Karen Petroff teaching Woody Plants at the University of Maryland.
It’s about time for me to report on the Woody Plants ID class I took last semester at U. Maryland, after cogitating over it a bit and asking around for answers and getting plenty of them.
All that memorization – really? And is Michael Dirr’s book still the best?
In addition to her job overseeing the entire campus landscape, Karen Petroff teaches woodies and she’s excellent, an opinion that I know is shared by her students. Yet, I still wonder if the best way to teach plants is memorizing hundreds of them – Latin names only, in full – so they can be recognized in the field or even on a lab table, with no leaves on them!
Which is fine if you’re good at memorization, but it might make me steer clear of pursuing a field that required it. Several memorization tips were offered but thankfully I didn’t need them because I was auditing the class. (For retirees, the class is also tuition-free.)
3 Landscape Architects I Know Respond
MY UMD Teacher Responds
In an email, Karen Petroff wrote that she thinks of it not as memorization but as “learning through association. I feel the same way about plants. By associating plants, plant images, names and other details such as common uses, ecological services, native origin or propensity to cause trouble, a student begins to make comparisons of one plant to another and to understand the complexity of a biodiverse world. I believe this skill also helps students apply the same understanding to biodiverse peoples collectively and individually, a side benefit.
Continuing, “Dirr’s text was last updated in 2009 and remains the standard for its comprehensive inclusion of not only morphology, landscape use and cultivars but relationships in nature, key aspects of cultivation, history, research citations, propagation and more. I would argue that ecological services are included but less prominent than they might be in a contemporary update. I continue to update my lectures each semester for the same reason. In my experience, I have met those who advocate for native plants even as they perish from an inappropriate landscape setting due to lack of appropriate support in a changing climate, or who discount aesthetics as a value, or who work with plants for a career without referring to them by an accepted name, and there is a place for everyone in a spectrum of professionals and hobbyists.
Garden Professor Group LOVES Woody Plant ID Classes!
I asked the 27K-member Garden Professors Blog Facebook group for their thoughts and experiences about use of the Dirr book and requiring memorization for identification tests. To my surprise, the consensus was overwhelming positive and some of the stories were actually moving! People who love plants seem to just love this class, much of which is conducted outdoors. Mine met every Friday afternoon for a walk through the tree-filled campus, where we discussed trees and shrubs with Eve Josar, the teaching assistant shown above.
Here’s how members of the Garden Professors group responded:
- “I took the exact same course and I remember the professor also inviting students to go around the campus (which is an arboretum) to see what plants they recognized from lectures. And after that semester it almost felt like a game to try to ID as many trees/shrubs on sight as possible. Later when I worked as a landscaper, it became very apparent and unfortunate to me that most job sites (both commercial and private) prefer to use the same 25~ woodies. Whereas like you said, the course goes over 178+ woodies to IMO try to show the diversity of what exists in this area even if you can’t just rattle them all out.”
- “I’m hoping plant materials is still about interacting with plants outdoors. No picture or pictures can imprint on you like looking at a plant in an outdoor setting, plus some characteristics aren’t about appearance. Which conifers are prickly, for example, or the scent of sassafras, even the sound of cottonwood leaves clattering in late summer breezes. Being “with” a tree and a group of students energized by walking and discussing made Plant Materials the class that determined my career path, and teaching it a few years later was probably the most fun job I’ve ever had. I loved grading the tests, since the results were my own test of how well I was teaching. And yes, the Dirr is still the standard in spite of the years. No other text has so much cultural information, or has the frank warnings against plants that are finicky or disastrously successful, especially especially for regional differences. I was immediately attracted to Dirr’s passion or loathing, personal relationships with plants and people, so much so that I read it from Abelia to Ziziphus. Mike and Bonnie (who did all the drawings and is equally as good a plantsman as Mike) are national treasures. It’s the one book that is never put away, and sits vigil beside my computer as I type this.”
- From a designer ,”If you memorize your plants to where you can recognize them on the fly, you will find yourself noticing how and where they’re growing and thriving. From a pro standpoint that’s pretty critical to being good at what you do.”
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“‘Necessary’ is specific to the individual. Necessary for what, exactly? If you’re in a LA program (or any Hort-adjacent field), there’s a spectrum of plant knowledge that you can expect of yourself. If you want to be an LA that intimately knows plants, their associations, and there needs in order to set yourself apart from, then do that. I think it’s important, but I love woody plants and see the immense need for this skill in the LA field”.
- “Plant ID is kind of a superpower for me. many years ago i competed in and won high school and collegiate competitions for it. I delineated hundreds of wetlands and did endangered plant surveys for about 15 years. I was initially threatened by ID apps but once i saw how inaccurate they were i got over it.”
