MEASURE UP IN THE GARDEN

A Guide to Figuring How Much Mulch, Topsoil, Gravel, Plants, and Fertilizer for an Area.
Now that you’ve got spring fever and caught the planting bug, you need some practical advice on how much material you actually need for your ambitious landscaping projects.
First Step: Calculate the Area for square footage using one of these formulas.
Rectangle: Length x width

Triangle: Length x width\2

Circle: 3.14xradiusxradius

Odd Shapes:
Break it up into individual forms and then add them together.

Odd shaped areas can be broken down into a series of squares, rectangles, triangles or circles. Calculate the area of the individual components and add them together.
Step two: How many plants do I need? Once you know your total area (square footage), you can then use another calculation to figure how many plants you need.
Suppose our rectangular bed was 4’ wide by 10’ long. Using our area calculation we figure out that the square footage of this bed is 40 sq. feet (4x10=40). Now in this 40 sq. ft. area we want to plant impatiens. The next step is to decide how closely we want to plant the plants together. Obviously, the closer you plant the plants together, the faster it will look “full and lush”; conversely, the more plants it will require. For this scenario, let’s plant the impatiens 6 inches apart or on 6 inch centers.
Follow these steps:
Multiply: 6”x6” = 36 sq. inches
Divide: 144 (number of sq. inches in a sq. ft) by 36 sq. inches = 4 plants per sq. ft.
Multiply: 4 (number of plants per sq. foot) x 40 sq. ft. (our bed area) = 160 plants.
Divide: Total amount of plants by the number of plants in the flat of flowers (for example some flats have 36 plants per flat and some flats have 48 plants per flat). We’ll use 36 here.
160 plants divided by 36 plants in a flat = 4.44 flats of impatiens to plant our bed.
To take the same bed and plant it with the perennial daylily in a 1 gallon pot and plant them 16 inches apart. Calculate the same way.
Multiply: 16”x16”=256 sq. inches
Divide: 144 (number of sq. inches in a sq. ft.) by 256 sq. inches = .56 plants per sq. ft.
Multiply: .56 x40 sq. ft (our bed area) = 22.40 plants.
Now figure how much mulch we need for our 40 sq. ft. flowerbed?
Depends on how deep we want the mulch to be. To put mulch on this bed 3 inches deep, figure as follows:
Multipy: area (40 sq. ft. here) by the depth (3”/12 inches per foot=.25 feet)
40 x .25 feet deep (cubic feet)=10 cubic feet.
Divide: Total number of cubic ft. we need (10 in this case) by the number of cubic feet in a bag of mulch (most come in bags of 3 cu. ft.) 10 divided by 3 = 3.33 bags of mulch.
These same basic calculations work for gravel and topsoil. Remember that there are 27 cubic feet in a cubic yard. If you are required to purchase the material by the yard, you will have to convert your cubic feet measurement into cubic yards by dividing the total amount of cubic feet by 27. For or rectangular 4’x10’ bed at 3 inches deep the calculations would look this this:
Lengthxwidthxdepth/27
4’x10’x.25 = 10 cubic ft./27 cubic ft. (cu. ft. in a cu. yard)=.37

This means we do not need a full yard (27 cubic feet) of material. We need 37% of a yard (roughly somewhere between a third to a half of a yard).
Now, let’s fertilize the lawn. For this exercise, let’s pretend the total lawn area is 20 feet x 20 feet or 400 sq. ft. and it is recommended that our lawn needs 1 lb of nitrogen per 1,000 sq. ft. We could use a formulation of 8-8-8 or 13-13-13 or 25-4-8 fertilizer, but the amount to apply would vary according to the amount of nitrogen (the first number in the formulation). To apply 13-13-13 to our 400 sq. ft. lawn at the rate of 1 lb. nitrogen per 1,000 sq. feet. Figure as follows:
Divide: the nitrogen (first number in the fertilizer formula) in this case 13 into 100 (available nitrogen per 100 lbs. of fertilizer), which would be 7.69 (100 divided by 13 = 7.69). So approximately 8 lbs of 13-13-13 would provide 1 lb. of nitrogen per 1,000 sq. feet. But we only have to do 400 sq. feet, so:
Divide: 400 divided by 1,000=.40 so we need 40% as much.
Multiply: 8 lbs. x 40%=3.20 lbs. of 13-13-13
If our yard had been 5,000 sq. ft., we would have multiplied 8 lbs. x 5 (5 times as much) for 35 lbs.
Knowing how to calculate how much material you need for any given area, helps prevent unnecessary purchases and leftover material.