Compost is the most beneficial organic mulch. Other organic mulches are humus, straw, grass clippings and other healthy plant debris, shredded bark, wood and bark chips, pine needles, cottonseed hulls, buckwheat hulls, cocoa bean hulls (but toxic to dogs), pecan shells, peanut hulls, chopped and crushed corncobs, mushroom compost or spent mushroom substrate, shredded newspapers or other papers (depending on ink used), leaf mold, chopped leaves, coir dust, and living plants. If you're an impatient composter, "almost compost" makes excellent mulch.
At least a 1-to-6 inch mulch cover should be laid down; 3 inches is good. In a very wet season, a mulch cover may keep soil too wet. Water logged soil due to excessive rain isn't a frequent concern for most areas in the Texas Panhandle. But if this does occur, pull back the mulch, or apply a thinner layer.
Benefits of Organic Mulch
Organic mulch provides many benefits to the soil and garden.
- Conserves moisture by slowing evaporation.
- Slowly creates topsoil through the decomposition of the organic matter. This is a slow process of soil building.
- Controls weeds by preventing and inhibiting germination.
- Protects and increases the root zone of the plant. With the mulch's protection and temperature moderation, roots of plants come up to the surface to the mulch line, where the soil is most fertile. The first few inches of un-mulched soil become too hot and crusted for roots to survive.
- Maintains even soil temperature, cooler in the summer, warmer in the winter and a more even temperature from dawn to dusk. For a quicker warm-up for spring planted vegetable beds, pull back the mulch to let the soil warm by the sun. On the other hand, keeping a thick mulch cover on fruit trees and tender perennials will delay their break from winter dormancy from our climate's erratic temperature swings.
- Prevents soil crusting and increases water in-soak and aeration.
- Helps stops soil erosion by holding it in place.
- Prevents heavy rain from splashing soil on the lower leaves of plants, keeping the pores open.
- Helps prevent compaction on walkways throughout the garden and beds.
- Minimizes cultivation. The less disturbance of beneficial microorganisms the better. Microorganisms secrete a sticky substance that glues the soil into little crumbs, promoting better soil structure.
- Helps feed and increases the beneficial soil life at the surface. Soil microorganisms breakdown the organic mulch and provides slow release of soil nutrients through the decay of organic matter. In the process, growth promoting hormones, antibiotics and certain toxins that don't harm plants are formed. This helps control diseases, root rot, and damping off fungi. A more fertile soil environment is conducive to growth of mycorrhizal fungi, which also increases the root zones of plants. Actively growing mycorrhizal fungi ward off root pathogens and damaging nematodes. Organic mulch should not be used as the sole means of adding organic matter to the soil.
- Using a mulch mow recycles lawn clippings and other plant material thereby reducing landfill space. It just doesn't make sense to pay for carting off your lawn clippings, then paying again for fertilizers. Lawn clippings recycled through a mulching mower immediately are returned to the soil. Yearlong mulch mowing provides from 25% to 35% of the required nutrients for turf. Mulch mowing is less maintenance than using a bagging mower and much less maintenance than bagging and composting the clippings.
- Saves you time and money by reducing your water, herbicide and fertilizer use and plant replacement.
- Landscapes and beds look tidier and prettier with a mulch cover.
(The Garden-ville Method, Lessons in Nature, Malcolm Beck, 1991)
Compost and Composted Manures
Nothing beats compost when it comes to benefits for plants, whether it is homemade in your own compost pile, purchased from a reliable source in bulk (certified organic) or a good quality bagged compost.
Be an informed gardener and consumer when it comes to products labeled compost. If you are not sure the product is free of weed seeds or harmful residue, don’t buy it. Bags of compost can contain any number of fillers that are either harmful, or at least not helpful. You may need to do research before buying and applying. (Click on the DirtDoctor.com for a start: www.dirtdoctor.com/view_org_research.php?id=5, and go from there). Especially beware of recycled rubber as an additive to the bag of compost.
