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A Composting Guide for the Home Gardener
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COMPOSTING 101 How It Works What To Use Carbon-to-Nitrogen Ratio The Finished Product A Bevy of Bins Using Worms Troubleshooting  This site is brought to you by www.PlanetNatural.com |
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 Nine Steps to Hot CompostingBy Jim McNelly, Earth 911 Active Composting Active, hot composting is a BATCH process. It differs from passive piles that just "sit there" seemingly forever or "continuous flow systems" where stuff is periodically dumped on top of the material already in the bin and removed from the bottom when it is dark and crumbly. My recommended steps for creating active, hot batches of compost are: 1. Prepare the Composting Area 2. Choose Your Bin 3. Stockpile 4. Inoculate 5. Mix 6. Balancing the Ingredients 7. Water 8. Aerate 9. Active, Hot Composting 1. Prepare the Composting Area Before beginning the active, hot composting process, the composting area must be properly prepared. Start with an empty bin or space on the ground where you wish to locate your compost pile. Make certain your space is well drained and that storm water runoff from the roof or the yard will not reach the composting area. Choose a point that has a higher elevation than the rest of the yard, but make sure that it is within easy reach of the garden hose because, like houseplants or garden vegetables, the compost pile needs occasional watering. Appearance and aesthetics are usually as important as where it is in vicinity to the intended use for the compost. While many people place their bin near the garden where the compost will be used, others find that a place centrally located between the front and back yard is convenient. If you don't have a garden, the first compost pile may be a good incentive to start one. Many gardeners say that compost is the secret to larger and tastier home-grown vegetables. An area where a landscape project is contemplated is also a good location for the compost bin. The wise landscaper knows that compost-enriched soil yields long-term growth dividends for trees and shrubbery. Avoid building bins against walls or fences that can rot and discolor. Choose a level spot away from drainage swales and roof overflow. Avoid low spots where water can stand or pond. Leave plenty of room to get into the area with a pitchfork and a wheelbarrow. The area should be from 6' x 6' up to 12' x 9' for multiple bins. A bin near the kitchen makes processing table scraps easier. It makes little difference whether the bin is in the shade or light, although a dark bin in the sun will warm up earlier in the morning during the springtime and fall. If you place a bin under a tree, you can expect the roots to climb up into the bin, making it difficult to remove the compost. Placing a bin ten feet or more away from the house will discourage bugs, especially termites that may come with wood mulch from moving into your home. Having the garage or storage shed nearby makes it easier to keep pitchforks, shovels, the screen and wheelbarrow clean and out of the weather. 2. Choose Your Bin With proper preparation, piles can be made to heat and decompose adequately without the need for bins. The main purpose of bins and enclosures is to help hold heat by keeping the composting mass as close as possible to the active composting center. A bin is like an oven, except that its purpose is to help hold moisture as well as heat. In small piles bins also allow air infiltration from the sides, assisting the "chimney effect" of warm air rising and aiding ventilation. Bins are an advantage since they help the pile look neat, containing unsightly matter within an enclosure. Avoid using an existing building or wooden fence as a sidewall since an active composting pile will decompose walls, discolor paint, and destroy untreated wooden fence slats. Use galvanized metal, plastic, or cedar for rust and decay prevention in the construction of the bin. (Redwood and cedar are decay resistant but usually come from "old growth" forests.) There are two basic types of bins: open-sided and enclosed. Enclosed bins tend to be smaller, but since they hold heat and moisture better than open-air bins, it usually take less time for the material inside to decompose. It is hard to believe, but small, enclosed bins may actually process more material over time than large, open-sided bins that may hold three times as much material. Small yards with a high percentage of table scraps often have the best results with enclosed plastic bins, preferably ones that can be lifted off, exposing the material inside for turning or curing. Plastic bins are often rodent resistant which is important if you will be composting a lot of table scraps. Large yards can use larger open-air designs or multiple plastic bins. For square or rectangular bins, large doors are better than small ones so that the material can be more easily loaded and unloaded. Three-stage systems are best, but only one or perhaps two bins are usually active at any given time. The three stages of composting are stockpiling, hot composting, and curing. Curing piles and small stockpiles do not typically need bin enclosures. When making compost on a batch system, the bin or bins should be sized for the total amount of material