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No matter where you live, your garden will benefit year-round from properly applied mulch: a layer of organic or inorganic material spread evenly on the surface of the soil. Today's gardeners have a wide variety of mulches from which to choose, but deciding which type to use takes a little research.
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 More Than Just Pretty
A carefully-designed landscape or flower bed instantly becomes a pièce de résistance by the simple application of decorative mulch. The varying shades and textures of a multitude of materials can be artistically contrasted with the shapes and colors in the garden. One's imagination is the only limit. But mulch has greater benefits for your landscape, two of which have great importance: conservation of moisture in the soil, and stabilization of soil temperature.
In a 1969 research project by Weyerhauser Company, it was proven that 2" of bark mulch
• reduced summer moisture evaporation by 21%
• reduced summer soil temperature in the upper four inches of soil by 10˚F
• delayed freezing temperature in soil by two days (compared to unmulched soil)
Additional benefits of mulching
- Prevents weed growth
- Reduces heaving in small plants (roots are forced up out of soil by alternate freezing and thawing)
- If organic, eventually adds organic matter to soil through decomposition
- Reduces soil erosion
- Prevents disease by keeping leaves, fruits, vegetables, and flowers from touching the soil
 What Kind Should You Use?
Mulch falls into two categories: organic or inorganic. Organic mulches are made up of plant or animal materials that break down over time. Inorganic mulches are composed of natural or artificial materials that either do not decompose, or decompose slowly.
Organic mulch increases the aeration of soil (especially clay) and increases the water retention capacity of sandy loam. Additionally, an organic mulch will improve and stabilize the soil structure to reduce the impact of rainwater, compaction from people walking on it, and increase ease of cultivation. While not a substitute for fertilizer, organic mulch does release some major and minor mineral elements that are important to growth. And lastly, the acidity or alkalinity (pH) of soil can be changed through the use of organic mulch.
Cost, longevity, and appearance play important roles in choosing mulch. For a small garden plot or flowerbed, cost is probably not an issue; however, when considering mulching large areas, determine the priority of the three criteria.
Since organic mulches break down, cost and longevity would be a major consideration in a large area. Mulches that decompose slowly also improve the soil slowly, but do not need replacement as often. For poor soil, the best choice would be a mulch with a shorter longevity to improve the soil more quickly. Large areas that simply require coverage for water retention and weed control can be spread with less expensive general mulch rather than decorative materials (pine nuggets, dyed mulches, etc.).
The following list of mulches and their features is taken from The Ohio State University Extension FactSheet HYG-1084-00 "Mulches for the Landscape," and HYG-1083-96 "Mulching Landscape Plants."
Organic: Traditional Bark Mulch
- Pine bark & nuggets: long lasting; slow to decompose, but excellent mulch material, excellent weed control
- Cypress: medium to long lasting; excellent weed control; may cause nitrogen deficiency
- Shredded hardwood: medium to long lasting; excellent weed control; may cause slight nitrogen deficiency
Organic: Recycled Products - Composted yard wastes (brush, leaves, grass, etc.): medium lasting; good for soil improvement; finely ground is suitable for soil preparation/coarse grind is used for mulching; useful on poor quality topsoil
- Composted leaves: short lasting; better as soil amendment than mulch; useful in preparation of seed and planting beds
- Ground & dyed wood pallets: medium lasting; good for paths, picnic areas, etc.; causes nitrogen deficiency, particularly annuals and perennials; some question of the effects of dyes on plant materials
- Wood chips: medium lasting; use on established landscape plantings and trees; causes nitrogen deficiency if not properly composted first; often available from tree trimming and removal companies; "green mulch" can get hot and damage plants that come in contact with it