Herbicide Carryover – Killer or Contaminated Compost
Unfortunately, one of the most natural and beneficial products, compost, is becoming contaminated. Farmers and home gardeners across the United States have reported damage to vegetable, flower and fruit crops after applying composted manure (whether from cows or horses) or composted hay, straw or grass clippings to the soil. Shortly after these applications as soil amendments or mulch, they noticed stunted growth, poor germination, death of plants, deformed plants and fruit. In most cases, the damage was caused by a group of synthetic chemicals known as pyridine carboxylic acids, sometimes referred to as pyralids, namely, aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr and/or aminicyclopyrachlor. Products containing these chemicals include Curtail, Forefront, Grazon Next, Grazon P+D, Milestone, Redeem R&P, Surmount, Confront, Lontrel, Millennium Ultra Plus and Plus2, Clopyr AG, Stinger and Imprelis. In September, 2009, Mother Earth News reported that a previously considered organic product, Grab 'n Grow, contained one of the above chemicals and caused damage to a vegetable garden of Grab 'n Grows manager, Don Liepold. Subsequently “I have been testing and detecting herbicide residues and thus rejecting cow manure, horse manure, turkey mulch, rice hulls, mushroom compost and yard trimmings,” says Grab n’ Grow manager Don Liepold. “I spent $20,000 in lab fees in 2008, and am on the same track for 2009,” he says.”
The Mother Earth News article continues “It is extremely difficult to keep contaminated materials out of commercial compost. “One load of contaminated grass clippings can ruin a batch of compost,” says Eric Philip of Anatek Labs in Moscow, Idaho. Philip has seen so many positive tests for clopyralid residues in compost that he would not use untested compost in his own garden.
“When folks have plants die in their home gardens, their first assumption is that they did something wrong,” Philip says. But with pyralid-laced commercial compost becoming more common, contaminated soil amendments are often to blame.
The effects of contaminated compost and composted manure might be transferred to foliar sprays as well, although I have not read any reports mentioning them specifically.
The source of pyralid pollution can be impossible to trace. For example, a horse stable may use hay brought in from a neighboring state, without knowing that it is laced with pyralid herbicides. If the horse’s manure or stable litter ends up in a garden, disaster is ready to strike. It’s better to be safe than sorry. Liepold stopped making one of Grab n’ Grow’s most popular products, Mango Mulch, for more than a year because he could not find an uncontaminated manure supply. Now he’s getting it from two local organic dairies.”
Mother Earth News first sounded the alarm on “killer compost” in 2008, and has continued to report as new information comes to light. In 2011, Dupont's Imprelis, an herbicide praised for being a “green alternative” because of its long residual, made headlines as it killed trees and shrubs in numerous states from New England across the Midwest into the northern Plains States. Currently, the EPA Stop Sale Order on Imprelis, but not on the other products by Dow AgroScience and Dupont.
Dupont did notice that Imprelis could create killer compost. From Page 7 of the 9 page label on Dupont's Imprelis: “Do not use grass clippings from treated areas for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/property managers/residents to not use grass clippings from treated turf for mulch or compost.”
It is well known that the “label is the law”. How many people do you imagine read the entire label when purchasing herbicides? Although Imprelis was sold only to licensed applicators, how many of them read the label or warned home or corporate owner/managers when they applied Imprelis of the long term effects regarding compost? In areas where community composting is practiced, it is easy to see how contamination of these resources can occur.
North Carolina University Cooperative Extension issued an excellent bulletin entitled “Herbicide Carryover in Hay, Manure, Compost and Grass clippings warning “farmers and home gardeners of reported damage to vegetable and flower crops after applying horse or livestock manure, compost, hay or grass clippings to the soil,” (http://www.ces.ncsu.edu/fletcher/programs/ncorganic/special-pubs/herbicide_carryover.pdf). Although the above mentioned products were licensed for use in agriculture by licensed applicators, Imprelis was licensed for use on residential lawns by licensed applicators.
