Sustainable Landscaping

Soils, Composting and Fertilizers 

Much of Colorado has heavy, clay soils. Clay texture can lead to poor water and oxygen penetration. In addition, Colorado soils often lack organic material. To improve plant health, soil amendments are often necessary. 

The choice of a soil amendment greatly depends on what is being planted. Native plants may be adapted to local soil conditions and might not necessarily benefit from soil amendments. Many non-native plants establish more quickly and develop a healthier root system with the addition of organic soil amendments. 

Improving the overall condition of your soil—including permeability, aeration and drainage—is a slow process. The addition of organic materials such as composted grass clippings, manure, and fall leaves can improve soil condition over a period of time. Garden soil that provides good water retention and both oxygen and water permeability (loam texture) may take 10 or more years to create. Incorporate 3-4 cubic yards of organic matter per 1,000 square feet per year. Be sure that organic matter is incorporated completely into the existing soil.  

Base fertilizer applications on a soil analysis and specific plant requirements. Many annual flowers or bedding plants and vegetables have a higher nitrogen and phosphorus requirement than herbaceous perennials, shrubs, and trees. Some native plants can actually decline from too many applications of fertilizers. Most have lower nitrogen and phosphorus needs, having adapted to the lower fertility conditions of Colorado native soils. Determine the fertilizer requirements for your individual situation. Excessive fertilizer application is not a sustainable practice.

Irrigation

Often, a portion of Colorado is in, or on the verge of a drought. Average annual moisture for the Denver Metro area is approximately 12 to 14 inches. The Front Range is a high plains desert with the San Luis Valley, Arkansas Valley and the Western Slope exhibiting even drier conditions. Therefore, water conservation is essential. Prevent water loss through evaporation by using organic mulches. Add 3 to 4 inches around flower beds and under trees but avoid mounding mulch against tree trunks as this practice can encourage disease and insects. 

Group plants that have similar water requirements together. Designate parts of your landscape for higher or lower water use. For example, place a vegetable garden in the higher use area and a native shrub border in a lower water use area. 

Using irrigation technology to reduce water use is an important rule of sustainable landscaping. Consult with a certified irrigation technician or a certified landscape irrigation auditor and request a water audit of existing systems. Consider drip or sub-surface irrigation for more efficient water use. Regular maintenance of existing systems is necessary to ensure efficient water utilization. 

Even if the system is new, irrigation heads may need realignment and adjustment to prevent overspray onto the sidewalk or street. Sprinkler systems should be designed for uniform coverage with some overlap. Irregular patterns will create dry areas interspersed with overly wet areas. Sustainable landscaping means using water appropriately and avoiding waste.

Hardscape Selection

The choice of building materials for the landscape is extensive. Explore options for utilizing reused materials in your landscape. For example, used bricks or broken concrete can be used for retaining walls or raised beds. Also, recycled plastic material may be an appropriate choice for decking or fences. However, an example of inappropriate recycled materials for use in a garden is the use of creosote-impregnated railroad ties to build a raised bed. The chemicals used to treat the wood can leach into the soil and are not safe to use near food crops. 

Plant and Turf Selection

Select the right plant for the right place. Plants not adapted to the local environment require more resources. Plants placed in inappropriate growing conditions (lighting, moisture, temperature, etc.) become stressed and are more prone to pest problems. Plants suited to Colorado, whether native or exotic, are more sustainable. Always consider the mature size of the plant prior to placement in the landscape. 

A principle of sustainable landscape is to limit the amount of irrigated turf to areas of high use by the homeowner. Select turf species adapted for your location and use.

Dealing with Diverse Sites

Plant for Shade  

Use deciduous plants to create shade in the summer to help cool the home, while allowing light penetration in the winter as solar heating. Evergreen trees planted close to the home can create shade year-round and block winter sun.   

South and west facing parts of the house receive the most intense sunlight; north and east exposures are generally cooler. Therefore, shading the south and west side will contribute to summer cooling.  

Often two large deciduous trees can provide sufficient summer shading for a single-family home. Consider the mature size of tree species before planting; plant the trees far enough from the house to avoid foundation problems. Avoid fast-growing species that are weak-wooded and easily break in wind or snow.  

Plant for Wind Protection  

Cold winds can penetrate a building in the winter and may be responsible for some heat loss during windy days. In Colorado, prevailing winds blow from the northwest, therefore, landscaping for wind protection should be concentrated on the north and northwest sides of the building at a distance of one to three times the mature height of the trees. Evergreens provide the most wind protection.  

Slopes 

An appropriately graded site should provide drainage away from permanent structures. Steep slopes should be terraced with a series of raised beds or planters to reduce erosion potential.

Landscape Lighting 

Municipalities and other government agencies are moving toward decreasing light pollution. For these reasons, incorporate appropriate light schemes into the landscape including down-lighting. A sustainable solution is to use solar garden lighting. 

Maintenance of the Sustainable Landscape

Many organic yard waste materials can be composted including leaves, grass clippings, vegetable and flower plants, and small amounts of woody material. Do not place weeds, diseased plants or plants sprayed with chemicals in your compost bin. Remember, compost is used as a soil amendment, not a soil fertilizer.  

Reduce Pest Pressure 

Most pest problems directly correspond with the health and condition of the plant. Stressed and weakened plants are more susceptible to disease and insect problems. Maintaining plant health will prevent most pest problems. 

Start with pest-free plant materials and supplies; check for diseases and insects by inspecting all plant parts including leaves, stems and roots, before you purchase them. Roots should be firm and light in color. 

Plant diversity in a yard can discourage plant pests. A diverse plant population often increases beneficial organism populations. Beneficial organisms include birds, insects, and microorganisms. Multiple plantings of a single species are less sustainable. 

If a pest problem develops, a correct diagnosis is important. Different plant problems have various solutions. Contact your local Colorado State University Extension office or garden center for diagnosis and treatment options. 

If treatment is needed, investigate all of the possibilities. Commonly, the first reaction is to opt for a pesticide, but there are alternatives. Some treatment options include physical barriers, pruning, sanitation, irrigation adjustments, mulch, and proper plant selection. 

If pesticides are the best option, choose one that has the host and the pest on the label. In most cases, a selective pesticide is better than a broad-spectrum pesticide because it tends to have less impact on non-target organisms. Make sure to read and follow pesticide label directions. 

Reference: CSU Fact Sheet 7.243