2.1   Existing Soil

Defined: Surface soil that is not altered, compacted to root limiting density, graded, or contaminated before or during the construction process. It is considered acceptable for planting and long term health of the plants specified either as it exists or with minor modification. 

Protection: Existing soil can be damaged by compaction, contamination, grading, creation of hard pan or drainage problems, and loss of the surface soil horizons (see Soil Definitions). Protect existing soil from compaction, contamination, and degradation during the construction process. Where possible, deliver and plant trees that require the use of heavy mechanized equipment prior to final soil preparation and tilling. Restrict the driving lanes to one area instead of driving over and compacting a large area of soil. Any soil that has been compacted during the delivery of plants to the planting locations, digging of planting holes, and installing plants should be tilled to a depth of 6 inches.

Modifications: Existing soil may need some form of modification in order to make it suitable for planting. Modifications to existing soil respond to the soil problems expected or encountered for surface soil that has been altered and/or graded before or during the construction process. (See x.x for types of Modification)

2.2   Imported Topsoil

Defined: Imported Topsoil should be fertile, friable soil containing less than 5% total volume of a combination of the following: subsoil, refuse, roots larger than 1 inch diameter, heavy, sticky or stiff clay, stones larger than 2 inches in diameter, noxious seeds, sticks, brush, litter, or any substances deleterious to plant growth. Soil texture should be considered USDA loam, sandy clay loam or sandy loam with clay content between 15 and 25% and a combined clay/silt content of no more than 55%.

If the percent (%) of the above objects is greater than 5%,  the amount should be controlled by source selection and not by screening the soil. 

Stockpiling: See section 1.1.

Topsoil shall be suitable for the germination of seeds and the support of vegetative growth.

Imported Topsoil should not contain weed seeds in quantities that cause noticeable weed infestations in the final planting bed.


2.3   Compost

Defined: Blended and ground leaf, wood and other plant based material, composted for a minimum of 9 months and at temperatures sufficient to break down all woody fibers, seeds and leaf structures, free of toxic material at levels that are harmful to plants or humans. Source material should be yard waste trimmings blended with other plant or manure based material designed to produce compost high in fungal material.


2.4   Course Sand

Defined: Sand particles that have a diameter within the range of 0.5mm to 1mm and should be clean, washed, sand, free of toxic materials.

2.5   Planting Soil

Defined: Mixes of Existing Soil or Imported Topsoil, Coarse Sand, and/or Compost to make a new soil that meets the project goals for the indicated planting area. This mix is intended to be moderately slow draining soil for planting beds. This soil may be mixed off site or onsite, and will vary in Mix components and proportions as indicated.

Mix Ratio:

Imported Topsoil (see 2.3): 45-50%

Coarse Sand (see 2.5): 40-45%

Compost (see 2.4): 10%

Mix Instructions: Mix the Coarse Sand and Compost together first, then add to the Topsoil. Mix with a loader bucket to loosely incorporate the Topsoil into the Coarse Sand/Compost Mix. Do not overmix! You do not need to screen the soil, and clumps of soil, Compost and Coarse Sand may remain in the overall Mix.

Installation: Install the Planting Soil in 12-18 inch lifts to the required depths. Apply compacting forces to each lift as required to attain the correct compaction. Scarify the top of each lift prior to adding more Planting Soil. Install the Planting Soil at a higher level to anticipate the reduction of Planting Soil volume due to settlement. A minimum settlement of approximately 10 - 15% of the soil depth is expected.


2.6  Wood Mulch

Defined: Mulch shall be coarse, ground, and from tree and woody brush sources. The minimum range of fine particles shall be 3/8 inch or less in size and a maximum size of individual pieces shall be approximately 1  to 1-1/2 inch in diameter, and maximum length of approximately 4 to 8 inches. No more that 25% of the total volume shall be fine particles and no more than 20% of total volume be large pieces. Remove pieces larger than 8”that are visible on the surface of the mulch after installation.

2 Materials