A mulch is a layer of\nmaterial (usually organic, but not always) that is used to cover the soil.\nMulching is natures way of gardening (it imitates the leaf fall in a deciduous\nforest) and provides a number of significant benefits. It protects the soil,\nsuppresses weeds, conserves moisture and adds nutrients, all without disturbing\nthe soil. It can be so simple and effective that some gardeners give up on\ncultivation altogether and become no-dig gardeners.<\/p>\n\n\n\n
The <\/strong>benefits of mulch<\/strong><\/p>\n\n\n\n Weed suppression<\/strong><\/p>\n\n\n\n Most annual weeds are\nadapted to growing on newly disturbed soil, so if the soil is never left bare\nthey won\u2019t be able to get established (this is an example of going along with\nnatural laws rather than trying to fight them).<\/p>\n\n\n\n If the mulch material is\nfree of weed seeds, it will eventually break down to form a weed free organic\nlayer on top of the soil. Any weed seeds in the soil will slowly get buried\ndeeper and deeper and won\u2019t get the chance to germinate. If you don\u2019t allow any\nmore weeds to set seed and don\u2019t disturb the soil, you can eventually almost\neliminate annual weeds entirely.<\/p>\n\n\n\n Mulching can also work with\nperennial weeds if it is thick enough and you give it enough time (maybe two\nyears or more).<\/p>\n\n\n\n Water conservation<\/strong><\/p>\n\n\n\n Mulch significantly reduces\nthe evaporation of water from the soil and in dry climates this is often the\nprimary reason to use it. Not only does it shade the surface from the direct\nheat of the sun, it also increases the humidity of the air under the mulch\n(that in direct contact with the soil). <\/p>\n\n\n\n Soil temperature stabilization<\/strong><\/p>\n\n\n\n On a sunny day the surface\nof bare soil may reach 90\u00b0F, which is a problem because when the soil gets\nabove 80\u00b0F, organic matter breaks down faster than it is created (this is one\nreason we always try to avoid bare soil). On a very cold day bare soil will\nquickly freeze, which makes it impossible to do any gardening. A thick organic\nmulch insulates the soil and slows down these temperature changes (it can\nreduce soil temperature by up to 10\u00b0F). On a seasonal scale it keeps the soil\ncooler in summer and warmer in winter. It\u2019s common practice to cover root crops\nwith mulch in winter to prevent the ground freezing.<\/p>\n\n\n\n Organic mulch is so\neffective at insulating the soil from the suns rays that it can be a problem in\nspring, as it may prevent the soil from warming up quickly. For this reason\nmulch should be removed from beds at least 2 weeks before you wish to plant, to\nallow them to warm up. <\/p>\n\n\n\n Light colored mulches keep\nthe soil cooler than dark colored ones.<\/p>\n\n\n\n Plastic mulches can be very\neffective for warming the soil, though they aren\u2019t much help in cooling it.<\/p>\n\n\n\n Soil protection<\/strong><\/p>\n\n\n\n Sunlight damages bare soil\nby burning up humus, liberating nitrogen and killing soil organisms. A layer of\nmulch protects the soil surface from direct sunlight and prevents these things\nfrom happening. It can also prevent erosion and reduces surface crusting and\ncapping.<\/p>\n\n\n\n Soil building<\/strong><\/p>\n\n\n\n Mulching\nis the easiest and most natural way to add nutrients to the soil and improve\nit\u2019s structure (it could even be considered a form of composting). Most organic\nmaterials break down quickly once they are in contact with the soil, as the\nhumid interface of soil and air is an ideal place for decomposing organisms. A\ntwo-inch layer of shredded leaves will have all but disappeared into the soil\nby the end of one season.<\/p>\n\n\n\n Soil life<\/strong><\/p>\n\n\n\n Mulch benefits soil\norganisms by providing food, blocking out the sun (with its lethal UV rays),\nstabilizing the soil temperature, giving refuge from predators and providing\nsuitable habitat. It is one of the best ways to increase the number of\nearthworms in the soil.<\/p>\n\n\n\n Cleanliness<\/strong><\/p>\n\n\n\n Organic mulches can make the\ngarden look more attractive and well cared for. They also make it less muddy in\nwet weather, which reduces the amount of soil splashing onto leaves (and hence\nthe spread of disease).