Turn Green into Gold –
Leaves Improve Soil and Benefit Trees
Fall Tree Tips from the Chicago Botanic Garden: Shred your leaves and apply to your tree and garden beds to create healthier soil.
Give Your Yard and the Environment a Boost
Did you know that over 10,000 tons of leaves are collected in Chicago during an average fall leaf season?
Reducing the amount of trash that reaches landfills and incinerators has become an urgent matter in many areas across North America. Yard waste is one of the easiest things to divert, yet millions of tons of lawn and garden waste go into landfills annually. We need to compost more and throw away less. Composting not only keeps these materials out of landfills but also recycles lawn, garden, and kitchen waste into a rich soil amendment for our gardens. On a grander scale, composting is an essential component of conservation and responsible stewardship of the environment.
Rake accumulated leaves into lawn areas before shredding.
Collecting and Applying your Leaves
Tree leaves make especially good compost because tree roots draw in nutrients and trace minerals, a large portion of which is held in the leaves. Leaves tend mat unless they are shredded, and matted leaves take longer to break down. Shredding leaves also reduces the bulk by about two-thirds, and speeds up the decomposition process as more surfaces are exposed to decomposition. The easiest way to shred leaves is to use a bagging lawnmower, although shredders are available for rent or purchase. As you collect the shredded leaves, you can apply directly to existing mulch beds in a one- to two-inch deep layer. In wind-prone areas (e.g. around the base of individual trees), you can top-dress with wood mulch to keep the shredded leaves in place. You can also mix a portion of your shredded leaves in with your garden compost.
What is Compost?
Compost, often referred to as “black gold,” is simply a mixture of soil and pieces of plants that have decomposed to the point of being unrecognizable. It has a rich, earthy smell if properly made. Dark brown and crumbly, compost makes an attractive addition to any garden. And the things it does for the garden are nothing short of magic!
Compost is the ultimate soil conditioner since it improves both texture and structure, giving soil that much-desired tilth that’s perfect for growing vegetables and flowers. Plants mulched with compost also have a degree of disease resistance that they might not normally have.
With heavy clay soils, compost loosens and aerates, making them drain better and making their nutrients more accessible to plant roots. In sandy soils, compost increases the water-holding capacity and nutrient-holding ability.
Mulching with compost also moderates soil temperature and provides some nutrients for the plants. Organic matter naturally changes soil’s basic chemistry to allow release of nutrients for use by the plants. The plants become stronger, healthier, and more easily able to fend off attacks from diseases and pests.
Understanding the Basics
The process of composting is simple: microorganisms in the soil consume the nitrogen in plants and manures and break down the ever-present carbon, changing the plant tissues into visually unrecognizable forms. This process gives off energy in the form of heat — which is why compost piles steam when turned.
Composting requires four basic components to set the process in motion: a blend of organic materials such as manure or garden waste, a population of microorganisms that function as decomposers, air, and moisture. Composting does not require an involved recipe, but rather a basic understanding of combinations that work well. Much of the knowledge you gain will be by trial and error. And, given varying temperature and rainfall, what works one time may not work the next.
Organic Materials
All garden and yard waste contains nitrogen and carbon. Decomposers consume carbon for energy and nitrogen to multiply. The more decomposers there are, the faster and more efficiently compost will be made.
Decomposers work most efficiently when the carbon-to-nitrogen ratio is between 25:1 and 30:1. The various types of garden waste have differing ratios. For example, dry leaves have a ratio of about 50:1, grass clippings about 19:1, and sawdust about 500:1. Finished compost has a ratio of around 10:1. Sawdust alone will break down very slowly since the decomposers have little nitrogen to reproduce, but the addition of a nitrogen source will speed the process.
It’s not critical to know exact ratios when home composting, but it is helpful to have a general idea of the ratios of common garden materials. Dry, bulky materials such as leaves, stems, straw, and sawdust have a high ratio of carbon to nitrogen and will usually require additional nitrogen to achieve an ideal proportion. Fresh, green, succulent materials such as grass clippings, weeds, and fruit and vegetable peelings have a low ratio of carbon to nitrogen and usually require little additional nitrogen to reach a good proportion.
Apply shredded leaves to planting beds. Courtesy Southern Living.
Materials to use
The more variety you have in your pile, the more diverse will be the nutrients in the final compost. Also, the smaller the size of the particles, the faster the pile will decompose. If possible, shred large pieces before adding them to your pile.
Use all types of landscape debris such as lawn clippings, leaves, weeds, hedge clippings, dead flowers, pine needles, and straw. Use kitchen wastes such as fruit and vegetable trimmings of all kinds, corncobs, melon rinds, peanut hulls, coffee grounds, eggshells, and tea leaves. Also feel free to use manures, wood ashes, hair, sawdust, and wood shavings.
Materials to avoid
Avoid adding stems or branches larger than 1 inch in diameter since they decompose very slowly. Also, it is very important to avoid meat, bones, oils, and other animal products. They are not only slow to decompose, but also make a compost pile stink and often attract animals.
Do not use manures from dogs, cats, or birds because they may contain parasites. Other manures are great additions to a compost pile, as long as the manure is from a plant- or grain-eating animal.
Weed seeds and plant diseases are killed by the heat in a functioning compost pile, so as long as your pile reaches high enough temperatures to steam, you can add weeds and diseased foliage. Avoid weed seeds and plants you know to be diseased if your pile does not steam when turned.
