Begin with healthy soil
A good lawn starts from the ground up. Proper soil preparation will minimize future weed problems. Adding compost will improve the water-holding capacity of sandy soils and open up air spaces in compacted clay soils.
Nutrients and essential micro-organisms in compost help get the growing process off to a good start.
The latest dirt on dirt
Soil is the growing medium for plants and its composition will affect plant growth. Both the physical (texture) and chemical (nutrient) composition of the soil is important for plant health. Your yard is comprised of two soil layers with different nutrient level and textures.
The topsoil (top layer) contains more organic matter, making it usually darker and looser than the deeper layers. The optimal depth of this soil for a lawn is 15 - 20 cm (6 - 8 inches). The subsoil (lower layer) is usually hard clay and often poor in nutrients.
The perfect mix
Soil is composed of rock particles (sand, silt and clay) and organic matter (humus). The texture of your soil depends on the proportion of loam, sand and organic matter.
The best gardening soil is loamy soil containing all three in ideal proportions. A good soil absorbs water easily and quickly yet allows water, air, nutrients, plant roots and organisms to move through it.
Finding a balance
The soil pH value reflects the acidity or alkalinity of the soil. Soil pH is measured on a scale of 0 - 14, with 7 being neutral. Values below 7 are considered acidic and those above 7 are alkaline.
The most common soil type in Edmonton is clay loam, and is usually a bit more alkaline, high in nutrient but lacking in moisture retention capability and proper drainage capacity. For detailed technical information, have your soil analyzed by a professional laboratory.
Modifying your soil
To modify your soil, add sand to improve drainage, loam to increase nutrients, and organic matter to improve moisture retention capacity.
Lay it on the lawn
If you don't have at least 15 cm (6 inches) of good soil for your lawn, rebuild your soil by top dressing with a 1/2 cm (1/4 inch) layer of soil containing equal proportions of loam, sand and organic matter. The soil for your lawn should be slightly acidic (pH 6.0-6.5) to allow the release of nutrients required for grass to grow.
Mulching your grass clippings returns nutrients and organic matter to the soil. Aerate your lawn in the fall or in early spring to allow water, nutrients and oxygen to get to the roots.
Source: Lawn Ecology brochure, Health Canada, 2002.