Naturalizing Perennials in the Garden Scheme
In “Naturalizing Perennials in the Garden Scheme,” we’ll take a look at the different ways ornamental perennial plants make themselves right at home in a cultivated garden.
Some of you may have read my brief post on The Renaissance Garden Guy Facebook page a few days ago about perennials naturalizing in my garden and the fact that different plants accomplish this in different ways. That’s what today’s article is about, and, like every single gardening topic I’ll be writing about on this site, I’m really excited to be discussing it with you. I’m particularly excited because, when I first started gardening last year, I could not even remotely THINK about having a discussion with anyone about plant behavior.
So, back in April or May of 2020, when it came to gardening, I didn’t know much. I didn’t know how or why plants do the things that they do. And I had never heard the term “naturalizing” as it applied to plants. But even though I was inexperienced and ignorant, I definitely did know that I wanted some cool looking perennials living and thriving in my garden. Even back then, I did actually know that a perennial was a plant that didn’t die after one growing season, and that I could expect perennial plants to rejuvenate themselves every spring here in the Midwest. But I had no idea how a perennial could accomplish this. I had no idea how, in general, a perennial plant would behave. I suppose I assumed that it would just “come back up” every year and maybe get bigger and have some flowers. I did not know that the term “perennial” can be subject to interpretation. I also didn’t realize that “a perennial” could, in fact, become “many perennials.” There were lots and lots of things I did not know about gardening, or more specifically, perennial plants.
Now it’s late spring of 2021 here in the Midwest and my hardiness zone of 5B/6A, and I’ve been gardening for approximately a year. Even though I’m still a definite novice, this last year has bestowed upon me a modest amount of gardening know-how. I’ve learned, both by making mistakes and by doing research. There’s no substitute for gleaning information from various experts like botanists, master gardeners, and horticulturalists, but my year spent at the College of Gardening Hard Knocks has also been edifying.
So, equipped with my newly acquired gardening knowledge, I’d like to get to the point of this article. I’ve got a bunch of perennials living together in my garden. Many of these are naturalizing, or at the very least, spreading as individuals (which might be interpreted to mean the same thing as “naturalizing”). I’m going to discuss what naturalizing means according to my research, and what it possibly could mean according to my own observations. I’m going to discuss three different ways that plants in my garden have been naturalizing/spreading. And finally, I’m going to relay my observations/concerns about my original planting scheme for some of these naturalizing specimens, which was conceived and implemented during a period of time when I knew even less than I know now.
Naturalization, Colonization, and Spreading
With respect to the plants growing in my garden, my research and personal observations have led me to come up with definitions for the terms “naturalization”, “colonization”, and “spreading”. Naturalization occurs when a species which is not native to an area survives, thrives, reproduces, and spreads on its own, without human assistance. (There’s that term “spreads” again. I’m going to talk about that in a minute). Colonization, as defined by Wikipedia, “is the process in biology by which a species spreads to new areas. Colonization often refers to successful immigration where a population becomes integrated into a community, having resisted local extintion.” In this case, the “population” refers to my plants and the “community” is my garden. Kind of sounds the same as naturalization, don’t you think? Spreading, according to me and what I’ve seen going on with the plants in my garden, means one of two things: 1) One plant, or a group of individual plants, each creating new plants of the same species, and spreading out to occupy new adjacent space – thereby naturalizing and/or colonizing, and, 2) One plant sprawling out and taking up more room in the garden, but essentially remaining only one individual. So, it seems to me that when plants behave according to the first definition of spreading, and when plants naturalize and colonize, then they’re doing the same thing – or at the very least, they are naturalizing/colonizing by spreading. But when a single individual plant grows according to the second definition of spreading, it is NOT necessarily naturalizing or colonizing – it’s just one plant sprawling out and taking up more space, but staying just one plant.
The featured image of this article and the picture immediately above on the left show Biokovo Hardy Geranium (Geranium x cantabrigiense ‘Biokovo,’ with the white blooms) naturalizing/colonizing/spreading utilizing one specific biological mechanism. The photo immediately above center shows Woodland Forget-Me-Nots (Myosotis sylvatica) also naturalizing/colonizing/spreading but using an entirely different means of accomplishing this. (The Forget-Me-Nots are also shown in the featured image, naturalizing right next to the Biokovo Geraniums). But both of these species are behaving as described in the first definition of spreading. The photo immediately above right shows a Birch’s Hybrid Bellflower (a hybrid of Campanula poscharskyana and Campanula portenschlagiana) spreading as an individual plant, according to the above second definition of spreading. Its branching stems are definitely radiating outward from the crown and the main stem of the plant, and it’s definitely getting wider, but it remains only one plant.
Please note that all of the info in this post represents the result of a combination of my reading and studying excellent information from various well-respected plant experts, and, my own observations from right here in my own backyard. It’s my attempt to reconcile what the experts definitely know with what I, a definite non-expert, have been watching go down in my own backyard. I apologize in advance for any potential inaccuracies. If there are any, they arise solely as a result of my own inexperience and nascent personal knowledge base.
