EDITOR'S ARMCHAIR: Considerate Horticulture Empowered by iNaturalist
By Tony Gurnoe, for Let's Talk Plants November 2026. All photos by Tony Gurnoe.
Considerate Horticulture Empowered by iNaturalist
This article is meant to stoke an important conversation brought up almost in passing by our recent presenter and iNaturalist identification champion, Jon Rebman. As described in the MEETING REPORT article, Jon provided a rich, educational presentation on the fern and lycophyte diversity of San Diego County. To conclude that presentation, Jon talked with us a bit about gardening with San Diego’s immense diversity of native plants and some important considerations toward gardening with any plants in a way that is sensitive to our impacts on the remnant natural spaces surrounding our gardens. Through this article I hope to summarize a couple of different facets of that effort, and to encourage an ongoing dialogue on the subject between our members and gardeners of our region.
Two different, although related aspects of horticulture came up in that Q&A session. One of which is more positive and one more potentially detrimental. Let’s start with a simple question provided by the San Diego Horticultural Society audience to Jon, “Should we avoid planting anything that is not native?” Although Jon is one of the most prominent botanists to have ever studied our region’s profound floristic diversity, his response was respectful and pragmatic. Jon said, and this is something that I generally agree with, that he doesn’t want to infringe on people’s ability to grow what interests them and to experiment within their own gardens. That wasn’t the extent of the conversation, though, and he went on to describe garden contexts that might warrant a bit more cautious care and attention to the details of how our gardening actions affect the world beyond our own plots.
This gets us into the framework of how to garden in a way that is considerate to the world around us, beyond the simple threshold of something being native or exotic to a given place. The first thing I would like to highlight, inspired by the discussion at our last meeting, is the concept of ecotypes. This may be a new word for many gardeners. We’re familiar with species and varieties, but what is an ecotype? Think of this in terms of diversity within a given type of plant. A specific example that I can provide comes from monkey flower research that I helped San Diego State University and an array of other partnering universities from around the county complete from 2022-2025. We grew 5,500 different scarlet monkey flower (Erythranthe cardinalis) plants from seeds which originated at 3 geographically unrelated locations. One group of seeds came from wild plants in San Diego County. Another group from populations in central California, and to study the entirety of their distribution, a third group of seed was sourced from as far north as southern Oregon. Would you expect all of these seeds to behave the same, or differently? They’re all the same species, after all.
The 5,500 plants that I helped manage and study were randomly planted in our common garden research plot to diffuse hyperlocal influences like water availability and sun exposure. Similar, replicate plots were also grown near those other seed source locations. To fast forward through several years of intensive data collection in the blistering summer sun, I’ll tell you the general pattern that we observed. By the end of the trial, the representation of surviving plants was substantially biased toward plants that grew from seed collected locally. This may come across as intuitive to some of you, but scientists need to see the data, which turned out to support the importance of ecotypes.
Ecotypes are distinctions within a plant taxon derived from the specific nuances of their exact environment, but not physiologically significant enough for those differences to separate various plants into different varieties or subspecies, at least yet. A simpler, useful way to characterize this is by considering subsets within a species to have certain “local adaptations.” For our gardening purposes this encourages that even within a species recognized as native, we seek out sources from locations as much like our own gardens as possible. Rather than buying a “California native seed mix,” which could come from anywhere, try to find local brands and plant material - not only for the sake of success in your gardening efforts but also as a way of being sensitive to the genetic drift coming out of our landscapes.
As a segway into the discussion of horticultural escapees, I’ll provide a nuanced local example of where all of these concepts intersect. San Diego has our own native cherries, the hollyleaf cherry (Prunus ilicifolia). They’re fantastic landscape shrubs with a lusher look than the care they require, nice clusters of white flowers at the branch tips, and copious crops of attractive and delicious (albeit mostly seed) fruits. A great choice to plant in many San Diego gardens. However, San Diego’s hollyleaf cherry is not the only one. Catalina Island also features native cherries from the same species. Plants from the Channel Islands are incredible and unique and it’s no surprise that many gardeners throughout San Diego have elected to feature them in their home gardens. What did prove to be a surprise is that these Catalina cherries have actually started to genetically displace San Diego’s own native cherry diversity!
Today, as scientists look closely at wild cherry plants, more and more of them are hybrids between the San Diego subspecies (P. ilicifolia ssp. ilicifolia) and the Catalina subspecies (P. ilicifolia ssp. lyonii). This demonstrates both that the question “is it native?” is insufficient, and that regardless of what we choose to plant, it will have an impact on the surrounding natural areas. This brings us to the premise of ethical planting choices and what that decision making process looks like.
