Tried and acid tested
With Diarmuid Gavin Knowing the pH of your soil is vital when you are planning which plants to grow next year
The dormant season is a good time for planning and deciding which plants you’d like to grow next year. And one important factor when choosing new plants, including vegetables and fruit trees, is to know the pH of your soil. It’s an area of gardening that many find confusing as it implies you need to know more about chemistry than plants, but it’s worth understanding the basics so you can make informed decisions and grow plants which will be happy.
Some of our favourite edge- ofwoodland planting, such as rhododendrons, magnolias and camellia, will only flourish in acidic conditions, so let’s have a look at what that means and how to find out if your soil is suitable.
The term pH is a measure of acidity and alkaline on a scale of 1 to 14. The mid- point, 7, is neutral. Anything below that number is acidic and above it alkaline. Most garden plants do best in a slightly acidic soil, which is between 6 and 7. To grow rhodos and camellias, however, you want a level of 5 to 6.
If you’re not sure what your soil pH is, there are a number of ways to find out.
If you have hydrangeas, the flowers will be blue on acid soil but pink on neutral to alkaline soil.
You can test with litmus paper, which you can buy cheaply in art and craft shops. Mix your soil sample with some distilled water and dip the litmus paper in for a few seconds.
The paper will turn red for acidic and blue for alkaline. This will just give you an approximate idea. To get a more accurate reading, use a soil testing kit available from garden centres. You can also use a pH meter which is like a probe you stick in the soil.
Finally, the Rolls- Royce method is the soil testing service available from the Royal Horticultural Society. This costs £ 30 and they will analyse samples of your soil – not only for acidity but for texture and major nutrient levels.
So if you find you have acid soil, then there are some really choice specimens to choose from. If your soil is alkaline you can still grow them in pots using an ericaceous compost, which is acid.
Ericaceous plants tend to be shallow rooting and can easily dry out, so a good mulching every year will help with water retention.
Leaf mould is ideal as this will help keep soil acid. Use ericaceous feed – liquid or slow release – and top up with sequestrene of iron to condition the soil.
If you try growing these plants in ordinary soil, you will notice the leaves going yellow – this is due to iron in the soil being unavailable to plant roots in alkaline conditions.
In years gone by, passionate gardeners would create peat beds so they would be able to grow these lovelies. However, using a lot of peat isn’t brilliant for the environment – something many gardeners hardly considered 20 years ago.
In the end, it’s best to know what soil type you have and then to garden in harmony with it.
Here are some of my favourite acidloving plants, also known as limehaters...