You may have heard of the Plant Select® program—a collaboration between Denver Botanic Gardens, Colorado State University and green industry partners. Its mission is simple: to introduce plants that are not only beautiful, but also tough, water-wise and perfectly suited for gardens in the Intermountain West.</p> Behind the Scenes: How Denver Botanic Gardens Shapes Plant Select®</strong></span> </span></h3> At the Gardens, we play a big role in this work. We trial new plants onsite (see an excellent overview of the process here</a>), manage demonstration gardens at both York Street and Chatfield Farms, and offer Plant Select plants at our annual Spring Plant Sale.</p> But here’s something you may not know: the Gardens also helps discover and develop new plants for the program. With over 17,000 plant varieties in our living collections, we have an unmatched resource to draw from. In fact, more than 70% of Plant Select introductions begin here at Denver Botanic Gardens with our staff.</p> Better Plants for the Intermountain West</h3> In recent years, our horticulture research team has launched a focused plant breeding program to create cultivars and unique varieties tailored for our region. Sometimes this means selecting naturally occurring traits from wild populations; other times it involves advanced tools that allow us to shape plant genetics more precisely.</p> Plant breeding is hardly new—it dates back nearly 10,000 years, when early farmers began selecting plants for better yield, flavor, or appearance. At its simplest, it’s just crossing two compatible plants to combine desirable traits. Over the last century, techniques such as mutagenesis and ploidy manipulation expanded what breeders could achieve, and today, gene editing and transgenics allow us to target traits with unprecedented accuracy.</p> At the Gardens, most of our work still relies on traditional breeding methods. That means crossing plants with traits we want to combine—say, the flower color of one species with the drought tolerance of another. By pairing a highly ornamental plant with a drought-hardy relative, we hope to create varieties that are both beautiful and better adapted to hot, dry conditions. It’s a long process, often requiring multiple generations before the right combination is achieved.</p> We also use mutagens, substances that can trigger changes in a plant’s genome. While these changes are random, they often produce predictable outcomes, such as compact growth, novel foliage color, or reduced fertility. We use this technique with plants that already have strong ornamental appeal and environmental tolerance but may benefit from a unique twist or refinement.</p> Beyond Beauty: Our Breeding Goals</h3> Unlike ornamental horticulture at large, our breeding priorities go beyond aesthetics. We aim to develop plants that are not only striking in the garden, but also resilient in our increasingly harsh climate and supportive of pollinators and ecological health.</p> In other words, we’re not just breeding plants to survive here—we’re breeding them to thrive. </p>
Scattering a few ounces of seed onto dry Colorado soil can feel more like hoping than planting. Folks who’ve tried store-bought wildflower mixes might know the frustration: despite following instructions, results are often inconsistent. Mixes may bloom for a season or two but can be patchy, lack coherent design, are soon overrun by weeds, or collapse into stands dominated by one or two aggressive species.</p> Still, direct seeding remains one of the most appealing ways to transform non-functional turf, medians and other tough spaces. Seeds are inexpensive, species are easy to source compared to potted plants, and installation is simple. Our horticulture research team at the Gardens has been investigating ways to make direct seeding more reliable, creating mixes that are beautiful, resilient and long-lasting.</p> Setting Parameters</h3> One challenge with many commercial mixes is the lack of crucial details. Sowing rates are often given in pounds per acre, which is nearly impossible to scale to a backyard or small urban lot. Even worse, weight is misleading: a gram of lupine seed equals about 30 seeds, while a gram of Artemisia can be nearly 10,000. To improve accuracy, we calculate sowing rates based on the number of seeds per unit area (i.e., 300 seeds per square foot). This method allows us to balance species more precisely and adjust mixes to specific sites.</p> Another problem is growth form diversity. Most mixes emphasize only wildflowers, overlooking grasses and shrubs—two of the most resilient growth forms in Colorado ecosystems. However, the right ratio of these various growth forms is crucial. Too many aggressive grasses or shrubs, and diversity disappears. But when balanced, each growth form contributes to a stable and enduring plant community.</p> Choosing the Right Species</h3> Species selection is just as critical. Every plant has unique traits: germination timing, bloom period, lifespan, stress tolerance and competitiveness – among many others. Many mixes rely heavily on species that sprout quickly, which may look good at first but fail to sustain long-term diversity or season-long blooms.