dry gardens

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Drought Tolerant Plants: Ice Plants

Among the various strategies plants have for tolerating drought, succulence is easily one of the most common and most successful. A recent article in the new open source journal, Plants People Planet, explores the world of succulent plants, commenting on, among other things, their evolution and extent. At least 83 plant families contain succulent species, and as many as 3-5% of flowering plants are considered succulents.

Succulence involves the storage of water in the cells of one or more plant organs (i.e. roots, stems, or leaves) as a mechanism for surviving drought. One way that succulent species differ is the location and nature of this storage. Some succulents are all cell succulents, meaning that the cells involved in storing water are also involved in carrying out photosynthesis. Other succulents are storage succulents. They have specific cells called hydrenchyma designed for storing water. These cells are non-photosynthetic.

Plants in the family Aizoaceae are storage succulents. Commonly known as the ice plant or carpet weed family, this family consists of hundreds of species and is mainly distributed throughout a region of South Africa known as Succulent Karoo. Species in this family earn the name ice plant thanks to numerous bladder-like cells or hairs that cover their leaves and stems causing them to sparkle or glimmer in the light. Aizoaceae diversity is incredible, and while this post focuses mainly on a few select species, it’s worth browsing through the profiles listed on World of Succulents to appreciate the breadth of forms these plants can take.

common ice plant (Mesembryanthemum crystallinum)

Among many interesting features that plants in this family possess, one particularly fun thing to note is that their flowers, which are unapologetically showy, lack true petals. Instead, what appear as a series of flat, thin petals encircling the center of the flower are actually modified stamens. They act as petals – drawing in pollinators with their bright colors – so calling them petals is acceptable, just not entirely accurate. Another fun fact is that seed pods of plants in Aizoaceae are often hygrochastic – upon getting wet they burst open and expel their seeds.

The photosynthetic pathway in succulents is generally different compared to other plants. Instead of the common C3 pathway, succulents use a pathway called CAM, or Crassulacean Acid Metabolism. CAM photosynthesis is similar to C4 photosynthesis – another photosynthetic pathway common among drought tolerant plants – in that it uses PEP carboxylase instead of rubisco to fix carbon and then sends it to a separate cell to be converted into sugars. In C4 photosynthesis, this whole process happens during the day. CAM photosynthesis differs in that it fixes carbon during the night and then sends it to another cell to be converted into sugars during the day. Fixing carbon at night is a way to avoid the water loss that occurs when collecting carbon dioxide during the daytime.

In discussing Aizoaceae, this is an important consideration because, unlike many other succulents, plants in this family don’t rely solely on CAM photosynthesis, but can instead switch back and forth between C3 and CAM. The ability to do this is likely because they are storage succulents rather than all cell succulents, and because they can do this, they are very efficient carbon fixers.

flowers fading on purple ice plant (Delosperma cooperi)

I live in a region where winter temperatures can dip into the single digits (°F) and sometimes lower,  so my familiarity with ice plants is with cold hardy species and cultivars of the genus Delosperma. If you are familiar with this group of plants, it is most likely thanks to the Plant Select program based in Colorado, particularly the work of Mr. Delosperma himself, Panayoti Kelaidis. Several Delosperma species are cold hardy in the Intermountain West. Thanks to their promiscuous nature, numerous crosses have occurred between species and varieties, resulting in a wide array of flower colors. And speaking of their flowers, the glistening leaves of Delosperma have nothing on their shimmering flowers, some of which may have the ability to temporarily blind you if you’re not careful. Sun is essential though, as they usually close up when shaded.

The cold hardy ice plants of the Delosperma genus are all groundcovers, maintaining a low and creeping profile. Some creep further than others. They are generally not fond of heavy clay soils, and instead prefer soil with good drainage. During the hot, dry days of summer, they appreciate a little water now and then, but watering should be cut off at the end of summer so that they aren’t sitting in saturated soils as winter approaches. They love the sun and will generally flower from late spring throughout the summer. Of course, thanks to their interesting foliage, they catch the eye and provide interest in the garden even when they aren’t flowering.

