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 adding 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. Drip or sub-surface irrigation may be useful. Using evapotranspiration controllers, soil sensors and refined control panels will reduce water loss. Irrigation heads may need 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. When deciding what kind of building materials to put on a site it is important to recycle as often as possible, such as for example by reusing old bricks. It is also important to be careful about what materials you use, especially if you plan to grow food crops. Old telephone poles and railroad ties have usually been treated with a toxic substance called creosote that can leach into the soils. Sustainably harvested lumber is available, in which ecological, economic and social factors are integrated into the management of trees used for lumber. 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 to flourish. Instead, drought-tolerant plants like succulents and cacti are better suited to survive.