- Remembering their professor as “so inspiring. Learning to identify all those trees and shrubs has been incredibly useful in varied jobs in and out of horticulture!”
- “27 years ago as part of the Environmental Horticulture with the great Jerry Sotomme at Santa Barbara City College – plant ID was just about my most useful class – even though I live in the Northeast now and many of the plants I memorized do not grow here
– the method of learning how to id plants has made me an id “whiz” even at 60 I trust my brain to be faster and more accurate in the field then calling up an app on my phone. So yes, I think plant ID is a very important, maybe even necessary skill for all the varied professions in the realm of horticulture.
- From another designer: “Having those plants in my memory bank is great. I do check my memory against newer lists and such. To be able to make some small tree suggestions on a consult in the field lets the client know I have some knowledge. And I enjoy the personal satisfaction of identifying plants as I drive down the road. Of course, at the Community college level most of us were staying local so having the experience of the instructors as to what grows here has been great.”
- “At Delaware Valley University we teach science with practice. So not only do our students learn to ID plants, but they learn how to plant, maintain and use them in the landscape.”
- “I appreciate all the time and effort I spent in my Plant ID class, which paid dividends in my observational skills and in understanding the natural world. IMO, time spent observing nature that intentionally is never wasted.”
- “There is nothing like knowing the entire gestalt of a plant in all it’s stages (think holly leaves when mature and immature). I can id plants based on “overall leaf color tone” and growth habit, and even veination while the id apps are still fumbling around and finding the wrong plant.”
- “I personally wouldn’t hire a landscape architect who had to use an app to identify what are presumably commonly used plants.”
- “In my opinion learning to ID plant material is still a valuable skill. And demonstrates a level of professionalism.”
- “As a garden professional is it compulsory? Of course not. As a garden professional is it useful and expected by others? Yes, I think so. And it’s great fun!”
More Stories from Plant ID Classes, and a Suggestion
- Another remembered his Plant ID classes at Cal Poly SLO, “learning 250 different plants per quarter and three quarters for the series. Hardest was winter ID from dormant twigs. And then there was Botany plant ID staring thru a microscope for hours keying out native plants to species. Good times.”
- Another remembered the NC Certified Nursery Professional course and exam that used botanical names only. “All the course IDs were in the field done in 2 area arboretum(s) of mature woody plants to prepare for the exam. The course and ID exam of 200+ woody plants concluded in late October after two hard frosts. The exam was the ID of mostly dormant juvenile plants, all in one-five gallon pots. That’s when it became important to recall the classroom instruction which covered dormant or semi-dormant twigs.”
- Memorization tips, like “Also, flash cards for botanical names. All. Day. Invent unique and crazy ways of remembering these names. The wilder the better.”
- “The curriculum should shift from bombing with facts to emphasizing how to find (and vet) information. In terms of process skills, the dynamics of gardening changes as well as, for example, considering perennial plants in terms of 20 years of predictable climate change or incoming pests. In both of these dimensions–the shift from facts to quickly locating them and the shift in the time dimension because climate change, new curriculum and new styles of teaching is required. Too often it is not done. Two more dimensions merit reform. The esthetic of garden design, its relation to local ecology (eg pollinator support, xeriscaping) is becoming more important as the conventional assumptions about local gardening are no longer applicable.Finally, the standard methods of pedagogy (classes, powerpoints, etc) have displaced on-site instruction of how to plant a tree or a shrub or undercover, or mulching with widespread adverse effects on hobby gardeners.” They seem like good points!
In This Corner, the Apps!
Source: Google Lens
Naturally people had lots to say about plant ID apps, the oft-mentioned alternative to memorization.
- UMD’s Petroff wrote “On the subject of apps, I read an article that stated that Google Lens could identify plants in any photo you’ve taken with just a swipe up and query and the first photo I opened, Myrica pensylvanica or northern bayberry was misidentified as a rhododendron LOL.”
- “Apps are often incorrect. I have used them both “for fun” to test and tested them with colleagues/students, they often fail at the level of genus and species. They are also not great with cultivars.”
- “They will improve as people upload images with correct IDs for these search engines to compare them to (such as Google Lens or iNaturalist), but learning to ID based on physiological traits and seasonality is more reliable. Some engines will ID North American shrubs as woody plants that live exclusively in South Africa, for example.”
- “I suspect many people, however, use the apps as entertainment…a brief, shallow distraction on the way to their next impulsive moment, but would be happy to be proven wrong.”
- “I always cross check apps but to add some data to ‘How accurate are photo-based plant identification apps?‘ by Illinois Extension.”
- “Apps may shortcut the experience and may bypass the deeper knowledge that an observed life can bring. But, they are useful as a starting point.”