Fire Spinner® ice plant (Delosperma ‘P001S’)

Within Aizoaceae there are several species that go by the name ice plant that are not so cold hardy. Some are grown as house plants, while others are common in gardens. Still others, like Carpobrotus edulis, were once employed by land managers in California to help control erosion. However, like a number of species introduced for this purpose, C. edulis (commonly known as highway ice plant or hottentot fig) has made itself at home in areas where it wasn’t invited. It has become particularly problematic in coastal ecosystems, spreading quickly across sandy soils and outcompeting native plants. Despite being brought in to control erosion, it actually causes erosion in steep, sandy areas when its carpet-like growth becomes heavy with water and begins sliding down the hill.

highway ice plant (Carpbrotus edulis) carpeting a slope near San Diego – photo credit: Sierra Laverty

Introducing plants to our gardens that come to us from the other side of the globe should be done with caution and care. We don’t want to be responsible for the next invasive species. Since ice plant species have become problematic in California, should we be concerned about cold hardy delospermas? In trialing their plants, invasive qualities are among those that the Plant Select program watches out for, and delospermas seem pretty safe. However, as Kelaidis observes in a blog post from 2014, we should remain vigilant.

Select Resources:

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Drought Tolerant Plants: Water Conservation Landscape at Idaho Botanical Garden

Demonstration gardens are one of the best places to learn about drought tolerant plants that are appropriate for your region. Such gardens not only help you decide which species you should plant, but also show you what the plants look like at maturity, what they are doing at any given time of year, and how to organize them (or how not to organize them, depending on the quality of the garden) in an aesthetically pleasing way. A couple of years ago, I explored the Water Efficient Garden at the Idaho State Capitol Building. This year I visited the Water Conservation Landscape at Idaho Botanical Garden in Boise, Idaho.

The Water Conservation Landscape is planted on a large L-shaped berm on the edge of Idaho Botanical Garden’s property. It is the first thing that visitors to the garden see, before they reach the parking area and the front gate. It is nearly a decade old, so the majority of the plants are well established and in their prime. Because the garden is so visible, year-round interest is important. This imperative has been achieved thanks to thoughtful plant selection and design.

This demonstration garden came about thanks to a partnership between Idaho Botanical Garden and several other organizations, including the water company, sprinkler supply companies, and a landscape designer. An interpretive sign is installed at one end of the garden describing the benefits of using regionally appropriate plants to create beautiful drought tolerant landscapes. If you ever find yourself in the Boise area, this is a garden well worth your visit. In the meantime, here are a few photos as it appeared in 2017.

February 2017

bluebeard (Caryopteris incana ‘Jason’) – February 2017

Sedum spurium ‘Dragon’s Blood – March 2017

winter heath (Erica x darleyensis ‘Kramer’s Red’) – March 2017

May 2017

avens (Geum x hybrida ‘Totally Tangerine’) – May 2017

July 2017

American cranberrybush (Viburnum opulus var. americanum ‘Wentworth’) – July 2017

Fremont’s evening primrose (Oenothera macrocarpa ssp. fremontii ‘Shimmer’) – July 2017

Fremont’s evening primrose (Oenothera macrocarpa ssp. fremontii ‘Shimmer’) – July 2017

August 2017

cheddar pink (Dianthus gratianopolitanus ‘Firewitch’) – August 2017

smoketree (Cotinus coggyria ‘Royal Purple’) – August 2017

gray lavender cotton (Santolina chamaecyparissus) – September 2017

showy stonecrop (Hylotelephium telephium ‘Matrona’) – September 2017

showy stonecrop (Hylotelephium telephium ‘Matrona’) – September 2017

Adam’s needle (Yucca filamentosa ‘Color Guard’) – October 2017

fragrant sumac (Rhus aromatica ‘Gro-Low’) – October 2017

More Drought Tolerant Plant Posts:

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Drought Tolerant Plants: Pearly Everlasting

Despite being such a widely distributed and commonly occurring plant, Anaphalis margaritacea is, in many other ways, an uncommon species. Its native range spans North America from coast to coast, reaching up into Canada and down into parts of Mexico. It is found in nearly every state in the United States, and it even occurs throughout northeast Asia. Apart from that, it is cultivated in many other parts of the world and is “weedy” in Europe. Its cosmopolitan nature is due in part to its preference for sunny, dry, well-drained sites, making it a common inhabitant of open fields, roadsides, sandy dunes, rocky slopes, disturbed sites, and waste places.

