Drought Tolerant Plants: Yellowhorn

A drought tolerant garden doesn’t have to be treeless. While the pickings are slim, there is a selection of trees that, once established, are well adapted to deal with extended bouts of little to no water. One such tree is yellowhorn, a species that demands to be considered for any waterwise landscape. Yellowhorn is rare in cultivation – and also restricted in its natural distribution – but perhaps that will change as word gets around about this beautiful and resilient tree.

Xanthoceras sorbifolium is native to several provinces in northern China and has been cultivated in a number of places outside of China since at least the 1800’s. Its ethnobotanical value is well understood in China. Its leaves, flowers, and seeds are edible and medicinal, and the high oil content of its seeds make them useful for the production of biofuels. Researchers are also investigating the use of yellowhorn for ecological restoration in arid habitats where desertification is a concern.

yellowhorn in bloom

Yellowhorn is the only species in the genus Xanthoceras, but is one in a long list of trees and shrubs in the Sapindaceae family – a family that now includes maples and horse chestnuts. It is considered both a large shrub and a small, multi-stemmed tree. It reaches a maximum height of about 25 feet, but arrives there at a relatively slow pace. It tolerates a variety of soil types, but like most other drought tolerant plants, it prefers soils that don’t become waterlogged easily. Its leaves are long, glossy green, and compound, consisting of 9 – 17 leaflets. The leaves persist late into the year and turn yellow in the fall. However, late spring, when the tree is covered in flowers, is when this tree puts on its real show.

Large white flowers with yellow-green centers that turn maroon or red-orange as they age are produced on racemes at the ends of branches. Small, yellow, hornlike appendages between each of the five petals of the flowers are what gives the tree its common name. Flowering lasts for a couple weeks, after which fruits form, which are about 2.5 inches wide, tough, leathery, and somewhat pear shaped. In my experience, most of the fruits are eaten by squirrels long before they get a chance to reach maturity. The ones the squirrels don’t get will persist on the tree, harden, and eventually split open to reveal several large, dark, round seeds nestled in chambers within the fruit.

To truly appreciate this tree, it must be seen in person, especially in bloom. At that point you will demand to have one (or more) in your garden. The seeds are said to be delicious, so you should give them a try if you can beat the squirrels to them. For a more thorough overview of yellowhorn, check out this article from Temperate Climate Permaculture, and for more photos of yellowhorn in bloom, check out this post from Rotary Botanical Gardens.

Squirrel nesting in yellowhorn, getting ready to go after more fruits.

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

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More Drought Tolerant Plants Posts:

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:

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.

Drought Tolerant Plants: The Yarrows

Few plants are as ubiquitous and widespread as the common yarrow, Achillea millefolium. A suite of strategies have made this plant highly successful in a wide variety of habitats, and it is a paragon in terms of reproduction. Its unique look, simple beauty, and tolerance of tough spots have made it a staple in many gardens; however, its hardiness, profuseness, and bullish behavior have also earned it the title, “weed.” Excess water encourages this plant to spread, but in a dry garden it tends to stay put (or at least remain manageable), which is why it and several of its cousins are often included in or recommended for water efficient landscapes.

Achillea millefolium - common yarrow

Achillea millefolium – common yarrow

Common yarrow is in the aster family (Asteraceae) and is one of around 85 species in the genus Achillea. It is distributed throughout North America, Europe, and Asia. European plants have long been introduced to North America, and hybridization has occurred many times among the two genotypes.

Yarrow begins as a small rosette of very finely dissected leaves that are feathery or fern-like in appearance. These characteristic leaves explain its specific epithet, millefolium, and common names like thousand-leaf. Slightly hairy stems with alternately arranged leaves arise from the rosettes and are capped with a wide, flat-topped cluster of tightly-packed flowers. The flower stalks can be less than one foot to more than three feet tall. The flowers are tiny, numerous, and consist of both ray and disc florets. Flowers are usually white but sometimes pink.

The plants produce several hundred to several thousand seeds each. The seeds are enclosed in tiny achene-like fruits which are spread by wind and gravity. Yarrow also spreads and reproduces rhizomatously. Its roots are shallow but fibrous and abundant, and they easily spread horizontally through the soil. If moisture, sun, and space are available, yarrow will quickly expand its territory. Its extensive root system and highly divided leaves, which help reduce transpiration rates, are partly what gives yarrow the ability to tolerate dry conditions.

john eastman

Illustration of Achillea millifolium by Amelia Hansen from The Book of Field and Roadside by John Eastman, which has an excellent entry about yarrow.

Common yarrow has significant wildlife value. While its pungent leaves are generally avoided by most herbivorous insects, its flowers are rich in nectar and attract bees, butterflies, beetles, flies, and even mosquitoes. Various insects feed on the flowers, and other insects visit yarrow to feed on the insects that are feeding on the plant. Despite its bitterness, the foliage is browsed by a variety of birds, small mammals, and deer. Some birds use the foliage in constructing their nests. Humans have also used yarrow as a medicinal herb for thousands of years to treat a seemingly endless list of ailments.

