Even people who are new to gardening probably know that not all soil is the same. Certain regions have a soil that is more acidic or more alkaline than others. Part of the reason many gardeners like to grow native plants is that they are more likely to do well in the soil as it is. For people who want to grow a specific plant, it is a practical idea to consider soil pH in a plan to cultivate and keep the plant healthy. With this information, gardeners will know how to test the pH and a few options to adjust it as needed.
How Soil pH Affects Plant Growth
The acidity of any substance ranges from zero, which is the most acidic, to 14, which is the most basic. As a general rule, most soil types range from 3 to 10. The acidity of the soil can make a significant difference in the way that the plant can grow and thrive. It also affects the likelihood that people will have to deal with weeds. Certain species need soil that is slightly more acidic, reflecting a wetter, more temperate climate. Others require a higher acidity, which is more common in drier regions.
Every spot of soil in a homeowners garden has an acidity that reflects the nature of its creation. In short, the components of the earth beneath, as well as the climate and vegetation growing from above, determine what is in the soil. Naturally dry soil tends to be more basic, while wetter soil is typically more acidic. Plants get nutrients from a combination of soil and water. The acidity of the soil determines how soluble those nutrients are.
When people select the types of plants they would like to grow in the garden, soil pH is an important aspect to test first. Soils with a very low pH can trigger certain nutrient deficiencies in plants, such as calcium or magnesium. Conversely, acidic soil may contain too much aluminum or manganese. By comparison, alkaline soil may be deficient in zinc or copper. Soil with the highest pH levels may also have too much salt.
Part of growing in maintaining a garden includes making sure that only desired plants grow in the space. Invasive species, or weeds, will grow wherever the environment makes it easy for them to thrive. For example, many people in different regions are accustomed to seeing dandelions grow on the lawn or in the garden. These prolific plants prefer acidic soil, which may serve as an indicator of the type of soil that a person is dealing with. Otherwise, invasive plants like chickweed or Queen Anne’s lace indicate soil that is more alkaline. Weed growth does not necessarily show that the soil pH is too far out of the normal range, however. Since most homeowners would like to mitigate weed growth, soil pH can be an important source of information to make weed removal and management efforts more successful.
How to Test Soil pH
Soil pH can be a significant determiner of a plant health and growth viability, so testing the soil‘s acidity may be helpful in planning or problem-solving. Most soil falls within a normal range of 5.5 to 7.5. Most plants can grow well in this type of environment, but not all of them. The type of testing the gardeners choose depends on the plants they intend to grow and the precision they need from the measurement. For example, someone who is testing pH after adjusting acidity might need to use test strips for higher accuracy.
Testing Soil pH Using a Kit
Testing soil pH using strips involves effectively making a kind of tea out of the soil. Gardeners should start by gathering a small amount of soil from about 4 to 6 inches below the surface. People may want to gather several samples, since the pH can vary at different points in the garden. They should put the soil in a clean glass and combine with distilled water, stirring the soil heavily to allow elements of the soil to dissolve.
After leaving the soil to rest for about half an hour, people can strain the soil through a coffee filter. The resulting water solution is what people need for the soil pH test. The test strip should indicate the pH, with color coding on the package of strips. Gardeners can repeat the test as needed, particularly if they need to adjust the acidity of the soil.
Testing Soil pH With Common Household Products
For people who do not need an absolutely precise estimate of soil pH, household products may be an effective alternative. Highly acidic substances like vinegar will react when combined with highly alkaline substances like baking soda. Gardeners should start with one cup of soil sample that is generally free of rocks and debris. Mixing enough water to turn the soil to mud makes the test easy to complete. If the soil is particularly acidic, combining the soil sample with half a cup of baking soda may yield a bubbling or fizzing reaction. If this does not happen, the soil is either neutral or basic.
It is also fairly easy for people to test for the reverse. Highly basic soil will react when combined with vinegar. Gardeners can take that one cup of soil and add half a cup of vinegar. If they observe the foaming or bubbling reaction, they can assume that the soil is alkaline. If they do not, the soil is either acidic or neutral. Since these tests may not be terribly precise, people may want to use official testing for plants that require a specific pH.
How to Increase Soil pH
Increasing the acidity of the soil may be necessary to allow plants to grow. In some cases, gardeners struggle to find plants that can handle the soil that they have. Increasing the soil pH may make it easier to grow plants that are not native to the region, as well as improving their health and overall lifespan. Gardeners have a few different options they can choose to change the soil’s acidity, although some are more long-lasting than others.
