2018 USGA RECOMMENDATIONS

Rootzone and Gravel Performance Factors When Intermediate Layer is Not Required
Bridging Factor
D15 (gravel)

D85 (rootzone)
≤ 8
Permeability Factor
D15 (gravel)

D15 (rootzone)
≥ 5
Uniformity Factors
D90 (gravel)

D15 (gravel)
≤ 3
100% passing a 12-mm screen
≤ 10% passing a 2-mm screen
≤ 5% passing a 1 mm screen

A minimum layer of 2 - 9.5 mm gravel is placed above the drain tile. The 12" rootzone mix is placed above the gravel.

 

Particle Size Recommendations When the Intermediate Layer is Used
Gravel Layer ≤ 10% particles larger than 0.5 inch (12 mm)
≥ 65% particles between 0.250 inch (6.4 mm) and 0.375 inch (9.7 mm)
≤ 10% particles smaller than 2 mm
Intermediate Layer ≥ 90% between 1 and 4 mm

A 4" layer of 1/4 - 3/8" gravel is placed above the drain tile.  A 2 - 4" layer of 1 - 4 mm Intermediate (Choker) Layer is placed above the gravel.  The 12" rootzone mix is placed above the Intermediate Layer. 

 

Recommended Particle Size Distribution for a Putting Green Rootzone Mixture
PARTICLE DIAMETER SIEVE % BY WEIGHT
Coarse gravel > 4 mm No. 5 0%
Fine gravel
Very coarse sand
2.0 - 3.4 mm
1 - 2 mm
No. 10
No. 18
≤ 3% gravel
≤ 10% combined in this range
Coarse sand
Medium sand
0.5 - 1.0 mm
0.25 - 0.5 mm
No. 35
No. 60
≥ 60% of the particles in this range
Fine sand 0.15 - 0.25 mm No. 100 ≤ 20%
Very fine sand 0.05 - 0.15 mm No. 270 ≤ 5%
Silt 0.002 - 0.05 mm ≤ 5%
Clay < 0.002 mm ≤ 3%
Total fines Very fine sand + silt + clay ≤ 10% combined
Coefficient of Uniformity (D60/D10) 1.8 - 3.5
2.0 - 3.5

2.0 - 3.5
Rootzone mixtures with peat
Rootzone mixtures with inorganic amendments
Pure sand rootzone mixtures

 

Physical Properties of a Rootzone Mixture
PHYSICAL PROPERTY RECOMMENDED RANGE
Total Porosity 35% - 55%
Air-filled Porosity 15% - 30%
Capillary Porosity 15% - 25%
Saturated Hydraulic Conductivity (Ksat) ≥ 6 inches/hour (150mm/hr.)

 

USGA Confidence Intervals for Quality Control Testing
TEST PARAMETER USGA CONFIDENCE INTERVAL (%)
Fine gravel 50
Very coarse sand 50
Coarse sand 15
Medium sand 15
Fine sand 15
Very fine sand 30
Total porosity 10
Air-filled porosity 15
Capillary porosity 15
Saturated hydraulic conductivity 25
1 Percent organic matter ± 0.2 for mixes with > 1% OM
± 0.15 for mixes with ≤ 1% OM

1 The confidence interval for organic matter is an absolute value, not a percentage of the target organic matter content. For example, a rootzone mixture with a target organic matter content of 0.7 percent would have an acceptable range of 0.55 to 0.85 percent.

USGA Recommendations for a Method of Putting Green Construction