As you may have observed from your gardening experiences and past columns, plants can be fussy things. The right location, amount of sunlight and 101 other factors influence your plant’s growing ability. One factor which is very beneficial in understanding before putting that new plant into the earth is soil pH. In chemistry terms, pH is a measure of how acidic or alkaline a solution is, while soil pH is a measure of how acidic or alkaline the soil is. Soil pH is measured on a scale of 1 to 14. If your soil has a pH value of less than 7 then you have acidic soil. On the other hand, if your soil has a pH value of greater than 7 then you have alkaline soil. A pH value of 7 is neutral, meaning the soil is neither acidic or alkaline.
Knowing the pH value of your soil before planting is very important as it has a direct influence on the health of the plant. The reason for this is that soil pH affects the availability of nutrients within the soil and plants have different nutrient needs. For example, the nutrient nitrogen, a very important plant nutrient, is readily available in soil when the pH value is above 5.5. Similarly, the nutrient phosphorous is available when the pH value is between 6 and 7. If a plant is placed into the wrong kind of soil, it will be lacking in nutrients that it needs which will promote disease. In general, the best pH value range for soil is approximately 6 or 7, as this is the range in which most nutrients can be readily available. The majority of shrubs, trees perennials, annuals and vegetables prefer soils in this range. There, of course, are a few exceptions.
Finding out the pH of soil is usually very simple if you purchase a pH kit at a garden supply nursery or store. The pH testing kit should include a small container / test tube, testing solution and a colour chart. A sample of soil is taken from your garden, placed into the container / test tube and a few drops of testing solution are added. The container is then shaken and left for a certain period of time. The colour of the sample in the container is then compared against the colour chart to determine the pH value of the soil. Note that if you want to determine the soil pH of a large area, it may be a good idea to take soil samples from many different locations, combine the samples and then perform the test on the combined sample. If you have multiple gardens you want to check, then you should perform a test for each garden separately, especially if you are planning on planting certain types of plants that have customized pH requirements.
If your soil is acidic or slightly acidic you can take steps to make it more alkaline to accommodate the plants you want to put there. You can make your soil more alkaline (increase its pH value) by adding a form of lime. Lime is a compound of calcium or calcium and magnesium. It is usually applied in the form of ground agricultural limestone, burnt lime or hydrated lime (slaked lime). The smaller the limestone particles then the quicker your soil will become more alkaline. For this reason. hydrated lime will offer the quickest performance because it is slightly soluble in water so it can permeate the soil quicker and reduce acidity faster. Increasing the pH of your soil is not an overnight process and it is best to allow two to three months to allow the lime to neutralize the acidity of the soil.
Some ornamental plants and fruit plants like blueberries require an acidic soil. To make your soil more acidic (decrease its pH value) you can use either aluminium sulphate or sulphur. Aluminium sulphate is the quickest acting as it will increase the acidity as soon as it dissolves into the soil. The downsides are though that its effects can be short term and it is possible to over-apply it. The more recommended but slower way to increase your soil pH is to use sulphur. Sulphur converts to sulphuric acid with the help of bacteria in the soil, but this takes time depending on factors like the presence of bacteria, texture of the soil and moisture levels. This could take months if conditions are not ideal.
Most gardeners do not give a second thought to the pH of their garden soils and for the most part, if your plants seem to be doing well, then the pH is probably in the proper range. If you do seem to be having evidence of poor growth then this should be the first step to help determine what your soil may need. I have had various calls from gardeners in the past asking for me to tell them what is happening to their garden “a few years ago it was great and now nothing will grow.” A few times, upon a quick observation, I noticed the trees around the property were mostly evergreens and oaks, which indicates a more acidic soil to begin with. The gardener claimed that there shouldn’t be a lack of nutrients as he added all the needles and leaves from the yard to the garden and composter. What the gardener didn’t realize is that evergreen needles and oak leaves are very acidic and the large amount being added directly to the garden and the composter were changing the pH of the soil considerably. Within a few seasons the soil in the garden had become very acidic, beyond a point where average vegetable and flowering plants will grow. After a pH test and a few applications of lime and some organic compost from off-site the gardener was back in a neutral range and his crops and flowers showed it the next season.
As you can see, a pH kit can be a very inexpensive way to determine if your soil meets the plants requirements. A tip to remember is that if you find your soil is either too acidic or alkaline, to retest the soil for pH a few weeks after you apply an amendment so you do not take the soil to the other extreme by adding too much product. Add nutrients slowly and over time so you do not add too much and follow all directions on the bags of nutrients carefully and in no time, you’ll have a great garden.
