by Cynthia Reiners
Phenology: the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life. — from Oxford Languages
“In 1492 Columbus did not so much discover The New World as begin to make A New World” [italics added]
— Charles Mann, 1493
“Knitting together the seams of Pangea”
— Alfred Crosby, The Columbian Exchange
On the eastern edge of the Rocky Mountains, the Front Range is well known for dramatic weather. The last 12 months, beginning with the temperature drop on October 9-11, 2019, from 81 degrees to 14 degrees and heavy snow, have seemed especially wild with a very hot summer, extreme drought, high winds and large wildfires. The science of climate change tells us that many of these conditions are exacerbated by the global greenhouse effect and can be expected to intensify in coming years.
What might this mean for urban/suburban Front Range gardeners?
For thousands of years there has been an established synchronicity between plants and their associated animals. Phenology tracks the timing and order of blooms with the arrival of pollinators, and the availability and dispersal of fruit and seeds with the presence of specific birds and mammals. My shorthand for the complex interrelationships of plants and animals, microbes, soil, water and weather is the “local web of life.” Climate change is clearly disrupting these relationships.
This article highlights over 20 years’ of my experience gradually creating and refining both dryland and irrigated gardens in a small suburban property in southeastern Denver and observing and recording this very local web of life. Notably, I have seen how my dryland shortgrass prairie plants are necessary but not sufficient to support the visible animals. I have seen queen bumblebees emerge and migrating hummingbirds arrive when their natural food sources are not yet available; extreme heat and drought cause blossom and/or fruit failure; early freezes spare the blooms but drastically reduce the active native bee population. An interim of 6 years gardening in Tucson deepened my appreciation of such plant adaptations and animal associations.
As this property is far removed from any natural area and is an entirely “constructed” landscape in a traditional 65-year-old neighborhood, it contains several non-native and irrigated plants from different continents and eco-systems. Many of these were inherited with the property, others I added both from traditional horticulture and the recommendations of the early phase of xeric landscaping when locally native plants were not so readily available. Overall, this diversity creates an opportunity to fill some phenological gaps. A more descriptive title for this article might be “Extending the season of bloom in a mostly native, mostly xeric World Garden to support the local web of life including native bees, butterflies and moths, other insects, birds and mammals, and also non-native honeybees, earthworms, bindweed, and Japanese beetles in my garden.” The continents of Pangea have indeed been stitched together.
II. THE GARDENS AND PLANTS
The original dryland garden began in 2000 with an extensive rescue of plants from an unplowed area of Highlands Ranch about to be bulldozed for development. Planted into a former bluegrass lawn and later augmented with other prairie species and recommended non-native xeriscape plants, over the years this garden has been largely unirrigated, 2020 being a notable exception. I have maintained a running record of plant loss or removal, sequence of bloom, and animal associations.
Highlands Ranch rescue site
May 2018July 2020
It is the periods of dormancy (both winter and summer), growth, bloom and fruiting of this dryland garden that provide the baseline. My memories of specific gardening years tend to run together, and some years major life events keep me away from the landscape more than I would like. For consistency, I use the following calendar “anchors” to log plant and animal observations consistently each year.
– CoNPS Landscaping with Native Plants conference in mid-February. Weather conditions and snow on the ground coincide with the appearance of tiny Crocus (see below) and first honey bees.
– DBG Mothers’ Day plant sale. Weather conditions and how open the landscape has been to this point. In 2020, I had already done quite a bit of volunteer seedling transplants and weeding by this time because there was no snow cover.- Any triple digit temps in June. In Tucson, May and June are known as the “dry fore-summer,” the hottest months of the year when plants are dormant, waiting for the arrival of the monsoon in early July. In a “normal” June in Denver, it can be peak bloom time. 105˚F is desert weather but these are not desert plants. What was the bloom response, which can seriously affect pollinator resources?
– Number of Yucca glauca blooms and subsequent fruit set. In 2020, for the first time, the answer was zero and zero.
– Date of the first frost hard enough to kill the Tithonia rotundifolia. In 2020, it was mid-October, right on average.
The following is a summary table of perhaps lesser-known plants that I can recommend as extending that baseline season of dryland shortgrass natives, with an emphasis on diverse families and general availability. As the list contains several non-natives in the publication of an organization dedicated to the promotion of native plants, it is important to explain my reasoning.
First, as briefly described above, there are clearly times when the cycles of bloom and their associated animals are not in sync. For example, the hummingbird-favorite honeysuckle growing with irrigation in a very protected location will often bloom when my various early season native orange-red-pink penstemon blossoms have failed due to either a late freeze or extreme high temperature. Crocuses flower well before the large blue blooms of Rocky Mountain Penstemon (Penstemon strictus), preferred by the equally large queen bumblebees. In the interim, I have watched those queens struggle to nectar on the early succession of native thin stemmed Prairie Bluebells (Mertensia lanceolata), Blue Flax (Linum lewisii), American Vetch (Vicia americana), and Harebells (Campanula rotundifolia).
