What is soil pH? Soil pH is the measurement of the concentration of hydrogen ions in a soil. By definition a hydrogen ion is an electrically charged atom or molecule. The more hydrogen ions present in the soil, the more acidic, the fewer ions present the more alkaline a soil will be. Very scientific isn’t it? In gardener and greenhouse grower terms, pH is the measurement of how “sweet” (alkaline) or how “sour” (acid) a soil is, whether that soil be garden soil or a soilless mix.
A sliding scale is used to measure pH with readings between 0 and 7 showing an increase in acidity and between 7 and 14 showing an increase in alkalinity, with 7 being neutral. A very important measurement, pH should not be taken lightly, because pH effects how your plants grow. Your soils ph levels should be checked each year before planting.
Gardening Tips: Why Aren’t My Plants Growing Right – Could It Be the pH?
There are different ways to do this. Take soil samples from different areas in your garden and send it out to your local cooperative extension. They will return to you a comprehensive list of the elements present in your soil and what to do to make adjustments, if necessary. Local garden centers sell pH-testing kits that contain dyes that are mixed with the soil and water and compared to a color chart to determine pH. Usually acid soils return a yellowy-orange color and alkaline give a greenish-blue result. The ideal pH level for gardens, lawns and vegetables is a range from 6.0 to 7.0. Ornamentals like a range of 5.5 to 6.5.
Too high or too low pH levels affect the plants ability to absorb nutrients that are present in the soil, this includes soilless mixes as well. Nitrogen becomes unavailable to plants at a pH below 4.6, likewise, phosphorous at 4.7 and potassium at 4.9. However, there are some plants that prefer and tolerate strong acid soils, for example, azalea, rhododendrons, blueberries and white potatoes. Soil pH also influences the effects on the activity of beneficial microorganisms. In strong acid soils, bacteria cannot breakdown organic matter, thus allowing the organic matter to accumulate to high levels, which then ties up the nitrogen that is contained within it.
Areas that receive heavy rainfall tend to have acidic soils and light rainfall areas tend to have and alkaline soil. How do you make adjustments? One key ingredient used to decrease acid levels is lime, which counteracts the acidifying nature of fertilizers and rainfall. It is added to increase your pH and also has the advantage of adding calcium and magnesium to the soil. The amount of lime applied to amend a soil is determined by a few factors: what the present soil pH level is, is the soil sand, clay or silt, and what are the pH preferences of the plants you will be growing. Three types of lime are available from garden centers; hydrated, which is best for a garden because it is quick acting, crushed, which is slower acting and longer lasting and dolomitic lime, which is very good because it contains the trace element magnesium.
Lime’s main function, in addition to adjusting acid levels, is to “unlock” much needed nutrients in the soil that become unavailable to plants because of high acid levels. Sulfur decreases alkalinity and is used less often because soils tend to be acidic more often.
The plants you are going to grow in containers pre-determine the type of soilless media you should use. Acid loving plants should be grown in a media that has a low pH level and alkaline lovers in a high pH mix. Levels can change during the course of the growing season and there are ways to correct pH in containers. Chemical fertilizers, except calcium nitrate, lower the pH of a soil by producing acids as they decompose. Calcium Nitrate, a form of nitrogen found in some fertilizers, is used to mitigate the effects of soil acidity, so your readings will determine which fertilizer you will be using at any given time. Checking the containers pH, using a pH meter, is much more convenient than taking soil samples. Check the pH often.
TO RECAP:
1. pH is a measurement of the soils acid and alkaline levels
2. pH effects the plants ability to take up nutrients
3. ideal levels are 6.0 to 7.0, exceptions being acid loving azalea and rhododendrons
4. test the soil by sending samples to your local county extension or by using a pH test kit or meter
5. too low a ph or too high causes nutrients to become “locked-up” in the soil
6. add lime to increase the pH and “unlock nutrients”. Sulfur is used to lower pH.
7. there are three kinds of lime available: hydrated, crushed and dolomitic
8. soilless media used in container crops can have pH levels adjusted by using different types of fertilizers
9. “sweet” soils are alkaline and “sour” soils are acidic.
10. pH levels change slowly. Check the pH every year. Do not assume your plants need fertilizer if they are not growing to their potential. Check the pH first!
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