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. Liz Stein says:

    Thank you, this is a nice FAQ, except that the information about wood mulches robbing nitrogen as they decompose has been generally discarded: “Actually, many studies have demonstrated that woody mulch materials increase nutrient levels in soils and/or associated plant foliage. My hypothesis is that a zone of nitrogen deficiency exists at the mulch/soil interface, inhibiting weed seed germination while having no influence upon established plant roots below
    the soil surface. For this reason, it is inadvisable to use high C:N mulches in annual beds or vegetable gardens where the plants of interest do not have deep, extensive root systems.” From http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/magazine%20pdfs/Woodchips.pdf (Part of Linda Chalker-Scott’s excellent web site about Horticultural myths; in turn, she is one of several Garden Professors at https://sharepoint.cahnrs.wsu.edu/blogs/urbanhort/default.aspx

    1. Margaret says:

      Welcome, Liz,. Thanks for the very good links. More reading for Margaret! :) Yes, I have read about these conflicting thoughts (so I wrote “may also rob soil Nitrogen” since I keep seeing both sides reported even now).

      I think from a practical standpoint the coarse-textured, uncomposted wood products when spread on a bed are certainly not the most helpful (in that they don’t degrade and improve the soil anytime soon). I also think, practically speaking, there is a very wide range of “bark” and other wood-based mulches out there, and probably no universal conclusion that fits all of them, since they vary so in their composition. A fascinating topic. Hope to see you soon again.

      @Robin: I wrote something about slugs last year, when we had a VERY wet season, too, and they were unusually problematic. My slug post is here. I think with thick mulch (like 3+ inches) and especially matted stuff like wet leaves (if they haven’t gotten pre-shredded/crumbly) or thick layers of straw and such, it can get ugly with slugs.

      They also really love plants that are starting to go soft, you know, things that are floppy/weak? I do a lot of grooming/cutting back/thinning in the garden as the season evolves, pretty regularly, to keep it airy.

      I normally have no problem with them — last year was one of maybe 2 years in 25 I have even noticed them much. But last year, wow. Awful.

      As for fungus, it is normal (depending what wood the mulch is made of) for certain fungi to sprout from the decaying material. I am fascinated by this, as I have mentioned.

      Expert mycologists like Paul Stamets would say that this is a sign of a healthy situation, in that higher plants rely on mycorrhizal relationships to thrive and on saprophytic fungi to recycle plants after they die, and replenish the soil. Certain trees and certain fungi just go together, natural companions in the environment. So if you brought in chips made from a particular tree that’s now decaying as mulch, you’ll have its appropriate partner, too. This is the stuff I really love…how all the pieces fit together, though it can look a bit odd in the garden, no? :)

  2. Robin says:

    Margaret, thank you for the in-depth info. Re: leaf mulch–I used it last year around tomatoes and marigolds. There was a lot of rain last season, and the area became infested with slugs. We always have some, but this time it was a total invasion. As a rule, do you think leaves are a particularly slug-friendly mulch?

    Also, we used some bulk wood chips from a local supplier 2 years ago that seemed to grow all types of exotic fungus after a while. Any thoughts on that?

  3. Tod says:

    What’s your local mulch contact? There’s a soil place in Philmont. Is that the same?
    Thanks for the informative article. Now I need a tractor to move all the mulch though. Can I borrow yours? [Just kidding!]

    1. Margaret says:

      I buy from Byron Clough in Malden Bridge, NY (north Chatham-ish I guess). His site I believe is here. He is wonderful; a longtime farmer who transitioned his business to this (composts, mulches, etc.). Loomis Creek uses him, too; we both have for years.

  4. Tod says:

    Thanks Margaret. I’ve been meaning to go to Loomis Creek. Thanks for reminding me. Another thing for the To-Do list. Drat!

    1. Margaret says:

      Welcome, Sara. Yes, horrible but true. The pitch is that you “never have to mulch again” (because the stuff lasts forever, ugh). I would prefer to see tires recycled into flooring and such things rather than into the garden! See you soon again.

  5. Jac says:

    I was surprised in your mulching blurb that you did not mention newspapers. Struggling as they are, newspapers may well go the dodo bird route, but as long as they are lying around [or obtainable at the town’s recycle centers], they make a great part of the mulching process. They allow in water from above, retain it from below, decompose readily and are really [in criss crossing layers] tough for unwanted plants to penetrate from below. And they don’t go to the dump.

  6. lisa mertins says:

    hi margaret, i wonder what you think of pine needles. i have a lousy crabgrass situation but noticed it had a hard time growing under needles i’d piled up. the only caveat is they don’t seem to break down easily.

  7. Great FAQ, Margaret. We’ve been mulching various ways for many years now, but you answered a few nagging questions for me. I especially liked your emphasis on buying local mulch. Around here, people often get together with their neighbors to order a truckload of mulch, then divide it after it arrives: easy on the wallet and you don’t have all the plastic bags, etc. Plus it’s often better mulch!

