Soil Amendments:

- Soil amendments improve the physical properties of soils.

- Amendments are mixed into the soil.

- The best soil amendments increase water- and nutrient-holding capacity and improve aeration and water infiltration.

To be effective, an amendment must be thoroughly mixed into the soil. If it is merely buried, its effectiveness is reduced, and it will interfere with water and air movement, and root growth.

There are two main and broad categories of soil amendment; organic and inorganic.

Organic amendemnts:

These come from something that is or was living. Some examples include: Peat moss, manure, kelp, sawdust, and fish meal.

Organic amendments are most beneficial when trying to increase nutrient, water-holding capacities and improve drainage and aeration. This helps counter the drawbacks of sand-based soils and can also help to develop soil structure in clay based soils. It is generally preferable to use organic amendments in most situations. In fact King County is passing legislation later this year mandating the use of compost as an amendment in the retrofit of existing soils.

Inorganic amendemnts:

Inorganic amendments are either mined or created by man. Some examples include: dolomite lime, gypsum, sand, pea gravel, vermiculite and perlite.

One reason to amend soil with inorganic amendments is to improve porosity and thus increase water and air permeability of the soil. In clay soils, porosity can be improved with the of some inorganic amendments including sand or pea gravel. Coarse amendments should be of uniform particle size. Amendments with a wide mix of particle sizes tend to pack tightly and reduce porosity rather than increase it.

Factors to Consider When Choosing an Amendment

- long the amendment will last in the soil

- soil texture

- soil salinity and plant sensitivities to salts

- salt content and pH of the amendment.

Accurate soil analysis and soil management strategies are critical to maintaining plant health and the dynamic ecological systems that effect water quality.

Mulch

- Reduces soil water loss and erosion

- Moderates soil temperatures

- Retains storm water

- Can aid in good root development by adding needed organic matter to soil

- Reduces or eliminates weed growth

- Reduces soil compaction and runoff

Aside from the arguable benefit of enhanced aesthetics, mulching of planting beds is of paramount importance in the conservation of water resources. It is estimated that mulch reduces moisture evaporation for soil by anywhere from10-50%. In fact it has become such an essential tool in the struggle for water conservation that the State of California enacted a bill which requires the use of mulches in that state: the Xeriscape Act of 1989 ( Campbell , 2001).

In addition to reducing water loss, some types of mulch can almost eliminate the need for weeding while others significantly reduce it. Though mulching will not eliminate all weeds, it does make those that break through easier to spot and easier to remove. This benefit has the additional effect of minimizing the use of herbicides that are commonly used in lieu of manual weeding and have the detrimental effect of being leached into the groundwater and contaminating the water supply.

In addition to these benefits, mulch also insulates soil from extreme temperature fluctuations and thus can make the soil ecosystem more hospitable for many plant species. Mulches may be incorporated into the soil as amendments after they have decomposed to the point that they no longer serve their purpose .

One thing to be careful of, if using mulch, is its proximity to tree trunks. Mulch should not touch the trunk, but should extend out to the drip line when possible.