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More for Your Mulch

Mulches are like sure-fire aces that protect plants and improve soil conditions.

In the game of gardening, it pays to play with mulches.

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Mulches are like aces in a poker hand. Given our region’s extreme temperatures and aridity, mulches keep plants in the game by protecting them and improving soil conditions. Mulches can be once-living organic materials like wood chips or pine needles, inorganic materials like gravel or weed-barrier fabrics, or living organic materials like cover crops such as ryegrass, buckwheat or oats.

All these materials control weeds by blocking sunlight, and help to maintain soil moisture by reducing evaporation. Mulches also moderate soil temperature by keeping the grow-zone cool in summer and warm in winter, insulating shallower roots from excessive heat and cold.

Mulch2Selecting a mulch depends on your goal. For example, if appearance is important, wood chips may be an appropriate choice. But if your garden is buffeted by heavy winds, gravel would be a better option. On the other hand, if you want to improve your soil, organic mulch that gradually decays is a good alternative. If the area is used primarily for annual flowers, organic mulch that can be turned under in fall is more practical. A cover crop is a wise choice if you want to increase the soil’s beneficial microorganisms and earthworms, as well as build soil structure. But turn the crop under before it seeds or you’ll end up with more problems than it’s worth. (Larger vegetables, like squash and potatoes, can be planted in the same bed you plant the cover crops in.)

My favorite mulch—especially for acid-loving crops like potatoes—is pine needles, which I scavenge from schoolyards and parks in late fall. (The trick is to catch the groundskeeper in the act of raking.) During our windy winters, leaf, straw and wood chip mulches are blown into the next county, but pine needles stay put. When garlic shoots first emerge in early spring, I pile a thick layer of pine needles on top to keep the soil temperature constant. As May temperatures shoot up in the daytime, the needles keep the root zone cool and the garlic happy.

Here are a few other mulching tips:

Mulch3Never use mulch material from the crop it’s intended to protect. For example, don’t use potato vines from last year’s crop to mulch this year’s potatoes, because the old vines might transmit disease.

Use a light-colored mulch during summer and early fall to reflect heat, and a dark-colored mulch in winter and early spring to help warm the soil and permit earlier planting and hastened growth.

A mulch of older grass clippings, leaves or sawdust can cause a temporary nitrogen deficiency in the soil, as microbes tap into soil nitrogen to break down the vegetation. If you use these types of mulch, add a nitrogen source, such as well-rotted manure, before laying down the mulch.

When you consider the soil in conjunction with the plant, you begin to work with close-at-hand materials that don’t require heavy inputs of energy, like powdered fertilizers do. That’s when you realize mulches are the highest cards in the holistic gardening game.

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Mulch Manual

Organic Mulches

-Cocoa-bean hulls

Advantages: Long lasting, dark brown color

Disadvantages: Compact; forms a crusty surface (harmless if stirred to break crust); expensive

Comments: Molds may form on surface

-Crushed corncobs

Advantages: Uniform in color

Disadvantages: May retain too much moisture at surface or compact if wet

Comments: Cobs dyed various colors; availability limited in some areas

-Grass clippings

Advantages: Readily available

Disadvantages: Must be applied in loose layers to reduce matting

Comments: Allow grass to dry before applying as mulch

-Hops

Advantages: Attractive color, non-flammable

Disadvantages: Disagreeable odor until dry

Comments: May be available from local breweries

-Leaves (composted)

Advantages: Readily available

Disadvantages: Not very attractive; may become matted

Comments: Good soil amendment

-Leaves (fresh dried)

Advantages: Readily available

Disadvantages: Not very attractive; may blow away; fire hazard; become matted when wet

Comments: Most appropriate in naturalized gardens or shrub masses

-Manure (with straw)

Advantages: Usually available

Disadvantages: Unpleasant odor; weed seeds

Comments: Better as a soil amendment than mulch; should be aged and/or heat-treated

-Peat (sphagnum)

Advantages: Usually available in bulk amounts

Disadvantages: May crust on surface; may blow away

Comments: The only acid-forming peat, but even this is variable with source; best used as a soil amendment, not as a mulch

-Pine needles

Advantages: Attractive; does not compact

Disadvantages: Difficult to obtain in quantity; can be a fire hazard

Comments: Best for winter protection of fall-transplanted material

-Shredded bark, bark chips, chunk bark

Advantages: Long lasting; attractive (chips are more attractive than fine shreds)

Disadvantages: Cost is relatively high; shredded bark may compact

Comments: Can be used for informal walkways

-Straw

Advantages: Readily available

Disadvantages: Blows away easily; highly flammable; weed seeds often present

Comments: Best used as a temporary mulch around plants needing protection in winter; anchor it with wire mesh

-Wood chips, shavings, pole peelings, recycled shingles

Advantages: Long lasting; readily available

Disadvantages: Texture and color not uniform

Comments: Rustic, but usually attractive; will not compact readily; moisten in windy areas after applying

Inorganic/Inert Mulches

-Clay aggregates (heat-treated)

Advantages: Lighter than gravel and easier to transport; weed-free

Disadvantages: Expensive

Comments: Brand names (Turface, Terragreen) available

-Weed-barrier fabrics

Advantages: Reduces weeds; allows air and water penetration; long lasting if covered with mulch; easy to apply

Disadvantages: Some may be costly; most deteriorate in sunlight unless covered with another mulch material such as wood chips

Comments: A good substitute for black plastics

-Gravel, stone

Advantages: Available in colors to match or complement the architecture; inexpensive

Disadvantages: Will not prevent growth of some weedy grasses

Comments: Use black polyethylene beneath to prevent weeds

David Wann is the author of The Zen of Gardening in the High and Arid West. A veteran scavenger of leaves, cardboard and shredded paper, he admits, “In late spring my well-mulched garden sometimes looks like a landfill, but by midsummer it tastes like a five-star restaurant.”

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