  8. Deirdre says:

    I swear by arborist’s chips. They’re full of green stuff that begins to compost instantly (a pile of chips heats up within HOURS). The heavier materials stick around to moderate soil temperatures, conserve moisture, and suppress weeds. The woodier stuff breaks down eventually and promotes beneficial soil mycorrhizae. It’s particularly good for woodland plants because it is very like the duff you’ll find on forest floors. Best of all it’s FREE. Arborists are happy to get rid of the stuff rather than pay to dump it. Look up arborists in your phone book, and ask for a truck load. Personally, I just follow the sounds of chainsaws whenever I hear them. You can’t get much more local than that! Moreover, it is a byproduct of trees that were being cut down anyway. No trees were specifically cut down to produce it.

    My back appreciates the woody stuff sticking around long enough that I don’t feel the need to renew it every year.

    If you’re concerned about diseases, let the pile sit for a week. It will heat up to at least 116 degrees. That kills 90% of all pathogens.

  9. Brenda Rose says:

    I’ve got a great barter relationship with a horse farmer. I drive over and get a pickup truck full of aged bedding, and his wife gets several new potted perennials. I have huge gardens and could never afford to buy that much mulch in bags. I often use 6 or more full-size pickup truck loads for my mulching. But my plants are happy! And it doesn’t cost anything. I told a friend and she gets a truckful by trading a meal – she brings a pan lasagna and salad and bread. Everybody’s happy!

  10. Steve Ambrose says:

    Cheers Ms M.

    Question.

    I remember reading (can’t remember where) a gardening tip.
    You shouldn’t mulch tomato plants until the plant starts to set fruit.
    If you mulch too early, the ground stays too cool and the plant will grow rather than set fruit.

    What do you think?

    Soil here in NJ still too wet for me to plant my peas… hopefully with this simply gorgeous weather…. maybe next week!!!

    1. Margaret says:

      Welcome, Steve. I have not heard that specifically before, and a quick look in my various tomato books didn’t specify. I set my tomatoes out into the garden around Memorial Day or even June 1, depending on the weather, and usually mulch them in the next week or two after that.

      I really do it to keep weeds down and (as summer heats up) slow the evaporation of the moisture I give the tomatoes, and I use a layer perhaps 2 inches deep, not heaps and heaps. Now you have me curious and almost tempted to experiment with some of my plants. :) See you soon again, I hope.

  11. lynn says:

    great mulch advice, i am excited about using some of Ruth’s mulching advice this year, i have been collecting piles of seaweed and sea hay, i plan to make holes for seed planting and just pile it high?? salt a concern, seems to be working so far. any advice is welcome, and perhaps needed. ha Happy Spring

  12. steve ambrose says:

    Cheers Ms M

    Tip: How I gather my “hay/straw mulch”…

    Seems people now enjoy decoratimng their homes for Halloween and Thanksgiving.
    Bales of straw, with pumpkins, gourds, cornstalks are quite common.

    On the weekend AFTER Thanksgiving, my wife and I drive around the neighborhood in our pickup truck. BONANZA of straw bales put out for the trash!!! If the bales were on a porch…. they are completely DRY.

    Currently we have 8 FREE, RECYCLED bales under a tarp in our garden, gathered last fall.

    HAPPY SPRING to all!!!

  13. Debra Colucci says:

    As to the newspaper comment ~ I did a little research into using newspaper in the garden a couple of years ago. I saw several comments about making sure the newspaper ink was soy based and not petroleum based so I called my local papers ~ NY Newsday and The New York TImes. Both companies still use petroleum based inks. I spoke to the print manager at Newsday for quite awhile as he was also a gardener looking to go greener. He said he would never put his newspaper in the garden, particularly an edible garden. He also said that soy based inks costs more and as far as he knew, Newsday had no plans on changing their printing ink.

    That being said, Newsdays own garden writer printed a story last spring on making and using newspaper seed pots. I sent her several emails asking her about the petro-ink but never did get a reply.

    I think newspaper makes a great mulch underlay to help supress weeds, but please check with the papers print department about which ink they use.

    1. Margaret says:

      Welcome, Debra. You bring up a very complicated topic, and I am not a scientist (surprise, surprise!). I think it was in the mid-80s onward that newspaper ink, which used to contain heavy metals like cadmium and lead, started to be less loaded with such toxins, though you are correct, they still contain oil. The newspaper industry has worked to have a cleaner waste stream and made big improvements (progress, not perfection, of course). Getting rid of the metals was a huge deal, and made the inks a lot safer — though I am not saying I would drink them. :)

      A number of state universities (Ohio State, West Virginia I think come to mind) have done a lot of research into the safety (or lack of safety) of newsprint because it’s also used widely in animal bedding, and I have read some of those reports, too, which term it a safe material for animals to bed on (not the glossy colored stuff). On the garden side, even Organic Gardening magazine recommends newsprint for use in the vegetable garden — though never the glossy or slick printed materials, which are far less reliably free of major toxins. Who knows what’s exactly right?

