Soil Chemistry

Soil chemistry for organic gardeners is a simple task after you have a your soil tested. Your test report will serve as a blue print to assist you in building the correct conditions for your favorite plants. It is simply a matter of amending it with the missing components in the correct amounts.

The following are the basic elements that your test will reveal:


Up to ninety eight percent (98%) of all plant of growth comes directly from organic matter.

Not enough organic matter and your crops growth and health is limited from the very start. When it comes to soil chemistry organic matter cannot be stressed enough.

Organic matter supplies many nutrients for development and stimulates the propagation of micro organisms, earth worms and other beneficial creatures.

The end result is abundant microbial activity that improves the overall structure, resists compaction and increases air penetration. An organic matter level of five percent is a good goal to work for. This is one component of soil that you are not likely to ever have too much of, so don't worry about having even higher levels.

To supplement low OM levels, use either bokashi compost or compost that you have otherwise made. Most garden centers now carry a brand called "Nature's Blend, cotton burr compost."

This is also a good time to start thinking about starting a bokashi bucket or your very own compost pile to help supplement your soil as well as recycling your organic waste.

PHOSPHORUS (P) is the first element of soil chemistry, it boss of all the elements. It controls root, seed and flower development in plant life, as well as the processes of cell division and sugar formation. These sugar levels regulate the plant’s susceptibility to insect and disease.

POTASSIUM (K) is the next element of soil chemistry, often to refereed to as the universal helper. It stimulates rooting, photosynthesis, chlorophyll formation, starch formation and sugar functions.

Adequate levels of potassium reduce susceptibility to insect and disease outbreaks. Low test levels indicate the need for K fertilization, especially where a low cation exchange capacity is present.

MAGNESIUM (Mg) is considered a secondary macro nutrient. The chlorophyll molecule is built around the atom on Mg so this nutrient is essential to plant growth and viability. Excessive Mg can cause nutrient deficiencies. The result is lifeless, sticky mess that becomes easily waterlogged during rainy periods and will not absorb water when it has become hard during dry times.

CALCIUM (Ca) is considered a secondary macro nutrient but it is considered the most important element for the following reasons. Calcium helps to form stable aggregates which give it structural capacity to hold nutrients and absorb water and air.

These characteristics promote prolific microbial growth and earthworm activity. Calcium helps to neutralize toxins, assists in root development and carbohydrate movement as well as being involved in protein synthesis and reproductive tissue.

pH LEVEL, While this is not an element of soil chemistry it is nonetheless an important factor in maintaining the overall health of you organic garden. pH is the measurement of alkalinity or acidity of the soil.

For some vegetables it is very critical. Tomatoes, for example must have an acidic level or they are going to be prone to blossom end rot. For most vegetables if the pH level is too low, roots are unable to absorb the needed nutrients. You can fertilize but it will not help much at all. Growing in raised beds will allow you to tailor the soil to particular plants needs.

Use lime to raise you pH. It is readily available and easy to do!

This level is directly related to the level of Calcium (Ca) in your soil, which is why lime is added to raise the pH level.
As Calcium is used up, the level drops below 7.0 and becomes ‘acidic’. When you add lime (nutrient fertilization) you raise the level.

pH is a measure of the balance between hydrogen ions and ions of the base elements called cations. Areas that are acidic typically has an extra hydrogen ion on the roots. This 'binds' the roots from absorbing the nutrients. Adding Ca (lime) neutralizes the extra ion and allows proper growth. (This is why test results that indicate low pH levels often show very high levels of Phosphorus.)

If test results show that the soil is also low in Magnesium (Mg) then a dolomite lime is recommended, otherwise continue to use calcitic lime. For situations where Ca is low but P is sufficient you can spray Liquid Lime as a foliar feed to instantly supply Ca for the plants.

CATION EXCHANGE CAPACITY (CEC) is a measurement of y0our soils ability to hold cations (Ca, Mg, K, and Na). This capacity is influenced by the amount of clay and humus present.
It is measured from 0 for pure sand and100 for pure humus.

High quality soils range from 18-25 the best getting as high as 35. If your have a high CEC value it is holding a lot of nutrients which can be released for plant and microbial growth.

The whole reason for learning about soil chemistry is so that you can bring everything into proper balance. The good news is that once you reach the correct levels it will be perfect for growing healthy, nutritious, organic vegetables. That is what it is all about!

You are not likely to have to do it again for quite some time as long as you are regularly amending your garden soil with compost (organic matter)

Fall is on the way

Remember, chemicals kill more than just pesky weeds.