While both Jon and I are reluctant to assert that non-native plants should be outright eschewed in local horticulture, the historical trend line is clear in that most of the large statured invasive plants in our region originated in somebody’s garden. Expensive, damaging, difficult to manage examples include giant reed (Artundo donax), pampas grass (Cortaderia sp.), iceplant (Carpobrotus sp.), Acacias, Mexican fan palms (Washingtonia robusta), etc. These were all offensive errors in their horticultural introduction, but in fairness we need to ask, “Did horticulturists at the time have the tools to understand the implications of their gardening actions?” Perhaps not in all of these cases, but today we do.
This brings iNaturalist into the conversation and reminds me of an interaction I had with a fledgling botanist and now avid iNaturalist user who asked, “Is there any value to me documenting non-native species through iNaturalist?” The answer is resoundingly, “Yes!” and I hope to encourage our group of cutting edge plant people to pay attention to the utility of this new tool.
For those totally unfamiliar, iNaturalist is a phone app that allows any person to simply upload photos and associated data of say a plant or a bird or a bug, and the entire community then has the opportunity to weigh in on what that thing is. Scientists today frequently use the monumental pool of data afforded through iNaturalist to study things like Jon described in his presentation - primarily what occurs where.
You don’t have to be a botanist or a data scientist to take advantage of all of this crowdsourced data, so I want to provide an example of how this new technology can play into our plant selection decision making, through a plant that Jon brought up during that meeting: the golden rain tree (Koelreuteria paniculata). Are they invasive? They’re not listed as such in our region, although this species is considered invasive in Florida. In fact, many of the municipalities throughout San Diego County are actively installing this species as either street trees or in parks, but how do we know they won’t become the next Sydney golden wattle (Acacia longifolia) or Canary Island palm (Phoenix canariensis)? In the old days this would involve mostly a “trust and verify” approach, but that unfortunately meant that by the time we realized some of our garden plants to be invasive (castor bean, Ricinus communis, and fountaingrass, Pennisetum setaceum as examples), the proverbial cat was already out of the bag and those plants have continued to displace native ecology, costing our state many millions of dollars annually in mitigation efforts of limited efficacy.
Pictured are all of the data points of this species within San Diego County. Admittedly, 20 data points is not enough to come to any definite conclusions. That brings us to the first call to action - get out there and contribute information about what you’re seeing so that we can all make more informed decisions going forward! Still, we can glean some useful understanding from any such publicly available data so let’s hone in on a single data point, one provided by Jon himself.
As you’ll see, the plant that Jon documented is a seedling out of place. While this isn’t a once and for all conclusion, it does suggest that maybe these plants pose a risk of “volunteering” themselves well beyond the boundaries of managed horticultural landscapes. If we dig in a bit deeper to this foundational data set, it becomes apparent that many of the plants observed are essentially “out of place.” As we all know, a weed is simply a plant in a location where it’s unwanted and that’s a fair statement about golden rain tree seedlings being found in natural areas such as the Penasquitos Canyon Preserve.
Let’s bring this back to your garden and your choices. Between the Plant Forum which I hosted at the beginning of the meeting and the discussion led by Jon Rebman, we collectively made a few categorical statements that I hope you’ll take to heart. Planting native plants, especially from local sources such as our friends at Walker’s Wildlands, is always a good primary consideration. Where you choose to grow something exotic, there are important things to keep in mind. Does that non-native plant produce bountiful seed crops which have the ability to disperse beyond your garden’s boundaries? Does that plant spread vegetatively either underground or by rooting easily from broken bits? If so perhaps it’s a candidate that should be relegated to planting in a container, if at all. What about the geographic context of your garden? Are you in a fully developed urban space or does your backyard bleed into a canyon of struggling remnant native plants and animals? The latter warrants much more caution when we consider how many of our most devastating invasive plants started out as either a seed or other propagule somehow escaping a person’s well-loved garden.
My hope is that this prompts questions and consideration on your end. I do not have all of the answers but it is clear that collectively we are much better equipped to evaluate such important choices than any isolated gardener. Get out in your garden and look at your own plants with new eyes. Are those native plant lovers among us aware of where the nursery sourced their beloved plant in the first place? Could some of your historic struggles relate to a lack of “local adaptation?” Is anything growing along your fence line also starting to encroach on either neighbor’s gardens or a nearby open space? Is beauty enough of an incentive to grow something providing evidence of invasion risk, such as the golden rain tree? Rather than just telling you my individual opinion on such things, I hope you will feel empowered to dig into the growing body of real-time information available to us, to come to your own best conclusions. We all love growing plants, but we can no longer plead ignorance about the consequences of the actions we choose to make in our own gardens. Instead we must come together and lead the culture part of horticulture toward more informed and responsible planting choices so that future generations can be afforded the opportunity to experience the incredibly diverse lifestyle of being a gardener in San Diego.