Its common name, pearly everlasting, refers to its unique inflorescence. Clusters of small, rounded flower heads occur in a corymb. “Pearly” refers to the collection of white bracts, or involucre, that surround each flower head. Inside the bracts are groupings of yellow to brown disc florets. The florets are unisexual, which is unusual for plants in the aster family. Plants either produce all male flowers or all female flowers (although some female plants occasionally produce florets with male parts). Due to the persistent bracts, the inflorescences remain intact even after the plant has produced seed. This quality has made them a popular feature in floral arrangements and explains the other half of the common name, “everlasting.” In fact, even in full bloom, the inflorescences can have a dried look to them.

pearly-everlasting-6

Pearly everlasting grows from 1 to 3 feet tall. Flowers are borne on top of straight stems that are adorned with narrow, alternately arranged, lance-shaped leaves. Stems and leaves are gray-green to white. Stems and undersides of leaves are thickly covered in very small hairs. Apart from contributing to its drought tolerance, this woolly covering deters insects and other animals from consuming its foliage. In The Book of Field and Roadside, John Eastman writes, “Insect foliage feeders are not numerous on this plant, owing to its protective downy ‘gloss.’ … The plant’s defensive coat seems to prevent spittlebug feeding on stem and underleaves. The tomentum also discourages ant climbers and nectar robbers.”

pearly-everlasting-5

Not all insects are thwarted however, as Anaphalis is a host to the caterpillars of at least two species of painted lady butterflies (Vanessa virginiensis and V. cardui). Its flowers, which occur throughout the summer and into the fall. are visited by a spectrum of butterflies, moths, bees, and flies.

Because the plants produce either male or female flowers, cross-pollination between plants is necessary for seed development. However, plants also reproduce asexually via rhizomes. Extensive patches of pearly everlasting can be formed this way. Over time, sections of the clonal patch can become isolated from the mother plant, allowing the plant to expand its range even in times when pollinators are lacking.

The attractive foliage and unique flowers are reason enough to include this plant in your dry garden. The flowers have been said to look like eye balls, fried eggs, or even, as Eastman writes, “white nests with a central yellow clutch of eggs spilling out.” However you decide to describe it, this is a tough and beautiful plant deserving of a place in the landscape.

pearly-everlasting-4

Read more:

Photos in this post are of Anaphalis margaritacea ‘Neuschnee’ and were taken at Idaho Botanical Garden in Boise, Idaho.

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Drought Tolerant Plants: The Junipers

When I first developed a real interest in plants, I was in the heyday of my zine writing career. As my interest in gardening grew, writing a zine about it became inevitable. Initially I envisioned the zine as a journal of sorts – the journal of a budding horticulturist (pun intentional). Since I was new to gardening – and plants in general – the zine was meant to follow my journey as I explored this new world.

A zine needs a name though, so what would I call it? It didn’t take long for me to land on, The Juniper. I was familiar with a common disdain for the unsightly, overgrown, neglected, evergreen shrub full of spiders and cobwebs that for whatever reason was at one point planted right outside just about every house in America (a fire hazard, by the way). I was aware that many people were resorting to tearing them out, cursing as they battled the pokey, dirty, half dead things.

That was basically all I knew about junipers – they were common landscape plants that were just as commonly despised. My affection for freaks, geeks, outsiders, and rejects led me to name my zine after a shrub that everyone hated. I guess I just felt like we had something in common, and that despite being the bane of people’s existence, it deserved some recognition.

the juniper zine

And it does. Junipers are an important species in their natural habitats. In some areas they are dominant features to the point where entire plant communities are named after them. Consider the piñon-juniper woodlands of western North America – prominent steppe habitats that occur throughout high desert regions and support diverse forms of wildlife unique to this part of the world. Dan Johnson writes in the book, Steppes, “the piñon-juniper zone dominates huge expanses of the West in varying stages of  health, providing a wealth of habitats and resources to the wildlife and the people who call it home.”