to be made as a single batch at any given time. Batch composting is best suited for managing large volumes of grass clippings that otherwise would be mulched into the grass or left on the curb in bags. If using a bin for grass clippings, collect the grass in a way that lets you know how much volume you have in a single cutting. A thirty-gallon trash can holds approximately four cubic feet. A wheelbarrow typically holds either four or six cubic feet. Pallets are an inexpensive (even free!) material to use to build a compost bin. Not all pallets are the same, however, and best results are achieved if pine, not hardwood pallets are selected. Believe it or not, most softwoods such as pine are more rot resistant than most hardwoods such as oak. Standard pallets at either 40" or 44" are higher than the standard recommendation of bin sides at 36". My experience is that a height of 32", about a man's waist, is the optimum. Hardwood pallets are rather heavy, making doors hard to open. When selecting pine pallets, find ones that have narrower spaces between the boards, which will help prevent material from spilling out. Check paint wholesalers as they tend to have the optimum size pallets for composting since paint cans need more flat surface than other products. If you produce four to six cubic feet of grass clippings per week, stockpile a week's worth of material for making a batch the following week, which will produce a batch of compost every two weeks. Accounting for volume reduction and adding old compost and wood chips as a bulking material, then you will need two plastic bins sized between ten and fifteen cubic feet. You will also need an area capable of handling an additional two stockpiles of curing compost without bins. If you use open-sided larger bins, you will need two bins approximately twenty to thirty cubic feet each with one stockpile area that can hold numerous five to ten cubic piles. Many composting books suggest making a bin 36" or even 48" high, but I have found that most people have a difficult time lifting material with a pitchfork more than 32" high. A problem I have with permanent bins, whether they are made out of blocks, boards, pallets, or whatever, is that they require an extra step to move material from one bin to the other. By this I mean that the material has to be lifted out of the bin through the door, then carried around the side wall, and then placed through the opening of the second bin and dumped. With easily removable sides or the new generation of smaller plastic bins, the bin can be removed like a "Jell-O" or "cake mold" and the material can be accessed from all sides, making the transfer process to the next bin, which could even be the same plastic bin, much easier. Many "do it yourselfers" pride themselves in making an elaborate permanent bin, but find that the work to actually use it for active, hot composting to be rather difficult. Some experts recommend treated lumber, but others express caution that the wood treating and paint compounds may contain heavy metals such as copper, chromium, arsenic, or other toxins that could leach into the compost. The uncertainty of long-term disposal for treated lumber also suggests against their use. Under no circumstances should treated lumber be burned because dangerous arsenic compounds can be released into the atmosphere. One recommendation is to use recycled plastic or bins made with scrap cedar. Enclosures of chicken wire, hardware cloth, and other types of wire mesh are popular. A wide variety of back yard compost bins are available, many of which have been proven to promote active, hot composting when used properly. Avoid bins with solid sides that keep out air and choke the compost. Several manufacturers sell cedar slat bins that assemble like "Lincoln logs" with open sides and can have modules added to expand into three separate bins. This type of bin is popularized as the original "Lehigh" bin in the 1950s. While the three-bin system is recommended in many gardening books, their disadvantage is that the adjacent sides have no open area from which to draw air. An advantage of shared sides is that less heat is lost from the common sidewall. Fifty-five gallon drums set upon blocks with holes perforating the base and sides can also be effective compost bins. A rotating barrel is another composting option. Barrel composters range in size from seven cubic feet up to twenty. The larger tumblers have been described by some users as difficult to turn due to their weight. Barrels are excellent mixers and condition organic material quite suitably in preparation for active bin composting. For those people who choose rotating barrel composters, a bin is still necessary for higher quantities of material, since most tumbling barrels have only a limited capacity. One writer on the Internet tells a story about placing a barrel perpendicular between the wheels of an upside down toy wagon, turning it between the wheels. Once the bin design is chosen, a suggestion is to construct two or more freestanding bins separate from, but close to each other. Open air bin sizes range between 3/4 cubic yards to 2 cubic yards in volume, such as a 3' x 3' x 3 square, 4' x 4' x 3' square, 4' x 4' round, or a 3' x 3' or 2' x 2' five or six sided bin. The cubic yardage of a box equals the length in feet times the width times the height divided by 27 = L x W x H /27. The area of a round bin is calculated by multiplying pi (3.141) times the radius squared times the number of feet in height divided by 27 (R2 x pi x H /27) A bin, three feet round and three feet high, contains 21.18 cubic feet. (1.5 x 1.5 x 3.141 x 3) or .78 of a cubic yard (/27). A four-foot diameter round bin that is four feet high contains 50.24 cubic feet or 1.86 cubic yards. Three foot widths are considered the minimum for open air sided bins if the pile is to hold sufficient mass to heat properly. If no bin is desired, a "stand alone" pile of 5' in diameter by 5' high (1.7 cubic yards) is optimum, although a small area at the base of the pile should be cleared to allow one end of a passive air flow system to reach the open air. Since the air entering the sides of the pile is as critical as air entering from the bottom, a 5+ cubic yard pile that is 4' wide by 4' high by 9' long has more surface area and better air access than a pile that is 6' by 6' by 4' high. A compost bin with easily removed sides is desirable. Some bins have slats that are removed by pins. Others have individual panels that slide out from the top or side. Still others have removable panels or hinged gates. Wire or plastic mesh systems often have fasteners that hold the two ends together. Removable sides also make turning and aerating the compost easier, so the householder is more inclined to actually use the bin and thus turn and mix material regularly. In choosing a bin design, always remember that it is air, not the container, that is the main secret to successful composting. The more open area, the more air can enter the pile. While an underside passive airflow system can help, it is no compensation for inadequate initial mixing. Avoid airtight bin designs unless you are prepared to let organic material sit for over a year, possibly generating odors if disturbed. Be certain that there is plenty of working area around the compost bins so you can get at the pile with proper leverage and without straining. A bin design with sides that can be disassembled and reassembled quickly will make pile turning easy. Holding bins are used mostly to make the composting area look neat and to keep leaves from blowing away. Most yards do not generate sufficient organic matter to support more than one active composting bin. If there is insufficient material to fill a bin, the dedicated homeowner interested in organic gardening will pick up yard trimmings from a neighbor's yard in order to keep the bins fully active, keep material out of the landfill, build up the topsoil, and enjoy some exercise. Once you have chosen your composting area and constructed your bin(s), the active, hot composting process can begin. 3. Stockpiling There is a natural tendency to slowly fill the compost bin with fresh organic matter and hope for the best. This is the basis of passive composting. But the composter who desires a hot, active pile waits until there is sufficient material accumulated to properly start a "batch" of compost. Other composting guides suggest that the person stockpile right in the bin, layer by layer. The mixing stage is completed some time later when the pile is "turned". While this process can be effective for passive composting, it is easier to stockpile outside the bin and mix everything all at once at the start of a hot compost batch. Separate from the active compost bin should be an area where grass clippings, leaves, and other soft stemmed yard debris can be stockpiled. Since active, hot composting requires that you fill the bin all at once, this usually requires stockpiling of at least half the volume of the size of your bin. Leaves, wood mulch, hay, shredded bark, oversized compost left over from screening, straw, pine needles and cones, old compost, and shredded paper products are easy to stockpile. Keep these small piles near the mixing area to avoid too much handling or moving of the material. When considering how much material to stockpile, you first need to know the capacity of your bin. For an open-air design, it is important to have about twenty cubic feet, or two thirds of cubic yard of raw material. For plastic bins, you only need to gather about half that amount. The important consideration is to have plenty of fresh material on hand, knowing that the remainder required to fill the bin can be made up with a blend of compost recycled back from the most recent batch. This "minimum batch requirement" may require gathering supplemental material from the neighbors. When stockpiling green material such as grass clippings, you may wish to immediately add wood chips and old compost inoculant to keep the material aerated while waiting to start the next batch. Once the active, hot composting process is established and there is an existing quantity of rich, active compost to use for blending, then fresh material can be added intermittently without as much need for stockpiling. Additional grass clippings or leaves should be watered and mixed with active compost culture in the mixing area before placing them on top of an active composting pile. This will help prevent the new material from restricting the natural aeration of the active compost underneath. Many composters keep a stockpile of leaves from the fall to add to the summertime grass clippings. These holding bins are usually larger than the smaller active