1. Entrance Garden/Gift Shop
2. Courtyard Garden
3. Herb Garden
4. Mixed Conifer Garden
5. Children's Garden
6. Constructed Wetlands
7. Willow Wash
8. Woodlands
9. Water Conservation Garden
10. Shade Garden
11. Triad Garden
12. Butterfly Garden
13. Wildflower Meadow/Meadow Grass Demonstration
14. Turf Demonstration
15. Concert Area
16. Penstemon Garden
    Horticulture Center

1. Entrance Garden/Gift Shop   back to top

2. Courtyard Garden   back to top

The Courtyard Garden displays a method of watering that is consistent with the ideas of ecological horticulture which is based on natural plant habitats. In the ecological landscape, you can create a zoned landscape by recognizing microclimates (cold and warm spots) on your site and choosing native plants that naturally thrive in similar zones and habitats. For example, plants in this garden receive excess water from rainfall through a drainage that runs from the roof to the garden. This method of watering cuts back on manual labor and takes greater advantage of nature’s watering system.

One plant that benefits from roof runoff is the rare Chiricahua dock (Rumex orthoneurus), native to the mountains of southeast Arizona. It is a perennial that prefers a habitat of moist organic soils near streams and springs. This relative of the prolific midwestern weed thrives in cultivation, but in the wild is threatened by cattle grazing, recreation, mining, and road construction. Protected within The Arboretum’s 12-foot-high elk fence, this species produces thousands of seeds when allowed to flower, in the protected environment of the garden.

Also found growing in this garden is the Arizona willow, another rare species that benefits from ecological watering methods. Threatened by habitat degradation, as well as cattle, elk, and insect herbivory (animals that feed on plants), the native willow grows only in Arizona and Utah near perennial streams and meadows at high elevations. Runoff from the roof feeds the drainage and provides supplemental moisture that might otherwise be lost to the plant. 

3. Herb Garden   back to top

Many familiar traditional herbs originated in the dry, temperate regions and mountains of Europe and Asia where the low rainfall is similar to northern Arizona. As a result, many non-native herbs grow well as hardy perennials here in the harsh climate of Flagstaff.

The ideal setting for growing herbs in the Flagstaff area is a site that provides them with morning or midday sun, with less exposure to full afternoon sun. While most herbs can tolerate full sun, the intense high elevation sun and dry air causes many herbs to become drought-stressed and wilt if exposed to full sun the entire day. In this garden, pine trees provide shade for various periods throughout the day. The adjacent building and trees provide protection from the southwest wind. Stone walls absorb heat from the sun and provide warmer microclimates.

When placing herbs in the garden, consider their individual needs for sun, warmth, soil richness, and drainage, and group plants with similar needs together. We’ve placed plants that need warmth near the stone wall or close to the house. Plants with large tender leaves are grown under the shade of the pine trees. Most herbs enjoy rich, moderately well-drained soils. Others from arid regions, such as lavender, rosemary, sage, and tarragon, prefer a well-drained, not-too-rich soil.

When starting a new garden, the Arizona Herb Association recommends spading six inches of organic material, such as mature compost and well-composted manure, into the top 12 inches of soil several weeks before planting. Gypsum will help break up heavy clay. We continue to add 2 inches of composted manure each spring to give the plants the food they will need for the coming growing season and to retain soil moisture.

Some species of herbs, such as tansy and catnip, are particularly aggressive growers and have a tendency to invade large areas of the garden. Either avoid growing such invasive species or grow them in containers to eliminate their ability to spread.

4. Mixed Conifer Garden   back to top

High Elevation Moist and Cool (6,500-10,000 ft, 25-30” precip/year)

The plant community surrounding the pond represents a native habitat in which annual moisture comes as snowfall, from November through May, and as rain in July and August. The small creek leaving the pond is an ephemeral drainage—meaning that it flows only during periods of snowmelt or after heavy rainfall. The pond was initially a cattle tank for an area ranch, but has been modified to accommodate aquatic life. In 1992 it was stocked with the Little Colorado River spinedace, a threatened species. These fish are successfully reproducing.

The rare water-loving Arizona willow growing on the slopes of the pond occurs naturally near perennial streams and high elevation meadows in eastern Arizona and southern Utah. Its populations are threatened by cattle, elk, insect, and rust herbivory (a fungus that eats plants), as well as habitat degradation. Arboretum researchers are examining reintroduction techniques and the impacts of wild and domestic ungulates (having hoofs) on plant growth.