</p> Our approach uses trait-based design. We include fast-germinating species that suppress weeds in the first year while leaving room for longer-lived species to establish. We also screen new species for how they perform over multiple seasons, tracking which ones persist, coexist well with others, and extend bloom time from spring through fall.</p> Timing Matters</h3> We’ve also studied how sowing season affects establishment. Standard advice is to sow in autumn so cold weather can break seed dormancy. But our trials show that spring sowing—using seeds pre-treated with cold in refrigeration—often yields higher germination, especially when paired with supplemental irrigation in the first year. Losses from winter die-off, predation, and moisture stress may explain why fall seeding performs less reliably.</p> Built to Last</h3> Direct seeding may never be as predictable as planting nursery-grown perennials. But with thoughtful design, it can be just as successful. By refining sowing rates, balancing growth forms, carefully selecting species, and timing sowing strategically, we’re creating custom mixes that are diverse, resilient and built to last in Colorado’s challenging conditions.</p> </p>
When I talk about my work as a scientist in the Research and Conservation Department at Denver Botanic Gardens, I explain how I study the role of genetic diversity in conserving biodiversity. People often ask for examples of this or cite famous stories of disease resistance, genetic rescue or environmental adaptation. Indeed, there are great examples, such as how a lack of genetic diversity led to widespread disease and die-off of potato crops resulting in the 1800s Irish Potato Famine, or the successful recovery of the endangered Florida panther after introduction of new genetic variation from Texas panthers. I want to highlight a few real-world examples that are specific to plant biodiversity conservation. </p> First, adaptation to new environments is facilitated by genetic diversity. Examples of this include colonization of toxic mine tailings by certain grass species (e.g. Anthoxanthum odoratum</em>), adaptation of yarrow (e.g. Achillea borealis</em>) and other species to serpentine (low nutrient, high heavy metal) soils, and existence of new species or varieties of wild sunflowers (e.g. Helianthus petiolaris</em>) in sand dune habitats. These studies of natural phenomena are particularly valuable to understand in the context of conserving biodiversity under ongoing threats of environmental change. </p> Second, genetic diversity can increase ecosystem function. While the mechanisms for this are still debated, there is ample evidence that complementarity, or differential strategies by different species or genetic variants, allows for improved functioning of ecosystems. In grasslands for example, it has been shown that species that utilize above- versus below-ground space in complementary ways results in higher productivity overall. Or in the case of threats such as herbivores and climate extremes, different plant species can protect or facilitate each other via mechanisms such as nurse plant effects. Together, these examples emphasize the role of genetic diversity in plant communities and the importance of conserving it. </p>
In 2018, Denver residents voted to pass the citywide green roof ordinance, sparking excitement about a greener, cooler, livelier cityscape. Many rooftops transformed into gardens, farms, and pollinator havens. But despite their benefits, green roofs are notoriously difficult to establish—especially in Denver’s semi-arid climate.</p> On a rooftop, plants endure full-sun exposure, with substrate temperatures soaring above 90 degrees in summer and plunging below freezing in winter. The shallow, fast-draining engineered soil holds little organic matter. As a result, designers often rely on sod seeded with Sedum species.</p> While sedum roofs offer benefits, they lack the biodiversity, dramatic colors, and rich textures one might see while visiting Denver Botanic Gardens or hiking the mountain trails of Crested Butte in summer. Colorado’s native species are well adapted to such harsh conditions, yet their potential on green roofs remains largely untapped. Recognizing this, Colorado State University graduate student Maria Schonewise partnered with the Gardens’ horticulture research team to develop native seed mixes capable of establishing naturalistic, resilient plant communities on rooftops.</p> Working with Manager of Horticulture Research Michael Guidi, Schonewise designed a mix of 34 wildflowers, grasses and shrubs, varying seed densities to test establishment. Once developed, her mix was then sown into approximately 60 plots across three Denver green roofs: CSU Spur, Community College of Denver and in the Green Roof garden</a> atop Offshoots Café at the Gardens.</p> Throughout the summer, Schonewise tended plots and collected data on species presence, abundance and weed coverage. These findings will help answer pressing questions: Which plants are tough enough to thrive? How can we create biodiverse, low-maintenance communities? What pollinators use rooftop habitats, and what resources do rooftop native plant communities provide urban pollinators? </p> Her research could help improve upon the industry standard sedum mats used in green roofs by creating a reliable, hardy and biodiverse method for establishing plant communities, making them just as colorful and rich as Colorado’s various landscapes. Next time you visit the Gardens, stop by the Green Roof garden above Offshoots Café to see this living laboratory in action.</p> This article was contributed by Horticulture Research Associate Reece Bailey</strong>.</em> </p>
