Lawn grass established by first tilling in compost is referred to as Tilled Compost-Amended Turf (TCT).  The maximum benefits of incorporating compost are achieved by amending the entire site, regardless of the vegetation to be planted and the nutrient requirements of it.  The installation of soil amendments, through TCT, on any site generally consist sof restoring soils by tilling in a large amount of compost, 2 to 4 inches of compost per 8 inches of soil, depending on soil type.  This is a method that has been utilized in the Puget Sound region to offset the clearing of forested areas for lawns in residential developments.¹ 

The installation of soil amendments, through TCT, usually follows the general sequence and guidelines outlined below.

General sequence of operations:

• Site Plan Preparation

• Soil and Site Preparation

Commercially formulated soil amendment, SOILPAM™
(Source: Earth Chem, Inc.)

without SOILPAM™

with SOILPAM™

Site plan preparation requires a thorough analysis of the existing vegetation, topography, soils as well as the presence of any other natural features that may be potential on-site concerns.  Site constraints that require special consideration include:

• Poorly draining sites or soils. In this case an alternative to planting a lawn should be considered as turf cannot be established on poorly drained soil or where a high water table is present, regardless of the increase in organic content brought about by soil amendments.

• Steep slopes. Soil amendments should not be attempted on slopes greater than 30 percent, provided the site is freely draining. If economically feasible, geotextiles or terracing are recommended to minimize the potential for erosion. Any slope greater than 30 percent should be planted in deep rooting vegetation to aid slope stability.

• Tree and shrub roots. The general rule is to avoid disturbance to the soil within a plant’s drip-line. For soil amendments within 3 feet of the drip-line, compost should be worked into the upper 3 to 4 inches of the soil, avoiding larger roots.

• Site grading and soil depth. While sites must be graded for proper drainage the final desire grade of the soil should range between ½ to 2 inches below the elevation of any proposed roads and sidewalks. Care must be taken to account for compost settling during the soil amendment process.

Soil Sampling at Cabin Branch Mine Restoration Project
Craters of the Moon National Monument, Idaho
(Source: National Park Service, Geologic Resources Divsion)

Soil and site preparation consists first of a thorough analysis of any site constraints as well as a pre-amendment soil evaluation including the use of soil surveys, soil borings, and possible physical and chemical analysis.  On-site preparation and soil criteria to be evaluated include: 

• The use of on-site soils. If the existing soil is of adequate organic content, at least 5 percent, it should be stockpiled on-site so that it can be incorporated back into the amendment process later. This is usually less expensive than selling the removed soil after site clearing and then importing top soil for landscaping later. However, care should be taken to assure that the top soil is stockpiled in an appropriate manner that will not cause it to be washed away or reduce or destroy its organic content and biological properties. 
• The use of excavated soils. Unless the A soil horizon consists of very deep, high organic content soils the use of excavated soils should be avoided in the soil amendment process as, besides having a low organic content, the potential to import invasive weed problems onto the site exists.
• Incorporation of compost. Once the necessary soil amendment quantities and nutrients have been determined for the compost it can be incorporated into the soil.  The suggested procedure is to rototill, or rip and rototill the subgrade, then remove rocks, distribute the compost, spread the lime and nutrients, rototill again and then hand roll the site. The use of a ripper is only recommended for use in extremely hard soil.
• Turf Installation. Turf is usually provided in new developments by hydroseeding or sod replacement. In amended sites hydroseeding is usually the preferred method of establishing turf due to its ease of application and greater root depth penetration over that of sod. A lawn can usually be established within 60 to 90 days after hydroseeding or seed application. In some cases irrigation will be necessary to ensure grass survival, especially in the establishment phase. Only grass mixes that are know to do well locally should be planted.
• Weed control. In any open soil area the potential exists for weed seeds to blow in and dormant weed seeds to sprout. Shallow tilling, approximately half an inch deep, performed two to three times over the course of a six week period is usually an effective means of controlling weeds during the turf germination period. Once the turf has been established regular mowing is usually sufficient to kill weeds.

References

¹ Chollak, T. and P. Rosenfeld, 1998: Guidelines For Landscaping with Compost-Amended Soils. University of Washington College of Forest Resources.