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What Makes a Good Mulch?

It’s not there just to look pretty

Good mulch should be dark brown, persist for at least one growing season, be compatible with all the plants in the landscape and control weeds by suffocation only. Superb mulch does all that plus providing slow-release nutrients to feed the plants it is mulching.
    Mother Nature provides us with an abundance of mulches every fall. Fallen leaves and pine needles are excellent mulches satisfying every standard except being dark brown.  I have never purchased a bag of mulch in my life. Leaves are my mulch. When they decompose, nutrients are released into the soil, thus feeding the roots of mulched plants.
    Bark mulches do not contain any of the major nutrients used by plants except for calcium. But bark can contain essential trace elements, such as manganese, that can accumulate in the soil and cause problems. Thus it is important to choose mulch that is compatible with the species of plants being mulched.
     If you insist on purchasing brown mulch, I recommend pure pine, spruce or fir bark mulches. These contain 90 to 100 percent lignins, a source of carbon not easily digested by microorganisms. Thus they do not decompose readily and last on the surface of the ground one to two growing seasons. These mulches also contain polyflavanoids, which are beneficial because they help make essential trace elements available to the roots.
    Pine bark is available as nuggets, ground or as pine fines. The nuggets and ground mulches are the most preferred. Pine fines are generally only recommended as a soil amendment to increase the organic matter and help in lowering the pH of soils. Pine mulches are acidic in nature.
    Pine needles can be used as mulch but have a limited life, lasting only two to three months.
    Pea stone makes good mulch providing it is laid over landscape fabric. Brick chips, volcano slag or crushed granite are also usable mulches. But because of their density, they will sink into the soil unless they are placed over landscape fabric. 
    In the vegetable garden, straw — not hay — works as mulch. Even newspapers can be used, applied in 10 to 15 layers and soaked with water immediately to stop them from being blown away. I use shredded paper because it is easier to spread and, once soaked with water, remains in place better than sheets of newspaper. You need not worry about the ink because most black ink is made from soy while the colored inks are organic. I would prefer the old zinc ink because most of our soils here in the East are low to deficient in zinc, a mineral important in our diet.
    Shredded cardboard also makes good mulch. The advantage of using straw, newspapers, shredded paper and cardboard is rapid decomposition without creating nutrient stress. As they are opaque, they control weeds by the shade they create.
    Black plastic and landscape fabric also make good mulch. Black plastic mulches prevent the loss of water by evaporation. But these must be removed at the end of the growing season. Landscape fabric has another drawback in that weeds such as Bermuda grass, pig weed and nut sedge can grow through the fabric, making it impossible to pull them without damaging the fabric. Removing the fabric at the end of the season is also harder because of weeds that have grown through it.
    Next week, I’ll give you more reasons to avoid other mulches.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.