Have you ever wondered how those deodorants which look like a stick of marble work? They work because they change the pH on your skin surface to a more alkaline environment, making the area where it is applied less hospitable to odor-causing bacteria.
A soil test last fall revealed that the pH was quite high in the VegHeadz demonstration vegetable garden at the Leon County Extension office. Plants did not thrive in our spring garden and we had a lot of bug problems.
So what is pH and why is it important? pH stands for potential of hydrogen. Hydrogen directly affects the acidity or alkalinity of your soil. The concentration of hydrogen ions in a sample can be measured, revealing the acidity or alkalinity of a substance such as soil, water, or blood. The pH scale ranges from 1.0 to 14.0 with 7.0 as neutral. pH above 7.0 is alkaline or basic, while pH below 7.0 is acidic.
Your blood has a pH ranging from 7.35 to 7.45, slightly alkaline. If blood pH exceeds that range in either direction, you will rapidly become ill, and will soon die if it is not corrected.
Every living organism exists within a certain range of pH. Some organisms have a very narrow tolerance for changes in pH, such as our own bodies. Others, such as plants, can survive in a wider range of pH, but may only thrive within a prescribed range. Most plants in your yard and garden can survive in soil with a pH from 6.0 to 7.5. Acid loving plants like azaleas, camellias, gardenias, and blueberries prefer a lower pH.
You can apply as much fertilizer as you like, but if the pH is out of the desired range, your plants cannot access the nutrients in the soil. Due to the complex interaction of pH and nutrients it is difficult to determine whether the pH is incorrect or there is a nutrient deficiency when plants do not thrive. A soil test is the only reliable way to do so.
The level of acidity also affects the activity of soil microorganisms--fungi, bacteria, algae--which play an important role in converting nutritional elements from one form to another as well as breaking down organic matter to a form accessible to plants. They are also helpful in degrading pesticides and other chemicals in the soil, and in suppressing disease pathogens.
The interactions between soil organisms and plants is not yet well-understood, but maintaining soil at a desirable pH is well-known to be beneficial to both the microorganisms and the plants and contributes to resistance to pests and plant diseases.
If a soil tests reveals a pH between 5.5 and 7.0 in your yard or garden, there is no need to adjust pH. Acid-loving plants can be accommodated by applying azalea and camellia fertilizer.
Soil pH can be raised or lowered, but a better approach is to select plants which prefer the existing pH. Applying chemicals to change pH has only a temporary effect. For instance, the soil near your home may have a higher pH, reflecting alkalinity from masonry materials in the foundation or left there during construction. Alkaline materials will continue to leach into the soil throughout the life of the home, so it is better to select plants which prefer a more alkaline environment rather than attempting to lower the pH. (Right Plant, Right Place) Organic mulch and soil amendments can slightly lower pH over the long term. Soil tests for your landscape should be done every 2 to 3 years and compared to previous results to determine if any major changes are taking place.
For individual plants and small vegetables gardens or container plants, changing the pH is possible. To raise the pH or make the soil less acidic, lime in various forms can be added. To lower the pH, or make the soil more acidic, elemental sulfur can be added, and peat moss, which has a pH around 4.0, can be incorporated to effect change over time. This should be done by following directions obtained from a soil test, as well as following the directions on the packaging of any amendments. A soil test before each planting season is ideal, particularly if you are amending the soil.
So what did we do at the VegHeadz demo garden to bring our pH down into a more desirable range? For each 25 foot row (about 3 feet wide), in a wheelbarrow, we combined 1/3 garden soil from the row, 1/3 mushroom compost, and 1/3 peat moss plus 2 cups of elemental sulfur. We mixed this well and added it back to the row. This only lowered the pH by two tenths of a point, possibly because mushroom compost tends to have an elevated pH. We did have a very nice garden this year with a minimum of pest and disease damage (except in our tomatoes). We will need to amend again if we want to lower the pH some more, and amendments only last for a year or two. We will be doing another soil test before we plant our fall garden.
Follow Up: For many seasons, we’ve been adding free wood chips to pathways to suppress weeds. Over a period of a year or so these decompose and more wood chips are added. This creates compost on site. At some point after the amendments were added described above, we dug the compost in some pathways and added it to the garden beds. A subsequent soil test revealed that the pH was perfect in those rows and we have not needed to add pH adjusting amendments since that time.
Soil test kits can be obtained from the Leon County Extension Office. They contain specific directions about gathering soil samples and obtaining a report. More information about Soil pH in your landscape or garden and the interaction of microorganisms can be found at http://edis.ifas.ufl.edu. Search for Publications #SL 256 and #HS1181
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