<\/p>\n\n\n\n Winter protection<\/strong><\/p>\n\n\n\n A thick mulch (up to 12\u02dd deep)\nof straw, tree leaves or other bulky material, may be applied after the\ntemperature drops in late fall. This can protect late crops and tender plants\nand help them to survive in otherwise inhospitable situations. It keeps the\nsoil warmer, reduces nutrient leaching and helps keep soil organisms\n(especially earthworms) active. It also keeps the ground from freezing, so you\ncan harvest over-wintering root crops. This mulch should be removed in early\nspring to allow the soil to warm up.<\/p>\n\n\n\n If\ngiven advance warning of freeze, you can protect tender plants by heaping mulch right over the top of\nthem. <\/p>\n\n\n\n Problems with mulch<\/strong><\/p>\n\n\n\n There are situations where\nmulch can be a problem.<\/p>\n\n\n\n In cool, humid climates where slugs are a big problem, mulching\nmay not work very well, because it provides a perfect hiding place for these\npests. <\/p>\n\n\n\n In some situations mulch has been known to create conditions\nwhereby normally harmless creatures such as earwigs and sowbugs become so\nnumerous they become pests. <\/p>\n\n\n\n It is well known that organic mulches can keep the soil cold in\nspring. Less well known is that a heavy mulch may actually increase frost\ndamage to plants in cold weather. This occurs because the well-insulated soil\nreleases less heat than bare soil. <\/p>\n\n\n\n Some mulches (sawdust, tree leaves, wood chips, seaweed) may\ncontain toxins that inhibit plant growth.<\/p>\n\n\n\n Some mulches (hay, manure) can contain a lot of weed seeds and\nother problems (though this may not matter very much if your soil is\npermanently mulched). <\/p>\n\n\n\n The biggest problem with mulch is that it takes a lot to work\neffectively. To lay 3\u201d of mulch on a 100 square foot bed, requires almost a\ncubic yard of material . <\/p>\n\n\n\n The application of mulch<\/strong><\/p>\n\n\n\n Before\napplying any kind of mulch you should remove any perennial weeds, otherwise\nthey will simply grow through it. <\/p>\n\n\n\n A weed\nsuppressing mulch must be continuous and impenetrable to be effective. The\ndepth depends upon the material used, it might be a 6\u02dd layer of straw, 3\u02dd of\nchopped leaves, two layers of cardboard, or 6 – 8 layers of newspaper. <\/p>\n\n\n\n Whenever you use a mulch to\nsuppress weeds you must pay particular attention to the edges, as weeds will\ntry to creep around the edges. This is especially true with plastic, so bury\nthe edges to prevent it happening.<\/p>\n\n\n\n If the mulch material is\nvery high in carbon, you might want to put down a high nitrogen layer\nunderneath it, to aid in its decomposition. Compost is probably the best thing\nto use for this, as it provides its own decomposing organisms to get to work on\nbreaking it down. Horse manure is good too.<\/p>\n\n\n\n Mulch materials<\/strong><\/p>\n\n\n\n A good mulch material should be:<\/p>\n\n\n\n \u2022 Relatively long lived.\n<\/p>\n\n\n\n \u2022 Free or inexpensive. <\/p>\n\n\n\n \u2022 Available in\nabundance. <\/p>\n\n\n\n \u2022 Heavy enough that it\ndoesn\u2019t blow away. <\/p>\n\n\n\n \u2022 Free of weeds, weed\nseeds, pests, disease and chemical pollutants. <\/p>\n\n\n\n \u2022 It should add\nnutrients and organic matter to the soil when it decays. <\/p>\n\n\n\n \u2022 Ideally it will also\nbe attractive. <\/p>\n\n\n\n Organic mulches<\/strong><\/p>\n\n\n\n Tree leaves<\/strong>: (2 –<\/strong>\n3\u02dd) Deciduous tree leaves, gathered after they drop in fall, are oneof\nthe best mulch materials. They add humus and nutrients, encourage fungi in the\nsoil and are usually free of weed seeds, pests and disease. They can be used\nwhole, but tend to blow away or mat down (mix with straw to prevent matting).\nThey work better and break down faster if shredded (use a shredder or a lawn\nmower).<\/p>\n\n\n\n Broadleaf evergreens can\nalso be used, but are best shredded to encourage decomposition.