Johnson goes on to describe some of these habitats:

In the Colorado Plateau this zone is dominated by Pinus edulis and Juniperus osteosperma, with J. scopulorum occupying drainages with more moisture. In the Great Basin, P. edulis is replaced by P. monophylla as the dominant piñon pine, still mixing with J. osteosperma, yet as one moves west, this juniper is increasingly replaced by J. occidentalis. Move farther north, and J. occidentalis dominates completely, with neither piñon pine making an appearance.

The genus Juniperus is in the cypress family (Cupressaceae) and includes up to 67 species, at least 13 of which are native to North America. They are long-lived plants that range from prostrate, sprawling groundcovers to expansive, bushy shrubs to tall, narrow trees. Their foliage is evergreen and can be either needle-like or scale-like. Most juniper species have needle-like foliage in their seedling and juvenile stages and then scale-like foliage at maturity. Some species, like J. communis, never develop scale-like foliage. Junipers are gymnosperms, so their reproductive structures are housed in cones. However, their cones are fleshy and so are commonly (and mistakenly) referred to as berries or fruits. Juniper cones are most often blue or gray-blue, but in some species they have a red, brown, or orange hue.

In general, junipers are quite drought tolerant, particularly those species that are adapted to hot, dry climates. Again referring to piñon-juniper steppes, Johnson writes, “in prolonged periods of drought, the piñon pines seem to suffer long before the junipers; whole hillsides of pine may go brown, leaving islands of olive-green juniper relatively unscathed.” In the book, Shrubs of the Great Basin, Hugh Mozingo attributes this drought toughness to the scale-like leaves: “Because they are smaller and so closely appressed to the twigs, these scale-like leaves are a superior adaptation to the frequently very dry conditions in piñon-juniper communities.” This herculean ability to survive on little water makes them a great addition to a dry garden.

But we may first have to get over our disdain for them. As this post on Chicago Botanic Garden’s website puts it: “Junipers have suffered from overuse and underimagination.” (This article also examines our hatred of juniper bushes). Probably a bigger problem is that, like so many other plants used in a landscape, mature height and width often isn’t taken into consideration, and rather than removing a plant when it gets too big for the site, sheers or a hedge trimmer are regularly deployed. I’m not a huge fan of the sheered look. I much prefer a more natural form to the boxes and globes that are so common in commercial and residential plantings. I’m even less of a fan of the misguided inclination to force a plant to fit in a space that it isn’t meant to be (unless you’re a bonsai artist, I guess). This treatment is what leads to exposing the ugly, brown insides of a juniper shrub – an unsightly look that only makes people hate them more.

Brown insides of juniper shrub exposed after years of forcing the plant to fit in a site that is too small for its britches.

Brown insides of juniper shrub exposed after years of forcing the plant to fit in an improper site.

There are numerous commercially available cultivars of juniper species, offering a plethora of sizes, shapes, and forms as well as various colors of foliage. For small or narrow areas, select dwarf varieties or columnar forms that won’t need to be kept in check, and in all cases let the plant express its authentic self, controlling the urge to sheer and shape it against its will.

As if their natural beauty and low water requirement wasn’t enough, junipers are also great for supporting wildlife. Birds and other animals use them for cover and for nesting sites. The fleshy cones are edible, the shredding bark is used for nesting material, and the evergreen foliage provides much needed protection during winter months. Oh and, among many other benefits that junipers offer humans, their aromatic, fleshy cones have culinary value and are used to flavor gin.

I don’t want to leave the impression that I am opposed to pruning and shaping shrubs. For aesthetic reasons, I think it should be done. However, my opinion is that unnatural shapes should be avoided. Sure, boxed hedge rows have their place in certain types of gardens, but my preference is towards more natural shapes. The following video by University of Illinois Extension provides a brief tutorial on how to achieve that.   