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“From my own review of plant ID apps, Google lens is best. I’m sure that this is ever-changing though.”
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“There are great plant identification books (some focus on herbaceous plants, some on trees, some include both, etc.) made for professionals and enthusiasts.”
- Make AI better by contributing to it, with date, so we can improve profession by our sharing. It spews out answers in seconds. “It’s a brave new world for home gardeners.”
- Suggesting that we make AI better by contributing to it, with date, so we can improve profession by our sharing. It spews out answers in seconds. “It’s a brave new world for home gardeners.”
On teaching plant design
Another landscape architect friend, Billy Goodnick in Santa Barbara, CA, told me he’s “shocked to hear LA students must take plant ID but not planting design. “My analogy is that it’s like going to cooking school and taking a class in ‘ingredients’ but no ‘cooking’ classes.” In his practice he uses the PlantMaster app, for its huge database searchable by regions, height, culture, design styles, uses, attraction for pollinators, nativity, and more. He says it’s replaced the 15 books he used to carry with him on client visits. Asked where he thinks the LA profession going, he says “Sadly, hort seems to be losing priority in the profession.”
I’ve thought a lot through the years about how things are taught and what value is placed on some information and not others. When I was still young and spent most of my time with teachers, I probably would have answered in a similar way as the professor in your post, but I’ve lived a little since then.
This post reminds me of one of my roommates in college. She took a botany course, and the tests were weighted. The professor told the class if they failed the Latin names, even if they excelled in everything else, they failed the course. I helped her with flash cards, and I ended up memorizing everything just fine. She didn’t. Problem was, I wasn’t taking the course. She could identify plants by common name just fine. She identified attributes, put plants in proper categories, everything — but she could not for the life of her remember Latin. She told me she barely made it out of high school Spanish. She just had a brain blip when it came to languages. She failed the course, and her courage was shot.
Memorization is its own skill. So is the ability to learn a language. Some people can do it. Some can’t, but it doesn’t mean that just because they can’t do one part, that they can’t do anything else. I lost contact with her, but I don’t think she went into any plant-related profession. It’s a shame because I think she would have enjoyed it and been really good at the hands-on application level.
I get that some programs try to weed out the candidates who aren’t serious, so they make some classes more difficult than they need to be. I also agree that knowing the taxonomy is of high importance, but I’m not so sure the memorization requirement is the way to do it.
I think what’s more important to teach is the courage to admit you don’t know something, the confidence to take the time to look it up, and the discernment to determine the quality of the source.
My husband has cancer. I’ve lost track of how many doctors he’s seen — one is even nationally renowned —but every single one of them has looked up information during his appointments. Knowing how to find the answer — and what to do with it when you find it — is more important to me than memorizing.
SO interesting. Thx.
I have been a garden designer, landscaper and horticulturist for almost 40 years and I use Dirr’s book all the time. While it’s hard to keep up with botanical name changes these days it is still an invaluable resource. In my experience no source comes close to providing the extent of knowledge of woody plants and information on them. Not just plant names but details on growing and propagating. My favorite class at Sandhills Horticultural program was plant ID. I love knowing plant names – botanic and common. We were responsible for knowing hundreds of plants and we had to spell them correctly! Sandhills has an extensive campus with a large collection of plants. Except for tests where maybe 100 or more cuttings were laid out on tables, all study was outside seeing them in place. I admit to being a plant person foremost, and I really don’t see how you can be in this profession and not want to know plants. It doesn’t seem like a chore to me but a delight! I will say the Dirr app was much less helpful. Also expensive and no upgrades. Dirr’s Woody Plants, though, is still the bible for woody plant reference.
Traditional taxonomists are a dying breed. Retiring taxonomists are not being replaced and academic taxonomy programs are disappearing, as are herbarium collections. The recent closure of the herbarium at Duke University is a case in point. Duke tried unsuccessfully to find a new home for the collection before deciding to close it.
Academic scientists are using modern analytical techniques to categorize species according to their evolutionary relationships. Given the new understanding of the colossal task of collecting rapidly evolving life, most accept that it can’t be done. About 1.2 million species have been identified and named. Estimates of the total number of species range from 8.7 million to 3 trillion. More importantly, species of life are constantly changing and dying out as they try to adapt to a rapidly changing world. Naming dynamic life is a constantly moving target, a task that is never done because life never stops evolving.
Many academic scientists believe that traditional taxonomy should be abandoned and replaced by a new system that reflects evolutionary relationships. For example, learning to identify plants as members of a specific clade (evolutionary branch with a common ancestor) is probably a more useful way to understand their shared characteristics based on their genetic relationships.
Once again my mind is boggled by your knowledge.