- Animal manures: short lasting; commercially packaged cow, horse, sheep, poultry, and zoological waste; amending, mulching, and fertilizing; weed seed sometimes introduced into the garden with this type mulch
- Composted municipal sludge: short lasting; can include municipal garbage, paper pulp, yard wastes; trade names include Earthlife™, Comtil™ and TechnaGro™
- Sphagnum peat moss: long lasting; derived from mosses containing long fibers which resist decomposition; primarily a soil amendment
- Pine needles: medium lasting; excellent mulch for evergreens and plants that prefer acidic soil
- Straw/Hay: short lasting; used for winter protection of perennials, strawberries and small plants, as well as newly-seeded turfgrass; blows away; weed seed often introduced into the garden
Organic: Blends- Typically, blends of finely ground compost and coarse products such as bark and/or dyed wood mulches
Inorganic Mulches
- Stone, gravel, lava rock, pebbles: very long lasting; fire resistant; resistant to blowing or washing away; used with underlying plastic or landscape fabric to control weeds; light-colored materials radiate sun and create overheating for some plants; cleanup of debris is difficult; does not break down--no benefit to soil; limestone products increase soil pH to sometimes detrimental levels
 - Ground or shredded tires: very long lasting; ideal for playgrounds; not conducive for home landscape
- Landscape fabric: medium lasting (susceptible to oxidation from ultraviolet light); excellent weed barrier; material is porous and allows water to penetrate soil beneath
- Black polyethylene: long lasting; some use in vegetable and vine crop production, but not recommended for landscape use since soil remains too wet (unless well drained)
- Aluminum foil: long lasting; limited mostly to vegetable gardens where the material significantly reduces insect pests and viruses carried by insects
Other Mulch Materials
- Newspaper: short lasting (one season); excellent weed barrier, retains moisture; good for soil between vegetable rows
- Grass clippings: short lasting (one season); excellent short term nutrient-rich mulch that breaks down and amends the soil; unpleasant odor as decomposition begins in warm weather
- Cocoa hulls: long lasting; adds nitrogen to soil; good weed control; high cost in most areas; absorbs heat; may develop mold
- Peanut shells: short lasting; adds nitrogen; good water retention and weed control; low to moderate cost
- Buckwheat hulls: long lasting; good weed control, but material may sprout; high cost; blows around in wind.
Not Foolproof
It is important to understand that "bargain" mulches can often bring you a lot of grief. Weed seeds and fungi thrive in what can only be termed "the perfect incubator". Thistle (Cirsium spp.) and Mugwort (Artemisia princeps) are two tenacious invasive weeds that have almost frightening adaptive powers, and are often lurking in bulk mulch. Once you've imported these species into your garden, you'll battle them for a long time. Nuisance and detrimental molds and fungi are often found in mulches that have the perfect combination of temperature, pH, and moisture content.
Shotgun or artillery fungus (Sphaerobolus) may cause serious problems in the garden. This organism grows tiny "cups" that are filled with spores resembling tiny black eggs. The fungus shoots these spores into the air and wherever they land, they stick and produce black spots that stain siding, furniture, plant leaves, and anything else they touch.
Slime molds also show up in mulch, appearing as slimy masses of yellow or orange; they can produce toad stools, some of which are toxic to humans.
In mulch that has been applied too deep (3 to 6+ inches), the underlying layers undergo high temperature decomposition during the summer. The mulch dries out to less than 34% moisture and, thus, becomes a dusty mass that invites fungi to settle in. The mulch becomes moldy and hard, and water runs off, causing drought beneath the mulched area.
Mulch prepared from trees that were killed by disease may often be colonized by pathogens such as Vericillium dahliae, a fungus that causes wilts and death of many shade trees and ornamental shrubs. Rhizoctonia solani causes damping-off of seedling plants and is stimulated by fresh mulch, utilizing the wood cellulose as food.
According to Harry A. J. Hoitink in "Control of Nuisance and Detrimental Molds (Fungi) in Mulches and Composts" (Ohio State University Extension FactSheet HYG-3304-98), "The best control strategy for homeowners and landscapers is to purchase composted products low in wood content."