Second, few people have had my advantage of rescuing 45 species of native shortgrass prairie plants. Most of those plants are not generally available through commercial nurseries, and if available, may have been treated with neonicotinoid insecticides. While experienced native plant gardeners may be comfortable ordering plants by mail or starting seeds or driving long distances at specific times to the limited number of places dedicated to growing and/or selling neonic-free native plants, newcomers may be discouraged by this supply problem.
Third, with research, it is possible to select non-natives that are most closely related to our local Front Range and Foothill natives. I use Weber’s Colorado Flora: Eastern Slope to define “local.” I like to stay with non-natives selected in the same genus or family as a “local” plant, or from a limited larger geographical area.
Ultimately, it is the function of any plant within the landscape that is most important. Research can help gardeners avoid those plants, native or not, that are too aggressive for a small garden. Observation will reveal which animals will utilize which plants and how that may change year to year. This is especially important in monitoring the native vs. honeybee pollination patterns, a potentially controversial point.
Plants to extend the season of bloom, by category
Native xeric Non-native xeric Non-native irrigated
1. Western Wallflower 4. Cosmos 11. Honeysuckle
Erysium capitatum Cosmos bipinnatus Lonicera sp.
BRASSICACEAE ASTERACEAE CAPRIFOLIACEAE
2. Snow-on-the-Mountain 5. Rose Campion 12. Mexican Sunflower
Euphorbia marginata Lychnis coronaria Tithonia rotundifolia
EUPHORBIACEAE CARYOPHYLLACEAE ASTERACEAE
6. Crocus sp.
9. Tulip sp.
3. Sundrops 10. Salvia/Meadow Sage 14. German Statice
Calylophus hartwegii Salvia x sylvestris ‘Blue Hill’ Goniolimon tataricum
ONAGRACEAE LAMIACEAE PLUMBAGINACEAE
These individual plants are discussed in order of their approximate bloom sequence. The numbers refer to the summary table above.
6. Crocus ancyrensis ‘Golden Bunch’: very small, earliest, tangerine color. The south-facing edge of the driveway is the first location to warm up in late winter. The bright blossoms emerging from Dragon’s Blood Sedum are very cheerful. This is the first place I see honey bees. A long season of bloom can be created with different varieties of crocus. I see queen bumblebees every spring on the later, larger crocus flowers. Once the crocus are gone, the queens struggle to get nectar from weak-stemmed Blue Flax and American Vetch until their preferred blooms, Rocky Mountain Penstemon are available.
‘Golden Bunch’ Crocus Tri-colored bumblebee
7 & 8. Chionodoxa and Scilla: Woodland spring bulbs. I initially planted these as a reminder of my Virginia garden. They grow in the east-facing, irrigated portion of the garden, in partial shade in late winter/early spring with the sun at a low slant. Both have blue flowers and attract honey bees. Their prolific spreading is a surprise as this is a very hot and sunny garden in summer.
9. Tulip polychroma: Height: 4”; Bloom: early, multi-stem, white flower. Located at the base of a south-facing wall, this is my earliest blooming tulip. It is so thoroughly pollinated by honey bees almost every flower goes to seed. There are many varieties of small species tulips available. I have not noticed any native bees visiting them.
11. Honeysuckle (Lonicera) sp.: This is extremely important for providing the first blossoms for returning hummingbirds. In 2020, the late spring freeze killed off the flowers and the birds were completely dependent on neighbors’ feeders. This plant grows up a porch trellis adjacent to a downspout, protected by an Amur Maple and therefore surviving any mild freezes. We enjoy the fragrance through the nearby living room window. Plant (13.) grows directly underneath the trellis.
1. Western Wallflower: This local native blooms in late spring, with bright yellow flowers on relatively tall and slender flower stems poking above the growing cool-season Sedge and June Grass. It is a biennial or short-lived perennial in the dryland garden. It moderately self-sows but is very easy to transplant or weed out. I purchased seed online. This is a good plant for providing Brassicaceae diversity.
A splash of early color
Photo from Lady Bird Johnson Wildflower Center
12. Salvia ‘Blue Hill’: This plant is from my earliest phase of xeric plantings, thriving since 1999 in my harshest dryland area between the driveway on one side and sidewalk/street in front. It is absolutely cold hardy and bone-dry xeric. It throws relatively few seedlings, probably because it is grown so dry. However, once established it can be somewhat hard to remove, so be sure to plant it where you want it!
It is included here because it is a repeat bloomer. In early summer the dark blue spires nicely complement the blooms of Rocky Mountain Penstemon (Penstemon strictus). Then, having been cut back hard, it will bloom again with the late summer/early fall spires of Dotted Gayfeather (Liatris punctata). This salvia appears to be visited primarily by honey bees. Native bees favor the adjacent native blue flowers.
I don’t know if the Great Plains native Pitcher Sage (Salvia azurea), would fill the same role; it is a much larger plant and only blooms in the summer.
Salvia and Rocky Mountain Penstemon in the hot dry corner, June 2020
Liatris and Salvia, with spent Penstemon stalks behind, Sept 2020
3. Sundrops: This is a yellow-flowered, summer daytime blooming member of the evening primrose family. It also grows in the hottest, driest section of the dryland garden. It is included as an extender because of what I call its “opportunist” blooming tendency. During drought it may lose many of its leaves and hold dormant flower buds at the tips of its stems. Any water, whether monsoon rain or irrigation, can stimulate it into sudden reblooming. The aging flowers turn from bright yellow to apricot/watermelon, quite a nice “color-pop”” It is heavily visited by hawk moths, and to a lesser extent by native bees.
