How Much Water Do Plants Need?
This is a question best left to the experts. Plants need just a little more than half a gallon per square foot per week according to https://www.youtube.com/watch?v=Kib_FquGP7s. Plants need 2 gallons per square foot per week according to http://www.ecoyards.com/an-inch-of-water-per-week/ Plants need one inch per week according to http://www.burpee.com/gardening-supplies/watering/watering-your-garden-article10365.html. This amount is the one most commonly used.How Much Is One Inch of Water?
To determine how much water equals one inch, it is best to start with cubic inches to determine how much water garden plants need. One cubic inch of water is determined by length times width times depth/height. 1 Cubic Inch = 0.00432900433 Gallons according to http://www.asknumbers.com/CubicInchToGallon.aspx.Convert gallons to ounces by multiplying 0.00432900433 gallons times 128 ounces and you get 0.55 ounces or approximately ½ ounce.
1 cubic inch of water is ½ ounce of water. Does this mean plants only need ½ ounce of water per week? No it doesn't. It means that every cubic inch of soil should receive ½ ounce of water per week.
Let say there is a 4 foot by 4 foot garden area. That is 16 square feet or 2,304 square inches (48 inches times 48 inches).
This converts to 2,304 cubic inches of soil (48 length times 48 height times 1 depth).
This converts to 1,152 ounces of water needed (2,304 inches of soil times ½ ounces of water).
This converts to a total of 9 gallons of water needed (1,152 ounces divided by 128 ounces in a gallon).
In summary, a 4 foot by 4 foot garden area needs 9 gallons of water per week according to the experts. Well, at least now we can more easily visualize 9 gallon jugs of water and do similar calculations for the actual dimensions of gardens.
The Number of Molecules in a Drop of Water
Plants don't use water by the gallon, ounce or inch. Plants use water by the molecule.There are 4.716278×10²⁰ water molecules in a single drop of water according to http://www.had2know.com/academics/how-many-molecules-drop-water.html. For a perspective on just how large this number is, 10 to the 7th power is 10 million. The number of water molecules in a single drop of water is 10 to the 20th power and then also multiplied by almost a factor of 5. Also, remember, we are told plants need a cubic inch of water per week. How many drops of water are in a cubic inch can be easily visualized. It's the size of four dice. Yet, in that little cubic inch of water are many drops of water and in those many drops are an unimaginable amount of molecules. Here's one last perspective: “...a cube of water, one inch on a side, contains about 600,000,000,000,000,000,000,000 ("6" followed by 23 zeros, or six-hundred sextillion) molecules! There are 120 times more water molecules in the cubic inch of water than there are stars in the observable universe![This includes the stars viewable with the use of the strongest telescopes] (Per https://www.grc.nasa.gov/www/k-12/Numbers/Math/Mathematical_Thinking/stars_and_drops.htm.) Okay, just one more perspective.
“...the number of stars in the heavens is "an unbelievably large number," but you will find the same number of molecules "in just ten drops of water." [There are 591 drops of water in one cubic ounce] (Paraphrased from, http://www.npr.org/sections/krulwich/2012/09/17/161096233/which-is-greater-the-number-of-sand-grains-on-earth-or-stars-in-the-sky.) The amount of water we are told plants need each week contains an amount of water molecules that makes the stars we can observe look like a drop in the bucket. Do humans really know how much water garden plants need? This is exactly why you don't water no garden. Gardening is a communal activity and watering is not a human task. Humans would be more productive and far more helpful to plants and ecosystem if, rather than applying more water, humans applied more wisdom and more mulch. The task of watering garden plants is best handled by experts such as Plants, Ancestors, Primordials and Nyame.
