Some of the solutions being developed are:
- Reduction of stormwater run-off through the use of bio-swales, rain gardens and green roofs and walls.
- Reduction of water use in landscapes through design of water-wise garden techniques (sometimes known as xeriscaping™)
- Bio-filtering of wastes through constructed wetlands
- Landscape irrigation using water from showers and sinks, known as gray water
- Integrated Pest Management techniques for pest control
- Energy-efficient landscape design in the form of proper placement and selection of shade trees and creation of wind breaks
- Permeable paving materials to reduce stormwater run-off and allow rain water to infiltrate into the ground and replenish groundwater rather than run into surface water
- Use of sustainably harvested wood, composite wood products for decking and other landscape projects, as well as use of plastic lumber
- Recycling of products, such as glass, rubber from tires and other materials to create landscape products such as paving stones, mulch and other materials
- Soil management techniques, including composting kitchen and yard wastes, to maintain and enhance healthy soil that supports a diversity of soil life
- Integration and adoption of renewable energy, including solar-powered landscape lighting
A sustainable landscape is designed to be both attractive and in balance with the local climate and environment and it should require minimal resource inputs. Thus, the design must be “functional, cost-efficient, visually pleasing, environmentally friendly and maintainable”. As part of the concept called sustainable development it pays close attention to the preservation of limited and costly resources, reducing waste and preventing air, water and soil pollution. Also, compost, fertilization, grass cycling, pest control measures that avoid or minimize the use of chemicals, integrated pest management, using the right plant in the right place, appropriate use of turf, irrigation efficiency and xeriscaping or water-wise gardening are all components of sustainable landscaping.
The geographic location can determine what is sustainable due to differences in precipitation and temperature. For example, the California Waste Management Board emphasizes the link between minimizing environmental damage and maximizing one’s bottom line of urban commercial landscaping companies. In California, the benefits of landscapes often do not outweigh the cost of inputs like water and labor. However, using appropriately selected and properly sited plants may help to ensure that maintenance costs are lower than they otherwise would be due to reduced chemical and water inputs.
The primary step to landscape design is to do a “sustainability audit”. This is similar to a landscape site analysis that is typically performed by landscape designers at the beginning of the design process. Factors such as lot size, house size, local covenants and budgets should be considered. The steps to design include a base plan, site inventory and analysis, construction documents, implementation and maintenance. Of great importance is considerations related to the growing conditions of the site. These include orientation to the sun, soil type, wind flow, slopes, shade and climate. The goal of reducing artificial irrigation and reducing use of toxic substances requires proper plant selection for the specific site.
Mulch may be used to reduce water loss due to evaporation, reduce weeds, minimize erosion, dust and mud problems. Mulch can also add nutrients to the soil when it decomposes. However, mulch is most often used for weed suppression. Over use of mulch can result in harm to the selected plantings. Care must be taken in the source of the mulch, for instance, black walnut trees result in a toxic mulch product. Grass cycling turf areas (using mulching mowers that leave grass clippings on the lawn) will also decrease the amount of fertilizer needed, reduce landfill waste and reduce costs of disposal.
A common recommendation is to add 2-4 inches of mulch in flower beds and under trees away from the trunk. Mulch should be applied under trees to the dripline (extension of the branches) in lieu of flowers, hostas, turf or other plants that are often planted there. This practice of planting under trees is detrimental to tree roots, especially when such plants are irrigated to an excessive level that harms the tree. One must be careful not to apply mulch to the bark of the tree. It can result in smothering, mold and to insect depredation.
The practice of xeriscaping or water-wise gardening suggests that placing plants with similar water demands together will save time and low-water or drought tolerant plants would be a smart initial consideration. A homeowner may consider consulting an accredited irrigation technician/auditor and obtain a water audit of current systems. In the event that the situation is difficult to manage, drip or sub-surface irrigation may be most effective. If the system has been in use for over five years, upgrading to evapotranspiration (ET) controllers, soil sensors and refined control panels will improve the system. Oftentimes irrigation heads are in need of readjustment to avoid sprinkling on sidewalks or streets. Business owners may consider developing watering schedules based on historical or actual weather data and soil probes to monitor soil moisture prior to watering.