Just because many of these products were for agricultural use, doesn't mean home gardeners are safe from the herbicides long term effects. The warning for vegetable growers and home gardeners is to be aware of your source for hay, straw, manure or compost from hay, straw or manure. These herbicides can be active up to four years or more. The person you purchase or receive these products from may not even know this class of herbicides have been sprayed on them, or be aware of the longterm effects.
Here is an example of why it is difficult to find out. A friend of yours offers you horse manure that has been composted. You might ask him/her if herbicides were used, with the farmer replying the manure/compost is "safe" because the animal has not been effected. The horse or cattle were fed hay that was sprayed with one of these herbicides (it's reported not to be harmful to animals). The horse eats the hay, and the resulting horse manure contains active residues of the herbicide, even after it composts. You spread the manure in your vegetable garden and your vegetables are stunted and fail to thrive, or die outright.
You might think this couldn't happen to you, but a case very similar to what I described happened to a family member of mine. After he did some research, he went back to the neighbor where he got the manure and found out the man did indeed spray his hay with one of these chemicals.
Unless you are absolutely sure hay or straw does not have a history with these herbicides, I would not use them in compost or on your garden soil or ornamental beds.
The affected composted manure would be safe to spread on your turfgrass. To be safe, I would not compost the grass clippings or use the grass clippings in beds or borders. It would be safe to cut your turf with a mulching mow, returning the clippings to the soil if you had already used contaminated compost there. I'm unsure of the effects of these chemicals on trees (except for Imprelis). The North Carolina bulletin goes on to describe how to do tests to determine whether the compost or hay/straw contains residues of one of these herbicides.
The latest warning has come from Mother Earth News, published in the February/March 2013 issue. They noted that livestock feeds now contain the contaminated chemicals and are passed through the animal into the manure in this manner. Because of the growing contamination problem, Mother Earth News advises gardeners that “the time has come for the public to stop buying compost or manure products unless they come from suppliers that are able to afford testing and can screen feedstocks for herbicide residues.”
Once again, the buyer needs to be very aware.
Read More: a FAQ sheet from the US Composting Council on contaminated compost: http://compostingcouncil.org/persistent-herbicide-faq/
Wood and Bark Chips
The best organic mulches are mulches native to your area, to your own backyard. I have used mulch obtained from Amarillo's Chipping sites for nearly two decades, without any spread of weeds and no incidence of disease. I use the chipping site mulch for adding to my compost pile, too, whenever necessary.
The four locations to obtain free wood chips from the City of Amarillo are:
- Broadway and Hastings across from Ross Rogers Golf Course
- Southeast Park
- South Soncy Road and 77th Street
- 801 N. Soncy Road
Just a few cautions on chips:
- Avoid wood chips from pressure treated or chemical soaked pallets, or other undesirable wood.
- Avoid wood chips with a sour smell, similar to vinegar. The sour smell can occur when chips decompose without sufficient oxygen. Sometimes wood chips from the center of the pile go anaerobic, and acetic acid builds up. These chips can kill your plants quickly. If you have wood chips with a sour smell, spread them out in a single layer away from your beds, airing them out exposed to the sun for several days. Once the smell is gone, it’s safe to use the wood chips. (Meyer, Organic Gardening Magazine, July/Aug. 97).
- When replanting in a wood chipped or bark mulched bed, do not let wood or bark chips fall into the planting hole. Too many wood or bark chips in the soil can create a nitrogen deficiency, though temporary, similar to what occurs with sawdust in the soil.
- If worried about insects or pathogens in chips, thinly spread the chips out in the sun for several days before using. If still worried about termites in chips, do not use the wood chips in borders right up next to buildings, use a different mulch material.
Leaves are a most valuable and renewable source of mulch and composting material. When the leaves fall, mow them with a mulching mower or use a regular bagging mower and add to your flower beds or compost pile. Large thick leaves should be shredded in this manner for better decomposition. Smaller leaves can be just left where they fall. If you're bothered by the idea of raking leaves, a low maintenance tip would be to plan ahead and plant only trees with smaller, finer leaves. Avoid trees like sycamores and mulberries with large leather-like leaves.