composting piles. They also keep a stockpile of wood chips for free air space and bulking. The other stockpile is cured or curing compost to use as an inoculant. Grass clippings can be stockpiled for a week or so, taking some table scraps mixed in during the meantime. You will be impressed at how quickly table scraps decompose when added to a trench in the top of a hot, active pile. Some stockpiles may be left as small mounds near the bins; others such as leaves may require containment. Leaves may be left in bags, however in yards with many trees, you may have to stockpile leaves in large bins, often over forty cubic feet, or four feet by four feet square. Shredding leaves or running them through the mower can reduce their volume and make them a little easier to compost. Brush should never be placed into the compost bin, at least an active bin, without chipping or shredding. Not only does it take months, if not years, for full-size branches to decompose, unchipped brush clogs the composting mass, making it nearly impossible to fork out the material. 4. Inoculating Inoculating the compost pile is the process of distributing an active biological culture evenly throughout the material to be composted. In the past, many compost guides have recommended using soil as an inoculant, even recommending several 6' layers of topsoil. Clinical studies have shown that adding soil does more harm than good for the composting process since most soils are low in organic matter. The number of active organisms in even a rich topsoil with 7% organic matter is insignificant compared to an organic compost with up to 90% organic matter. Some composting experts correctly point out that the essential micro-organisms are already present in leaves and grass clippings and will eventually decompose the organic material. But distributing high populations of organisms evenly throughout the raw material has been shown to accelerate the composting process tremendously over piles with no inoculant. In large commercial composting facilities, the percentage of compost recycled is closely controlled to keep the composting piles performing at their optimum. Compost inoculation is like starting a yogurt culture or adding yeast to bread. The active culture must be thoroughly blended in order to produce the desired effect. Mixing the active culture at the start of the process is essential because all raw organic material must be inoculated with micro-organisms before the composting process can begin in earnest. An active, hot compost process requires immediate decomposition. There is not enough time to wait for organisms to migrate up from the soil or move down from a layer on the top of the pile. Several compost inoculants are available on the market which claim to accelerate the composting process. Some are active bacteria cultures that may help the inoculation process when first initiating or re-starting the active composting process. The best commercial inoculants are bacteria concentrates cultured under laboratory conditions. Inoculants that are merely old compost in a small bag can be quite expensive. Many composters report positive results using packaged inoculants. However, millions of active composting piles have been created and have generated wonderful compost without extracts and supplements. The existing beneficial micro-organisms in the raw material or the added culture inoculated from an active composting pile will provide all the essential micro-organisms sufficient to initiate active composting. Saving old compost to "re-seed" the next batch is a sure and inexpensive means of maintaining the active compost culture without having to purchase inoculants time and time again. If you have no old compost pile to inoculate the first pile and your topsoil has little organic matter in it, you may wish to purchase some inexpensive bags of composted cow or other manure from the garden center. You could also harvest some old leaf mould from a wooded area to help start the first composting culture. Once you have made your first batch, however, you will have plenty of older compost to blend in with new materials. You don't have to keep excess amounts of cured compost in the active bin area if you need the space for fresh material. Once a pile has cooled, compost can be taken out of the bin to finish curing on the ground. The bin is primarily for heating and aerating. Once you start the composting reaction and have an active culture of micro-organisms, you will discover that inoculating new piles becomes easier with practice and your piles will consistently heat and decompose rapidly with a minimum of odor or effort. 