So that’s my take on plant naturalization, colonization, and spreading. I hope I’ve somewhat cleared up this little semantics issue, because it’s time to move on to the next discussion.
Three Observed Ways That Plants Can Naturalize/Colonize/Spread
Through my research and observations, I’ve learned about different mechanisms which various perennial plants can use to spread (naturalize/colonize) in a garden. This article is not intended as a scientific treatise on plant biology and reproduction. It’s just a way for me to relay some info I picked up through lots of reading and lots of hands-on learning this last year in my garden. My goal is to be conversationally informative, and ultimately, hopefully, helpful. So I’m going to try to keep this kind of short and light and hope that I can relay the basics of this topic effectively. So, without further ado, I’m going to focus on three of these mechanisms, namely rhizomes, stolons, and self-sowing.
Rhizomes. A rhizome is primarily an underground stem, the main stem actually, of a rhizomatous plant. Although there are above-ground rhizomes, they are apparently rare. Even more rare are multi-tiered rhizomes which form many different layers/levels of growth. For the purposes of this discussion, I’ll be focusing on rhizomes of the underground, or subterranean, variety. That’s the only kind of rhizome I’ve got growing in my garden and the only kind for which I can honestly say I’ve observed firsthand.
A rhizome grows horizontally underground and, again, is the main stem of the rhizomatous plant. As it grows horizontally, it produces nodes, from which new shoots (leaves, branches, etc.) originate. The nodes of a rhizome also produce subterranean roots. On a rhizome, the shoots originate from the top of the node, and the roots grow from the bottom. The length of horizontal stem between the nodes is called an internode. Rhizomes typically have short internodes, so the shoots and roots emerging from the nodes are close to each other along the rhizome’s underground length. The key point of rhizome anatomy, that which makes it different from the next discussed spreading mechanism (stolons), is the fact that it is the main stem of a rhizomatous plant. It originates directly from the root crown of the original plant and continues its subterranean, horizontal growth from axillary buds, which are located on the shoot end of the nodes and develop into stems. Rhizomes are also known as “rootstalks.”
Because the rhizome continues to grow outward and generate new leafing and rooting nodes (which are essentially new plants unto themselves), a rhizomatous plant can be easily divided and separated into new plants by cutting the internodes between each growing node/plant. In this way, a gardener can obtain and plant many new plants from just one. Whether this type of plant is divided mechanically by a gardener, or naturally, or if it just continues to generate new growing sections uninterrupted through rhizome biology as described above, it is definitely capable of establishing itself in a garden, with or without the assistance of humans. From an ornamental gardening aesthetic perspective, however, there are many rhizomatous garden plants that benefit from mechanical division. At least in terms of appearance. If left to their own devices, these plants can become overcrowded and appear intermittently scraggly. They will continue to thrive, but not in the aesthetically pleasing fashion desirable to ornamental gardeners.
The picture immediately above on the left shows Hardy Plumbago (Ceratostigma plumbaginoides), which have each multiplied from one plant to several via rhizomes. I planted several individuals in plenty of good soil and room to grow, anticipating their potential spread. They are very healthy and have begun to spread wider than general projections since being planted last July. In addition to Hardy Plumbago, the above mentioned Biokovo Hardy Geranium, and Shasta Daisies (Leucanthemum x superbum) are examples of rhizomatous perennials growing in my garden.
Stolons. From a general perspective, a stolon, as defined by Oxford Languages, is “a creeping horizontal plant stem or runner that takes root at points along its length to form new plants.” Stolons can grow at the surface of the soil or below ground, close to the surface. Plants that spread via stolons are categorized as stoloniferous. Stolons are very similar to rhizomes and share other characteristics with them besides growing horizontally. Like rhizomes, they form roots from their nodes, and are obviously a means of propagation for a naturalizing/colonizing/spreading plant. A new plant is essentially formed at each node. But stolons do differ from rhizomes in a number of notable ways. The most notable difference, anatomically speaking, is the fact that stolons sprout from existing stems at the base of the plant, above ground, as opposed to the underground root crown/axillary buds, as in the case with rhizomes. Further, stolons typically have much longer internodes than rhizomes.
Obviously, I don’t know enough about either rhizomes or stolons to cite all of their similarities and differences. I’m no scientist and I’m not a master gardener either. I just know that rhizomes and stolons are the same, but different. And they each involve the dynamic of one plant potentially, through an actual physical connection, becoming many plants.
As in the case of rhizomatous plants, a stoloniferous plant can be easily divided into separate plants. Unlike rhizomatous plants, however, the stolons between spreading stoloniferous plants eventually deteriorate and disappear on their own, leaving separate and thriving individual plants.
The photo directly above center shows a McDaniel’s Cushion Creeping Phlox (Phlox subulata ‘McDaniel’s Cushion’) which is a stoloniferous perennial, spreading as described above. There is another variety of Creeping Phlox, Phlox stolonifera, which spreads exactly the same way. They are both varieties of stoloniferous Creeping Phlox sharing practically identical anatomical and biological qualities, differing only by virtue of their respective light requirements.