Another method for shredding leaves was recommended to me. Rake them up and fill a large plastic or metal garbage can. Wear protective eye gear and insert your string trimmer. This will really whip up and shred the leaves, but it's more time consuming, dusty and laborious than just mowing them. I tried this technique one fall when we were in-between lawnmowers; I hope I never have to do it again. It’s very dusty, but it does shred them up.
If leaves fall in flower beds, there generally is no harm to leaving them so long as there aren’t too many layers to form a mat. They eventually break down, adding needed nutrients to the soil and provide a degree of cover for wildlife over the winter months. Sometimes the wind will swirl them around into piles along the corners and backyard fences. You'll probably have to rake these up and compost them. It'll take too long for them to decompose before they smother whatever is underneath them. Water won't be able to penetrate through to the soil either.
It is wasteful to rake up leaves, bag them and discard. The deep roots of trees draw up minerals and nutrients from the subsoil. Everything in nature is recycled. Leaves have a high mineral content along with their organic benefits. If your neighbors haven't realized the tremendous benefits of recycling their own leaves, offer to rake them up and compost them for your own use – free raw materials! Do not use leaves from plants that have recently been sprayed with an herbicide or pesticide.
Many people favor cocoa hulls for its delicious aroma, deep brown color and relative permanency. A by-product of the chocolate industry, cocoa hulls are safe to use as mulch for plants. However, cocoa hulls contain two compounds that are toxic to dogs, even in small amounts. To protect your pets and pets of others, it would be better to forgo this delightfully fragrant mulch and choose some other material. For chocoholics, it is better to grow chocolate flower, Berlandiera lyrata, (not on the list of plants toxic to animals, http://www.aspca.org/pet-care/poison-control/plants/ and breathe in its tantalizing scent on summer mornings.
The terms mushroom compost, spent mushroom substrate, recycled mushroom compost or mushroom soil are used interchangeably. These products are recommended for use both as soil amendments and mulches. But as with any product, cheap imitations with fillers may be added to the bag. (For more information: www.mushroom-sms.com, and Extension article on mushroom compost.)
Mushroom compost is listed on OMRI (Organic Materials Review Institute) Generic Materials List with a restricted status.
Green Manures, Cover Crops and Living Mulches
A green cover or living mulch is a type of organic mulch, only growing. They are referred to as green manures or cover crops when it is tilled back into the soil. Cover crops or green manures can be used as a soil management technique to increase soil fertility. Mainly it is used because it is cheaper than applying large amounts of compost. Tilling cover crops into poor, infertile soil over a period of years will return fertility to the soil and make it productive.
Some common cover crops are hairy vetch, alfalfa, clovers, annual rye or buckwheat or other annual grasses or legumes. It just takes a little longer than adding compost. Even tilling in a natural covering of weeds before their seed production has started will add to the soil.
If using green manure to increase fertility, the soil should be tested to see if it is lacking in any minerals. Add the deficient minerals according to soil test recommendations. One drawback in arid regions to consider is whether your cover crops will be competing for the limited available moisture.
Cover crops are often seeded in fall as a winter cover. In addition to being used to increase soil fertility, cover crops prevent erosion, crowd out weeds, and return nitrogen to the soil. The deep-rooted grasses and legumes bring up minerals and nutrients from the subsoil.
Living plant mulch can be used during and alongside plants or crops in the growing season. Sometimes living mulches such as clover or sideoats grama are planted between rows of vegetables or trees in orchards depending on climate and water supply. Flowers or vegetables can be planted, so that at maturity, their leaves mesh, shading the bare ground below. Groundcovers, such as thyme, creeping veronicas and phloxes, vinca, and hardy blue plumbago are considered to be living mulches too!
Pecan and Walnut Shells, Hulls and Leaves
Both pecan shells, and their leaves may and should be used as mulch, if you have them. With Texas being a major pecan growing state, their use as mulch is encouraged.
The use of walnut hulls have been considered as an effective weed control for organic operations because its allelopathic characteristic. Walnuts, and particularly black walnuts, contain a substance, juglone, a phytotoxin. However, increased weed control benefits were not realized in at least one control test using walnut hulls and shells (Use of Walnut Hulls for Weed Control.).
