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