Limestone is one of the most common components that people can add to soil in order to increase the pH. As a general rule, people do not need to add very much to see a difference. The typical amount ranges from 2 to 5 pounds per 100 square feet, depending on the type of soil. Wet soil that resembles clay needs the most. Limestone has the added benefit that it can increase nutrient absorption in certain types of tropical plants. However, gardeners may not notice a change in the acidity for up to a year or two after the initial application. Cover crops that can handle acidic soil in the meantime include buckwheat and oat.
Adding a combination of water and baking soda to the soil can increase its pH quickly, even if it does not last as long as limestone. People who need to alter the pH quickly may combine a tablespoon of baking soda per gallon of water. Applying the solution to the soil can yield positive results within a few days. It is also less likely to damage the plants than other approaches. A lower ratio of baking soda to water may change the pH too quickly, so people should take care in the amount that they use.
Wood ash is another natural component that gardeners can add to the soil to decrease the acidity. In order to use this approach, the wood in question must be:
- Generally clean
In this case, people should plan to add a thin layer about a quarter of an inch thick to the top of the soil. Turning the wood ash into the soil and watering completes the process. Like baking soda, wood ash yields quick results but does not last very long. People may need to repeat it several times or consider a supplemental method for long-term results.
As a general rule, gardeners may want to plan to test the pH at least once every few months during the growing season. For those who are trying to make significant changes over a shorter period of time, testing weekly can be helpful in determining which approaches are the most effective. It is worth keeping in mind that the soil in one part of the garden may be more receptive to adjustment than others. As such, several test samples may be necessary to get an average rate of progress.
How to Decrease Soil pH
Since most plants prefer a soil pH that is slightly more acidic than neutral, gardeners may be more likely to need to lower the pH in order for their plants to thrive. Increasing the overall acidity requires a variety of possible methods, depending on the target pH for the plant. As with increasing the alkalinity, too much of any approach can be harmful. As such, gardeners may want to take care in the amounts that they use, with few exceptions.
Organic compost naturally increases the acidity of the soil. As organic matter starts to break down over time, it produces acids that lower the soil pH. Natural components of soil like peat moss alternatives or pine bark mulch are the most effective at increasing overall soil acidity. This approach is also one of the safest and most practical for long-term use. However, gardeners should plan to add quite a lot in order to see a difference. In some cases, they may be effectively replacing much of the existing soil with a soil combination that has a high quantity of organic matter.
Nitrogen or Ammonia-Based Fertilizer
Fertilizers can be an effective addition to other soil approaches. Because the fertilizers are absorbed more rapidly, they can trigger the benefits of a lower pH in less time. On the other hand, too much of an ammonia-based fertilizer can lower the pH too quickly. Gardeners should follow the manufacturer’s instructions to confirm that they know precisely how much to use and avoid using more than that. For plants that need a comparatively low pH, like blueberries or azaleas, these fertilizers may be the most practical choice.
Most approaches to raise or lower soil pH will only affect the soil by 0.2 to 0.5 units. People who need to lower the pH by more than that may want to try using elemental sulfur instead. This compound takes longer to show up in the soil because gardeners have to wait for the bacteria in the soil to convert the sulfur into sulfuric acid. However, adding elemental sulfur may be one of the best ways to increase the acidity to a higher degree and for a longer duration. It can take up to a year to see a difference, although people who incorporate the sulfur into the soil directly may notice a quicker result.
As with any other practical changes to the soil quality, gardeners should plan to test the soil regularly while they are lowering the pH. The area that they need to test depends on the plant in question. Most approaches to increase soil acidity are effective only for soil that is less than 12 inches below the surface. For the vast majority of plants, that will be enough to increase their nutrient absorption through the root structure. For deep roots in plants like large bushes or trees, these methods may be insufficient. It is also possible that they can help, but will take longer to show a difference.
For the most part, gardeners do not have to worry excessively about the soil pH of their gardens. In cases where the plant is particularly finicky or the soil highly acidic or basic, people may want to test and adjust it as part of their overall gardening plan. Making sure that plants are in a healthy environment for their growth will improve their lifespan and, depending on the type of plant, their output. These tools make it easier for gardeners to meet these needs.