mulch faq

Q. What is the purpose of using mulch in the garden?
Q. What makes good mulch?
Q. What do you use for mulch in your garden?
Q. When do I apply it, and how much should I use?
Q. Do I have to move the mulch before adding compost and fertilizer?
Q. Are cocoa hulls good for mulching?
Q. Can I use mulch made from recycled tires?
Q. Is black plastic or landscape fabric a good mulch?
Q. What about Ruth Stout’s mulch methods?
Q. Do you mulch your pots and other containers?

Q. What is the purpose of using mulch in the garden?

A. Mulch (such as bucketful, above, about to be spread) serves several purposes. It will not just suppress weeds and slow moisture evaporation, but should also break down into the underlying soil gradually and thereby improve the soil’s texture. A layer of mulch helps moderate soil temperatures. Mulch serves as a buffer from soil compaction caused by rain, and helps prevent the crusting-over of bare soil that can sometimes prevent moisture from being absorbed.
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Q. What makes good mulch?

A. This can be very confusing, particularly because what’s sold as “mulch” in many cases isn’t really very suitable for performing the full range of duties that I think mulch should accomplish (above). Briefly, I look for a material that is:

  • An organic substance (meaning deriving from some living or formerly living matter);
  • Fine- to medium-textured so it will break down gradually into the underlying soil…
  • …but substantial enough to stay put;
  • Preferably aged before I use it;
  • Dark in color, like soil is (if for the ornamental beds);
  • Available locally at a good price, preferably in bulk delivery unbagged;
  • Not a source of contaminants, pests or diseases.

To elaborate: Any mulch I use in my ornamental beds must be fine-to-medium textured and dark colored so it looks good. Forget anything that’s going to sit there and never break down, like big hunks of bark (which I call “baked potato mulch” because they look like giant spuds sitting on the ground to me), or anything that’s bright orange. I am completely opposed to dyed mulches.

One caveat: Very fine-textured materials like sawdust do not make good mulch as they can cake and fail to decompose. Even pure compost is not my idea of mulch–I put mulch on after a top-dressing of compost in spring.

Why use a product that has been aged or composted before you use it as mulch? That extra step really makes a difference in the mulch being ready to do its job as a soil-improver.

I used to use bagged mulches, including cocoa hulls and various bark products. I have since switched to local materials I can have delivered in bulk, sans plastic bags (and minus all the fuel used in processing and trucking of bagged stuff across the nation to my local garden center). Environmentally, it’s important to buy locally when you can, especially with bulky items.

Technically, plants can serve as a sort of living mulch as well; that’s why certain ones are termed groundcovers, but many other plants can shade the ground and help prevent weeds and so on. Landscape architect Claudia West famously has said, “Plants are the mulch,” and I love her philosophy (explained here).

Borrowing tactics from farming, cover crops (whether grasses, legumes, grains…) can also be sown as living mulch on idle areas of the garden to help keep weeds down and also then be turned in to add organic matter.
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Q. What do you use for mulch in your garden?

A. On my ornamental beds, I use a composted stable bedding product–a local agricultural byproduct from horse or dairy farms that has been allowed to age first. It’s simply wood shavings (not too fine, not too coarse, as you can see in top photo) that farmers spread on the floors of animal stalls to absorb manure and urine, and then muck out and compost afterward to recycle it. (It is composted “hot” to kill weed seeds in it.) I expect you can find a local source via your county cooperative extension office; this website give a sense of the kind of product I am talking about, though I buy from a local farmer in the Hudson Valley (at this link).

Leaf mold (partially rotted and shredded leaves) would also be great, if your local landfill offers it, or start a leaves-only compost pile in fall and pre-shred it like this.

In my vegetable garden, I sometimes use straw (which is of course not dark-colored), preferably chopped, or the rotted, shredded leaves. In rough areas such as along the roadside outside my fence, I will use wood chips from the power or phone company, or from a fallen tree. I will also use wood chips or bark chips on utility-area pathways (behind sheds, between vegetable rows).  I pile up wood chips and let them age before using them. Again: I do not use chips in my beds.