 How Much is Enough?
The recommended depth for most mulches is 2 to 2-1/2 inches; this application will address the primary objectives of weed control, water retention, and temperature stabilization. Mulches with large pieces, such as giant nuggets, will not cover as much area, due to their bulk. These mulch products are more suitable for decorative use, and should be used in conjunction with underlying landscape fabric.
The biggest mistake most homeowners make is applying mulch anywhere from 3 to 6 inches or more. This practice can lead to serious conditions for many landscape plants. A heavy layer of  mulch drastically reduces the soil's ability to dry out, leading to soggy, water-logged soil around the roots of plants and shrubs. This condition is extremely damaging to azaleas, rhododendrons, most conifers, all taxus or yew, and many perennials.
Mulch piled up against a stem or trunk results in constantly wet bark--perfect conditions for disease development. Additionally, rodents may nest in this thick mulch and, during winter months when food is scarce, will feed on the softened wood.
Purchasing the correct amount of mulch for your situation will save you time and money. Garden centers stock mulch in bags containing enough material to cover 2 cubic feet or 3 cubic feet. To determine what coverage you'll need, multiply the width of your space by the length; this will give you the number of square feet to be covered.
- At a 2-inch depth, 2 cubic feet will cover 12 square feet
- At a 2-inch depth, 3 cubic feet will cover 18 square feet
- If you buy bulk, you'll need know that 1 cubic yard covers 162 square feet at a 2-inch depth.
- A small pickup will probably hold 1.5 cubic yards (coverage for 243 sq. ft.); a full-size pickup will hold at least 2.5 cubic yards (coverage for 405 sq. ft.).
Timing is Everything
Depending on where you live, when you spread the mulch determines the benefits. When the soil has warmed and begun to dry, it's time to plan how much you'll need. Don't mulch too early or the material will keep the soil from drying out. Plants begin root growth as sufficient oxygen becomes available and the soil temperature warms reasonably in the root area. If you live in a region where the temperatures stay cold, or the rainfall is heavy in early spring, put off mulching until May or June.
In areas where winter comes long and hard, apply a second application of mulch in the autumn, especially on new plants with shallow roots: shrubs and evergreens, herbaceous perennials, or strawberries. Water established plants thoroughly in late fall, then apply mulch. To reduce heaving on new or small plants, apply mulch immediately following the first hint of frost on the ground.
Mulch can be your best helper in the garden if you use the right material and follow accepted guidelines for use.
 | Toni Leland has been writing for over 20 years. She has written a biweekly gardening newspaper column as a spokesman for the Ohio State University Master Gardener program, and writes for Grit magazine and Romance Writers Report. She has been a gardener all her life, working soil all over the world. In her day job, she scripts and produces educational DVDs about caring for Miniature Horses, as well as writing and editing books about this unique height breed. |
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Subject: Mulch
Posted by DianeEG (from Galva, IL) on April 14, 2008 at 10:55 AM:Great article that covers everything. Thanks for the research. Mulching is hard work. I have found the best mulch help is my grandsons! They are at an age where they love to show how strong they are but have not reached the age where they find grandma too boring for words. Plus, the "breaks" we take from mulching allows us to talk and enjoy each other. Thanks again. ...
Subject: comfrey as organic mulch
Posted by dianne99 (from Brookville, KS) on April 7, 2008 at 6:39 PM:I was reading about it in OG. I don't know where I'll ever get enough mulch if I don't grow some.
