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How Deep Should Mulch Be?

June 06, 2016

a lady with a thought bubble reading how deep much should mulch be


We mulch for several reasons: to discourage the presence of weeds, encourage plant root growth, improve soil conditions, add aesthetic appeal, and maximize the effects of water and fertilizer on plants. While mulching seems like a straightforward gardening activity, there are still wrong and right ways of going about it. One of the most important ones is knowing how thick the mulch should be spread over and around a plant or flower bed.


Consider your purpose for mulching


First things, first: are you mulching for aesthetic purposes, weed control, or any other specific reason? Its purpose is a good gauge for how much mulch you’ll need, and how thickly you will be applying it. For instance, mulching to prevent weed growth requires around 2-3 inches of evenly-spread mulch on de-weeded soil. This amount is also effective enough to retain moisture in the soil and maximize the effects of fertilizer on plants.


Using mulch for mosaic-type landscaping designs require a pattern beforehand. Drawing and coloring the design can help determine the texture, size, and other volume of mulch to get (including for each color). For other specific purposes, it’s best to consult a gardener or the mulch supplier on how much to use.


Mulch according to soil conditions


If your soil is always damp and found in a low area, then too much mulch is not a good idea. Mulch that is applied in thick layers can retain excess moisture in an already moist environment, and could cause roots to rot and fungus to grow. In the same vein, an arid area with mostly dry soil doesn’t need a thick layer of mulch, either; it could bake delicate plant roots. Sloping areas need a thicker layer, around 4 inches, and a border to keep the mulch in place.


Know where to thin out mulch or avoid applying it altogether


Where NOT to mulch? Up against the base of tree trunks, for one. Piling up mulch right against tree roots is called volcano mulching because of the conical shape it takes, and also because it causes so much heat that it can kill a tree. Leaving a mulch free six-inch radius around the base of the tree will allow the roots to grow properly. Avoid heaping mulch around seedlings, too.


Quickly calculate based on the size of your garden


Most reputable mulch suppliers have customer care representatives or an online square footage calculator to help you gauge how much you need based on your garden’s dimensions. If you want to do it yourself, simply multiply your garden bed’s length by its width in feet, then divide the product by three. You will have an idea of the volume required in cubic feet if you’re aiming to cover an area with around four inches of mulch.