Water Requirement to Prepare Soil

The Water Requirement to Prepare Soil calculator estimates the minimum and maximum water range for plant growth to apply in order to initially moisten soil so that plants will not suffer from over or under watering.

INSTRUCTIONS: Choose units and enter the following:

• (Vs) Volume of Soil

Water Requirement for Soil (Vw): The calculator returns the minimum and maximum amount of water in gallons.  However, this can be automatically converted to compatible units via the pull-down window.

The Math / Science

Maximum Water

The maximum percentage of water typically required for most plants to survive is based on a rough estimate derived from a factor known as the field capacity.

The value for the field capacity (`sigma_"fc"`) is estimated between 0.1 `"vol water"/"vol soil"` and 0.35 `"vol water"/"vol soil"`.  This equation uses the upper bound of this field capacity range.  To be more conservative  you will want to use less water than this equation estimates but this equation will give you a starting point for your estimates.¹ 

Minimum Water

The percentage of water typically required for most plants to survive is based on a rough estimate derived from a factor known as the permanent wilting point. the permanent wilting point, `sigma_"wp"`, is given as a range because different plants endure different levels of dry soil.  We have used the upper bound of this range so that this equations computes the safe minimum of water for your specified volume of soil.

The value for the permanent wilting point (`sigma_"pwp"`) is estimated between 0.01 `"vol water"/"vol soil"` and 0.25 `"vol water"/"vol soil"`.  This equation uses the upper bound of this permanent wilting point range.  To be more conservative  you will want to use more water than this equation estimates but this equation will give you a starting point for your estimates.

Potting Mix and Garden Soil

Potting Mix is combination of organic materials (e.g., peat moss, aged bark and pumice) but no soil (dirt) that is used in lieu of potting soil to improve drainage.  Because potting mix has no soil, it tends to be lighter than potting soil and provides a more sterile medium for plants with fewer disease carrying agents.  Potting mix is most commonly recommended for plants in containers, and potting mix is particularly desirable for starting seeds.  Garden Soil is a gardening product sold that contains natural soil (dirt) comprised of mixture of loam, clay and sand.  Garden soil is often used in raised gardens or planters as a healthy and easy medium for plants and seeds on top of the natural soil in one's yard.  Garden Soil differs from Potting Mix in that garden soil contains real soil (dirt), where Potting Mix does not.

Potting Mix and Garden Soil Price Survey

vCalc conducts a periodic pricing survey from nationally advertised retailers for various materials.  The current Garden Soil Price Survey sample information for Garden Soil and Potting Mix is as follows:

• Date: 5/14/24
• Store: Menards
  • Garden Soil (1 ft³): $6.49
  • Garden Soil (1.5 ft³): $7.49
  • Garden Soil (2 ft³): $9.99
  • Potting Mix (1.25 ft³): $13.71
  • Potting Mix (2.5 ft³): $27.43

Always use local pricing!  There is NO implied guarantee that these prices are available in your area or that products will be available.  This pricing is purely provided for estimation convenience.

Raised Garden and Planter Soil Calculator

• Soil for Box Planter: Computes the soil volume of a rectangular box shaped raised planter.
• Soil for Circular Planter: Computes the volume and associated amount of soil for a circular planter (tapered or straight) based on the top diameter, base diameter and height.
• Soil for Tapered Rectangular Planter : Computes the volume and associated amount of soil needed for a tapered rectangular planter based on the top and bottom side lengths and height.
• Soil for Polygon Shaped Planter: Computes the volume of soil needed for a polygon shaped planter based on its shape (number of sides) and dimensions including the length of the sides and the height (depth).
• Soil for Triangular Planter: Computes the volume and associated amount of soil for a triangular shaped planter based on the side lengths (a, b, c) and (h) height.
• Soil for Hexagon Planter: Computes the volume and associated amount of soil for a hexagon shaped planter based on the length of the sides and height.
• Soil for Octagon Planter: Computes the volume and associated soil amount for an octagon planter based on the length of the sides and the height. 
• Soil Needed for 3 Tier Raised Garden: Computes the amount of garden soil or potting mix needed for a three tier (step) raised garden based on the dimensions of the tiers.  
• Cost of Soil: Computes the cost of a volume of soil base on unit price.
• Water Requirement to Prepare Soil: Estimates the minimum and maximum water range for plant growth to apply to initially moisten soil so that plants will not suffer from over or under watering.
• Conversions to Common Kitchen Units:  This takes any volume measurement (you choose the units) and converts it into house-hold kitchen units.  For example, 0.9 ft³ turns into 6 Gallons, 2 Quarts, 1 Pints, 1.5 Cups, 3 Tablespoons and 1.54 teaspoons.  This is useful in measuring soil and nutrient supplements.

IMPORTANT NOTE: Use the interior dimension of the planters and a height to match the depth of soil desired.   

References

1. ^ http://en.wikipedia.org/wiki/Water_content#Earth_and_agricultural_sciences