How useful is pH testing for fruit trees in backyard gardens?
Have you ever tested the pH of your soil? Many people haven’t ever tested their soil pH, and instead focus on maintaining soil structure. While this generally is the right idea, it’s beneficial to know the science behind your soil acidity, and what it means for your fruit trees.
Explaining soil pH
pH is a measurement of the acidity of a solution. When measuring a solution, three terms are used in relation to the pH scale: acidic (pH below 7.0), neutral (pH 7.0), and alkaline (pH above 7.0). The pH scale ranges from 0 to 14 – 0 and 14 are absolute extremes that you will rarely ever witness in soil samples. For an explanation of how to measure soil pH, check out our video presented by Emma on how to test soil pH.
Take note that good soil structure can resist changes in pH towards high acidity or alkalinity. This means that sandy soils, for example, don’t have good pH buffering capacity due to the poor soil structure. Loamy soils have good soil structure and therefore high pH buffering capacity – this means that additions of nutrients or elements in high quantities (for example if you’re using a potassium rich fertiliser) may not change the soil pH.
How pH affects fruit trees
The pH value directly affects the nutrients or elements that are available to a fruit tree for absorption via the roots. In other words, your fruit tree can’t access certain substances (essentially plant food) depending on the pH range of your soil. The table below describes nutrient and element availability in acid and alkaline soils:
Table 1: A general guide on nutrient availability in relation to pH
| Extreme Acid (<5.5) | Extreme Alkaline (>8) | |
| Available | Iron Manganese Aluminium | Molybdium Calcium Magnesium |
Limited Availability | Calcium Molybdenum Boron Phosphorus | Iron Zinc Copper Manganese |
Explained simply – Acidic soils are deficient in major nutrients, and alkaline soils are deficient in trace elements. Neutral range (around 7.0) is the pH range where most elements and nutrients are available, particularly the major nutrients; nitrogen, phosphorous, and potassium, AKA our important NPK group. The ratio of NPK is how we determine which fertiliser can be used on what plant in our backyards!
Maintaining our soil at a neutral level, or as close as we can get, will allow our fruit trees to absorb the maximum amount of nutrients possible. This is important for our fruit trees biologically too – soil pH affects beneficial microorganism diversity and function, as well as the vigour and function of fruit tree roots!
Correcting and maintaining soil pH
To correct acidic soil, use garden lime at the recommended rate (on packet instructions), and take care in selecting fertilisers – those with high nitrogen can contribute to acidifying soil. When building a new garden bed or preparing your soil for fruit trees for the first time in acidic soil, use garden lime at least 6 weeks before planting. Lime can be used at the same time as compost and other organic matter you may be planning on using while preparing your soil.
To correct alkaline soil, use elemental Sulphur at the recommended rate (on packet instructions). You will easily be able to find this product at any good garden centre. When correcting your garden with Sulphur, be aware that elemental Sulphur is slow acting, therefore you might not see noticeable changes for 3 months or more.
Remember – soil structure matters when we’re talking about pH. Take note of your soil structure and be aware that in soil with a dense structure, ie clay, adjustments to the pH can take longer to occur than if you had sandy soil.
The best way to maintain your soil pH is to correct your soil gradually, and ensure you are adding organic matter into your soil profile at least once a year in each patch of the garden. Your fruit tree will benefit from organic matter once a year (don’t fertilise while they’re flowering though!), and you could take this opportunity to:
- Before adding organic matter, test your soil pH,
- Add lime/Sulphur if needed,
- Add organic matter after a week or more (lime) or immediately (Sulphur).
How much does it matter?
While it’s important to know about your pH, it’s more imperative to maintain your soil structure and microorganism community for best growth from your fruit tree. Most fruit trees will grow well in a pH range of 5.5 to 7.5. Adding organic matter, mulch, and performing a pH test early in your garden development are the best ways to ensure you have healthy, productive fruit trees.
Much of this advice is targeted to those of you who have problems with extremely acidic or extremely alkaline soil – for everyone with soil sitting somewhere in the middle, you should have productive PlantNet® fruit trees if you follow our Ultimate Guide to Growing Fruit Trees.
For further reading, visit our article sources listed below, and our Plant Care page.
pH probes make testing soil pH easy!
References
Hannnan, J 2016, ‘How To Change Your Soil’s pH’, https://hortnews.extension.iastate.edu/2016/02-12/soilpH.htm.
Relevant, L, Hardy, S, Sanderson, G 2004, ‘How to manage soil for citrus’, https://www.dpi.nsw.gov.au/agriculture/horticulture/citrus/content/crop-management/orchard-management-factsheets/soil.
Van den Ende, B 2017, ‘Check your soil pH!’, https://www.fgv.com.au/grower-services/latest-updates/technical-articles/501-check-your-soil-ph.