Man mulching yard

Mulch dressing prevents soil erosion by wind and normal rainfall and helps to conserve soil moisture so your plants can stay hydrated. It regulates weed development by suppressing their growth and blocking their seeds from getting to the soil below so they can’t even germinate in the first place; your gardening will be much easier for it.

A layer of mulch will also protect the plants from accidental damage by lawnmowers and string trimmers. The organic ones even break down and feed the soil and, by extension, the plants. A modern yard requires a sufficient amount of mulch to maintain its gardens and the plants they support.

You need an accurate estimate of the total amount of mulch to optimize your yard’s productivity. This helps in budgeting and logistics. A mountain of leftover mulch lying around your property is a waste of resources and a potential health risk because it harbors pests.

Overapplication of mulch is also not a solution as it becomes counterproductive. On the other hand, you want to avoid skimping on mulch when the project is halfway because you underestimated your yard’s requirements.

By the end of this article, you should be able to estimate how many bags of mulch are needed in your yard and take the guesswork out of the equation.


Determining How Many Bags of Mulch Will Be Sufficient for Your Yard

The volume of mulch required is a factor of the landscaping area and the depth of fill required. While the size is constant, the recommended fill depth might vary from one planting bed to another.

You can’t accurately estimate the amount of mulch you need without factoring in how thick a layer of mulch you will dress the beds with. We will address this shortly.


Establishing the Size of the Landscaping Area

Measure the length and width of the planting bed(s) that are to be treated with mulch.

You can use a tape measure, which would be more accurate.

Or you can improvise and count your steps along the edges of the beds to estimate the dimensions--Did you know the average step covers approximately 2.5 feet? Simply multiply the number of steps by 2.5 to get the dimensions in feet. 

Use the same units when taking down the measurements to make calculations easier.


Calculate the Surface Area

You need to multiply the length and the width of a normal-shaped planting bed (square or rectangle).

If the shape is odd, you might have to split the bed into a couple of regular shapes, measure their lengths and widths separately and add their surface areas to get the total surface area. The same applies to situations where you deal with more than one planting bed.


Calculate the Volume of Mulch Required for the Yard

Now that you have the surface area, you need to establish the adequate thickness of mulch that will produce the best results given the conditions of your yard. There are several considerations to guide you that we have captured in this article.

Once you have settled on the depth, multiply this by the surface area to get the volume of mulch your yard needs.

If different sections or garden beds require different mulch depths, you should calculate their volumes separately and add the figures at the end to get the overall volume of mulch required for the project.


Calculate the Number of Mulch Bags Needed to Cover this Volume

Getting the number of bags is easy once you have the required volume. You need to establish the volume of mulch in each bag to calculate how many you will need for appropriate mulch cover. The most common mulch bags hold two cubic feet of mulch, but others hold three cubic feet.

Divide the volume required in the yard by the volume contained in each bag to get the total number of bags of mulch needed in the yard.

If the figure has a fraction at the end, take the next whole number to ensure you don’t have a shortage. The little that is leftover can be spread evenly throughout the yard.


Converting the Required Volume to the Units Used on the Mulch Bags

Many landscape supply stores sell mulch in bulk which is easier done by cubic yards. This could be confusing if you measured your yard in feet or inches (as you will most likely do, considering the available resources).

Just remember there are 27 cubic feet in one yard of mulch. Therefore, you will divide the yard requirements you have in cubic feet by 27 to get the requirement in a cubic yard for the conversation to make sense.


What Determines the Appropriate Depth of Mulch?

Too much mulch and the soil will retain too much moisture and might become waterlogged, hampering the circulation of oxygen in the soil. This interferes with lawn care, plant development, and encourages plant diseases.

The plants might even grow molds or start rotting beneath the mulch. If the layer is too thin, on the other hand, it won’t be effective in conserving soil moisture and controlling weeds.

Getting the ratios right will promote plant health and significantly improve the aesthetic appeal of your planting or garden bed.

The generally recommended thickness of mulch cover on a planting bed is three inches. This is thick enough to protect the soil and plants while keeping your average weeds out, yet sufficiently light for the soil to aerate and plants to thrive.