5. Mixing Mixing prior to active, hot composting is absolutely essential for rapid and efficient decomposition. Mixing evenly distributes micro-organisms throughout the pile. It blends several types and consistencies of organic material together to produce a "composite", the term from which compost was derived. Mixing allows essential reactions to occur in the compost pile related to air migration, carbon to nitrogen balance, moisture availability, and fresh food for bacteria. Mixing at the start of the batch is the single most important step needed to facilitate hot composting. This is true in large-scale commercial piles as much as it is in backyard bins. When layers of different types or ages of material sit on top of each other without mixing, they want to react and decompose at different rates. This means uneven composting rates, failure of the composting process, odors, and material that does not decay properly. The food in one layer may be just what is needed in the next layer, and mixing is the technique for getting the layers together. The trick is to layer your various ingredients outside the bin, watering each layer as you go. Think "green and brown" or "grass and leaves" when you make the layers. Add up to 10% bulky matter like wood chips to keep the pile loose to avoid matting. Then fork the layers into the bin, mixing as you go, blending wet with dry, watering as necessary. Make several small mini-batches of three layers or so, only four to six inches high, of your ingredients in the mixing area and fork them into the bin, one small mini-batch at a time. Now (and during the three to six weeks of active, hot composting) is the time to add table scraps. Avoid adding lime; it can disturb the natural pH shift and delay decomposition. Again, if your bin is the "oven", your mixing area outside the oven is like a "mixing bowl". When making hot, active batches of compost, resist the advice from other composting guides to mix ingredients inside the bin. It is very difficult and time consuming, not to mention messy, to try to mix various layers of material inside a bin. Continue mixing and adding until the bin is full. If material is left over, use it as a part of the stockpile for the next batch. There are two types of mixing. The first is the initial layering and mixing required for starting an active pile. The second is the mixing necessary to add fresh material to an existing active compost pile. A great deal of information is available in gardening and composting books on the importance of layering materials when starting a compost pile. However, there is hardly any mention of the importance of mixing those layers together before placing the material into the composting bin. All too often, backyard composters think that layering and placing the material in the bin is sufficient and that then they can then leave the pile alone. This is true of passive composting but is not recommended if they want a hot, active pile! Once a pile is active, fresh material can be added on a periodic basis. In a two-bin system, green grass or other raw material can be blended in layers at a ratio of 1 to 2 with the old material as it is being forked over into the next bin. The new material is in one stockpile; the active, hot compost is in the first bin, the new active, hot compost pile is the second bin. There are several hand-held compost mixers available that can help agitate a pile without removing it from the bin, but they should not be substituted for proper mixing prior to placing fresh material into a bin. An inexpensive pile mixer is an anchor for mobile homes sold at many hardware stores and dealers that sell parts for recreational vehicles. It has an auger at the base and an "eye" hole at the top. Put a piece of wood in the eye as a handle and you have a mixing tool for less than $5.00 that works better than most of the hand-held mixing tools on the market. This "auger" can be screwed into the bin then pulled up, erupting the compost, adding air, and providing a measure of mixing. Wood chips assist aeration tremendously. Chips reduce odors by keeping the pile loose and allowing air to move freely through the pile. Unchipped brush or large pieces of wood should never be added to the compost pile since they get in the way of turning. More importantly, large pieces of wood won't decompose within the lifetime of a backyard compost pile. Always chip wood trimmings first before adding them to compost, but even then limit their volume to no more than 10%. Two types of garden shredders are available for residential use. The first chops leaves only. The second chips brush and small branches. Reports from users suggest getting at least a seven horsepower chipper. There are reports of neighbors pooling their resources to jointly purchase a commercial gas powered chipper that provides additional power and capacity. Renting a chipper can also save time and effort, especially if it becomes a community project. A tree service firm may contract to chip brush on an hourly rate, often reducing the rate if several neighbors save their brush for the visit. Use caution when using a mower to chip brush. Always follow the manufacturer's recommendations to avoid injury or damaging your equipment. What helps composting, the process, is not necessarily advantageous for compost, the product. Wood chips are an example since they assist aeration during composting, but can be a nuisance in some planter mixes and may even cause nitrogen starvation problems in topsoil. Wood chips may have to be screened out before using the compost. Many gardeners screen their compost whether they add wood chips or not. Begin placing the material from the mixing area into the bin until it is full. Since the material will decompose quickly and shrink to less than one half its original volume in a few weeks, a little extra on the top is suggested. When adding the mixture to the bin, remember to add water to dry spots as required. 