I’ll join the chorus of people who LOVED their plant ID classes in college. Two semesters of woody plants and one on herbaceous. Those three classes were absolutely the most useful things I took away from college. I use the skills I learned in those classes on a daily basis… And I’ve had done a lot of contract work for gardening publications that basically was just me being paid of my ability to look at a picture of a plant and know what it is. And it is a skill that only gets more valuable with the deluge of AI nonsense filling the internet with nonexistent plants and bad information.
What a well-researched and thoughtful article. Thank you!
Thank YOU for the encouragement. Means a lot.
Susan, very well written article. I have been in Horticulture for 40 years. I learned woody plants from Mike Dirr when he was at the Univ of IL. My class was the first class after his first book was published. Due to that, he was brutal to us, claiming that we had it so easy. All his classes before the book, had to write all of the notes thru him dictating them to them. Don’t get me wrong, I learned so much and still remember it to this day. I love his first addition because it focused on plants in zone 5 where I work. Twig and bud ID seemed ridiculous back then, but I use it every day even now. Thanks for all that you covered about the apps.
Thank you for the encouraging words! Much appreciated.
Great overview. Dirr’s book has been a mainstay in my long career as a horticulturalist and botanist. The more recent Trees Book by Dirr and Warren should be utilized as an updated version of the Manual, only in the sense it has numerous new cultivated varieties of trees added. Warren and Dirr have been active releasing new oaks for example into the field of Urban Horticulture. Municipalities and their designers should be infusing by using many of these improved cultivars in terms of pest and pathogen resistance to diversity our tree canopies. I do find Dirrs manual still a go to source for woody plant propagation, more so than Dirr and Hesuer. As a former plant taxonomy teacher, it doesn’t hurt to have students take small samples of trees and draw the features. It was also fun to teach the tradition of herbarium vouchering, or sampling leafy twigs and/or flowers and artfully pressing and preserving them as a way to get both the tactile and sensory fulfillment of working intimately with plants. Our current students all do this at the Polly Hill Arboretum. Cheers!
Glad you liked it, and that it elicited this interesting comment.
I was an LA undergrad and happily took those courses: I knew most of the plants like the back of my hand, unlike most of my classmates. While I enjoyed them (and their almost pain-free A grades), I found out after graduating that these skills were of no use to actual landscape architecture firms–they would inform me during interviews that they didn’t need such expertise since they would simply hire landscape designers for that work.
I chose to go into a profession where plant knowledge actually matters, but pay is far lower. I’ve always wondered if I made the right decision.
Oh yes, I keep hearing about cases of landscape architecture firms just out-sourcing all the plant decisions to horticulturists or garden designers. Makes sense for LAs working on big projects, mostly engineering.
I’ve never thought of Dirr as a plant identification book, but rather a great resource on learning more about a plant once you’ve IDed it.
About 60 years ago at the University of Florida (north Florida), I took a course titled, “Native Landscape Plants of Florida.” We had to memorize 20 plants each week. The first week we learned about palms and I can still ID and remember most of the palm names although I rarely see a palm.
As to the landscape architect who said memorizing plants as part of his training wasn’t important in his work, I am reminded of what a horticulturalist that I volunteered for said: “Landscape architects know less than 10 plants and they keep using them over and over.” I love the exception: “Wow! A landscape architect who knows plants.” Mike Mostrota at the American University Arboretum is a great example of a landscape architect who knows plants. I can learn a lot just walking around with him.
After reading this Rant, I immediately downloaded Google Lens. I’ll be testing it out for the next few months. At my age I often recognize a plant and know nearly everything about it except its name (same with people). The app should be a way to remind me of the name of the plant.
Great to hear from you, John! You’re still one of the most in-the-know people in the DC gardening world.
Thanks Susan, I enjoy reading your articles. It’s good that you took advantage of U.MD’s continuing education opportunity. GW used to have a landscape design program and I took the introductory course on plants. We can always learn something new.
All successful and better landscapes are based on smart and diverse plant selections. Exceptional plant knowledge is what separates the best gardeners and designers from the pack. Exceptional plant knowledge begins with knowing the culture, size, habit, universally known name, and identifiable features of a wide palette of plants. And a good starting point for whether a given plant is garden worthy or not is at least one expert’s opinion. Dirr’s manual gives you all of this. Nothing else does.
My dear Scott, you are wise beyond your years!
Ha! LOL
As a retired electrical engineer, I’m looking forward to starting classes next Fall at UMd Institute of Applied Agriculture and can’t wait to tackle the Woody Plants classes. Of course, I thought Thermodynamics and Electromagnetic Fields classes were fun many years ago.
I loved my dendrology class, with all that memorization and association with characteristics. When I go on my solo retreat every November to a wooded state park, I take my materials to review and brush up my ID skills. Quirky, yes, but I love it.