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Mulch: Monthly Garden Tip for March

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Mulch: Monthly Garden Tip for March

March 10, 2020

Mulch is the finish coat in your garden. Wondering what to do this month in the garden? It’s nearly spring and if you haven’t mulched yet, now is the time. Bulbs and perennials haven’t yet burst forth, so it’s the perfect—and easiest—time to add a fortifying top layer to garden beds.

But how to choose a mulch? We’ve created a simple design guide (taking into consideration the nutrients that some mulches add to soil) to help narrow the choices.

Photography by Mimi Giboin for Gardenista.

Mulched. Our favorite mulches include (clockwise, from bottom right) black bark, quarter-inch fir mini bark, cocoa bean hulls, shredded &#8\2\20;gorilla hair&#8\2\2\1; redwood, and small polished pebbles. All are available at Martin Brothers Supply in Mill Valley, Calif.
Above: Mulched. Our favorite mulches include (clockwise, from bottom right) black bark, quarter-inch fir mini bark, cocoa bean hulls, shredded “gorilla hair” redwood, and small polished pebbles. All are available at Martin Brothers Supply in Mill Valley, Calif.

How do I choose the right mulch?

When you’re choosing a mulch, consider what the mulch will do for your garden’s health and how it will play against your plants and architecture. We recommend a natural color palette, which means avoiding garish dyed mulches. For gardens, we also choose bark mulch over wood mulch. Most of a tree’s nutrients are in the bark, which means bark mulch becomes a healthy treat for your plants as it decomposes. Plus, bark tends to keep its color longer and usually has a more uniform appearance.

Unless you’re mulching a pathway isolated from plant materials, avoid mulches that haven’t been aged. Freshly chipped, shredded, or ground mulch material can draw nutrients away from the very plants you’re mulching to nurture. We like to limit shredded “gorilla hair” redwood to garden paths, where it is effective in controlling excess water.

Read on for the nitty-gritty about our top picks.

Black Bark Mulch

Mulches made from black bark create a dramatic backdrop for plants. Because the color is so dark, it also will be a bold contrast to the facade of your house.
Above: Mulches made from black bark create a dramatic backdrop for plants. Because the color is so dark, it also will be a bold contrast to the facade of your house.

Bark mulches are available in nuggets, shredded, or finely chipped. After they decompose, they can be used later in potting mix or turned into the soil for a healthy addition. Expect a bark mulch to last in your garden from one to three years, depending on its rate of color fade and decomposition.

Fir Mini Bark

Mulch made of quarter-inch fir mini bark also adds nutrients to the soil, but with a softer look than its black bark counterpart.
Above: Mulch made of quarter-inch fir mini bark also adds nutrients to the soil, but with a softer look than its black bark counterpart.

A warmer brown fir mulch complements Spanish-style architecture and gardens, and also houses sited in woodlands, where the natural color blends in with the surrounding landscape. The brown color pairs naturally with clay roofs and Mediterranean oranges, greens, and creams (though beware of clashing with some orange and red facades). Fir mini bark is particularly effective on paths, as it will stay in place and is easy to walk on.

Beware that barks tend to be more alkaline and will raise the soil’s pH level as they break down. Keep an eye on your plants and amend if they look peaked. When purchasing, note that mulches designated “bark mulch” must contain 85 percent bark of the named tree.

Cocoa Bean Hulls

Cocoa bean hulls are expensive ,compared to other mulches, but have a unique texture and wonderful fragrance.
Above: Cocoa bean hulls are expensive ,compared to other mulches, but have a unique texture and wonderful fragrance.

Cocoa hulls are a dark, rich color that—like black bark—enlivens just about every color of foliage. Hulls are particularly effective beneath specimen plants to create a stop-and-stare moment or in areas where visitors can enjoy the fragrance.

Hulls come with several notes of caution: In addition to being pricier than other mulches, they are relatively lightweight, so may be prone to disperse. Also, cocoa bean hulls can contain theobromine and caffeine, which can harm pets if ingested. Check the bag to see if hulls have been treated. In some instances, hulls can mold.

Polished Pebbles

Though stone mulches offer nothing in the way of nutrition, they can bring a clean but earthy style to the landscape.
Above: Though stone mulches offer nothing in the way of nutrition, they can bring a clean but earthy style to the landscape.

The obvious choice for a desert and native gardens, stone mulch also looks handsome against a board-formed concrete or shou sugi ban wall or fence.  Stone mulch also complements a fountain, pond, or other nearby water feature. Have your plant materials in mind when choosing stone mulch. Above, the red tinge of the succulent plays off the dark brown and black coloration of the stones. A variety of sizes (and polish options) are available, so keep scale of plant material and bed dimensions in mind when choosing.

Word to the garden-wise: Paired with shedding plants, such as bamboo, stone mulches become a nightmare to keep tidy. Try using a landscape fabric under your stone mulch to smaller pebbles don’t sink into the soil. Remember that stone mulches are less effective in reducing water loss, as the stones tend to keep the soil warmer. And don’t forget the obvious: once placed, stone mulches are there to stay.

What is the best way to add mulch to a garden?

After you’ve chosen the type of mulch, it’s time to apply it. Here are some tips for smart application:

  • A layer of mulch should be 2-4 inches deep, depending on type. Use a thinner layer around soft-stemmed annuals and perennials.
  • Don’t place mulch against the base of trees or shrubs. Excess moisture can cause rot problems.
  • Keep mulch away from the wood siding of your home (to avoid inviting wood-destroying pests).
  • Generally, mulch in early spring or late fall. Late summer mulching can insulate soils, keeping their temperatures too high.
  • Be judicious about when to use landscape fabric as a barrier. Placing mulch over the fabric makes it nearly impossible for mulch nutrients to reach the soil. Plus, weeds can work their way through the fabric and become tough to remove.
  • With regular mulching, beds can eventually rise above the base of plant materials. Simply remove the excess mulch and use it as planting mix for containers.

How much mulch do I need?

Nurseries sell prepackaged bags, typically in quantities of 2-3 cubic feet. Often, mulch is also available by the cubic yard. A standard pickup truck holds about 1 cubic yard, or 27 cubic feet.

For a 100-square-foot area, you’ll need:

34 cubic feet for a 4-inch layer.
25 cubic feet for a 3-inch layer.
17 cubic feet for a 2-inch layer.

N.B.: For more about mulch, see Landscaping 101: Mulch and Straw Mulch, the Ultimate Winter Garden Blanket.

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