The soil has been amended with organic material and an irrigation system added. The upland component of this habitat has gentle slopes of clay soil and rock. Organic matter in the soil supports several species of coniferous trees and other vegetation naturally occurring on the San Francisco Peaks.

Low Elevation Moist and Warm (4,000-6,000 ft, 13-23” precip/year)

The lush riparian (streamside) ecosystem reproduced along the banks of the creek flowing into the pond receives naturally occurring moisture as well as a moderate amount of supplemental irrigation during dry periods. Temperatures are generally moderate and soils moist. Riparian ecosystems provide abundant food, water, and shelter for a unique community of native plants and animals not found elsewhere. You can find this environment in the canyons at the southern edge of the Colorado Plateau, such as Oak Creek Canyon near Sedona. Water in this section of our creek recirculates with the help of a pump.

Throughout the world, streamside habitats are threatened due to development, dams, and introduction of non-native plants and animals. Non-native species often outcompete natives, which leads to decreased biodiversity and reduced support for life, weakening the system’s ecological stability.

5. Children's Garden   back to top

6. Constructed Wetlands   back to top

Like many facilities in rural areas, The Arboretum is located too far from the city to connect to a sewer system. Instead, wastewater generated by staff and visitors must be treated on site. Our former system, a conventional septic tank and leach field, worked well until annual visitation to The Arboretum began to top 10,000. To address the concern that the increased volume would surpass the system’s capacity and potentially contaminate the groundwater, The Arboretum decided to experiment with a constructed wetland treatment system, which was constructed in 1995.

The system consists of three shallow ponds, or cells, that are lined with an impermeable material, filled with three feet of gravel, and topped with one foot of mulch. Water-loving plants have been placed in the mulch and their roots extend into the gravel bed. Sewage-digesting microorganisms live on the surface of the gravel and the plant roots, where they feed on the materials in the wastewater, breaking them down into nutrients. The plants then take up the nutrients to meet their needs for growth. By the time the wastewater reaches the end of the third cell, the system has cleaned the water sufficiently well that it can be reused on some of our landscape plantings.

This wetland treatment system is unique in two ways. First, it is the only wetland treatment system operating at this high an elevation where the upper parts of the treatment cells are frozen during most of the cold winter months. And yes, it still works through the winter when our wastewater production is low. Second, most of the plant species growing in this system have not been used for wastewater treatment before. The Arboretum is evaluating these native species to determine which ones have the best survival rates and are the best for cleaning the wastewater. The use of native species will eliminate the potential for the spread of unwanted, non-native wetland plants into our local riparian habitats.

7. Willow Wash   back to top

8. Woodlands   back to top

9. Water Conservation Garden   back to top

Each zone occurs in a different microsite, created by differences in topography, soil, and level of exposure to sun or shade. Microsites and their associated microclimates influence a zone’s growing conditions and are controlled by a variety of factors. To determine those factors, staff evaluated this garden for the following:

Aspect (the direction the slope is facing)

Hours of direct sun or shade

Soil moisture

Soil type

Presence or absence and type of slope

After site evaluation, the existing conditions were manipulated in order to create the six different zones in this garden. Methods applied include soil amendment, creation of desirable slope, and rock placement. The natural and created characteristics of these zones are described in the individual Garden Guides found throughout the six garden zones.

Catchment channels divert storm water runoff from the nearby roof, sidewalks, and visitors’ parking lot to the garden. Runoff is a valuable resource that can provide supplemental water for natural and created landscapes. Even in the semi-arid climate of Flagstaff, more than 13 gallons of water can fall annually on each square foot of these surfaces. Terraces, swales, and amended soils help to retain water for those plants and animals that prefer damp conditions.

10. Shade Garden   back to top

Trees, buildings, and steep slopes create shaded areas within the landscape. In northern Arizona, our numerous ponderosa pine trees shade many sites. You can diversify your landscape and grow an entirely different palette of plants by creating a shade garden beneath the trees. Shade-tolerant plants are those adapted to low light intensities. They tend to have large leaves, which improve their ability to collect light.

This shade garden consists of a mix of native and non-native shrubs and groundcover plants. Many non-native species you see here originated in other places in the world with climates similar to Flagstaff’s.

