Why should you care about soil pH?
I’m aware that for most non-soilies this question will evoke many yawns. But what I’m about to tell may very well blow your mind. The pH of soil changes nutrient availability! How amazing is that! So, in plain English, what does that mean?
1. Soil increasing in alkalinity (pH > 8.0 - 10.0) makes nutrients such as nitrogen, iron, manganese, copper and zinc less soluble/available to plants.
2. Soil decreasing in acidity (pH < 6.0 – 4.0) makes nutrients such as nitrogen, phosphorus, potassium, sulphur, calcium and magnesium less soluble/available to plants.
3. Most plants like a moderately acidic to neutral pH (pH 5.8 – 7.0), this is the range where most nutrients are available.
So, what does this mean in practical terms? Here’s some examples.
1. If your plant foliage is yellowing, it could mean either nitrogen, manganese and iron are less available, not because of insufficient supply but because its unavailable due to an alkaline pH. This is particularly detrimental to acid-loving plants such as Camellias, Magnolias, Photinia, Rhododendrons that thrive in lower pHs (pH 4.5 – 5.5).
2. If your plant foliage is exhibiting a purple edge, it could mean that phosphorus is less available, not because theres insufficient supply of phosphorus but because the pH is too low.
3. If your plants are underperforming or dying a reason could be an extremely acidic pH consequently making aluminum, manganese, zinc and copper available. In high amounts, these nutrients are toxic to plants. Hydrangeas on the other hand don’t mind some aluminum and in turn will provide you with vibrant blue flowers.
What is my soil pH and how can I change it?
For a precise result, laboratory analysis is always recommended.
pH can be raised by applying lime and lowered by applying iron sulphate (or similar). However, I caution against the “apply and see what happens approach”. Once applied it can be difficult to reverse the process. Therefore, I recommend pH analysis plus a pH trial to determine the exact application rate. Not only will it avoid potential dramas in the long run but its likely to save costs and the environment by only applying the correct ratios of what is needed.
For more information please call your local Urban Soil Doctor.
