Organic Matter: “Black Gold” for the Garden

Organic Matter: “Black Gold” for the Garden

weevil parasitoid

Homemade compost from kitchen scraps (top) or leaves (bottom) is a great amendment option that is usually abundant, weed free, and low in salts.

Plants need water, air, nutrients, and sunlight to grow.  Proper soil preparation in the vegetable garden will increase plant health by facilitating gas exchange as well as water and nutrient uptake.  Conversely, soils with poor structure can have drainage problems, nutrient deficiencies, and ultimately result in decreased plant health or death.  A common issue in Utah is the alkalinity of garden soils.  Alkaline soils cause certain micronutrients to become less available leading to nutrient deficiencies in garden plants.  Iron chlorosis, for example, is a deficiency of iron available for plants and is one of Utah’s most troublesome nutrient deficiencies.  Poor soil drainage, compaction, lack of nutrients, high soil pH, or reduced plant growth and can be improved by amendment with high quality compost, or "black gold".


  1. increases soil moisture retention
  2. improves soil structure
  3. decreases soil compaction
  4. improves soil drainage and tilth (workability)
  5. certain soil-supplied nutrients more available
  6. provides essential nutrients for plants
  7. provides food and habitat to many soil macro- and micro-organisms

Organic matter (once-living sources of carbon-containing materials) acts as a binding agent or the “glue” that holds soil particles together and is the key to creating a well-structured soil.  Soil structure refers to the combination of primary soil particles such as sand, silt and clay.  Soils with organic matter will have improved drainage, higher water holding capacities, increased aeration or gas exchange, and promote root growth.


Organic matter can be applied as compost or mulch.  Compost is organic material that has decomposed to a state where the original parent material is no longer recognizable.  It looks and smells like rich garden soil and is typically incorporated with rotary tillers or other mechanical implements to improve soil quality.  It can also be incorporated using the double-digging method which involves digging soil from an area of the garden, mixing it with organic material, and then returning it to the same area.  Mulch is material that is applied to the soil surface and is usually not fully decomposed.  It is typically used to smother out weeds, protect trees and shrubs, reduce evaporation, or beautify the landscape.  Incorporate 2 to 3 inches of organic matter 6 to 8 inches deep into the soil annually to improve garden soil over time.  In heavy soils, it may take 2 to 3 years before improvement is seen.

DO Compost
DON'T Compost
Vegetable/fruit scraps Meats
Leaves Bones
Wood chips, sawdust, or bark Large branches
Manure Dairy products
Grass Clippings Synthetic products
Paper Plastics
Garden and/or canning waste Pet wastes

Keep in mind that each type of organic matter varies in the amounts of nutrients (N, P, K, etc.) it provides.  Some types may be high in certain nutrients and low in others, so it’s important to know which type of organic matter and fertilizers the soil needs.  Soil testing before adding organic matter will help ensure that your garden will have all the needed nutrients and be the ideal place for plant growth.  Soil samples can be submitted to the USU soil testing laboratory (see for more information).

Organic matter can be the single most important amendment that improves plant growth in Utah soils.  Patience is the key to using organic matter to improve your soil; it takes time for garden soil to improve and differences in plant growth and health may not be seen the first year organic matter is incorporated.  Keep feeding the soil and the soil will feed your plants.

Resources (orange text links to web)

Preparing and Improving Garden Soil

Backyard Composting in Utah

Using Compost in Utah Gardens

Using Mulches in Utah Landscapes and Gardens

Selecting and Using Organic Fertilizers

Solutions to Soil Problems (link to a series of fact sheets)

weevil parasitoid
Mulches, like the straw used above, can reduce moisture loss from soil, moderate surface soil temperatures, control annual weeds and grasses, reduce compaction, and decrease runoff and soil erosion.

-Bonnie Bunn, Vegetable IPM Associate