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Organic Matter and Soil Amendments


Part 4 of 4

Organic mulches, including tree leaves, grass clippings, straw, wood bark, and wood chips, decompose and contribute to soil organic matter. Using organic materials available from your yard or neighboring yards keeps them out of landfills and recycles nutrients from plants to soil and back to plants.

  • Mulched or shredded leaves rot faster than whole leaves and are an excellent substitute for wood or bark mulches. They can also be spread on vegetable and flower beds to protect the soil over the winter. Move the leaves to plant in spring and then re-apply them as mulch.
  • Grass clippings (no herbicides) can be used as a mulch around plants or added to your compost pile.
  • Leave plant roots in the soil to decompose by cutting off the tops of annual plants when their season is over.

Mushroom compost
Compost from mushroom farming is made from manures, wheat straw, corn cobs, feather meal, peanut meal, peat moss, lime, etc. Once the mushrooms are harvested the compost they grew in is removed and sold. The approximate N-P-K analysis is 2.75-1.5-1.5. It can have high soluble salt levels and should be watered prior to planting to leach excess salts.


ARTICLE Organic Matter and Soil Amendments Mulch Mycorrhizae

Beneficial fungi that occur naturally in soil and grow symbiotically on plant roots (ectomycorrhizae) or in plant roots (endo mycorrhizae). It’s estimated that 80% of all land plants on Earth are colonized by endo mycorrhizae. They extend the root system by sending out tiny filaments to forage for water and nutrients used by plants. They have been shown to also help plants fend off pathogens. Some crops, like blueberry, rely heavily on mycorrhizae for nutrient uptake. These fungi are prevalent in Maryland soils. Research does not show any benefit to garden plants when mycorrhizae are purchased and applied to the soil. This is especially true when plant nutrients and soil moisture are plentiful, and also because commercial mixes contain a narrow subset of mycorrhizal species. You can increase the populations of beneficial fungi through plant diversity (especially native plants), reduced soil disturbance, and planting cover crops.

Peat moss
Partially composted moss mined from prehistoric non-renewable bogs. Peat moss is light and porous, absorbing 10-20 times its weight in water. Contains little nutrient value, but has a  high nutrient-holding capacity. More sustainable options like compost and pine bark fines should be substituted when possible.

Pine bark fines

ARTICLE Organic Matter and Soil Amendments Mulch Pine Bark

Finely shredded pine bark product that retains moisture. Sometimes a component of soilless growing media. It can be incorporated into annual and perennial beds. Very acidic, so watch soil pH levels if large quantities are used.

Can be used to improve the soil for succulents, but a minimum of 50% by volume is necessary. Use only coarse builder’s sand, not play sand. Adding organic matter, not sand, on a yearly basis is the key to improving clayey soils.

Only well-decayed sawdust should be incorporated into the soil. Fresh sawdust can burn plant roots and “tie up” nitrogen as it decomposes. (Soil microbes that break down the high-carbon sawdust need nitrogen and can access available nitrogen more easily than plant roots.) Good for mulching blueberry beds.

There are no quality standards for topsoil and it is not a regulated product in Maryland. If you plan to buy topsoil in bulk, go to a reputable nursery or topsoil dealer and ask for soil test results and information on the origin of the soil, on-site mixing, and storage practices. Examine the soil before purchase or delivery. Topsoil should be dark and crumbly with an earthy smell. Do not purchase soil that is very high in sand or clay, foul-smelling, or has grayish mottling or a chalky, sticky, or rough texture. Some businesses sell a topsoil/compost mix which can make an excellent growing media for raised beds.

  • The bags of “organic soil” you may see for sale typically don’t contain topsoil (i.e. mineral soil with clay, silt, and sand particles). These products contain various combinations of wood waste, bark fines, compost, peat moss, and other organic materials.

Wood ashes
Ashes from wood and pellet stoves contain large amounts of potash (10%) and calcium carbonate (25%). For liming purposes, two pounds of wood ash is equivalent to approximately one pound of calcitic limestone or dolomitic limestone. Use ashes based on soil test results and don’t exceed 20 lbs./1,000 sq. ft. per year. Apply wood ashes in the fall or winter. Dispose of excess ashes in the trash, not the compost bin.

Worm castings
Worm ‘poop’ produced by red wiggler (Eisenia fetida) and other earthworms that is rich in nutrients and microbes. Commercial castings are produced by vermicompost businesses that use worms to convert organic materials into compost in a controlled environment. Vermicompost is a combination of worm castings and partially decomposed organic materials. You can produce your own vermicompost in a homemade or purchased bin.

An excerpt from the article “Organic Matter and Soil Amendments“, courtesy of the University of Maryland. Author: Jon Traunfeld, Director HGIC, Extension Specialist, Fruits and Vegetables

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  • University of Maryland Extension
    University of Maryland Extension (UME) is a statewide, non-formal education system within the College of Agriculture and Natural Resources and the University of Maryland Eastern Shore.

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