First bloom and later fade, Sundrops
4. Cosmos: Contrary to its typical horticultural description, this ubiquitous garden annual from tropical America has surprised me with its ability to thrive throughout the summer with very low water, persisting until the first hard freeze. I dug out most seedlings from their original site in the irrigated garden, but a few migrated to the adjacent dryland area, forming nice tight foliage. The pink and white flower color is a welcome alternative to the predominantly yellow and purple of the adjacent late season dryland flowers. It is visited by honey bees, native bees and numerous butterflies.
Cosmos grown very dry, about 18” high.
A very large bumblebee for such a thin stem.
5. Rose Campion: This long-blooming biennial or short-lived perennial in the Pink Family comes from Southeast Europe. The drought-adapted silvery felt of the basal rosette, stem and leaves fits perfectly into the low water or dryland garden. It is a moderate self-sower but the volunteers are easily removed. In summer, the magenta blooms provide a very pleasing contrast with the orange blossoms of Butterfly Weed (Asclepias tuberosa).
It is the structure of the flower that makes it of particular interest as an “extender” plant. The flower opens on the horizontal plane, with five petals and has a long, tubular shape. This makes it highly attractive to hummingbirds and hawkmoths, and to a lesser degree large butterflies, which can access the recessed nectar with a long proboscis.
Rose Campion. Can you see the small native bee clinging to the underside of the leaf?
13. Plumbago: Interestingly, this plant is from a completely different family but has essentially the same flower structure as the Rose Campion above. Here, the flowers appear in late summer/fall with intense indigo bloom, and foliage that turns a beautiful deep bronze. It grows in the irrigated garden adjacent to a downspout, in part sun to full shade. Included is a photo of another Plumbago species native to Tucson, greatly enlarged to show the flower structure.
Plumbago, High Country Gardens
It’s easy to overlook smaller, drabber moths.
Plumbago scandens, Tucson
14. German Statice: Originally from southern Russia, this Statice is a staple of the cut flower trade. With its very large leathery leaves, its 15-year longevity in my irrigated garden is surprising. The dried flowers are an attractive addition to the late fall landscape of grasses and composites.
I consider it an important extender both because of its unusually tiny bluish-white flowers, and mid-late summer bloom period when so many xeric plants are dormant. Those very tiny flowers provide essential food to many species of small wasps, flies, bees and other insects, often so small and moving so fast it can be hard to identify them. Interestingly, in Tucson I grew a plant from the Chihuahuan Desert, Wright’s Buckwheat, with similar characteristics and pollinator-support function, from a completely different family. Eriogonum wrightii var. wrightii, ‘Snow Mesa’ Buckwheat, is now available through Plant Select. It should thrive with less water than the Statice.
In the full sun irrigated garden, Statice is the large purple mound on the right, in front of the bird. The two tall plants with orange flowers are Mexican Sunflower.
This is Wright’s Buckwheat, now available through Plant Select.
12. Mexican Sunflower: If you try only one plant from this list, this is my top recommendation. This tropical annual has very bright orange ray flowers and golden disk flowers, held horizontally. They are an absolute magnet for southbound migrating monarch butterflies, if you are so lucky as to have any in your area. Of course, other butterflies and bees, especially bumblebees, also partake. I think the horizontal aspect of this sunflower makes it more attractive than the local native annual sunflower, which is mostly vertical as it tracks the sun. In this case, the plant is “native” to the pollinator, not the Front Range pollinator garden.
At the hardware store or nursery I have been able to purchase packets of seeds guaranteed to be free of neonicotinoids from Botanical Interests, and have a friend start them in a greenhouse. None of the seeds I sow directly have sprouted, possibly because the soil stays cool too long. The straight species can grow to a bushy 6 feet tall, so give it room. There is also a much smaller cultivar, ‘Fiesta del Sol’, which is an All American Selection and widely available, but I don’t know its pesticide status.
Good to watch for other, smaller pollinators, too
3. Snow-on-the-Mountain: This tour through the growing season concludes with a dazzling annual native to Eastern Slope outwash mesas and plains and across the Great Plains. More than any other species, passers-by ask me “What is that plant?” It’s fun to help them see how the tiny flowers and larger variegated bracts are related to poinsettias. Each year volunteer plants appear (easily thinned) to fill the hottest driest area when almost everything has gone dormant. My last task of the seed collecting calendar is to pull the plants with their fully ripened seed capsules before they blow away in yet another strong wind.
Snow-on-the-Mountain is the big white patch in the dryland, September.
There are many ways to support the local web of life while minimizing supplemental irrigation. The best guide is your own long-term observation of your garden and the animals that inhabit it. It can be helpful to consult lists recommending certain plants for specific wildlife benefits, yet be prepared to be surprised at how the web of life actually shows up. Figure out what pleases you and have a good time in your garden.
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