Self-sowing. This is exactly what it sounds like. Plants that naturalize/colonize/spread by self-sowing drop their seeds right around where they’re planted. Many times these seeds do end up far from the site of the original plant. The seeds germinate and new plants are born.
This dynamic can lead to a potentially curious interpretation of the word “perennial.” The picture immediately above on the right is a close up of the seed pods of my Woodland Forget-Me-Nots (Myosotis sylvatica). I’ve circled the seed pods for ease of viewing. This plant is often sold as a perennial. In truth, it is a short-lived perennial, or biennial. Individual plants do not live more than a couple of years. But they naturalize in the garden and persist and spread year after year by means of really aggressive self-sowing. So, can it be considered a perennial because it’s growing in the garden more profusely every year due to it’s self-sowing nature? Yeah, in my book, I guess it’s a perennial. In any event, it definitely appears to be naturalizing in my garden.
On a sort of confusing note, there is another variety of Forget-Me-Not, the True Forget-Me-Not (Myosotis scorpioides), which is a true perennial. This plant is rhizomatous, but it can also spread by self-sowing. There are many other varieties of perennial that spread in this manner. But for the sake of time, and putting an end to my long-windedness, we’ll save this topic for another article.
Naturalizing Perennials - My Planting Scheme
In this, the final section of this article, I want to quickly relay to you a couple of situations that are arising in my garden as a result of my inexperience as a gardener. I’m hoping these situations might just work out for me in terms of a favorable aesthetic and a healthy environment for my plants. These situations involve plantings incorporating naturalizing perennials. You’ve seen the pictures of one or two of these planting combinations already, and there are a couple more pics directly above.
I like planting my plants close together. When I research a plant and buy it, I plant it as near to the minimum spacing requirements that the nursery suggests as possible, without spacing them too closely. And sometimes, I space them even closer. Many times. Almost all the time. Like I said, I like ’em close.
This methodology may or may not present a problem in my garden in terms of both maintaining an attractive design and planting scheme and maintaining the health of my plants. If a plant is, individually, only going to grow to a maximum size – and stay at that size – then I don’t believe my close planting penchant will be a problem. I do want a lush and verdant look, after all. I’m worried that a problem, however, might arise with plants that naturalize being planted too closely together.
The picture directly above on the left shows a Shasta Daisy ‘Becky’ (already spreading via rhizomes) and some clumping Garden Phlox ‘Fashionably Early Flamingo’ growing in the same planting feature. Already, they are overlapping as a result of each plant’s spreading growth habit. The combination looks good now, but for the sake of appearance and the wellbeing of the plants, it may have to be adjusted sooner than later by dividing the plants. This is a beginner’s mistake. I was ignorant of these plants’ growth habits when I first bought them and planted them. I’ll let you know how this situation works out. It’s not the end of the world if I have to divide these plants.
The picture on the right represents a bigger problem. In it, you can see three types of enthusistically naturalizing and spreading plants, all growing within fairly close proximity to one another in a section of my garden. Biokovo Geraniums, Woodland Forget-Me-Nots, and Hardy Plumbago are all doing their thing in clumps stationed really close together. When I planted these last year, as usual without all of the necessary info in my head, I thought they looked pretty cool planted all together. Now that I know what they can do, I’m a little worried about the massive, tangled clump into which they may coalesce. This situation may not be as easily solveable as the potential Shasta Daisy/Phlox dust-up. As I have read, and now understand, the Forget-Me-Nots and the Plumbago can be pretty invasive and very difficult to rein in. While the Forget-Me-Nots are definitely aggressively spreading, they are easy to pull. The Plumbago, on the other hand, is not only assertive, it’s firmly entrenched and tightly interconnected by its incredibly tough rhizomes. I think it all looks pretty good together now, but it’s only been a year. Time will tell. I’ll let you know how it works out.
In this article, my goal was to relay to you some of the jargon concerning perennials that expand their presence in the garden through sheer numbers. Naturalizing, colonizing, rhizomes, stolons, etc, etc, etc. I also wanted to show you how a beginner’s ignorance could result in plants going crazy, squeezing each other out, and, potentially, eventually looking like crap. I hope I succeeded in accomplishing all of this without boring you too badly. I know that this article was sort of on the long side. I wrote it halfway because I thought it might interest (and even maybe benefit) some of you. I wrote it halfway because I felt obligated – I sounded off about this particular subject on a recent Facebook post on The Renaissance Garden Guy page and told everyone I’d write about it on this site. I’m sorry the article ended up being so lengthy and that the topic was kind of heavy. Maybe next time on Facebook, I should promise to write about clowns or beer, or something like that. In any event, thanks so much for sticking around. Cheers, and Happy Gardening!
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You are absolutely amazing in your knowledge and love for plants … I enjoy so much reading about your discoveries. Everything you write about is so well portrayed and documented so much passion and love for those beautiful plants!
It’s absolutely fascinating, actually you are ….
Beautiful images too. ❤️
Wow – thank you, Roxxy! It’s my pleasure to share what I’ve learned. I always tell readers that I learn best from my mistakes. Since I’ve made so many, I’ve learned alot! Thanks so much for your kind words and your interest. I’m so glad you enjoyed the article.