How to Assess and Correct Soil pH

A Gardening Practice that can Vastly Improve Dirt Based Gardens

Oct 4, 2007

Many times Hydroponic gardeners have results that seem extraordinary; but, with proper attention to detail, these same results can be had by soil based gardeners as well.

Successful hydroponics depends first and foremost on monitoring the pH of the nutrient solution, yet soil based gardeners often neglect this critical factor with their chosen growing medium.

To more specifically define an acidic or basic substance, scientists devised a numerical scale, called a pH scale, to categorize substances as an acid or base. Numerically, the scale is from 0 to 14, with 7 being the midpoint. Any solution or substance having a pH value of less than 7 is known as an acid and above 7 is considered a base. Seven is considered neutral. A special test paper can be used to numerically measure pH. Depending on the acidic or basic nature of the test solution, the paper turns a specific color which can be matched to a standard color chart correlated with pH values. A pH meter can also be used to measure the pH of a solution or substance like soil. The meter consists of a probe, which is placed in the solution and the meter displays a digital readout of the pH.

Importance in Gardening - The pH value of soil and water is a critical variable for all gardeners to consider. Particular crops and plants require a specific pH to thrive and produce high yields. Whether it is growing tomatoes in a small garden or corn over many hundreds of acres, knowing and maintaining the correct soil pH is a must. A pH of 6.5 is found to be the most favorable for the availability of all plant nutrients and is the pH to which most soils and soil based composts are adjusted.

Nitrifying bacteria work best above pH 6. Therefore nitrogen is more available. Vegetables vary to some extent in their requirements, but most garden crops will do well with a soil pH of 6.2 to 6.8. This is a little below neutral, or slightly acidic. If soil pH is too high or low, poor crop growth will result, largely due to the effects pH has on the availability of nutrients to plants.

It may not be possible to water with pH adjusted water, but it is still helpful to test the water source to know which way it is moving the ph of the soil. For container plants that are watered by hand it is possible to easily correct the pH of the water using the same pH-up or pH-down products used in hydroponics or aquaculture. These can be purchased at fish stores or hydroponics suppliers.

Water pH test kits can be purchased for less than $5 and soil test kits that use paper strips can be purchased for around $5. pH meters that are inserted into moist soil to test pH can be purchased for $12 and up. The good news is that most of these kits come with charts showing the optimum pH for various garden plants and if they don’t come with the kit, such charts can be found online.

How to Amendments Levels - Lime and sulfur are common amendments to change soil pH. Dolomite limestone (calcium carbonate and magnesium carbonate) add calcium and magnesium and increases the pH. Agricultural (elemental) sulfur is used to acidify alkaline soil. The amount to add depends on the current and the desired pHs. Fortunately, most horticultural lime and sulfur products provide application charts showing how much is needed to move the PH from the tested level to the desired level for a particular size garden or planting container.

By monitoring and modifying soil pH, as needed, the soil based gardener will take a huge step towards matching the strengths of the controlled hydroponics environment. Plants grown in soil or media with the proper pH can readily use the nutrients available to them resulting in spectacular gardens. See the following articles for additional information:

The copyright of the article How to Assess and Correct Soil pH in Vegetable Gardens is owned by Christopher J. Kline. Permission to republish How to Assess and Correct Soil pH in print or online must be granted by the author in writing.