To create a shade garden, select plants according to the amount of shade they can tolerate and still grow well. Interior areas and those under the largest trees tend to be more shady, while the edges of the garden receive more sunlight. Consider thinning dense trees or some of their branches to create more dappled light, which will support a greater variety of species. When selecting non-native plants, look for cold-hardy and drought-tolerant species for the Flagstaff area.

Trees consume large amounts of water during the summer growing season. Therefore, shade gardens may need supplemental watering during the dry season. In addition, pine needles build up over time beneath the trees and can smother smaller plants and reduce the amount of water reaching the soil. Remove pine needles once each year in the spring to allow the soil to warm up and to increase the amount of sunlight reaching low-growing plants.

For sun-loving groundcovers, please visit our Groundcover Garden.

11. Triad Garden   back to top

12. Butterfly Garden   back to top

With modest effort you can construct a butterfly garden or convert an existing garden not only to be a showcase of foliage and color, but also to attract many of these beautiful insects. You can provide nectar plants for the adults or a complete habitat, including food plants for larvae, if you want to study the insect’s life cycle. For more information see the Visitor Center for the Creating a Butterfly Garden bulletin.

The following are requirements for creating anattractive environment for butterflies:

Sunlight—Place your garden in an area with strong or direct sun for at least three or four hours a day. Butterflies are sun-loving creatures.

Blocks of color—Butterflies can see in color and have eyes sensitive to a wider spectrum than humans. Use any colors you wish, in whatever combination suits your taste, as long as you include well-defined splashes of color.

Fragrant plants—Butterflies’ antennae are able to detect the aromatic nature of nectar-bearing flowers. Design a garden with blocks of fragrance, as well as color.

Rocks—Being cold blooded, butterflies need places to bask and soak up warmth when clouds cool down the temperature.

Water—Butterflies get as thirsty as we do on a hot Arizona day. A shallow basin of water or bird bath placed near your garden will attract many pollinators and provide them with water they need to drink.

In the winter, mulch butterfly gardens. In northern Arizona, pine boughs are used to insulate plants when snowpack is insufficient to protect them. Remove mulch in the spring to allow the ground to warm.

13. Wildflower Meadow/Meadow Grass Demonstration   back to top

The site of a wildflower garden is dependent upon by the availability of sunlight and soil conditions. Wildflowers generally like full sun and soils with low fertility and good drainage.

A wildflower meadow that begins with 15 or more species can end up with less than seven species in just a couple of years. The change in species will occur until stabilization has been reached by a group of dominant plants. This natural reduction in species is known as ecological succession.

Native and drought-tolerant perennial and annual species with colorful, numerous, or large flowers grow here. Grasses are an important component of wildflower meadows. Actually, most meadows are a matrix of grasses with wildflowers interspersed. The grasses generally predominate. Avoid using rhizomatous grasses, such as Kentucky blue grass, because they will take over the landscape.

Native species are well adapted to the harsh, environmental extremes of these open, unprotected meadows. Full sun dries out the soil quickly and the open exposure means these meadows experience the full extremes of high and low temperatures. Most native wildflowers typically wait until the monsoon rains before putting on their big show. Hence, selecting wildflowers and bunch grasses with attractive foliage is important for creating full season beauty.

In the fall, our meadows are mowed to a height of four to six inches. This simultaneously scatters ripened seed and adds a layer of organic mulch. Also, to improve or retain species diversity, ripe seed is collected and redistributed. Exposed meadows with well-drained soils can benefit from a light mulch in the fall to protect the plants, especially those recently established, from harsh winter conditions.

14. Turf Demonstration   back to top

15. Concert Area   back to top

16. Penstemon Garden   back to top

Native only to North America, with 272 different species found from Canada to Mexico, and from the Atlantic to the Pacific, the genus Penstemon is truly remarkable.  Penstemons are amazingly diverse in shape, form, and color, and they grow in many different environments, from low, dry deserts to high, moist forests.

Nearly all penstemons share a love for well-drained soils.  Once established, they require very little water beyond what nature provides.  Botanists and gardeners consider penstemons to be xeric, or water-thrifty plants.  With their beautiful flowers (loved by pollinators like hummingbirds and hawkmoths), they are excellent plants for dryland gardens, especially here on the semi-arid Colorado Plateau.

Formerly the Groundcover Garden, the Arboretum’s new Penstemon Garden is a work-in-progress.  This garden displays the diverse penstemon species of the high altitude West and Southwest.  The garden’s south arm (farthest from the San Francisco Peaks) was planted in September 2003, and includes eight different Flagstaff-area penstemon species, from the rare Penstemon clutei (Sunset Crater penstemon), to Penstemon whippleanus (Gray Whipple's penstemon).  Clutei is endemic to the volcanic soils around Sunset Crater, meaning that it is found nowhere else in the wild.  Whippleanus grows in higher, cooler, and moister elevations than clutei.  Take a closer look: the leaves of each species reveal these elevational differences, with the clutei displaying tougher, thicker leaves that conserve water.  Other common native plants of the southern Colorado Plateau are growing as “companions” of the penstemons in this bed, like Quercus gambelii (Gambel’s oak).

The garden’s west arm (nearest the Horticulture Center) was planted in late June of 2005.  This bed features penstemons that are native to the larger Colorado Plateau bioregion and its edges.  These include Penstemon eatonii, (firecracker penstemon) a red-flowered species that typically grows between 3,000 and 6,000 ft., and Penstemon neomexicanus, (New Mexico penstemon) a high elevation, blue-flowered species native to New Mexico’s Sacramento Mountains.

Like the south bed, the west arm is organized to show elevational differences: penstemons that typically grow in lower elevations (below 7,000 ft.) begin on the bed’s south end, while penstemons that prefer higher elevations (above 9,000 ft.) are planted on the bed’s north end, toward the San Francisco Peaks.

As mentioned above, nearly all penstemons grow best in very well drained soils.  To improve drainage, gardeners added black volcanic cinders to The Arboretum’s clayish, poorly drained soils.  The cinders also act as a water-saving mulch.  In addition, we built small berms and added local “malpais” rocks (a kind of volcanic stone), to create slightly warmer microclimates. 

Besides adding volcanic cinders to the soil, The Arboretum’s gardeners have also done a great deal of “hardscape” work, as part of the process of transforming the old Groundcover Garden into the new Penstemon Garden.  Using malpais stones, we completely rebuilt the garden’s east-facing dry stack walls.  No mortar was used to create these solid retaining walls. 

Using mortar and flatter pieces of malpais we also re-capped the garden’s already existing concrete walls.  We also designed and constructed two new interior beds with sandstone blocks and mortar, and removed the old dirt pathways, replacing them with “Sedona Red” crusher fines and “Stabilizer Solution.”  This latter substance gives the pathways their hard texture.

In future years, the Penstemon Garden will continue to evolve and change.  We will be planting many more native plants in this garden, focusing on the penstemon species of Utah and the Intermountain West.

We hope that you enjoy The Arboretum at Flagstaff’s beautiful and exciting new Penstemon Garden!  We are grateful to the Margaret T. Morris Foundation for financial support in this ongoing project.

Penstemon Garden Species List

ambiguus
barbatus
brandegei
clutei
commarhensus
eatonii
linarioides
mensarum
neomexicanus
nudiflorus
palmeri
virgatus
whippleanus

Horticulture Center   back to top

The passive solar greenhouse depends largely on renewable solar energy for its heat. Radiant heat enters the system through the translucent Lexan panels that make up the sloped roof, which faces south to maximize the available solar energy. During the day, heat is absorbed by the thick, dark-colored concrete floors, tile walls, and by the water in the fiberglass tubes along the north side of the greenhouse. Heat is then released by these storage devices into the greenhouse as the temperature drops in the evening.

During the coldest time of the year water is heated by a pellet stove. Hot water is then pumped into and stored in insulated tanks before it is transferred through pipes to heating vents in the offices, classroom, and greenhouse where heat is released by convection.

Another resource-conserving feature is the water collection tank. Rainwater and snowmelt is collected in a 3,500 gallon underground cistern via the roof, gutter, and rainspout. Should a water shortage occur, water from the cistern is pumped into the watering system for the greenhouse.

White-colored shade paint is used on the Lexan panels in the summer to maintain desired temperatures and prevent overheating of plants. Evaporative pads (swamp coolers), fans, and vents circulate cooler air near the floor and heated air out of the roof to keep the greenhouse from overheating.

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