      If there is any doubt or discomfort, use newspaper and cardboard (uncoated, not colored) in ornamental beds and borders, and use a good-quality organic mulch (like chopped straw or composted stable bedding) in the vegetable beds, as you say.

  14. Kelly says:

    Have you noticed how earthworms are attracted to the newspaper? I love using it under mulch in all my gardens, veggies and ornamentals.

  15. Anita Bower says:

    Thanks for this informative post. One of the main problems I have with mulching is the dividing line between garden beds and grass. If I put the mulch all the way to the edge of the bed, the mower can’t get close enough to cut all the grass, leaving ta border of tall grass around the beds. Do you have any ideas for solving this problem?

    1. Margaret says:

      @Anita: Ihave to confess that because I have not installed a “mowing strip” (some kind of paver between bed and lawn) I just have to put one set of mower wheels in the bed on the mulch. OR: Mow close to the edge, then use a weed-whacker for the actual edging. Mowing strips would be better. But my ground is so uneven, they would be impossible to install.

    1. Margaret says:

      Welcome, Carla. Technically, yes (thought only plain brown matte corrugated stuff — nothing printed/glossy since you are growing food). BUT: You want to be careful not to prevent rain and other water from getting to the roots, so I might be inclined to not put such a thick mulch around them right now. Any chance of scoring something a little more water-friendly and also without any chance of contaminants in it (which is why I say no colored/glossy cardboard), like straw or hay or ???

  16. Jenny says:

    I agree about the dyed mulch, hate it. The red mulch is very popular here in the south, I guess people like it match the red clay soil.

    I, too, like dark mulch, however, I’m cheap. I have an endless supply of partially composted hay with sheep poop (we have a flock of 60 sheep), so I just use that.

  17. Marilyn Wilkie says:

    This year I will be shredding my many piles of leaves for mulch. We have 7 maple trees and several oak trees as well as various other hardwoods. We built 6 – 4’x8′ raised beds this spring and filled them with a garden soil/compost mix from this farm:
    http://www.tuthillfarms.com/1/235/index.asp
    He delivered about 6 yards to our home. It takes approximately one yard to fill each bed. He is similar to Margaret’s source in that they have gone into composting “big time”. A sign of the times hopefully. I agree wholeheartedly about using tires for mulch being detrimrntal to the environment. I also really dislike artificially colored mulches. The bright red mulch seems to be a requisite in the subdivisions around here.

  18. Mareline Staub says:

    This is great information. Any idea where such mulch is available in my area by the truckload? I live near Albany airport.

  19. Roxann says:

    Fall mulch question: The 14+ inches of rain I’ve had in the last four weeks in my Washington, DC area garden (yes–I use a rain gauge) has been too much for some of my perennials. The lambs ears foliage, for example, not getting enough sun to dry out and rotting on the ground. I’ve had to cut back some plants prematurely when here they would normally look great well into October. Once the foliage is gone it appears crowns and roots are ok (whew!) but all the mulch is totally broken down. Do I need to wait until the ground has dried out a bit before I re-mulch for winter?

    1. Margaret says:

      Hi, Roxann, and yes, I’d wait a bit. I feel as if there is so much potential right now for rot and fungal issues, and I want to clean up and hopefully let things air a bit before tucking it all back in. If you’re only going to topdress with a little bit, fine, but if the soil is soggy still and you want to put an inch and a half or two inches of mulch on, why not let the beds get a tiny breather first — even a week of sunshine would help right?

  20. Roxann says:

    Thanks Margaret. We actually saw the sun here today and perhaps we will see it for the next week so I’ll wait–some areas will need an inch or more. Hopefully we won’t have an early hard freeze before I get the “tuck in” chores all done. Wouldn’t that be the icing on the cake (excuse the pun) after losing two months of summer gardening to rain?

  21. Lauren says:

    This article has some great information. Thanks, Margaret!! I am going to share!
    Lisa, pine needles are a wonderful mulch! I, too, have had success with them. And no trees are harmed in making pine needle mulch. It is great under pine trees where grass will not grow, your pine trees will replenish your mulch for you each year. The needles will mat together and do a good job of keeping weeds at bay, including crabgrass, once you have accumulated enough. I have always been told not to use fresh wood chips. You should let them sit for atleast a year before using them around your plants. Fresh wood chips will steal nitrogen from plants as it begins to break down. It won’t kill you plants, but it will slow their growth and cause them to look anemic. Fresh wood chips would be great for a garden path of sorts. Anita, try digging a shallow trench around the outside of your mulch bed to keep the mulch from dispersing into your lawn. Also, you can mow right up to the edge. You can dig it by hand or rent an edging machine that will create your “natural cut edge” extremely quickly. Installing a barrier like brick, vinyl or stone requires a lot of work, money and maintenance. If you live in a cool climate and you use a material for bed edging, that material will probably frost heave out the ground after a couple cold seasons and you will spend a bit of time repairing it or living with the roller coaster look. If you have a natural cut edge, you will have to re-edge ever other year or so….that’s where the edger comes in handy!

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