Celebrating the Seasons

Mulch Madness

If the summer's heat and humidity has got you down, imagine what it's doing to your garden plants! One way to help plants beat the heat is by protecting soil with a thick layer of organic mulch, such as bark chips and pine straw.

Mulch serves several purposes:

  • It helps keep soil cool by insulating against the summer sun and heat.
  • It conserves water by preventing evaporation and keeps heavy soils from drying and cracking.
  • It blocks weeds, keeping gardens attractive and eliminating competition for water and nutrients.
  • It adds nutrients to the soil as it decomposes.
A circle of mulch around trees and shrubs also prevents damage by string trimmers and mowers.

Calculating the Amount of Mulch

How much do you really need? That's the tough question. You can purchase mulch by the bag, by the truckload, and by the cubic yard. You can eye your garden and take a stab at guessing how much you'll need, or you can do a bit of measuring for a more accurate estimate. Here's how the experts do it:

  1. Calculate the square footage of the area to be mulched.

    For square or rectangular beds, measure the length and width of the garden bed, then multiply (length x width = square feet). For example, if the bed is 90 feet long and 5 feet wide, you've got 450 square feet of garden. A 10-foot by 10-foot garden is 100 square feet.

    For circular beds, measure the diameter and divide by two to get the radius (r). The formula for determining the area of a circle is 3.14 x r x r. For example, if you have a circular bed that measures 10 feet across, the radius is 5 feet. The calculation is 3.14 x 5 x 5 = 78.5 square feet.

    Irregularly shaped beds are more difficult to estimate. Sometimes you can divide them up into rectangular or circular sections, calculate the square footage for each, and then add the results. Remember that this is an estimate so don't worry about being precise.

  2. Decide how deep you'll layer the mulch. In most cases a 3-inch layer of mulch is best.

  3. Calculate the amount of mulch. Here's the calculation for a sample 100 square foot garden mulched 3 inches deep. (Note that you'll divide by 12 to translate the 3-inch depth into feet.)

Bagged mulch is typically sold in 3-cubic-foot bags. You'll need between 8 and 9 bags for this sample garden.

Bulk mulch is sold by the cubic yard, so it requires one more calculation. There are 27 cubic feet in a cubic yard (imagine a cube with 3-foot sides). Divide the cubic feet you need by 27. The garden above will require about 1 cubic yard of mulch. "Cubic yard" is often shortened to "yard," as in "I would like one yard of mulch."

When you're shopping for mulch, keep in mind that nine bags equals one cubic yard of mulch (if bags contain 3 cubic feet). This will help you determine the most economical source.

Mulching Tips

Before you spread your mulch, lay down four layers of plain (not glossy) newspaper. Wet the paper and cover with mulch. The paper is a perfect weed barrier, is easy to cut into if you decide to plant, and will eventually decompose into the soil.

Keep mulch a few inches from plant stems and tree trunks, to prevent problems with rot.

A few inches of mulch is plenty. More is not better! Too thick a layer of mulch can smother plant roots.

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