[HYPERLINK@www.organicgardening.com] ... Posted by DianeEG (from Galva, IL) on April 14, 2008 at 11:18 AM: I would caution you about comfrey. I was given some free and it does have a wonderful Victorian garden appeal BUT it is very invasive and almost impossible to kill if it comes up in the wrong place. It self seeds over acres. If the active seeds turn up in mulch, you will have plants. The tap root is huge and even a heavy dose of weed killer only stunts the plant for a few months. The little needles on the stems & leaves hurt if you touch w/o gloves. It gets ragged & ugly in early fall and only looks good again if you cut down to ground level and let it come back up. If you live where nature can run wild, it is pretty with the soft pink and blue bells and it makes a good ground cover in densely wooded areas (it does well under walnut trees). It is very difficult to tame in beds where I want other plants. I have often been asked for starts because of the lovely English garden look, but, I refuse terming it "my plant from hell". ...
Subject: lasagna gardening
Posted by Lancemg (from Aylett, VA) on April 7, 2008 at 2:02 PM:How would you compare your recommendations on limiting mulch with the extensive layering recommended by those that employ lasagna type gardening or other heavy mulch methods? ... Posted by lgksgarden (from Carol Stream, IL) on April 27, 2008 at 9:37 AM: Could someone please tell me what "lasagna gardening" is? Thanks. ...
Subject: Just a few comments...
Posted by HoosierGreen (from Danville, IN) on April 7, 2008 at 8:58 AM:This is an excellent and informative article. There are a few comments I would like to add, based on my experience as a professional landscaper for almost 25 years. 1.) The use of ground and dyed wood pallets as mulch is increasing and popular because of the color options. I strongly advise against the use of this in foundation plantings because of the danger of termite infestation. This is a pure wood-pulp product, i.e, termite food. Although I have not yet seen this happen, I am sure it will eventually and has already been a problem with 2.) wood chips used as mulch from tree trimming companies. Years ago, I had a customer who insisted on taking advantage of free wood chips from the local utility company. I told her that it was fine for around trees or flower beds away from the house, but she also mulched large areas of foundation landscaping. Within two years, she had a terrible termite problem that resulted in thousands of dollars of repairs to her home. When we raked back the mulch, it was teeming with termites that had colonized there and tunneled into the home's foundation and basement. Unfortunately, termite exterminators tell homeowners to not use ANY wood mulch, but I have never had any problem with chunk of shredded bark mulch of any type. However, 3.) I do not recommend using cypress mulch, as I have concerns about the environmental effects of harvesting of whole trees in the South for this purpose. Also, I have read more than one report of termites in cypress mulch (Feedback from any of you Southern gardeners is welcome!). 4.) Commercial-grade landscaping fabric will last indefinitely if covered with mulch. I've gone back to plant at jobs where I put down landscape fabric over twenty years ago and the fabric was like new. There is a difference with products though. Many cheaper grades deteriorate in just a few years. Also, 5.) NEVER use black polyethylene under rock mulch as a cheap way to suppress weeds. The worst job I get hired to do is to rake tons of rock mulch in order to remove all of the little pieces of black plastic that are the result of deterioration. Nasty! 6.) While discussing rock mulch, be sure whatever rock product you choose is esthetically compatible with your home. Too many times, homeowners use white marble rock mulch (or some other) that looks just awful (contrasts too much) with the brick, stone, or color of siding of the home. Finally,7.) I have found that pine bark nuggets (not shredded) are too easily washed or blown about the landscape. If your landscaping is very level, it might work for you, but otherwise shredded mulches work better. Happy mulching! ... Posted by lgksgarden (from Carol Stream, IL) on April 7, 2008 at 12:30 PM: I actually have a question. I put down about 1-2" of shredded leaves (shredded with a lawnmower and/or leaf blower) on all my beds last fall. Over the last few days, I broke up any sections where the leaves had become somewhat matted and moved the leaves away from any plants that were starting to come up Should I now come back in May and apply 2" of shredded hard wood as additional mulch? I live in the Chicago suburbs. Any advice you can give me would be appreciated. Thanks. ... Posted by tonileland (from Nashport, OH) on April 7, 2008 at 12:45 PM: HoosierGreen: Thanks sooo much for all the additional details. I love to post an article that gets a large amount of information flowing!
lgksgarden: If your leaf mulch stays soggy for too long, you'll have a safe haven for critters you don't want! See my article on slugs [http://davesgarden.com/guides/articles/view/736/] Also wet leaves get moldy quite fast. I just removed a layer of wet leaves from a bed (they'd blown in there), and what a slimy, stinky mess that was!