Our research scientists collect a lot of data every summer—and this work can be challenging. From our work in the field, we’ve learned to come prepared to clear one road that is invariably blocked by downed trees. Then there are the hours we spend on our hands and knees keenly searching for and measuring hundreds of individual rare plants. In small plots at study sites throughout each species’ range, we mark every individual and track their fate year after year. </p> This annual data allows us to correlate climate variables to survival and reproduction. We can then estimate the population’s risk of extinction. In addition to the annual demographic monitoring, we are developing methods to efficiently and effectively estimate the total population size</a> of rare plants. Population counts help us estimate the level of genetic diversity within a population. A sufficiently large population can potentially adapt to climate, habitat and plant community changes. Our data serves to address global challenges. An estimated one million species face extinction worldwide. There is a need to prioritize species and put resources to those most at risk. Tools like the U.S. Endangered Species Act</a> and the International Union for Conservation of Nature Red List</a> rely on population counts and predictions of risk. </p> While we annually collect data all over Colorado on six rare species, all of these help improve and promote effective data collection methods. We are chipping away at the biodiversity crisis by collaborating and sharing expertise with federal and private conservation partners. Our efforts are extended through our participation in the Global Strategy for Plant Conservation</a>. </p> The task may be daunting, but I look forward to clearing the way to collect meaningful and impactful data for years to come. </p>
With leaves falling outside, temperatures getting lower and Halloween creeping closer, it’s the perfect time to curl up inside with a good mystery, thriller or horror novel. If the book is plant-related, that’s even better!</p> The Helen Fowler Library</a> has a great selection of fiction works, and we invite you to browse our offerings this spooky season. </p> Mystery</h3> Mystery books make up a good portion of our fiction collection, including puzzling and atmospheric works like:</p> “Thyme of Death” by Susan Wittig Albert. The first entry in the China Bayles series introduces the mystery-solving herb shop owner who stars in 29 books to date.</li> “Garden of Shadows” by local author Amy Marie Turner. Set in 19th century Spain, botanist Linnea Wren must navigate political intrigue, romance and more while solving a murder. </li> </ul> Thriller</h3> Thriller books in our collection include:</p> “Goldilocks” by Laura Lam. A science fiction thriller set in space with the survival of humanity on the line. The Goldilocks Zone is supposed to be just right for human life but getting there won’t be easy.</li> “The Slime Mold Murders” by Ellen King Rice. A unique ecological pandemic thriller set at Halloween time where the lead character’s expertise on Myxogastria slime molds proves crucial in saving lives.</li> </ul> Horror</h3> Horror works we have lean toward cosmic and ecological horror, which can be really terrifying. Check out these selections:</p> “Parable of the Sower” by Octavia Butler. A dystopian novel with ecological horror elements written in 1993 and set in the then-distant future year of 2024. We have the graphic novel adaptation on hand, and its dark illustrations match the original novel’s tones of horror and societal decay perfectly.</li> “Annihilation” by Jeff VanderMeer. This first entry in the Southern Reach series introduces us to Area X and the cosmic horror lurking within. Winner of both the Nebula and Shirley Jackson Awards.</li> </ul> Nonfiction</h3> Finally, for a great nonfiction book that traces the use of plants and gardening in mystery novels, take a look at “Gardening Can Be Murder.” Expert gardener, historian and author Marta McDowell informs the reader on a plant-by-plant basis of which flora have been implicated in murder in which authors’ novels.</p> For more recommendations, come visit us at the Helen Fowler Library! </p>