Coir fiber or coir dust is a byproduct of the coconut processing industry that can be used in place of peat moss. Although used initially and primarily for soil less planting mediums, it can be used as mulch. It’s viable mulch for containers; its use in landscape beds may be prohibitive due to cost. Coir dust is usually sold in bricks at garden centers and catalog and Internet specialty garden suppliers. (For information, click on Coir Dust as a Peat Moss Substitute).
Coir is the fibrous material of the middle layer of the coconut fruit. Until the 1990’s coir dust piled up in the processing of coconuts as there was no known use for it at the time. Some piles were a hundred years old. Seeking an alternate growing medium to peat, growers turned to coir dust as a soil less medium for seeding plants. Initial stockpiles of coir dust were quickly snatched up as the demand grew. Now coir dust only replaces about 5% of the demand for peat moss.
Advantages to using coir over peat are:
- Equal to or greater water-holding capacity
- Excellent drainage
- Absence of weeds and pathogens
- Greater physical resiliency (withstands compaction better)
- Eco-friendly -- from a renewable resource, use of a by product previously unused
- Slower in decomposition
- Similar pH to peat (slightly acidic), acceptable cation exchange capacity
- Easier wet-ability without a wetting agent.
One drawback noted is a higher saline content in coir fiber processed from green coconuts due to salt water curing for easier processing. However, the sodium quickly leaches out with irrigation. Coir processed from ripe coconuts is fresh water cured. With the increased demand for coir fiber in the horticulture industry, salt water curing is now discouraged. (Click on www.rolanka.com/index.asp?pg=coirarticle for information on coir products and processing.) Higher potassium content was also noted. A slight draw down in nitrogen content in the soil was also noted, but in soil well amended with organic matter this is not seen to be significant.
I don't recommend using peat moss. Peat moss is strip-mined for our use as an amendment or mulch and is replaced in nature by about an inch per century, if the capacity to replace it still remains at all. Ecologically minded gardeners are turning away from peat moss as a soil amendment. Additionally, "peat moss added to southwestern soils makes the surface dry faster, and once dry, repels water, making it difficult to re-wet." (Natural by Design, Judith Phillips, 1995) Even in wetter climates, peat moss is no longer recommended: "Peat moss is not a good topdressing because it contributes no nutritional value to the soil. As topdressing, peat sheds water rather than absorbing it. Finished compost is a far better choice than peat moss (almost anything is)," writes Ann Lovejoy from the Pacific Northwest (Ann Lovejoy’s Organic Garden Design School, Ann Lovejoy, 2001).
Recycled Rubber Products
I’m including this paragraph with both organic mulch as well as inorganic mulch because of its importance. Even though certain substances advertised as “recycled material” might appear good and beneficial to use in the landscape, they should be approached with caution and research. Just because a product is called “organic” doesn’t mean it should always be used or trusted as safe for our environment.
Recycled rubber products are such products to avoid as mulch. Although rubber mulch is hailed as an effective weed barrier and safe alternative to use that doesn’t need replenishment, research has proven otherwise. A study by Linda Chalker-Scott, Ph. D., Extension Horticulturist and Associate Professor at Puyallup Research and Extension Center, Washington State University, (Horticultural Myths about Rubber Mulch) cites that
- “Rubber mulch is not as effective as other organic mulch choices in controlling weeds
- Rubber mulch is highly flammable and difficult to extinguish once it is burning
- Rubber mulch is not permanent; like other organic substances it decomposes
- Rubber mulch is not non toxic; it contains a number of metal and organic contaminants with known environmental and/or human health effects.”
Rubber mulch leaches, in particular and in addition to other metals, high levels of zinc that kill plants and smells bad, actually “stinks” in hot weather. Rubber mulch is sometimes included in bagged compost products to bulk up the bag, without disclosing on the bag cover its inclusion. Buyer Beware! (www.paghat.com/rubbermulch.html)
Angie Hanna, July, 2006