I think I'd thin the mulch out so it can dry quickly, then put down the hardwood mulch. ... Posted by lgksgarden (from Carol Stream, IL) on April 7, 2008 at 12:49 PM: Thanks, tonileland. ... Posted by tabasco (from Cincinnati (Anderson, OH) on April 7, 2008 at 4:31 PM: Hi toni-- I found your mulch article most informative with lots of good information.
I was not very familiar with mulch until we moved from California to our Ohio suburb where everyone here seems to (literally) buy into it in a big way. It's no wonder Weyerhauser supports research on it--having it in there product line with such research to back it up probably really helps their stock go up!
I wanted to add this link from one of my favorite gardening sites that offers some additional thoughts on mulch for the flower gardener.
[HYPERLINK@www.frenchgardening.com]
I don't agree with everything the French Gardening author says, but I think she makes some valid points.
Thanks again for your article. t.
This message was edited Apr 7, 2008 4:32 PM ... Posted by sghfuller (from Grand Junction, CO) on April 7, 2008 at 7:06 PM: I would like to learn more about using aluminum foil as mulch...never heard that idea before! ... Posted by dun1kirk (from Berkeley, CA) on April 7, 2008 at 9:38 PM: Ditto on the aluminum foil! ... Posted by hearthandhome (from Johnston, IA) on April 8, 2008 at 10:59 AM: A couple of comments from a garden care professional....I have never understood the use of landscape fabric underneath organic mulch, though I see that it is commonly done. 1) when the organic mulch breaks down, it composts on top of the fabric, thus providing a growing medium for weed seeds anyway, 2) when it rains, most non-shredded mulches simply wash or float off. My personal rule of thumb (apart from the large bark nugget scenario) is organic mulches should go in contact with soil; inorganic (rock, etc.) mulches can go on top of fabric. I agree with HoosierGreen--please use a heavy/professional grade fabric--I too have spent hours picking out little pieces of stretchy black plastic from rock mulches that were being amended, moved, or removed.
One thing I learned in hort school which may or may not yet be true, is to avoid mulches made from recycled tires, and I'm wondering if the same might be true of aluminum, due to plant toxicity due to leaching metals (in the case of tires, zinc). I have seen compost (properly composted compost where weed seeds have been destroyed through the composting process) used quite successfully as a mulch. It "crusts" after being misted or a light rainfall and then creates an excellent barrier for weed seeds and retaining moisture. It also doesn't erode. And, I have seen articles that talk about its ability to suppress certain plant diseases and bacterial issues.
Good article and good discussion! Thanks! ... Posted by HoosierGreen (from Danville, IN) on April 8, 2008 at 6:55 PM: I'm glad heartandhome added the comment about weed fabric under organic mulches. I should have included that as one of my comments! It's definitely a waste of labor and money and prevents the decomposed mulch from incorporating with (and improving) the soil. Unscrupulous landscapers will say that it's a good idea, but it's just a way to get more $$$ out of a job (kinda like paying to have sod stripped and removed when it can be either killed or tilled and planted over). The only time I would advocate using fabric under organic mulch is when there is a severe weed problem with pernicious weeds such as thistle or bindweed. Even then, using several layers of newspaper will usually do the trick of smothering the weeds for good, and add to the soil. ... Posted by lgksgarden (from Carol Stream, IL) on April 27, 2008 at 9:31 AM: HoosierGreen: Do you recommend a certain distance away from the house in applying shredded hard wood mulch to minimize the possibility of termites? ... Posted by HoosierGreen (from Danville, IN) on April 29, 2008 at 10:08 AM: lgksgarden: From what I know, termites tunnel through wood or underground to reach a new food source; they don't ever go into daylight or open air. So, keeping any wood PULP mulch away from the house (by several feet) is a good idea. This is not the same with using shredded BARK mulch (or cypress or cedar mulch). In twenty-two years of landscaping business, I have NEVER seen a single termite in bark mulch of any kind. Although termite exterminators will routinely tell homeowners to not use any wood mulch, they don't distinguish between wood PULP and wood BARK. I have used shredded (or chopped) wood bark mulch for over 30 years around my own home, which is in a wooded area, and have never had a termite problem (or ants, snakes, pill bugs, etc.). Note: There is a tiny amount of wood pulp in bark mulch, but not enough to make any difference. ... Posted by lgksgarden (from Carol Stream, IL) on April 30, 2008 at 10:09 AM: HoosierGreen, thanks so much. ...
