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Marin IJ Articles

Mulch, a good return on your garden investment

  • Nanette Londeree
  • What’s one thing you can do in your garden that will save you time, effort and money, be good for your plants and the planet? Mulch! This rather simple action can help moderate soil temperature, reduce water consumption, reduce weeds and improve the garden’s appearance. And if you choose an organic mulch, over time, you’ll also add nutrients to the soil, improve drainage and encourage earthworm activity. Dollar for dollar, that’s a pretty good return on your investment.

    Mulch is any material that covers the soil surface, and can be organic, inorganic or synthetic. Gravel, decomposed granite, shredded rubber and plastic sheeting are examples of inorganic and synthetic mulches; they can be effective at reducing soil evaporation and weed growth, are generally pH neutral, and may be more cost effective in the long term since they don’t need to be reapplied as often. They don’t improve soil quality, may have a higher initial cost, and in the case of gravel, can result in an increase in reflected heat and light.

    Organic mulches like wood chips, ground or shredded bark, tree leaves, pine needles and straw, can improve the condition of the soil as the material breaks down, adding organic matter and nutrients to the soil, and creating a haven for beneficial soil organisms. They do need to be reapplied periodically, and their appearance may change, becoming less attractive over time.

    There’s no one mulch that works in all situations. What you use for a high foot-traffic walkway is likely different than what you’d use to blanket your flower or vegetable beds. The best mulch is one that fits your needs functionally, aesthetically and financially. It’s good to know the pros and cons of any mulch you might consider, especially related to its impact on soil and any potential safety concerns. Some of these include:

    • Cocoa bean hulls, the dark brown shells of cocoa beans, are attractive, easy to apply and are fairly stable. Mold tends to develop on the surface that can be unsightly. The National Poison Control Center alerts homeowners that this delicious smelling mulch may contain residual theobromine and be toxic to dogs.

    • Woven or layered synthetic landscape fabrics allow air and water to pass through, while reducing weeds and evaporation. It works best when covering large areas of soil between trees and shrubs, and is less practical in tightly planted areas. It also reduces earthworm activity that’s important for healthy soil.

    • Trendy dyed wood bark can yield an eye-popping visual impact. Often produced from recycled wood that is ground into chips and dyed, the source wood may have been pressure-treated and contain chromate copper arsenate so it shouldn’t be used around edibles.

    • The mulch commonly known as gorilla hair is finely shredded bark from redwood and western cedar trees and frequently used to mulch sloped areas. According to a study done by the Universities of California and Nevada’s Cooperative Extensions, this fibrous, coarse-textured mulch ranked highest in the “most rapid rate of fire spread.”

    It’s usually best to add mulch after heavy rains have stopped and the soil has warmed up. In most situations, covering the soil with 2 to 3 inches of mulch is optimal, and 3 to 6 inches for coarser materials like wood chips. Remove any weeds before applying mulch.

    Keep mulch at least 6 inches away from trees, so that you’re able to see the “flare” at the base of the trunk. It should look somewhat like a flattened donut with plenty of space in the middle for the plant to breathe. Piling mulch against trunks causes moisture to build up, creating ideal conditions for insect pests and disease. Where possible, extend the mulched area to the drip line of the branches.

    Add mulch this spring and you and your garden will enjoy a good return on your investment.