Identify the purpose of your landscape design. Are you designing an entire property landscape that will show off your home to best advantage? Are you creating an enclosed garden, possibly to grow food crops or fruit trees in the desert? Or do you want to maximize the environment for a new tree, shrub or flower bed that you intend to plant?
Reducing water usage by getting rid of the lawn to is very important in the western United States. Instead of grass, consider pavers or gravel paths meandering by garden beds containing drought and heat tolerant plants. Low water, low maintenance landscaping can provide a pleasing, care-free area surrounding your residence. Vegetation that supports native wildlife year round can provide additional interest at little or no cost.
Landscape architecture includes walls used to create shade, divert wind, and provide privacy; raised garden beds that provide soil drainage and keep rabbits away, walkways and steps to direct traffic and make climbing easier; and rock or masonry channels that divert water and prevent erosion.
Designing an Entire Property Landscape
Start your garden design with a list of plants to be used, and their needs. Group plants according to their water requirements. This allows for efficient watering by group, and takes less time. Also group plants into those that can handle full sun and those that need part shade, especially western shade.
On paper, position trees and shrubs spaced according to their mature width. Do not be fooled by the appearance of a tree when young. It will outgrow its 3-5 foot width and become, depending on species, a 15-30 foot wide tree. Trees that will be 30' wide need to be 35' apart from each other and from houses. Trees with aggressive side roots need to be 35' apart to avoid competition.
In your garden design, create microclimates by careful placement of 4-8' high walls, raised garden beds and earthen mounds around low areas for water collection. Keep the sun's path both winter and summer in mind while doing this. Also plan arrangements of tall shrubs and trees that can provide shade for other plants. The mature size of trees should be proportionate to the total area covered by the walls if you have an enclosed garden. Smaller walled enclosures need smaller trees or large shrubs instead.
If you can, select plant species that are adapted to the climate of the southwest desert - hot, dry, infrequent rain, periodic drought and alkaline soil and water. Just because a garden is in a dry landscape, though, does not mean it has to be cactus and sharp thorns. Many thornless and leafy plants are adapted to heat and dry conditions.
Select young trees to plant that come in 5 gallon containers rather than very large ones. They will require less water initially and grow to the same size as bigger trees. They are also more adaptable and less likely to fail. Avoid large, water-hogging trees such as Western Cottonwood, Sycamore, Aspen, or ornamental fruit trees that will rob water from other plants.
Many water-wise plants attract butterflies and hummingbirds. Some of these plants are long bloomers and will attract wildlife for months. Others produce berries that tempt birds at different seasons. Plan to have a variety of plants blooming and fruiting throughout the year and your landscape will be a perpetual motion of interest.
Many plants need part shade in the hottest parts of the year. Walls and the shade of trees or large shrubs can help. Know which trees are inhospitable to plants growing underneath because of chemicals released by their roots.
Most desert plants need well-drained soils and do best in raised garden beds or on top of earthen mounds at least 12-18" above surrounding soil. Raised garden beds formed of rock or masonry block are often used. Avoid treated lumber because the poisons in the lumber can be picked up by any plant used for food, such as mint, basil, tomatoes or edible flowers.
Double masonry walls can be built, a tall outside wall and a lower inside wall, about 18-24" apart. Filling the space between them with soil provides a well-drained, linear space for flowering perennials or garden herbs.
Walkways can be made of tamped earth, gravel, brick, concrete block, or even more creatively, mosaic stone with an infinite variety of patterns. Weed barrier cloth with gravel on top will allow rain to drain into the soil and slow the runoff of water onto the street. In Tucson, Phoenix, and elsewhere, monsoon rains frequently lead to erosion. Paths on slopes should be lined on the sides with rock, brick or block to reduce rainwater erosion and water flows that turn to ice sheets in winter. Steps may have to be situated at internals along a path to reduce steepness. Steps can be made of concrete, block or treated lumber.
Unless the soil area is shaded, drip irrigation has the disadvantage of forcing roots close to the surface where they need thick mulch to avoid getting baked in the hot desert sun. If drip irrigation is to be used, make sure that the soil has a thick layer of straw to reflect the sun's rays and reduce evaporation.
Provide raised soil or stone ridges to channel rainwater and dig low areas in the soil – ponds with bare soil bottoms that may be dry part of the year – to collect rainwater so that nearby plants can receive water that slowly soaks into the ground. Have an overflow channel of rock or block so that rainwater can escape without erosion if it exceeds the depth of the pond.
During a drought, run stored rainwater or tap water into these low areas to provide needed water. Pools for a group of plants can be flooded every two to four weeks. Individual trees can be set up with their own basins to collect rainwater and flood their roots to the drip line every one to four weeks. This is especially necessary for fruit trees.
A rainwater collection system that collects rainwater from a roof and stores it in large barrels will help provide water when rains fail.
Use mulch that is suited to each plant. Mulch reduces evaporation from the soil. Penstemons, for example, prefer crushed decomposed granite, which provides nutrients, or small gravel. But avoid using only rock for the landscape to avoid a moonscape look. Bare soil between plants in the desert is fine. Low groundcover plants for dry landscapes can also help.
A Tropical Fruit Garden for the Desert
The first key to building a desert garden that grows tropical fruit is to surround it on all sides with 6' high block walls. Block walls reduce wind which dries out soil and blows humidity away. Block walls keep sun from heating nearby soil and baking shallow roots. Walls also keep some critters, like javelina, at bay.
The second key to a successful fruit garden in the desert is to provide a "roof" on the garden with tall, fast-growing shade trees. Overhead shade will protect fruit trees and shrubs from too much sun and high temperatures. One fast-growing shade tree is Moringa. Another is Castor Bean: Ricinus communis. The combination of walls and tall trees creates a cool, moist climate where tropical plants can thrive.
Third, use cultivation practices that provide the right kind and amount of soil amendments, fertilizer, mulch and water. Every fruit tree and shrub will differ in what it needs. Group plants according to their cultivation requirements.
Fourth, water every day. Trees can be planted closer together with daily water, and their growing roots will further improve soil drainage. Your garden will become a tropical forest that holds humidity and stays cooler than the surrounding desert.