Yarrow’s popularity as an ornamental plant has resulted in the development of numerous cultivars that have a variety of flower colors including shades of pink, red, purple, yellow, and gold. While Achillea millefolium may be the most widely available species in its genus, there are several other drought-tolerant yarrows that are also commercially available and worth considering for a dry garden.

Achillea filipendulina, fern-leaf yarrow, is native to central and southwest Asia. It forms large, dense clusters of yellow-gold flowers on stalks that reach four feet high. Its leaves are similar in appearance to A. millefolium. Various cultivars are available, most of which have flowers that are varying shades of yellow or gold.

Achillea alpina, Siberian yarrow, only gets about half as tall as A. filipendulina. It occurs in Siberia, parts of Russia, China, Japan, and several other Asian countries. It also occurs in Canada. Unlike most other species in the genus, its leaves have a glossy appearance and are thick and somewhat leathery. Its flowers are white to pale violet. A. alpina is synonymous with A. sibirica, and ‘Love Parade’ is a popular cultivar derived from the subspecies camschatica.

Achillea x lewisii ‘King Edward,’ a hybrid between A. tomentosa (woolly yarrow) and A. clavennae (silvery yarrow), stays below six inches tall and forms a dense mat of soft leaves that have a dull silver-gray-green appearance. Its compact clusters of flowers are pale yellow to cream colored. Cultivars of A. tomentosa are also available.

Achillea ptarmica, a European native with bright white flowers, and A. ageritafolia, a native of Greece and Bulgaria that is low growing with silvery foliage and abundant white flowers can also be found in the horticulture trade along with a handful of others. Whatever your preferences are, there is a yarrow out there for you. Invasiveness and potential for escape into natural areas should always be a concern when selecting plants for your garden, especially when considering a plant as robust and successful as yarrow. That in mind, yarrow should make a great addition to nearly any drought-tolerant, wildlife friendly garden.

More Drought Tolerant Plants Posts:

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.

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.

Drought Tolerant Plants: Water Efficient Garden at Idaho State Capitol Building

water efficient garden sign

As drought and threats of drought continue in the western half of the United States, as well as in many other parts of the world, people are increasingly looking for ways to use less water in their landscapes. For many it is a change they are reluctant to make, worried that they will have to sacrifice lush and colorful yards and gardens for drab, dry, gray, and seemingly lifeless ones. Not so, though. The palette of plants that can survive in low water environments is actually quite diverse and contains numerous plants that are just as lush and colorful as some water hogging ones. If planned, planted, and maintained well, a water efficient garden can be incredibly attractive and can even consist of some plants that are comparatively more heavy water users. So, for those who are apprehensive about getting down with brown, don’t fret – there is a better way.

How does one go about creating such a garden? The answer to that is a book on its own – much too long for a single blog post. It also depends who is asking the question, or more specifically, where they are asking it from. Luckily, demonstrations of water-wise gardens are becoming more common. These gardens, planted with regionally appropriate plants and showcasing various water-saving techniques, are great places to start when looking for ideas and motivation. Such gardens can be found at public parks, city and state government buildings, botanical gardens, nurseries and nursery centers, and water company offices. If you are looking to transform your landscape into a more water efficient one, seek out a demonstration garden in your area. It’s a great place to start.

There are several such gardens where I live, one of which is the Water Efficient Garden at the Idaho State Capitol Building in Boise, Idaho. This garden began in 2010 as a partnership between United Water Idaho and the Idaho Capitol Commission. Its mission is to introduce visitors to “low-water native and adaptive plants that thrive in Idaho’s climate.” The plants that were selected for the garden are commonly found at local garden centers and nurseries – an important objective when introducing people to water-wise gardening. The ultimate goal of this garden is to “show homeowners that they can maintain attractive landscaping while conserving water.”

I have my criticisms of this garden regarding plant selection, design, etc., but I’ll spare you those details. I also don’t know the specifics about how this garden is maintained or how often it is watered. All that aside, I am just happy that it exists, and I encourage you to seek out similar gardens in your area. There are numerous approaches to designing and constructing water efficient gardens – again, a book on its own – but demonstration gardens like this are an excellent place to get ideas and learn what other people in your area are doing to conserve water and create landscapes that better reflect the ecology of your region.

United Water Idaho offers a brief introduction to low water gardening here, as well as a list of plants that are in the capitol building garden here.

Blanket Flower (Gaillardia x grandiflora 'Goblin') Plants in the garden are accompanied by a sign with a number on it. The sign corresponds to the plant list that is provided at the entrances to the garden.

Blanket flower (Gaillardia x grandiflora ‘Goblin’). Plants in the garden are accompanied by a sign with a number on it. The sign corresponds to a plant list that is provided at the entrances to the garden.

Dianthus sp.

Dianthus sp.

Coreopsis sp.

Coreopsis sp.

Geranium sp.

Geranium sp.

Liatris sp.

Liatris sp.

A drift of pearly everlasting (Anaphalis margaritacea)

A drift of pearly everlasting (Anaphalis margaritacea)

Purple coneflower (Echinacea purpurea)

Purple coneflower (Echinacea purpurea)

Yellow ice plant (Delosperma nubiginum)

Yellow ice plant (Delosperma nubiginum)

Other “Drought Tolerant Plants” Posts on Awkward Botany: