Orton Botanical Garden is located on the northerly fringes of the Great Basin Desert. The average annual precipitation here in south central Idaho is 10 inches. The garden demonstrates landscaping that requires minimal irrigation or in some cases no irrigation at all. There are over 400 species and varieties of plants demonstrated in the garden, including many Idaho native plants, as well as plants from the southwest and other dry climates around the U.S. and a few other countries.
Principle #1: Planning & Design
Start by mapping the area you intend to plant. There are many factors to consider, including micro climates, shade, land contour, soil types, and planned irrigation systems. There are many different landscaping styles from which to choose. Some examples are: 1) a rock garden with mostly low growing plants, such as buckwheats, 2} cactus garden, 3) southwest garden with yuccas, agaves, cactus, and desert shrubs, 4) traditional flower garden, 5) pollinator garden, 6) a native plant garden, 7) shrub and tree garden, and 8) succulent garden with hen & chicks and sedums. A combination of several styles may also be desired.
Principle #2: Soil Improvements
Before amending soils, one must decide what the majority of plant species are that will be used. Native western plant species have evolved not needing high organic content. Many of the native western species actually will die or be short lived with too much organic matter. Western soils also tend to be alkaline in ph. Many soil amendments that are traditionally used (humus, compost, lime, wood ash) are not needed for xeric gardening. Because western native species have evolved in mineral rich western soils, adding trace minerals to the soil may be beneficial.
If your soil is heavy clay, it will need to be amended with cinder, some compost and/or small gravel to improve the drainage. Clay soil is dense, slow to absorb and release water. Good drainage is very important for most Idaho native plants. Placing the most water sensitive xeric plants on berms will help to direct water away from the plants’ roots. This is especially important in winter and early spring in Idaho.
Principle #3: Practical Turf Areas
One way to reduce watering requirements is to reduce the amount of bluegrass turf in your landscape. Good, xeric design does not mean that turf grass cannot be used. Lawns can be a component of xeric landscape design. Just remember to keep the lawn areas to a minimum and site them where you can enjoy it easily from your home. There are alternatives to bluegrass such as blue grama grass, buffalo grass, and fescue grasses, but these can be more difficult to establish and to maintain.
Principle #4: Efficient Irrigation
Many advancements in irrigation equipment and systems have been made in the past years, making it possible to irrigate even more efficiently. These irrigation improvements may lower water usage some, but it is only by installing water efficient landscapes that water usage will go down significantly. Xeriscapes can be irrigated efficiently by hand or with an automatic sprinkler system. If you're installing a sprinkler system, this should be included in your landscape design. It is best to zone your turf areas separately from other plantings and use the irrigation method that waters the plants in each area most efficiently. For grass, low-pressure, low-angle sprinklers irrigate best. Drip, spray or bubbler emitters are most efficient for watering trees, shrubs, flowers and groundcovers. If you water by hand, try to avoid oscillating sprinklers and others that throw water high in the air or put out a fine mist. The most efficient sprinklers put out big drops and keep them close to the ground. The most efficient method to apply water is through some type of drip system. Many systems are on the market and the best types use controlled flow rates through emitters. The best subsurface systems also have check valves at the emitters to regulate flow through the irrigation line, ensuring that the last emitter will have the same flow as the first emitter on the line.
Water deeply and infrequently to develop deep roots. Adjust your controller regularly to meet seasonal needs and weather conditions. A rain shutoff should also be installed.
Principle #5: Proper Plant Selection
The plants you choose determine how water-wise your landscape can be. To achieve maximum water-efficiency, choose plants that do well in southern Idaho. The “List of Drought Tolerant Plants for Southern Idaho” in this website is a helpful guide to plant selection. There are many Idaho native plants that do well in a drought tolerant garden, but there are many others from other states as well as other counties that may work well for your design.
Keep in mind also that almost all gardens have micro climates due to wind protection, water retention, sun and shade relationships, fences, etc. A micro climate may be as simple as the south side of a large rock placed in a sunny location. These micro climates allow a larger selection of plants than may at first be recognized.
Finally, remember that plants need a period of time to become established. During the establishment phase, plants will need more water than after they are well rooted into the surrounding soil in which they are planted. Many plants need very little irrigation once they are well established and growing.
Principle #6: Mulching
Mulching helps to control weeds and retains water, but not all plants like to be mulched the same. Some plants prefer rock mulch over wood mulch, but rock mulch can be harder to weed and to add additional plants. A combination of different colors of rock mulch makes the large landscaped areas look less harsh; it also adds interest. A combination of rock and wood mulch can accomplish the same effect. Wood mulch is often quite a bit less expensive than rock mulch, and it is easier to move around, and plant into. It is also easier to modify a bed. If wood mulch is used, remember that not all plants like to be heavily mulched. If you use wood mulch, use a thin layer and be sure not to over-water.
Principle #7: Maintenance
It is important to remember that not all plants have similar needs and not all plants like more water. Regular maintenance is important to preserve the beauty of your landscaping. Weeding is especially important. Your landscaping should be walked regularly to ensure that weeds are under control. In addition to weeding, proper irrigation, pruning, fertilizing and pest control are necessary to keep your landscape beautiful and water thrifty.
Following is a list of drought tolerant plants that we have found do well in south central Idaho. It is not intended to be an all inclusive list.
This tall slender evergreen is an excellent plant that looks similar to the Italian cypress commonly grown in warmer climates. It grows to 4' wide and up to 30' tall. Excellent for use as a single focal specimen, for screens and buffers. Requires no trimming to keep its form.
Native in southern Idaho. Very xeric and reaches 20' tall. As it ages, it can take on unusual and interesting forms.
This evergreen plant is native in Idaho and throughout much of western USA. It grows to 16', but is can be trimmed easily and can be used as a hedge plant.
Fern bush is an Idaho native plant that grows 5-6' tall x 6-8' wide. It is semi evergreen and greens up quickly in early spring. It blooms late in summer and attracts many native pollinators and honey bees. Easy to trim and keep at any desired size. Foliage has a pleasant odor.
This deciduous desert plant is native to the southwestern USA and Mexico. It can grow to 15'-20' high. In Idaho it starts showing leaves in late May, starts blooming in late June and continues to bloom the rest of the summer. The flower color varies depending on where the plants originate. Lucretia Hamilton and Art's Seedless cultivars have grown well in Idaho and have purple flowers.
This evergreen shrub can reach 3' to 6' high and about the same in width. It has small white flowers in early spring that are fragrant. This plant does much better in a xeric garden than our Idaho native Ceanothus velutinus.
This very xeric plant is 4" tall x 15" wide spreading with underground roots. Excellent for stabilizing soils. It blooms from June until frost.
This beautiful native plant is 4-6" tall x 15-18" wide spreading with underground roots. It blooms in mid to late summer. Hummingbirds love it.
This night blooming southwest native has beautiful purple flowers from mid summer until frost. The plants can reach 2'-3' high and as much as 10' or more wide. After frost they die all the way back to their large underground tubers.
This southwest yucca is the largest yucca native to the USA. It can reach a height of 40', but usually stays much smaller in colder climates. Plants from the northerly part of its range will usually do well in Idaho. Once it is established it needs little irrigation. They bloom in early May here in Idaho.
This beautiful blue yucca is native to west central Utah and east central Nevada. It can reach 3' - 5' high and wide. The white flowers bloom well above the leaves in May.
This desert yucca is common throughout much of southwestern USA. When it blooms, its flowers are held within its leaves. The fruits look somewhat like a banana. It can reach 5' high and 6' wide here in Idaho. As there are no yucca moths in Idaho, fruits rarely form on the plants.