Page 40 - 7166 - Rain Garden Handbook

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OPTION 2—EXCAVATE AND AMEND SOIL FOR REUSE HOW MANY CUBIC YARDS DO YOU NEED?

Option 2 should be used when you have moderately good to good quality Soil and compost suppliers deliver material in
soils without too much clay. Excavate the soil and set it aside for mixing with cubic yards. To calculate how many cubic yards
compost on-site. you need, use the top surface of the ponding
area as the square footage for soil placement.
Mix Compost with Excavated Soil as Follows: Convert the depth of material you want to order
65% Excavated Soil to 35% Compost
from inches to feet.
Excavation Depth Examples and Mixing Instructions: Example: 18 inches x 1 foot = 1.5 feet

6" Overflow Containment (Assuming No Berm is Constructed) 12 inches
+ 6" or 12" Ponding Depth Now multiply your soil placement area by the
+ 12" to 24" Rain Garden Soil Mix (Created On-site) depth of material to calculate CUBIC FEET.

= 24" to 42" Excavation Depth Example: 392 square feet x 1.5 feet = 588 cubic feet

Excavation depths will be the same as Option 1. However, compost will be There are 27 cubic feet in a CUBIC YARD, so to
blended with on-site excavated soil to create the rain garden soil mix. convert, divide by 27.
Example: 588 cubic feet / 27 cubic feet
= 21.78 cubic yards

Refer to www.raingarden.wsu.edu for additional
information, including worksheets for calculations.

Rough Up the Bottom

Before adding rain garden soil mix, use a rake, shovel, or rototiller to rough
up (scarify) the bottom of the excavated area (but avoid compaction of the
area). Loosening the soil at the excavated bottom of the rain garden will
enhance drainage and promote root growth.
Patricia Pyle