6. Balancing the Ingredients The organisms of decomposition, like all plants and animals, require a balanced diet in order to thrive and reproduce. While organic materials are the basic food for decomposition, not all organics are equally nutritious. Products like grass clippings are high in nitrogen while woody items like leaves, sawdust, wood chips, and paper are high in carbon. Micro-organisms need nitrogen and oxygen in order to decompose carbon and convert it into carbon dioxide. If there is too much nitrogen, foul smelling ammonia can be produced. If there is too little nitrogen, the carbon is decomposed very slowly. Organics can be easily rated according to their carbon to nitrogen ratio. Most composting experts recommend a 30 to 1 ratio as the ideal composting blend. Refer to the carbon to nitrogen ratio chart for more information on how to determine and select the proper ingredients. For the beginning composter, a slightly lower carbon to nitrogen ratio of 40 or 45 to 1 is recommended to prevent odors from developing. Equal parts grass (25:1) to leaves (60:1) plus 10% wood chips for free air space makes an ideal composting mix. Some composters keep a stockpile of leaves and wood chips over the winter to mix with the summertime green material. Leaves are less prone than grass clippings to become odorous as they sit over prolonged periods. When composting leaves without grass clippings, adding other green matter supplements or additional fertilizer formulas containing nitrogen can accelerate the rate of decomposition. Some experienced composters recommend bone, blood, fish, or cottonseed meal in limited quantities to help supplement nitrogen when the compost pile is made largely from high carbon material such as straw, leaves, sawdust, paper, and wood chips. They also recommend dustings of minerals such as diatomaceous earth (ancient microscopic sea organisms) granite dust, greensand, rock phosphate, and limestone. Some gardening books recommend using chemical fertilizer formulation such as a 10-10-10, a 10-4-4, or even a 20-10-10 to supplement nitrogen. Many packaged compost starters or inoculants contain high nitrogen levels. Nitrogen is a "high performance" fuel for composting. Additional turning or aeration may be necessary when using added nitrogen. It is important to know the proper mixing formula based on the carbon to nitrogen ratio of the woody material before mixing in nitrogen indiscriminately. As suggested earlier, too much nitrogen can produce a foul ammonia smell, even a sulfurous rotten egg odor. Not all manures add nitrogen either, especially if they come with straw or woody materials bedding. Some composting specialists recommend using limestone, lime, or calcium carbonate in various quantities. Aside from adding a few micronutrients, however, limestone usually does more harm than good in the compost pile. The notion of adding limestone comes from the old practice of using lime to sterilize outhouse "night soils". Active, hot composting and lime treatments are totally different processes and should not be used together. The composting process does not require added calcium and the acidic shift that occurs is a necessary and natural condition of a properly functioning composting pile. The pile will gradually return to near neutral pH without adding lime to create alkaline conditions. 7. Watering As layers are formed in the mixing area outside the bin, it is critical to water the incoming material, layer by layer. If you wait until after the pile is formed, water tends to sheet off the sides or soak in unevenly when watered from the top. Light watering of dry material is essential in the initial mixing stage. The watering technique should be gentle, as if moistening a new seedbed. If water runs off, turn the pressure down and switch to a fine spray. Use a sprayer that has a pressure control mechanism so that the mist can be turned down and the water off when necessary. Each layer should be dampened, never soaked! The compost layers should be moist like a squeezed sponge. To prevent odors, it is better to have too little water than too much. You can easily add more water later when turning the pile after a week or so, far easier than adding dry material to compensate for an overly saturated pile. Watering is best performed at the beginning of the batch as the layers are formed and again as the layers are mixed and placed in the bin. Old compost, which was added as an inoculant at a ratio from 10% to 25%, helps the new dry material gradually take on moisture since old compost holds water better than fresh material. If the pile is too wet and odors have developed, you must dry it out. Mixing in dry leaves, straw, or old and dry compost can help absorb excess water. Spreading the pile to dry in the sun can also be effective. Rototilling wet compost into the soil is another technique, although wet soils clog most tillers. A pile that is too dry is also a concern. Many a novice composter has regretted not watering during the previous fall when the year old, passive leaf pile still looks much like it did the previous year. Letting weeds grow in the compost is a sure means of drying out the pile. Turn under weeds as soon as they appear since their roots compete with the bacteria for moisture. In fact, weeds have been known to completely dry an active compost pile in a matter of weeks. Placing a bin in an open area that is exposed to the wind can also quickly dry the pile, especially if the pile has too much free air space. The presence of ants can also be an indicator of too little moisture. 