The use of compost in urban green areas – A review for practical application

The use of compost for soil amendment and mulching can increase quality during the establishment and management phases of plants in urban green areas. Costs can be reduced, especially in the management phase, but a number of conditions have to be met before benefits from the use of composts can be fully realised. Descriptions of the quality of the composts must be comprehensive enough for the green industry to be able to predict the effect their products will have on the growth and development of plants at the point of use. Users in urban green areas must be able to make specific demands on the quality of compost based on how it is to be used and in relation to the effects planned. General quality factors that have to be fulfilled concern high stability, the absence of unpleasant smell, a low or medium salt content, and absence of polluting substances or particles inhibiting germination and growth. The specific quality demands on compost have to be related to nutrient content and particle size. There is no such thing as the “perfect” compost, but several types, each designed for a site-specific purpose.
• As a soil amendment to shrubs and trees, composts should be limited to an amount that supplies the plants with no more than 100–120 kg of plant available nitrogen per hectare.
• For mulching, the total compost thickness has to be no more than 10 cm. The lower layer (2–5 cm) should consist of small particles of nutrient-rich compost and the top layer (5–8 cm) of nutrient-poor particles larger than 20 mm. In this way, nutrients are supplied to the trees and shrubs and weeds are given a seed bed poorly conducive to growth.