Aeration
Air is essential to the microorganisms making your compost. Without oxygen they will die, and a pile that has no oxygen (anaerobic) usually smells bad because the dying organisms release ammonia and sulfur. The best way to ensure that your compost pile has plenty of air is to use a variety of materials, layer them, and turn the pile frequently to aerate it. Also, to avoid compression, limit the height of the pile.
Spread leaf compost on tree mulch rings and lightly scratch in to boost soil nutrition and moisture retention.
Moisture
Water is also essential to the decomposers, and a properly working pile should feel like a squeezed sponge. Too much or too little water will stop the decomposition process. If you add plenty of green, succulent material, it may provide enough moisture without adding water; a pile with more dry materials will benefit from an occasional sprinkling. Locate your compost pile in a somewhat shady spot to prevent the sun from drying it out, use a raincover when needed, and make sure the pile sits on a well-drained area. If a pile does become too wet, add more dry materials to reach a balance.
Temperature
The microorganisms that are working your pile give off heat as they break down the plant matter. A working compost pile will build in temperature until the maximum breakdown is reached, and then the temperature will subside. Checking the temperature regularly with a soil thermometer will let you know whether the pile is working properly and when it is essentially finished. The temperature of a pile can reach as high as 160 degrees, high enough to kill even the most stubborn weed seeds and disease organisms. Satisfactory results can be achieved at a temperature of 120 degrees, however. When a pile has cooled and cannot be made to reheat by turning, it is finished and ready to use. By this time it should be a dark, crumbly material that smells like freshly tilled soil.
How to Build a Compost Pile
The most efficient compost pile is arranged in layers with fairly uniform distribution of organic material. Few home gardeners have all the resources they need for the “perfect” pile all the time, so the construction of layers is usually a matter of personal taste and the availability of materials.
An easy recipe for a typical pile is a layer of vegetable waste such as potato peelings and carrot tops, grass clippings, hay, straw or weeds; a layer of soil that adds microorganisms to the pile; and then a layer of manure or a handful of commercial fertilizer to add extra nitrogen to feed the microorganisms. If most of the materials are green and succulent such as grass clippings and vegetable waste, the extra nitrogen is usually not necessary since these wastes break down quickly.
The depth of the layers is not critical but thick layers take longer to break down than thinner layers. A pile can have continual layers built until it is about 3 feet high. A height greater than this makes the pile unmanageable, and the weight may cause the pile to compact, reducing air circulation.
The key to quick composting is turning the pile. The center of the pile heats up and decomposes more quickly than the outer edges, so turning and mixing up the pile will help all the materials decompose.
After you have built your 3-foot-high pile, stop adding materials to it. Use a manure fork or tool of your choice to mix the pile thoroughly. One of the easiest ways to do this is to have an empty bin to turn it into. If you turn the pile as often as every three days, you will have finished compost in about two weeks. Turning it less often means a longer wait for usable compost. Some gardeners construct a pile and leave it without turning for the season.
The pile is finished when it no longer steams and has few recognizable plant parts in it, and is reduced to about half of its original volume. If you cannot use your finished compost immediately, arrange to cover it so that rain doesn’t leach its nutrients.
Bins
Although there are countless types of commercially made bins available, it is fairly easy to construct your own system. One possibility is to build round wire cages to hold the compost. A very popular system that is one of the most efficient is the three-bin system. The first bin holds fresh garden waste, the second bin holds working compost that is turned regularly, and the third bin is filled with finished compost. When the first bin is full, the finished compost in the third bin is spread onto the garden. The new pile in the first bin is then turned into the third bin to begin working. The working pile in the second bin should be almost finished and ready to use. A new pile can be started again in the first bin.
These bins can be constructed from wood or wood and wire. Whatever the materials, it is necessary to build them so that they are easily accessible from the front, so that they can be covered if necessary and so that they allow plenty of air circulation. Rot-resistant wood will make them last longer.
Troubleshooting
Bad odor
Odors are caused by lack of air, too much moisture, or unsuitable materials. Correct by turning the pile and adding dry materials. Remove any unsuitable materials.
Slow decomposition
Lack of moisture retards natural processes. Correct by moistening and turning the pile.
Warmth and dampness only in the center of the pile
The pile is too small. Add more material.
Lack of heat
If a pile does not heat, it is deficient in nitrogen. Correct by adding green material or a nitrogen source. Also check air and moisture content.
Using Your Black Gold
Compost is a superb soil amendment, topdressing, and mulch. Use it in vegetable and flower gardens, and tree and shrub borders, as well as on the lawn. To amend the soil, dig compost several inches into the existing soil. In annual flower and vegetable beds, this can be done every year. Through the growing season, spread compost around plants to give them an extra nutritional boost. In permanent plantings, use compost as an attractive mulch, and then scratch it in lightly at the end of the season. For trees and shrubs, apply a layer of compost under a decorative layer of shredded bark or wood mulch. Use compost in containers too, as part of a potting mix.
Composting is a relatively easy way to give your garden a boost. Put the powers of compost to work for you, and know that your efforts benefit the environment.
(excerpted from Chicago Botanic Garden Plant Facts No. 41: Compost. For more information, visit www.chicagobotanic.org)