8. Aerating Once the stockpiled material is properly layered with older and active compost, when it has been lightly watered, has the proper carbon to nitrogen ratio, and has been thoroughly mixed, then the active, hot composting process will begin. Like any other form of livestock, your "herd" of bacteria requires food, air, and water. You have added food with a balance of carbon and nitrogen, which are the green and brown materials. You just added water while you mixed everything together. Now the bacteria need air. Old compost theory suggests that you "turn the pile" for aeration. Recent studies, however, show that a pile uses up its oxygen in as little as 1/2-hour after turning! It is a challenge to get air deep inside the pile, especially at the base. Air vents in the side of the bin let in some air, but often the result is too much on the sides with none in the middle. Not to worry! If you follow these simple steps, you will be able to make well-aerated compost in only a few weeks without turning! For some individuals, an analogy of a barbecue helps in understanding the importance of proper compost pile aeration. Turning a pile is like opening the lid of a "kettle" barbecue to aerate the coals. The "fire" starts going out soon after the cover is closed. As in the barbecue, air must be provided continuously by ventilation holes from underneath in order to properly aerate the composting process. Opening and closing the lid, like regular turning, will not maintain even and thorough combustion. Here is the secret; like a grate under the fire in a barbecue or a fireplace, a pile needs ventilation from below. Provide a "passive aeration base". Some people use a thin layer of brush, stalks, rocks (over 1-1/2" but under 3"), or coarse wood chips, under the pile, but these tend to get mixed in with the compost after the first batch. More permanent solutions include: 1) using flat aeration pipe, 2) a 1" hardware cloth screen over boards or bricks, 3) sections of flexible 4" HDPE perforated drain pipe cut in half, 4) a pallet type of solid deck (treated with water sealant) with 1/2" holes drilled every six inches. Bargylia Ratever, a master composter in California who has been teaching composting and organic gardening for over fifty years, recommends a bed of twigs and stones at the base of the compost pile to form a "composting grate." An important additional step will let you make full use of the airflow principal by poking and aerating the pile with a 1/2" rod of rebar used in forming concrete, from the top to the base of the pile. The air will rise up due to the natural process of convection, "the chimney effect", of warm air rising. With wood chips added in the initial mix, the piles will self-aerate twenty-four hours per day with an aeration grate at the base of the pile, without the hassle of turning. Poke holes every three to six inches over the entire top of the pile, plunging down all the way to the ground or to the ventilated airflow base itself. Rebar is available at most hardware stores and is very inexpensive. Active, hot composting has the advantage of not over-heating, which is a cause of slow decomposition and odors. Current composting research has shown that pile temperatures over 150° F. for extended periods actually kills off beneficial bacteria. When it comes to heat, you can have too much of a good thing! To keep the pile from self-pasteurizing, a passive air system allows just the right amount of air to oxygenate and remove excess heat. Commercial composting facilities all over the world are switching to temperature controlled rates of air to take advantage of this important discovery. 9. Active, Hot Composting Once mixed, watered, formed, and poked, the material will become an active, hot compost pile. Within a day, the pile will heat to over 140° F. and will maintain elevated temperatures for weeks. The mass will shrink of its own accord and continue decomposing without additional turning. If the pile was under-mixed, over-watered, or is being initiated for the first time, turning after the first three to seven days will give the pile an additional boost. Another turn of the pile after 10 to 14 days will further accelerate decomposition, although turning while mixing in new material saves this additional step. Each time the pile is turned or new material is added, the pile should be poked again to keep the new layer from sealing off the air from the bottom. Once an active composting culture is established, the process of turning can be eliminated or reduced. Turn only when necessary for incorporating new material or blending undecomposed spots. A well-mixed and aerated compost pile can produce a compost ready for curing or mulching in three to four weeks without turning. If the pile cools prematurely or generates odors, turn it immediately! Blend in fresh material or add moisture as necessary. If the pile is over-saturated with water or is foul smelling, add equal quantities of dry leaves or straw. If no dry material is available, spread the compost out to dry. It is not neighborly to allow a compost pile to become an odor nuisance. Under-watering is the largest single cause of slow composting. A pile sitting in standing water is the largest single cause of odors. |
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