PHOTOGRAPHS BY JAMES ROPER
Like icing on a cake, a layer of mulch gives a garden a neat, finished look while also performing the important functional role of reducing moisture loss. While mulch for flower beds and landscape plantings may be chosen for its decorative qualities, features such as cost and sustainability typically get more consideration for mulch in a vegetable garden or orchard.
In addition to conserving moisture and suppressing weeds, organic mulches—those made of plant-derived materials—benefit the soil as they decompose, adding organic matter and modest amounts of nutrients. By keeping the soil cool and moist, mulch also creates inviting conditions for earthworms and other beneficial soil-dwellers.
Think about where most of a plant’s roots are located and apply mulch accordingly, advises Robert Kourik, author of Roots Demystified and Understanding Roots. “Mulch trees and shrubs out to the drip line [branch tips] and beyond, while keeping mulch materials away from direct contact with trunks and stems.” In thirsty California, Kourik combines mulch with drip irrigation, placing the water lines on top of the soil and then covering them with mulch both to hide them from view and protect them from degrading in sunlight, all to make the most of every precious drop.
A 2- to 4-inch layer of most materials is enough to get the desired benefits without impeding air and water from reaching the soil. Loose mulches such as straw and hay may be deeper—as much as 6 inches—or can be applied over a weed-suppressing layer of newspaper or cardboard. In spring, cool, damp organic mulch can slow the emergence of bulbs and perennials and keep things too chilly for seeds of annual flowers and vegetables. Pull the mulch back to let the sun warm up the soil, then replace and refresh after plants get growing.
Woody mulches, including sawdust, wood chips, and even straw, can monopolize the soil’s supply of nitrogen while they slowly decompose, leading to nutrient deficiencies and lackluster growth of the mulched plants. Before spreading woody mulches, apply a nitrogen fertilizer such as fish emulsion or alfalfa meal.
The byproducts of farming and food processing often make excellent mulch. Because things like hulls, stems, and other crop residues are viewed as waste materials to be discarded, they may be cheap or even free. Be aware that chemicals applied to the crops may remain on the mulch and cause unintended harm to plants the mulch is meant to benefit. A few examples of these regional mulches include bagasse, a byproduct of sugar cane processing; cocoa, peanut, or pecan shells; ground corncobs or cornstalks; rice hulls or rice straw; salt hay, grasses gathered from marshes in coastal areas; and seaweed.
Pros: The best for weed suppression; free and abundant; great for smothering unwanted turf to create new garden space.
Cons: Unattractive; plastic tape and labels, staples need to be removed before applying.
Pros: Free or inexpensive where pine trees are abundant; weed-free; attractive and long-lasting. Its reputation for acidifying the soil is largely undeserved.
Cons: Pricey (or hard to obtain) if not locally produced; not dense enough to fully suppress weeds.
Pros: Often available for free (or cheap) from tree-care companies or utilities; fairly long-lasting.
Cons: A sour or vinegar-like smell indicates the chips are decomposing anaerobically and producing alcohols that can harm plants. Free chips may contain poison ivy or weed seeds. Wood mulches may harbor artillery fungus, whose black spores can permanently mar light-colored surfaces.
Pros: Free if you (or a neighbor) subscribe; best when layered 5-6 sheets thick beneath another mulch.
Pros: Looks nice; adds nutrients to soil; improves moisture retention and drainage; may help prevent disease organisms from spreading from soil surface onto plants.
Cons: Almost too valuable as a soil amendment to use as mulch; better used in targeted applications or as a thin layer under another mulch.
Pros: Inexpensive in farming areas; great for vegetable gardens; good moisture retention; breaks down quickly to improve soil; helps deter some pests; provides habitat for beneficial insects.
Cons: Can tie up nitrogen; can contain weed seeds or invite slugs and rodents; flammable.
Pros: Attractive and long-lasting; complements flower beds and looks natural around trees and shrubs; better for slopes and pathways than chunkier mulches.
Cons: Expensive if you have a large area to mulch. Beware of cheap imitators, especially dyed wood products that may be made of shredded particle board or chemically treated pallets.
Pros: Fine-textured and attractive; clean and weed-free; good at weed suppression and moisture conservation; may be used in shallow (1-2 inches) layer compared with coarser mulches.
Cons: Costly; may blow away when dry, or wash away in heavy rain.
Pros: Free wherever deciduous trees are found; easily shredded with lawn mower or string trimmer; inviting to earthworms; attractive and natural looking.
Cons: Lightweight when dry and prone to blowing.
Pros: Free; nitrogen-rich; attractive.
Cons: If there are weeds in the lawn, clippings can carry their seeds into the garden; residues of lawn weed-killers can harm garden crops. A more efficient use of clippings is to leave them on the lawn.
Pros: Nice-looking; available in a range of sizes; largest chunks break down very slowly and need to be replenished less often; less likely than wood mulches to support artillery fungus.
Cons: Costly; nuggets can float away in heavy rains; not good for pathways; larger sizes may need another barrier beneath them to keep weeds from sprouting.
Pros: Inert, long-lasting, attractive; color and texture can be coordinated with landscape style; good for permanent plantings.
Cons: No appreciable benefit for the soil; can make conditions too alkaline for acid-loving plants; reflected sunlight in summer can create hot spots in the landscape.
Pros: Shavings and sawdust (from lumber mills or woodworking shops) look nice in the garden. Weed-free; good at conserving moisture; inexpensive or free.
Cons: Breaks down quickly; can tie up nitrogen in the soil as it decomposes; acidifies the soil. If sawdust becomes compacted, it can shed water away from plants.