There are circumstances and situations which demand a deviation from this standard if you are to get the best returns from your mulching project. Let’s go through them to get the full picture.


Type of Mulch

Biodegradable mulch like bark chips, wood chips, chipped brash, or partially composted plant matter will settle and break down in the soil. Depending on what you are using, you should add an allowance for the settling.

Add half an inch to an inch above your planting bed’s recommended mulch thickness if you use wood chips. If you are using hay or straw, you can add an allowance of up to two inches; their loose nature allows them to compact easily, so the layer will thin out significantly.

Non-biodegradable mulches like gravel, shingle, slate, woven sheets, or landscape fabric don’t break down, and the recommended thickness is applied. Woven sheets and landscape fabric will settle slightly, but the difference is negligible because they have other enduring qualities. Slate, gravel, shingles, and pebbles will last for years and don’t need any allowance.


Purpose for the Mulch

Mulch distribution

If the main motivation is to suppress weed growth, there is always a minimum recommended amount of mulch. If the weeds in your garden are particularly resilient, you might have to layer them up to six inches thick.

If you fall short, your mulch will lack the capacity to suppress the weeds, but you should still exercise restraint so you don’t stifle the wrong plants.

Some mulch is applied for specific seasons due to climatic extremes. Winters are particularly cold or even freezing in some regions, and your plants and bulbs could do with a little extra protection.

Winter mulch insulates ground heat so the soil does not freeze and protects the soil from winter rain which might wash away nutrients. The depth ranges from three to as high as six inches, depending on the need.

Remember to remove the protective mulch layer during spring before you start planting, as it can block the heat that plants require to grow and prevent the soil from warming up.


Soil Texture

Three to four inches of bio-degradable mulch, like shredded bark or woodchips, will be sufficient for well-drained soils. The heavier the soil gets, the more vulnerable it is to flooding, so you should reduce it to between two and three inches if your soil is heavy.


Plant Type

Leave a bit of space at the foot of trees and shrubs. Their roots need to spread naturally, and the trunks should be dry to hold their weight, so they need the sun. Covering them up with mulch piles makes them susceptible to root rots, fungal cankers, and pesky rodents.

Thin your mulch layers in the areas immediately surrounding plants and trees. Don’t allow the mulch to come in contact with the actual stems or trunks; give them a radius of at least 6 inches.


Whether the Garden Had Been Treated with Mulch Previously

Planting beds that are being mulched for the first time should be layered to the recommended depth with regard to all our previous considerations.

If the previous mulch was biodegradable, similar treatment should be given to beds that have not been mulched in a while, say three to four years.

Biodegradable organic mulch decomposes with time and thins out. It takes between three and four years to biodegrade completely to bare soil. Consequently, the longer the interval between consequent redressing, the thicker the layer of mulch you will need to apply. Most materials settle with time (even the non-biodegradable ones which don’t break down).

Before adding mulch to a previously mulched bed, it is good practice to dig down and confirm the thickness of the existing mulch so you can determine the deficit from the recommended depth.

Only add what you need to restore the mulch to its recommended depth. This will typically range between two and three inches for biodegradable mulch if the land has been previously treated with mulch. There are just enough to cover the old mulch without overdoing it unless other variables are considered.

Occasionally you will be forced to remove the old mulch entirely. Sometimes you will discover they harbor pathogens that cause diseases and decide to mitigate the risk of future infestation by getting rid of the old mulch. When applying the replacement mulch, you should treat it as a new garden and layer the mulch to the recommended depth.


Application of Landscape Fabric and Woven Sheet Mulch

While these non-biodegradable varieties of mulch are generally frowned upon for garden beds, they are less porous and provide better resistance against weeds. They come in handy when you feel like the weeds are railroading you to apply mulch beyond six inches of thickness. This is wasteful, unsustainable, and unnecessarily expensive.

Applying more than six inches of bagged mulch to your garden bed is also risky due to the significant amount of heat and flammable gasses expelled from the decomposition process. The combination is a potential fire hazard, and the organic mulch is capable of feeding a huge fire.

Never exceed six inches when calculating how much mulch the yard needs. There are safer and more efficient alternatives for these extremes.

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