Have you ever been disappointed with the performance of your garden plants, even though you gave them the best care that you could? It is quite possible that the soil pH might have been the problem. The pH level of the soil determines which nutrients are available to the plants. The roots absorb nutrients only when they are dissolved in water. If the soil pH is not correct, some nutrients, such as nitrogen, potassium, phosphorus, calcium and magnesium, cannot be dissolved properly and as a result, they are unavailable to plants. These nutrients are “locked up”, thus your roses or tomatoes won’t grow or produce to their full potential.
What does soil pH mean?
When you are measuring the pH of your soil, you are actually measuring the number of potential hydrogen (H) ions, hence, the abbreviation to pH. The more hydrogen the soil contains, the lower the pH level and the more acidic the soil. The pH is measured on a scale of 0 to 14. If the pH is less than 7.0, the soil is said to be acidic, and if the pH is more than 7.0, the soil is said to be alkaline. If the pH is 7.0 the soil is neutral. To use a common example of something acidic, lemon juice has a pH level of 2.0. Baking soda is alkaline at 8.5. Pure water is neutral, or 7 on the pH scale. Generally, soils in moist climates tend to be acidic while drier climates are alkaline.
The acceptable pH range for all around gardening is 6.2-7.2, slightly acidic to barely alkaline. This range provides the best mix of nutrients for most plants. If the soil is too acidic or too alkaline, some of the nutrients will not be dissolved and thus they won’t be available to the plants, causing nutrient deficiency and an unhealthy garden. Below a pH of 6.0 (acidic), some nutrients such as nitrogen, phosphorus, and potassium are less available. Above a pH of 7.5 (very alkaline), iron, manganese, and phosphorus are less available. Most home garden plants prefer soil that’s slightly acidic at around 6.5.
Other nutrients such as zinc, iron, copper, aluminum become toxic to plants when the pH approaches 5.0, although some plants prefer acidic soils, such as camellias, orchids, peanuts, potatoes, and tomatoes. There are a few plants that require a soil pH of 4.5 to 5.5. These “acid-loving” plants include azalea, rhododendron, raspberry and blueberry. There are plants that prefer alkaline soil such as onion, cucumber, cabbage, cauliflower, date palm and acacia. Many desert plants will also thrive in alkaline soil.
Hydrangea flowers change color depending on the soil pH. Hydrangeas react uniquely to soil pH by producing blooms ranging in color from blue in acidic soil to pink in alkaline soil. The key factor causing this is due to the availability of aluminum. Acidic conditions convert the aluminum compounds normally present in the soil into a form that the plant can absorb, resulting in a blue flower. In an alkaline soil, the aluminum remains locked up in insoluble compounds, producing pink flowers. If the hydrangea is moved from an alkaline soil to an acidic soil its flowers will change from pink back to blue. So if you have a hydrangea in the garden it will be a good indicator of your soil pH level.
Many environmental factors, including amount of rainfall, vegetation type and temperature can affect soil pH level. In general areas with heavy rainfall and forest cover have moderately acid soils. Soil in regions with light rainfall and grass cover tend to be near neutral. Areas of drought and desert conditions tend to have alkaline soils. The pH of developed soil will often differ from that of the native soil. During construction, for example, the topsoil may be removed and replaced by a different type. Hence, your garden soil pH could be very different from your neighbor’s. The only way to know the pH for sure is to have the soil tested. Testing kits are available at garden and hardware centre’s or can be purchased online. These are supplied with all instructions on their use and many also include advice on how to adjust the pH of your soil.
It is easier to neutralise an overly acid soil than it is to neutralise an alkaline soil. Highly alkaline soils may require several amendments applied over several months or even years. Adjusting soil pH is an ongoing process, not a one-time event. There are many factors that leach nutrients from the soil, altering the pH levels over time.
Soil can be brought back into balance quickly if it is close to the ideal pH range of 6.2 to 7.2. The best way to make pH adjustments is to incorporate compost and mulch. Adding organic matter to the soil also tends to make both acid and alkaline soils more neutral. On the other hand, applying chemical fertilizers makes soil more acidic. So if you apply too much chemical fertilizer to your garden you will find that the soil will become more acidic over time. If you instead use organic compost, your soil will be more balanced and have a healthier pH range.
If you need to raise the pH of your soil (your soil is too acidic), you need to add alkaline material. The most commonly used alkaline material is powdered or ground limestone. Ground limestone is less potent and slower acting than powdered limestone. Other options for raising soil pH include woodchips, bark or wood ashes. Wood ashes contain up to 70 percent calcium carbonate, as well as potassium, phosphorus, and many trace elements. Because it is powdery, wood ash is a fast acting alkaline material.
To lower the pH of your soil (your soil is too alkaline) you need to add acidic material. Options include pine needles, shredded leaves, sulfur or sawdust. Pine needles are a good source of acid and mulch. Over time, you can lower the pH of your soil by the regular application of organic matter such as compost or manure. Add soil testing and pH adjustment to your permanent list of garden tasks to produce healthy plants and prolific blooms. The rewards will be well worth the trouble!