For more details about pros and cons of different mulches, try this fact sheet from e-Organic (part of the Cooperative Extension services).
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Q. When do I apply it, and how much should I use?

A. I mulch my perennial and shrub beds in spring, but not until after the soil has a chance to warm and dry a bit. I also am conscious of areas where I want biennials and other self-sown plants to have a chance to do their thing; mulching these too soon may prevent successful reseeding.

You want a 2- or 3-inch layer, generally speaking, and if you use the right stuff, about half of that will work into the underlying soil before you go to replenish in fall or the next spring.

Keep the mulch a couple of inches away from trunks of trees and shrubs; never pile it up, volcano-like, against them, as that can invite pests and diseases.

Anytime I work in an area and disturb the mulch, I add a bit more rather than leave bare spots. I apply mulch to new beds whenever I plant.

Mulch is sometimes also used in winter in cold zones to help keep newly planted things frozen solidly in the ground (applied after the ground freezes), or to shield tender plants from damage (such as the graft union on roses). For that purpose, materials like evergreen boughs (which would not normally be good for mulch) may also be used.
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Q. Do I have to move the mulch before adding compost and fertilizer?

A. If you use a mulch that has the correct texture and has been composted first, this should not be a problem. I simply “topdress” (spread compost and all-natural organic fertilizer right on top of last year’s partly decomposed mulch) then replenish the mulch as needed.

The problem with most mulches, even bagged shredded bark, is that they haven’t been composted before they are sold and/or are too coarse, so they don’t break down very well, but rather form a sort of coating on top of the soil.

Good mulch, on the other hand, breaks down and improves the soil below. I don’t mean it breaks down in a week or a month, but over the course of a season or two.

If you have a thick layer of mulch that’s not breaking down nicely, and the layer is just getting thicker and thicker each year, rake some away and then add your amendments and start using a new, better-quality mulch this year on top of that.
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Q. Are cocoa hulls good for mulching?

A. I used to use bagged mulches, including cocoa hulls, many years ago. I have since switched to local materials I can have delivered in bulk, minus the plastic bags. There is no cocoa-processing plant nearby and hence no local source of this recycled product.

Cocoa hulls can be very high in potassium, which can be a problem for some plants in some soils, and they may be toxic to pets (particularly dogs) if they are swallowed. So those factors added to the “buy local” environmental argument put them on my “no” list today.

Additionally, cocoa hulls are hard to spread and either blow away or clump together if the bag got wet (sometimes they can be moldy in damp weather, too). However, they have many of the qualities I want in a mulch: They are dark in color and fine textured and look good on the beds.
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Q. Can I use mulch made from recycled tires?

A. To me this is a real environmental no-no–yet another wacky thing that is being tried out on us unsuspecting consumers. Yes, it’s re-using worn tires…but putting them into the landscape, and nature, in shreds is as bad or worse as piling them up at the dump whole. They don’t break down and become incorporated into the soil, so they’re no good, and even dangerous. Remember that animals and much smaller living organisms interact with and inhabit the soil–I don’t think a worm wants to process tire shreds while making worm castings, or a robin wants to rustle around in the tire litter (though they love the leaf litter!), or worse: choke on a piece mistaken for something to eat.

My rule: To be a mulch, it must be organic (a living/formerly living material) so it can decompose over time and return to the soil, not taint it. The one exception to my mind re: the organic rule would be some stone materials used in certain zones and certain types of landscapes.
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Q. Is black plastic or landscape fabric a good mulch?

A. Black plastic can be used to heat up an area (such as for sweet potatoes or pumpkins), and as part of the weed-control regimen, but should not be left in place as it prevents moisture from entering the soil and otherwise interferes with soil health. Roll or fold it and reuse the plastic year after year (I use 5 mil or 6 mil sheeting, not flimsy one-use plastic).

Suppressing weeds with black plastic is called tarping, technically; using clear plastic is called solarizing. Those useful tactics are explained by a University of Maine researcher in this interview.