Subject: Got Mulch?
Posted by candyinpok (from Poughkeepsie, NY) on April 7, 2008 at 8:20 AM:This article answered a lot of my questions about mulching. I would like to mention at least one environmental controversy regarding the use of Cyprus mulch. I would not want to be using an environmentally friendly mulch only to discover that it's production was causing environmental destruction. Its still not clear whether this is the case or not, but I prefer to be careful. Here's a link. [HYPERLINK@www.npr.org] Your articles are always so well done. ... Posted by quiltygirl (from Wildomar, CA) on April 7, 2008 at 10:36 AM: You mentioned peanut shells - do these need to be unsalted? I was thinking I could get tons of shells from those restaurants that serve peanuts and you toss the shells on the floor. ... Posted by tonileland (from Nashport, OH) on April 7, 2008 at 12:39 PM: I suspect the salted peanut shells in huge quantities wouldn't be all that great for the soil. Salt from the roadways does damage things growing nearby, but it's a different kind of salt. I'd ask your extension agent for an opinion.
Thanks Candyinpok for your comments. I agree about the cypress, but of course, had to include it in the article because it's so readily available. ... Posted by lgksgarden (from Carol Stream, IL) on April 27, 2008 at 9:21 AM: Thanks for the great article. Can you give me some additional advice? I have a privet hedge at the back of my yard. The space is about 70' x 5'. I had the hedge trimmed to about 4' a few weeks ago as it usually grows to 12-15' high each summer. I continue to get little 'privets' sprouting out of the ground everywhere which I have been pulling out. I just had shredded hard wood mulch delivered. Are there any advantages or disadvantages to laying down newspaper (how much?) before I top it with 2" of the mulch? Will the paper and mulch keep the new little privets from coming up? By the way, the only plants I find will grow under the privets is snow on the mountain (between the bushes) and hosta. But a friend just told me I will eventually be sorry with the snow on the mountain as it will spread like crazy. What are your thoughts about the newspaper and snow on the mountain? Thanks. Linda ...
Subject: Great information
Posted by pirl (from Southold, NY) on April 7, 2008 at 7:59 AM:Mulch is often overlooked for all the values you mentioned and for the unifying look it gives to a garden. Your article is thorough and comprehensive as well as much appreciated. After having tried many types we settled on the long needled pine last year. Aside from the fresh scent it worked well in gardens and also in paths that were first covered with the weed fabric. I'm pleased to report that in one garden there isn't a single weed and for that alone it's well worth the money, time and effort. Thank you for explaining the dangers of too much mulch, also. ... Posted by carrielamont (from Milton, MA) on April 7, 2008 at 9:01 AM: Thank you, Toni. Wonderfully useful information, and perfectly explained, again! xx, Carrie ... Posted by tonileland (from Nashport, OH) on April 7, 2008 at 12:46 PM: Thank you both for the compliments!
I love the look of pine needles, but haven't found a good source for them around here. ... Posted by Dutchlady1 (from Naples, FL) on April 7, 2008 at 8:33 PM: very useful article. ...
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