<\/p>\n\n\n\n The\nneedles of coniferous evergreens can also be used, but aren\u2019t as good as\ndeciduous leaves because they contain toxic resins and can lower the pH of the\nsoil. They work best on acid loving plants such as blueberries and evergreens,\nbut can also be used with other plants if you add lime. In some areas these are\navailable commercially under the name pine straw.<\/p>\n\n\n\n Straw<\/strong>: (4 –<\/strong>\n6\u02dd) This bulky material is clean, attractiveand a rich source of humus.\nIt can be used to enrich the soil, suppress weeds, protect plants from frost\nand to insulate the soil. If it isn\u2019t organic it may contain pesticide\nresidues, but this isn\u2019t normally a problem.<\/p>\n\n\n\n Hay<\/strong>: This is\nsimilar to straw in many ways, but containsmore nutrients. However it\nalso contains a lot of weed seeds, so isn\u2019t a good mulch material for intensive\nbeds.<\/p>\n\n\n\n Compost<\/strong>: (2 –<\/strong> 3\u02dd) Compost is a good mulch materialbecause\nit contains a lot of nutrients and can suppress some pathogens. It can also\nsuppress weeds quite effectively if at least 3\u201d thick, Most gardeners don\u2019t\nmake enough compost to be able to use it as mulch, though if you buy it you may\nbe able to. If compost is laying on the surface, exposed to the sun, some\nnutrients may be lost to oxidation. To prevent this you can cover it with a\ncoarser mulch, such as straw or tree leaves. <\/p>\n\n\n\n Manure<\/strong>: (1 –<\/strong>\n3\u02dd) This can be a good mulch material,if you have enough of it that you\ncan afford to lose some nutrients (nitrogen is lost when manure is exposed to\nsunlight). It is rich\nin nutrients and organic matter. Some manures (horse, goat) aren\u2019t digested\nvery completely and may contain a lot of weed seeds. <\/p>\n\n\n\n Fresh\nmanure <\/strong>may contain\nso much nitrogen that itcan actually burn plants. It is often applied\nto the soil in autumn, so some of the nitrogen can leach out over the winter.\nAged manure is safer because it has less nitrogen. Composted manure <\/strong>is even better, as ithas\nalso heated up enough to kill weed seeds.<\/p>\n\n\n\n As with compost it may be a\ngood idea to cover manure with a couple\nof inches of a coarser mulch, such as straw or tree leaves. <\/p>\n\n\n\n Seaweed<\/strong>: (2 –<\/strong> 3\u02dd) A rich source of trace elements,seaweed breaks\ndown very quickly into the soil, but doesn\u2019t add much humus. It was once widely\nused in coastal areas.<\/p>\n\n\n\n Grass\nclippings<\/strong>: (2 –<\/strong> 3\u02dd) These are rich in\nnutrientsand humus, but decompose rapidly so need replacing regularly\nif they are to keep weeds down. They are best put down in thin layers as they\nbecome available. Thick layers tend to mat down.<\/p>\n\n\n\n Sawdust<\/strong>: (1 – 3\u02dd)\nSawdust is highly resistant to decay because it is very high in carbon, so is long lasting when used as\nmulch. If incorporated into the soil it may cause a nitrogen deficiency, but\nthis doesn\u2019t happen very much if it simply remains on the surface. Fresh\nsawdust may also contain toxic terpenes and tannins, which can inhibit plant\ngrowth. When it does finally break down it is an excellent source of humus. If\nyou really want to use a highly carbonaceous mulch such as this, you might want\nto put down a layer of high nitrogen material first.<\/p>\n\n\n\n Wood waste<\/strong>: <\/strong><\/p>\n\n\n\n Shredded bark <\/strong><\/p>\n\n\n\n Shredded yard waste <\/strong><\/p>\n\n\n\n Wood shavings <\/strong><\/p>\n\n\n\n Wood chips<\/strong>: (2 – 3\u02dd) <\/p>\n\n\n\n These woody materials are\nvery durable and effective weed suppressing mulch materials and work great for\nperennial plantings. They are not so good in the annual garden as they don\u2019t\nbreak down and release their nutrients for a long time. When fresh they may\ncontain toxins that actually inhibit plant growth. They are best suited for\nmulching paths and around permanent perennial plantings, such as trees. They\ndon\u2019t rob the soil of nitrogen if they are left on the surface, as they would\nif they were incorporated.<\/p>\n\n\n\n I live in a heavily wooded\narea and tree trimmers are always looking for places to dump their wood chips.