Posted by Tom Thomas on Fri, Mar 19, 2010 @ 06:01 PM
What is soil pH, and why is it important for my garden?
Some gardeners say that adjusting the soil pH is the single most important thing you can do to ensure healthy plants. It may be a matter of life and death for your garden. So what's the big deal about pH, anyway?
The scoop on soil pH
The acidity or alkalinity of your soil is measured by pH, which stands for potential Hydrogen ions. Alkaline soil is known as "sweet" and acidic is known as "sour." In humid climates, soil tends to be acidic, and in dry climates it tends to be alkaline.
pH is measured on a scale from 1 to 14:
pH less than 7: acidic soil
pH greater than 7: alkaline soil.
pH of 7 exactly: neutral (neither acidic nor alkaline)
How soil pH affects plants
pH affects the availability of nutrients in the soil to plants, and a proper pH level helps prevent soil-borne diseases.
Each plant has its own recommended range for soil pH, which you can research through a quick online search. Sweet potatoes, for example, prefer more acidic soil (4.5 - 6.0). Tomatoes, however, prefer more acidic to neutral soil (6.0 - 6.5) and asparagus prefers more neutral to alkaline soil (6.0 - 8.0).
Testing your soil pH
Check your soil pH regularly, at least twice per year. It's easy to find out the pH of your soil using a kit available at most garden stores, hardware stores, and online. A good garden center will most likely test a soil sample for you.
Test kits normally contain a test tube, solution, and a color chart. You place your soil in the tube, add a few drops of solution, shake up the tube, and let it settle for about an hour. Then match the color of the tube's contents to the chart.
A creative way to test your soil pH is to plant a hydrangea. If your soil is acidic, the blooms will be blue. If the soil is alkaline, on the other hand, the blooms will be pink.
Adjusting your soil pH
Before you use chemical products to adjust your soil pH, make sure you've read the instructions and wear protective gear, such as gloves and a dust mask.
It's generally easier to make your soil more alkaline than it is to make it more acidic. (Fortunately, nature tends to make soil acidic.) To make your soil more alkaline by increasing the pH, add hydrated lime to your soil, less for sandy soils and more for clay and peaty soils. Bone meal, ground limestone, chalk, and crushed marble all contain significant amounts of lime.
Making your soil more acidic by lowering the pH takes time and is best done over a growing season, or even several seasons. You may want to consider building a raised garden bed and filling it with neutral soil.
If your soil is already slightly acidic but you want to increase the acidity, add peat or iron sulphate to it. For a more dramatic increase in acidity, use ground rock sulfur mixed thoroughly with the soil before planting. To ensure the effectiveness of the sulfur in the root zone, the most crucial area affected by pH, apply Great Big Plants Organic Liquid Compost along with this mixture. The beneficial microbes contained in Great Big Plants react with the bacteria in the sulfur to create minor amounts of sulphuric acid. It is possible that you have enough sulphur in your soil already, but have a sub-optimal microbe population. Additions of Great Big Plants should remedy this condition.
Finding the pH balance
Adjusting soil pH is not a one-time task, but rather a regular process. Over time, nutrients will be leached from the soil, and the pH will shift. Keeping tabs on it at least twice per year will encourage your plants to grow efficiently and beautifully.