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Drought Tolerant Plants: Rabbitbrush

Gardener seeking shrub. Must be drought tolerant. Must have year-round interest. Must be easy to grow and maintain. Preferably flowers in late summer or early fall. Must be attractive – not just to humans, but to wildlife as well. Serious inquiries only.

My answer to a solicitation such as this would be rabbitbrush. While there may be other perfectly acceptable plants that fit this description, I think rabbitbrush deserves major consideration. It’s easy to grow and can be kept looking attractive throughout the year. When it is flush with vibrant, golden-yellow flowers at the close of summer, it not only becomes the star of the garden visually, but also a savior to pollinators readying themselves for winter. Plus, it requires little to no supplemental water, making it a true dry garden plant.

There are many species that go by the common name rabbitbrush. The two that I am most familiar with are Ericameria nauseosa (rubber or gray rabbitbrush) and Chrysothamnus viscidiflorus (green or yellow rabbitbrush). Both of these species are native to western North America, and both have a number of naturally occurring varieties and subspecies.

Rubber rabbitbrush - Ericameria nauseosa

Rubber rabbitbrush – Ericameria nauseosa

Rubber rabbitbrush is a densely branched shrub that reaches an average height of 3 feet. Its leaves are slender and numerous, and its stems and leaves are covered in short, white, felt-like hairs giving the plant a light gray appearance. Native Americans used the flexible branches of this plant to weave baskets. They also made a tea from the stems to treat coughs, colds, chest pains, and toothaches. Bundles of branches were burned to smoke animal hides. The stems and roots contain a latex sap, and certain Native American tribes are said to have used this sap as chewing gum, possibly to relieve hunger or thirst. A rubber shortage during World War II led to investigations into extracting the latex from rabbitbrush. This idea was soon abandoned once it was determined that even if every rabbitbrush in the West were to be harvested, the resulting increase in rubber would be modest compared to other sources.

Green rabbitbrush is typically smaller than rubber rabbitbrush, reaching a maximum height of about 3 feet. Its stems and leaves appear similar to rubber rabbitbrush except they lack the dense, white hairs and are brown and green respectively. Also, the stems and leaves of green rabbitbrush have a stickiness to them, and the leaves are often twisted or curled.

Rabbitbrush is a member of the sunflower family (Asteraceae). Plants in this family generally have inflorescences that are a combination of ray and disk flowers (or florets) clustered tightly together and arranged in such a way that the inflorescence appears as a single flower. Consider sunflowers, for example. What appear to be petals around the outside of a large flower are actually a series of individual ray flowers, and in the center are dozens of disk flowers. Both rubber and green rabbitbrush lack ray flowers, and instead their inflorescences are clusters of 5 or so disk flowers that are borne at the tips of each branch creating a sheet of yellow-gold flowers that covers the shrub. Native Americans used these flowers to make dyes.

The fruits of rabbitbrush are achenes with small tufts of hairs attached. Each achene contains one seed. The tuft of hair (or pappus) helps disseminate the seed by way of the wind. Many of the fruits remain attached to the plant throughout the winter, providing winter interest and food for birds.

As rabbitbrush ages it can become gangly, floppy, or simply too large for the site. This can be avoided easily by cutting the plant back by a third or more each fall or spring, which will result in a more manageable form. It can also be cut back nearly to the ground if it is getting too big.

Seed heads of rubber rabbit brush (Ericameria nauseosa)

Seed heads of rubber rabbit brush (Ericameria nauseosa)

The leaves, flowers, stems, and seeds provide food for a variety of animals including birds, deer, and small mammals. The plant itself can also provide cover for small mammals and birds. Oh, and did I mention that it’s a pollinator magnet. It has wildlife value, it’s drought tolerant, it’s easy to maintain, and overall, it’s a beautiful plant. What more could you ask for in a shrub?

More Drought Tolerant Plant posts at Awkward Botany:

–Fernbush

–Blue Sage

–Prickly Pears

–Water Efficient Landscape at Idaho State Capitol Building

–Desert Willow

The photos in this post were taken at Idaho Botanical Garden in Boise, Idaho.

