Acidic Soil Guide

The pH of your soil is one of the most important factors in determining what will grow well where you live. Along with climate and conditions, soil pH should be in your mind when you are planning and maintaining your garden. In any garden, the soil pH will fall into one of three categories. If the pH is below 7, your soil is acidic – between 3.0 and 5.0, it is extremely so. If your soil pH is around 7, it is neutral, and if it above 7 it is alkaline in nature. In this article, we’ll talk about acidic soil. Acidic soil is also sometimes referred to as ericaceous.

Soil pH is one of the factors that will determine what will grow in your garden, and how well different plants will so. So it is important to have at least a basic understanding if you want to make the most of the space available for home growing.

Do You Have Acidic Soil?

The easiest way to determine whether or not you have acidic soil is to use a pH test. These can be purchased relatively cheaply online. One thing to note is that the pH can vary in different parts of the same garden. So it is a good idea to test the soil from several different spots around your growing areas.

Another way to determine if your soil is acidic is to undertake a small home experiment. Mix some of your soil with water to make a muddy paste, then add some bicarbonate of soda. If the baking soda froths up, this is a sign that the conditions are acidic. (If soil is alkaline, it will react when vinegar is added, and not with bicarbonate of soda. This will not tell you how acidic or otherwise your soil is, but it could help give you a general idea of conditions.

You can also get plenty of clues about the pH of the soil in your garden by simply observing the plants (and weeds) already growing there. By seeing which plants thrive, and which do not do so well, you can often make a range of assumptions about the pH in your garden.

Is It a Problem?

Whether or not acidic soil is a problem very much depends on the degree of acidity. If your soil is somewhat acidic – (below 7.0 but above 5.0) – then this need not be too much of an issue. In fact, a slightly acid soil (with a pH of around 6.5) is said to be the best pH for gardens. This pH allows the widest variety of plants to grow. And when the pH is at this level, microbial and earthworm activity are at their best.

If soil has a pH below 5, it is considered to be extremely acidic. Unfortunately, this is far more of a problem. At this pH, most plant nutrients will become more soluble. They will be more easily washed away. Most phosphates will be locked up and become unavailable to plants. Since all plants need phosphorus, along with nitrogen and potassium, to grow – this is a big problem. Below a pH of 4.7, bacteria cannot rot organic matter and fewer nutrients become available to plants. Such extreme acidity is fortunately rare here in the UK. But if the soil where you live is extremely acidic, you will need to amend it to bring it back into a more favourable pH range.

What Causes Acidic Soil?

Acidic soil is commonly simply the natural result of the breakdown of acidic organic matter in the soil over time. This is most commonly found in the UK in peat bogs, or areas of pine forest. The geological nature of the area where you live will also be a major determinant of soil acidity. Soil formed over granite or sandstone will be acidic, while those formed over limestone or chalk will be alkaline, for example.

Extremely acid soil, however, can also be caused by human interventions. One way that humans can make soil more acidic is by over watering or excessive irrigation, which leads to key nutrients such as potassium, magnesium and calcium being leached from the soil. (Occasionally, heavy rainfalls can also encourage excessive nutrient leaching.)

Another way that humans damage soil and make it excessively acidic is by overuse of nitrogen based fertilizers. Synthetic fertilizers are hugely damaging – both in the garden soil, and when we look at the global picture. Ammonia based fertilizers are responsible for huge carbon emissions, and also increase soil acidity. To do the best thing for your local environment and the planet – always avoid synthetic fertilizers (and pesticides and herbicides) and garden organically.

Other forms of pollution can also cause acidification. Bioremediation of polluted soils can bring acidity down. Sometimes this involves using micro-organisms, sometimes it involves planting certain specific plants to draw pollutants from the soil.

How to Make Your Garden Less Acidic

If you have extremely acid soil, it is important to be realistic about what you can grow. It is unlikely that you will be able to amend your soil sufficiently to grow plants that need neutral or alkaline conditions. But you will be able to make soil somewhat less acidic, to lessen the issues mentioned above, and to grow acid-loving (ericaceous) plants.

To reduce soil acidity, the usual remedy is to add lime. It is also possible to use wood ash to increase soil pH. However, amending large areas of soil can be very challenging, and involves careful assessment and monitoring. Often, it may be better simply to grow in raised beds or containers if the soil is very acidic where you live.

The good news is that with mildly acid soil, there are plenty of plants you will be able to grow. Usually, if you only have mildly acidic soil, it is best to embrace the soil you have. Rather than trying to amend the soil to make it less acidic, you should work with what you’ve got. Choosing acid-loving plants like acacia, rhododendrons, camellia, heathers, blueberries, cranberries etc. can help you create a beautiful acidic soil garden.

How to Make Soil More Acidic

Sometimes, if you have a neutral or mildly alkaline soil, you may wish to amend your soil in certain growing areas to make it possible to grow some acid loving plants like those mentioned above. You may also wish to amend alkaline soil slightly to make it better for growing certain crops – like potatoes for example.

You may also wish to make soil more acidic if you have extremely alkaline soil. Like excessively acid soil, very alkaline soil can also cause problems with phosphorus uptake etc..

You can make soil more acidic by adding sulphur, a mulch of pine needles or other acidic material such as oak leaves, or liquid feeds containing acidic substances like vinegar. Generally adding plenty of organic matter – compost, mulches etc. can slowly and gently lower soil pH.

As above, however, it is generally best to embrace the soil you have. Rather than trying to make soil more acidic, you should choose plants that are best suited to the soil in your area. If you still want to grow a few ericaeous plants – consider growing them in containers.

Whatever pH you have in your garden, it is important to look not only at this soil characteristic but also at other characteristics of your soil. PH is only one of the factors that will determine what you can grow in your garden and how well your plants will do.

Do you have a garden with acid soil? Have you taken steps to alter the pH in your garden? Share your comments, tips and experiences below.