because of the passionate way she wrote about it in her original description of the species.
Lastly, my friend and mentor Dr. Warren Stoutamire. In many ways I have modeled my own career and interests after him. He was among the first to propagate native orchid species from seed, tended a personal greenhouse full of botanical rarities from around the world, and was a professor at University of Akron. Some of my most treasured interactions with other human beings were with him at his home and greenhouse.
What messages or goals do you aim to project through your work? Some plant breeders aim for enhancing or improving the efficiency of the food supply, others beauty, and few the twin joys of monetary and posthumous gains. I remember reading about plant breeders and chefs who collaborated to identify and improve flavors and other traits that make vegetables more delicious.
I want to be known as an innovator in the fields of plant breeding and botanical exploration. In ornamental plant breeding, it seems like good good ideas come along relatively rarely, but are rapidly adopted by everyone out there and beat to death. Look at genera like Heuchera and Echinacea. The people that initiated breeding in these genera are true innovators, but subsequent efforts are by others that have just jumped on the bandwagon and essentially repeated the same thing over and again. This is exactly what I want to avoid.
Plant collection is vital to plant breeding and provides a means for botanical gardens to contribute to conservation and differentiate themselves. In my opinion it is more important than ever, and while it may seem like every place on earth has been visited by humans, there still remains a plethora of places where plant hunting has been limited. This was a big part of the reason I went to Myanmar. I hope to continue with this and visit some of the world’s remaining botanical treasure troves.
Any advice for those interested in diving deeper into plant breeding as a career?
It’s harder and harder to find good training in ornamental plant breeding in academia. I feel exceedingly lucky to have had training in ornamental horticulture. Training in vegetable or crops breeding can provide a solid background, but because of the laboratory intensive nature of those breeding programs, there exists a disconnect between them and traditional breeding techniques. Many of the breeders coming out of these programs have more in common with molecular biologists than traditional plant breeders. So if you want good training, my suggestion would be to seek out the right academic institution and try to get experience through internships at breeding companies and botanic gardens.
Follow your intuition and be individualistic. There are too many people working in ornamental plant breeding that are repeating what has already been done. Don't be afraid to promote yourself. This is a competitive field, just because you might produce fantastic plants, that doesn't mean they will make it big or your accomplishments will be recognized.
Don't be afraid to make crosses when you have a good idea and the plants to make it happen. It’s easy to romanticize about using sophisticated techniques like embryo rescue or mutation breeding, but basic principles of plant breeding are still responsible for some of the best new plants out there.
Cheers to those interested future plant breeders!
Thank you Peter! Check out his blog at http://www.botanicazales.com