\nJust ask them and they will dump a truckload on your driveway (the trick is to\nask them before anyone else does – and have an easy place for them to dump). <\/p>\n\n\n\n Bracken fern<\/strong>: (3\u02dd) If\nyou can get it in quantity it can be used to enrich the soil, suppress weeds\nand protect plants from frost.<\/p>\n\n\n\n Miscellaneous plant materials<\/strong>: Cottonseed meal, cocoa hulls, spent hops, tea leaves and coffee grinds all make fine mulch, but\nare rarely available in sufficient quantity.<\/p>\n\n\n\n Newspaper<\/strong>: (6 – 12\noverlapping sheets) This is technically organic in it is made from trees, but\nit is so thin it doesn\u2019t add much organic matter to the soil when it\ndecomposes. <\/p>\n\n\n\n Newspaper\nis most often used as a weed suppressing mulch, either alone or in combination\nwith other mulches (it is rather ugly to use by itself). It is most often used\nas a second weed suppressing layer underneath other mulches. You lay down a\ncontinuous layer of overlapping newspaper and cover it with a layer of leaves,\nhay or other organic mulch. It is so light it may blow away if not weighted or\npinned down.<\/p>\n\n\n\n Pages with a lot of colored\nink may be safe, or they may contain petrochemicals and other toxins. I\u2019m sure\nyou could use them without problems, but I feel better just recycling them. <\/p>\n\n\n\n Cardboard<\/strong>: (1 overlapping layer of corrugated) Another material that is\ntechnically organic, but that doesn\u2019t add much organic matter to the soil. <\/p>\n\n\n\n Cardboard is very effective as a weed suppressing mulch and can\neven be used to eliminate tough woody weeds like blackberries. It isn\u2019t quite\nas ugly as newspaper, but still looks better when covered with a layer of more\nattractive material. <\/p>\n\n\n\n Cardboard is most often used as a second layer, underneath other\nmulches, to make them more weed proof.<\/p>\n\n\n\n Other mulch materials<\/strong><\/p>\n\n\n\n These materials don\u2019t add\nnutrients to the soil, but are useful in some circumstances.<\/p>\n\n\n\n Carpet<\/strong>: May be\norganic or inorganic, depending on the fibers and backing materials (it\u2019s best to avoid synthetics unless\nyou want to end up with a layer of matted synthetic fibers in your garden).\nCarpet is good for suppressing weeds and keeping the garden clean and is great\nfor paths. Lay it upside down for the most natural appearance, unless you\nreally want to bring the indoors outside.<\/p>\n\n\n\n Plastic sheet<\/strong>: I\nprefer to avoid plastic whereverpossible and wouldn\u2019t use new plastic\nmerely to keep weeds down. I might use recycled plastic (such as that from\ngreenhouses or cloches, if it isn\u2019t too far gone) to clear land of weeds, to\nwarm the soil, or to mulch around newly planted trees.<\/p>\n\n\n\n Plastic is so light it may\nneed weighing down to prevent it blowing away. You can use soil or rocks, or\npin it down with pieces of wire (old coat hangers can be used).<\/p>\n\n\n\n The color of the plastic has\na significant effect on its properties as mulch. Black plastic increases the\nsoil temperature by as much as 10\u00b0F and also kills weeds. Clear plastic acts\nlike a miniature greenhouse and can increase soil temperatures even higher (as\nmuch as 15\u00b0F), but may allow weeds to grow underneath it (if it doesn\u2019t cook\nthem).<\/p>\n\n\n\n A big problem with plastic\nis that it degrades in sunlight. It is also ugly. Large areas of plastic might\nhave an adverse effect on soil air exchange. It certainly does affect water\nabsorption \u2013 watch that runoff<\/p>\n\n\n\n Aluminum foil <\/strong><\/p>\n\n\n\n Mylar film<\/strong>: These\nhave many of the same properties as plastic, but are highly reflective which\ngives them some special uses. They help to keep the soil cool (they shouldn\u2019t\nbe applied until the soil is warm) and reflect extra light back on to the\nsurface of the leaves, increasing photosynthesis. In this way they have been\nknown to increase yields by 100% or more. The extra light may actually\ndisorient insect pests such as aphids, preventing their preying upon the plants\n(it may also disorient the gardener as well, as it is pretty bright, as well as\nvery ugly).<\/p>\n","protected":false},"excerpt":{"rendered":"