Landscape fabric, or so-called geotextiles, are not a substitute for mulch. They should not be used in garden beds, though they may have a role as a weed-block beneath gravel of pathways or patios, for instance, or on the floor of a greenhouse.
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Q. What about Ruth Stout’s mulch methods?

A. Long before phrases like “lasagna garden” were making the rounds of the as-yet-uninvented internet, Ruth Stout (author of “Gardening Without Work,” 1961) was layering all her organic materials on top of her soil—sheet composting, as it might be traditionally called. Her tactic served to thwart weeds, reduce the need for fertilizers, conserve moisture and spare her the work of composting in a conventional heap with all the toting and turning of materials.

Her approach to gardening starts with the foundational principle of applying mulch, mulch and more mulch, and then simply moving it back a tiny bit each year a bit to make room for a row of seeds rather than all that turning and tilling (and weeding).

She said the “aha” came one spring when the plow man hadn’t come yet to till, and she was eager to get planting. She saw that the asparagus (a long-lived perennial vegetable crop) was already up and growing, right through the layers of fallen leaves and such. “I walked over and said to the asparagus, ‘We don’t have to plow for you; why do we have to plow for the other vegetables?’” Stout recalls. “And the asparagus said, “You don’t.’”

Where do you get all that mulch? The garden creates it, or at least some of the raw material that becomes it: spent cornstalks and uprooted pea vines and the like, to which Stout added fall leaves and also bought-in straw or hay (“spoiled” hay was fine, and cheaper; don’t worry about a little decay, she said).

More on Ruth Stout’s methods (plus video of her) is in this post.
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Q. Do you mulch your pots and other containers?

A. I do apply mulch to the soil surface in my containers, to help keep roots cool and keep moisture in. Depending on the plant, I may use composted stable bedding or a small stone (pea stone).

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  1. So glad to see Ruth Stout’s name again. She was a neighbor of my parent’s in Redding, Ct., and my father learned her methods by helping her mulch her gardens with hay. I remember as a child, watching her plant seed directly into random, left over bales of straw and returning to see growing plants there weeks later. She was a wonderful gardener and an inspiration to many who knew her in our town.

  2. Margaret Clark says:

    Thanks for the great information! I revisit this article every year for my mulch refresher. Now it’s time to source my mulch and get out there. Happy Spring!

  3. Darinka says:

    I love the ‘straw’ in your vegetable beds. Do you have a source for composted stable bedding – is it perhaps called something else when buying online.

    thanks so much !

    Darinka

    1. margaret says:

      The only product I have known of that was not local but sold bagged in some areas is called “Sweetpeet”. I did use straw some past years for potatoes, and on some vegetable beds I used last year’s shredded, aged leaves from fall cleanup — mostly oak and some maple.

      1. Betsy says:

        Country caretaker garden in New Lebanon NY sells sweetpeet in bulk and they deliver (Not sure how far they travel)
        Been using this for years and love it!

  4. Batya Gorin says:

    Margaret: I kept intending to write and let you know how much I enjoyed your recent talk at NYBG. It was eloquent and funny, but most importantly you really conveyed a sense of your deep symbiotic relationship with your garden. I can definitely relate. A garden is definitely not just a garden.

  5. cintra m fricke says:

    I’ve been reading about how mulch can “explode” from artillary fugus and cause splatter on houses and cars parked near mulched garden beds….
    What is your experience with artillary fugus from mulching? I’m nervous to mulch my garden beds this year since we got new siding on our house.

  6. Peg McKeown says:

    Do I need to blow/rake my garden of last fall’s leaves before I put down new mulch? I feel when I blow out my gardens I’m removing a lot of last year’s “composed” material.

    1. margaret says:

      You can leave a layer for sure, Peg. I tend to reduce the thickness of the layer if it’s on top of delicate or tiny things (like my earliest all spring bulbs) that might not get through. With the veg garden you could just move aside a bit of it to open up a narrow row for planting.

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