Mulch---The Gardener’s Friend

Mulch is one of the most important tools in a gardener’s arsenal. In fact, it can make many of the other tools unnecessary over the course of the growing season. 

Mulch reduces water evaporation from the soil. (Less use supplemental watering.)  It also prevents germination of weed seeds and suppresses existing weeds. (Put away that hoe.)  As organic mulches decay, they add nutrients to the soil and improve soil structure. (Less fertilizer)

Mulches come in two categories: organic and inorganic. Organic mulches include bark (in various forms), leaves, straw, lawn clippings, and pine needles. Inorganic mulches are things such as plastic, carpet pieces, gravel and stone, and landscape fabric. 

Landscape fabric has been a popular option for perennial beds and around trees. This material is available in different lengths and widths to be cut to fit the specific need. It is treated to resist short term decomposition and allows water and air penetrate. It needs to be staked down to prevent being pushed aside by perennial weeds. Typically, this method is paired with another type of mulch, either inorganic (stone) or organic (bark mulch). While the weed barriers are quite effective at preventing weeds from sprouting through them, over time a layer of soil will build up on top of the fabric. This soil is made up of decomposed organic mulch and is nutrient rich. In reality the weeds that grow on top of the landscape fabric are much more difficult to remove than if there had been no fabric there at all. Eventually the fabric will degrade and will need to be removed, a larger task than one might imagine.

Black plastic is used in the same applications as landscape fabrics. Unlike the fabrics, plastic does not decompose when covered and does not allow for water and air movement. Therefore, slits must be made to allow for water movement and provide for drainage. Anytime a slit is made, there is opportunity for weeds to come through. Anyone who has ever had to remove black plastic from a bed will question using it again.

Using 2-3 inches bark mulch is effective even without a barrier. The primary advantage of this mulch is that it is beneficial to plants. As it decomposes, it improves both the structure and nutrient content of the soil. Unfortunately, the disadvantage of it is that it decomposes and has to be renewed periodically. 

Inorganic mulches such as gravel and rock do not decompose.  The initial expense will be higher, but they do not need to be renewed. They do not, however, add any benefit in terms of nutrients or soil structure.  And, they become flying missiles if inadvertently picked up by a lawn mower.

Summer mulches used around annuals and in vegetable gardens are typically applied after the soil has warmed.  If no herbicide has been applied, grass clipping are a good option.  Other good choices include clean straw and chopped leaves.

Before applying any type of mulch to an area, first weed it thoroughly. Spread a 2-3 inch layer of mulch over the entire plant bed, keeping several inches away from woody plant stems. This prevents decay caused by wet mulch coming in contact with the stems during the winter. Finally, keep mulch 6-12 inches away from the walls of buildings.

Carol Shirk

Certified Master Gardener