Refreshing and Reusing Mulch

Mulch: the protective blanket of organic material that keeps soil moist, suppresses weed growth, and maintains healthy soil temperatures. Mulches come in a variety of materials and colors, and are available for purchase at garden centers and businesses that sell landscape materials in bulk. Because mulch is so important to soil (and therefore plant) health, it is critical to maintain a thick layer in planting beds throughout the garden in each season. Typically, mulch needs to be replaced once every one to two years, depending on factors like the level of traffic in mulched areas, water runoff, and climate (including wind). The best time to replace mulch is during your yearly application of compost to the soil, which should take place in February before new spring growth emerges for the season. To replace and refresh mulch, follow these general steps:

Assess the Mulch Situation

Walk around your garden, taking a good look at the mulch coverage in your planting beds. If you notice any bare spots, take note of about how large the bald spot is. At the end of your stroll, you should have a good idea of the square footage you'll need to re-cover with a fresh layer. If you don't already know the total square footage covered by mulch in your garden, this is a good time to calculate it. Start by taking approximate measurements of your beds' widths, lengths, and diameters. Check out the measurements below for an example.

Make your calculations

Now that you've assessed the situation and taken some necessary measurements, it's time to calculate how much mulch you'll need. Begin by adding up the total square footage of your beds by multiplying their widths by their lengths. You'll need to convert inches to decimals (for example 4 feet 6 inches = 4.5 feet). Then, once you have your total square footage, multiply that integer by the desired depth of mulch in feet. For 1 inch, use the multiplier 0.083. For 2 inches, use the multiplier 0.167. For 3 inches, use the multiplier 0.25. Using the example garden above, this is what this process looks like:

Mulch Areas:
​Veggie Beds: (8.5 x 3.5) x 2 = 59.5 square feet
Planting Bed: 17 x 2.5 = 42.5 square feet
Planting Bed: 22 x 3.5 = 77 square feet
Planting Bed: 20 x 4 = 80 square feet
Shade Tree Area: π 5^2 = 78.5 square feet

Calculations:
​59.5 + 42.5 + 77 + 80 + 78.5 = 337.5 square feet
Then, multiply by the depth of mulch in feet:
337.5 x 1in (0.083 feet) = 28.01 cubic feet
337.5 x 2in (0.167 feet) =  56.36 cubic feet
337.5 x 3in (0.25 feet) =  84.38 cubic feet​

The depth multiplier you'll use depends on how much your mulch has degraded. If you are mulching for the first time, a two or three inch layer of mulch is suggested. For yearly upkeep, one or two inches should suffice.

Find your Mulch Source

Now that you've figured out how many cubic feet of mulch you'll need, it's time to find a place to purchase your material. Most garden centers and even some big box stores like Target, Walmart and Costco will sell pre-bagged mulches. Bags are typically either sized in 2 or 3 cubic foot quantities. Regardless of the bag size, you'll need to calculate how many bags you'll need for your space to determine the price you'll pay for material. To do this, divide your calculated cubic footage by the volume of each bag. For example, if the store you visit has mulch in three square foot bags and you've decided to add 2 inches of mulch across the landscape, your equation will look like this:

56.36 cubic feet / 3 cubic feet per bag = 18.79 bags
19 3-cubic-feet bags of mulch will be needed to cover a square footage of 337.5 to a depth of 2 inches.

If a large area of the garden needs to be covered, if you are applying mulch for the first time, or simply if the price is better for the amount of mulch you need, it may be more realistic to purchase your mulch from a bulk supplier. On average, these landscape material suppliers will charge between $25 and $80 per cubic yard of mulch. Most of these places charge by the cubic yard, so your cubic footage will need to be calculated before shopping. There are 27 cubic feet in 1 cubic yard, so the number of cubic feet can either be divided by 27 or multiplied by 0.037037. Using the above example again:

56.36 cubic feet / 27 = 1.97629 cubic yards  OR
56.36 cubic feet x 0.037037 = 1.97629 cubic yards

Depending on which type of mulch is purchased, getting this much mulch from a bulk landscape material supplier can run between $50 and $160. Purchasing mulch by the bag from a garden center or other retailer may run between $95 and $150. Although the prices at the bulk seller may be a bit better, the mulch will not be bagged, and therefore will not be as easy to distribute around the yard, and will require a trailer or truck bed to transport. An upside, however is that these places also commonly sell compost, which can be purchased at the same time as mulch to cut down on trips back and forth to the store. A last point about using bulk sellers is that sometimes they will have a minimum purchase amount; to check, simply call ahead. 

Applying the Mulch

If you are applying compost at the same time you are mulching, which is recommended, you'll pull your mulch layer back so that the soil surface is exposed. The compost will then be applied and distributed, and then mulch can be put back on. The old mulch should be mixed with the new before it is added back to the surface. Not all old mulch should be re-used, however. If mulch is diseased or overly moldy, it should be thrown away. Rake mulch to level., and then water it (and the compost) in. And there you have it: a simple way to refresh the health and aesthetic appeal of your garden in a days' work.

Happy Gardening!