With cooler, rainy weather and a late June hailstorm punctuating the early weeks of our growing season, the water gardens got off to a slow start this year. Fortunately, aquatic plants are resilient and ours have made a triumphant comeback. August is a great month to take a walk around the water gardens to see them in their full glory. </p> Begin your stroll at the small pool in the Ellipse</strong>, home to the glass sculpture Colorado by Dale Chihuly</a>. A unique plant displayed in this pond is mosaic plant (Ludwigia sedioides</em>). This South American native thrives in warm water, making this pool the ideal spot for it to show off its intricate pattern of tiny floating leaves arranged in a mosaic pattern on the water’s surface. Hardy and tropical waterlilies (Nymphaea</em> hybrids) including ‘Purple Passion’, ‘Paul Hariot’, ‘Black Princess’ and ‘Albert Greenberg’, along with Colocasia esculenta</em> ‘Black Magic’ and Canna</em> ‘Chiquita Punch’, round out the display in this pond.</li> Next, head west to the Romantic Gardens’ pool</strong>, where you will find a display of star waterlilies. These waterlilies are named for the shape of their blooms, which are stellate and held high above the water’s surface. One waterlily species, Nymphaea gracilis</em>, has been used by hybridizers to create cultivars of star waterlilies with flowers in a rainbow of colors. N. gracilis</em> is native to Mexico and has solid white blooms and green leaves. Cultivars displayed in this pond include the pink flowered ‘August Siebert’, ‘Rhapsody in White’ (which boasts white blooms and mottled leaves) and ‘Rhonda Kay’ (which rounds out the collection with purple flowers). A pair of Santa Cruz water platters (Victoria cruziana</em>) surround a recirculating pottery fountain in the center of this pond.</li> Continuing to the west, you will find the Four Towers Pool</strong>. This pond borders the south and west sides of the Science Pyramid</a> and showcases a collection of hardy intersubgeneric waterlilies (crosses between hardy and tropical waterlilies that have proven to be winter hardy here in Denver). Included in this pond are hardy waterlilies, tropical waterlilies and an assortment of marginal plants (plants that typically grow in shallow water around the margins of a pond) including Canna </em>‘Sunrise Trumpeteer’, Canna </em>‘Ra’, red stemmed thalia (Thalia geniculata</em> f. rheumoides</em>), swamp hibiscus (Hibiscus</em> ‘Berry Awesome’), Mexican petunia (Ruellia simplex</em>), golden Japanese sweetflag (Acorus gramineus</em> ‘Ogon’) and imperial taro (Colocasia esculenta</em> ‘Illustris’). Water platters (Victoria</em> ‘Longwood Hybrid’) grown from seed each spring in our greenhouse complete this display.</li> The next pond on our walking tour can be found at the west end of the Steppe Garden just as you enter the Annuals Garden</strong>. This pool is home to a collection of taro (Colocasia</em>) cultivars that showcase the range of foliage and stem colors that have been developed in this genus. Colocasia esculenta</em> is also displayed in this pond with an interpretive sign detailing its importance as a food crop in tropical regions. Hardy and tropical waterlilies accent the display along with the feathery foliage of mare’s tail (Hippuris vulgaris</em>) and the thorn-encrusted leaves of gorgon plant (Euryale ferox</em>). </li> As you walk through the Annuals Garden</strong>, you will come to the next ponds on our tour, situated on either side of the walkway at the north side of this garden. The east pool highlights the Rocky Mountain Legacy Collection—waterlilies that have been tested for performance at the Gardens over the years and which have historical significance. This collection includes the hardy waterlilies ‘Colorado’, ‘Denver’, ‘Denver’s Delight’, ‘Joey Tomocik’, ‘Bea Taplin’, ‘Attorney Elrod’ and ‘Cynthia Ann’. Tropical waterlilies in the collection include ‘Stan Skinger’, ‘William McLane’ and ‘Bob Hoffman’. The pond on the west side of the walkway includes showy tropical plants to complement the Annuals Garden. Dwarf Egyptian papyrus (Cyperus papyrus</em> ‘King Tut’) along with Canna</em> ‘Lemon Punch’, Colocasia</em> ‘Diamond Head’, Victoria cruziana</em> and an assortment of colorful tropical waterlilies make the perfect aquatic companions for the annuals in the bed bordering this pond.</li> North of Sacred Earth’s pond and our outdoor café, the Hive Garden Bistro</a>, Monet Pool</strong> stretches west to the border of the Japanese Garden and is our largest display pond and the final stop on our tour. This water garden features the always-popular water platters (Victoria </em>‘Longwood Hybrid’, Victoria amazonica</em> and Victoria cruziana</em>) as well as hundreds of hardy and tropical waterlilies, water-loving Canna hybrids, aquatic Iris </em>and other marginal plants including pickerel plant (Pontederia cordata</em>), lizard’s tail (Saururus cernuus</em>), powdery thalia (Thalia dealbata</em>) and common rush (Juncus effusus</em>). Stands of lotus (Nelumbo</em> cultivars) can be found throughout the pond as well. These begin blooming in mid-July and continue into August before dropping their petals to reveal showy, decorative seed pods. </li> Be sure to find the display of Australian waterlilies at the southwest end of Monet Pool near Le Potager garden</strong>. These tropical waterlilies need consistently warm water and sunny days to thrive and can be a bit finicky in our unpredictable climate. Their impressive size and beautiful, giant blooms make them worth the effort and worthy of a few final photos.</li> </ul>