One important part of sustainable landscaping is plant selection. Most of what makes a landscape unsustainable is the amount of inputs required to grow a non-native plant on it. What this means is that a local plant, which has adapted to local climate conditions will require less work on the part of some other agent to flourish. For example, it does not make sense to grow tomatoes in Arizona because there is not enough natural rainfall for them to survive without constant watering. Instead, drought tolerant plants like succulents and cacti are better suited to survive. Also, by choosing native plants, one can avoid certain problems with insects and pests because these plants will also be adapted to deal with any local invader. The bottom line is that by choosing the right kind of local plants, a great deal of money can be saved on amendment costs, pest control and watering.
Plants used as windbreaks can save up to 30% on heating costs in winter. They also help with shading a residence or commercial building in summer, create cool air through evapo-transpiration and can cool hardscaped areas such as driveways and sidewalks.
A house surrounded by local trees or bushes enjoys multiple benefits. Plants release water vapor in the air through transpiration and water has the ability to reduce temperature extremes in the areas near it (as it boasts very high heat capacity). The larger and more leafy the plant, the most water vapor it produces. Additionally, the presence of trees is crucial in the creation of stable, healthy and productive ecosystems (such as forests). In fact this is an important principle of permaculture.
If the surrounding trees are chosen to produce edible fruit they can provide a sustainable food source for the occupants of the house. Even if some are fairly demanding (especially in the summer), irrigation is an excellent end-use option in greywater recycling and rainwater harvesting systems, and a composting toilet can cover (at least) some of the nutrient requirements. Research suggests that diluted human urine might be as effective as chemical fertilizers. Not all fruit trees are suitable for greywater irrigation, as reclaimed greywater is typically of high pH and acidophile plants don’t do well in alkaline environments.
An intelligent choice for direct energy conservation would be the placement of broadleaf deciduous trees near the east, west and optionally north-facing walls of the house. Such selection provides shading in the summer while permitting large amounts of heat-carrying solar radiation to strike the house in the winter. The trees are to be placed as closely as possible to the house walls but no closer than 1 meter – otherwise the roots can cause substantial foundation damage. A sustainable house will most likely be equipped with south-facing (north-facing in the S. hemisphere) photovoltaic panels and a large, south-facing glazing as a result of passive solar heating design. As the efficiency of both systems is very sensitive to shading, experts suggest the complete absence of trees near the south side.
Another intelligent choice would be that of a dense vegetative fence composed of evergreens (e.g. conifers) near that side from which cold continental winds blow (usually north in the N. hemisphere) and also that side from which the prevailing winds blow (west in temperate regions of both hemispheres). Since north winds are most cold and westerlies blow most often, such choice creates an effective winter windbarrier that prevents very low temperatures outside the house and reduces air infiltration towards the inside. Calculations show that placing the windbrake at a distance twice the height of the trees can reduce the wind velocity by 75%. It then follows that, with some planning, both arrangements (deciduous and evergreen) can be applied simultaneously.The above vegetative arrangements come with two disadvantages. Firstly, they minimize air circulation in summer (although in many climates heating is more important and costly than cooling) and, secondly, they may affect the efficiency of photovoltaic panels, thus prompting the need for a shading analysis. However, it has been estimated that if both arrangements are applied properly, they can reduce the overall house energy usage by up to 22%.
Maintaining plant health will eliminate most pest problems. It is best to start with pest-free plant materials and supplies and close inspection of the plant upon purchase is also recommended. Establishing diversity within the area of plant species will encourage beneficial organism populations (e.g. birds, insects), which feed on potential plant pests. Because plant pests vary from plant to plant, assessing the problem correctly is half the battle. The owner must consider whether the plant can tolerate the damage caused by the plant. If not, then does the plant value justify some sort of treatment? While pesticide is often chosen to solve the problem, physical barriers and repellents may help. If pesticides are the chosen method, selective organic or natural pesticide is often better because it has less impact on non-target species.
Proper pruning will increase air circulation and decrease the likelihood of plant diseases. However, improper pruning is detrimental to shrubs and trees. Hedging, topping and shearing of landscape plants causes excessive plant growth. In addition, topping is a hazardous practice which creates a hazardous tree which is highly susceptible to wind damage. Natural pruning techniques during the proper season, on the other hand, promotes healthier, more stable plants. In temperate areas, deciduous plants should be pruned during dormancy. Plants should never be pruned at the end of a growing season because growth is stimulated and such new growth will be too tender to survive winter freezing temperatures.
Landscape managers should make use of the Integrated Pest Management (IPM) to reduce use of pesticides and herbicides and reduce non-point source solution.
Organic horticulture is the science and art of growing fruits, vegetables, flowers, or ornamental plants by following the essential principles of organic agriculture in soil building and conservation, pest management, and heirloom variety preservation.