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Drought Tolerant Plants: Desert Willow

Hailing from dry washes and riverbanks of the desert southwestern United States and northern Mexico, desert willow is a tough tree or large shrub with delicate, showy flowers and wispy foliage. Its beauty and its ruggedness has made it a popular plant for dry gardens. It requires little attention maintenance-wise, yet attracts all kinds of attention otherwise. If you live in a desert climate that generally stays above 0 degrees Fahrenheit during the winter, this plant belongs in your garden.

Desert Willow - Chilopsis linearis

Desert Willow – Chilopsis linearis

A member of the family Bignoniaceae – a family that consists of at least 8o genera including catalpa (Catalpa spp.) and trumpet vine (Campsis spp.) – Chilopsis linearis is the sole member of its genus. The common name, desert willow, refers to its habitat and its long, slender, oppositely and alternately arranged leaves that resemble those of many willows (Salix spp.). Other common names include flowering willow, willowleaf catalpa, desert catalpa, and false-willow. There are two recognized subspecies – linearis and arcuata.

Desert willow is found most commonly in areas where seasonal flooding occurs. Known as desert dry washes – or simply dry washes or desert washes –  these are areas in the desert where runoff from heavy rains accumulates resulting in saturated soils followed by a prolonged dry period. Groundwater often remains accessible year-round to the deep roots of plants in this type of habitat. Desert willow shares this habitat with several other large shrubs and small trees including mesquite (Prosopis spp.), palo verde (Parkinsoinia spp.), and smoketree (Psorothamnus spinosus). Desert willow occurs along stream banks and river banks as well, where seasonal flooding also occurs.

Desert willow generally reaches a width of 10 to 15 feet and a height of at least 15 feet, although it has the potential to grow taller than 30 feet. It often has an open and sprawling or leaning habit, but it can be pruned to look more tree-like. Pruning can also result in more flowering, since flowers appear on new growth and pruning encourages growth. Watering this plant during the dry season can also lead to a flush of growth and more flowering. This is something to keep in mind, as it is the flowers that are the star of the show.

Persisting from late spring through midsummer (and sometimes longer), the 1 to 2 inch, trumpet-shaped, pink to rose to purple blossoms are hard to miss. They occur singularly or in clusters at the tips of branches. The ruffled-edges of the petals and the prominent streaks of color within the corolla tube add to the attraction. Hummingbirds, butterflies, and bumblebees are common visitors to these fragrant flowers. Summer rains or occasional watering can encourage flowering throughout the summer. Overwatering, on the other hand, can be detrimental.

The flowers eventually form long slender seed pods called capsules that reach up to 10 inches long. Inside the capsules are a series of hairy seeds. The hairs form small wings on the sides of the seeds. The seeds are eaten by a variety of bird species. Various species of birds can also be seen nesting in desert willow, and a variety of other animals use desert willow for browsing and/or for cover.

The fruits of Chilopsis linearis.

The fruits of Chilopsis linearis

The hairy, winged seeds of Chilopsis linearis

The hairy, winged seeds of Chilopsis linearis

Desert willow prefers sunny, southwest facing sites and tolerates most soil types. It performs best in soils that are well drained, low in organic content, and have a pH that is neutral to alkaline. The soil can be saturated at times, but should be given a chance to dry out – just like in its natural habitat. Avoid the impulse to add fertilizer.

Desert willow is said to be easy to propagate from cuttings or from seeds. It is commercially available, and several cultivars have been developed offering diverse flower colors and other special traits. It’s easy to grow, requires little attention, and provides an eye-catching floral show – all excellent reason to add this plant to your water-efficient landscape.

One tip from my experience seeing it survive the winters of southwestern Idaho: the deciduous leaves of Chilopsis linearis don’t reappear until very late in the spring – so late, in fact, that one might start to worry that the plant has perished. Don’t fret though; some winter kill is possible if sub-zero temperatures were experienced, but most likely it is still alive.

More information about desert willow:

–Encyclopedia of Life

–USDA Plant Guide

–Native Plant Information Network 

The photos in this post were taken at Idaho Botanical Garden in Boise, Idaho.