What is pH?
pH is the measure of how acid or alkaline something is. The pH scale goes from 0 to 14 with 7 being neutral, less than 7 is acid (sour), higher than 7 is alkaline (sweet). Some examples: Lemon juice has a pH of 2, Baking Soda however has a pH of 8.5.
Why pH matters
If the soil pH differs too much from a plants requirements then the plant may not be able to take up nutrients, the nutrients become ‘locked’. For example a pH below 7.5 means that iron, manganese and phosphorus are less available to a plant. A pH below 6 can cause Nitrogen, Phosphorus, potassium to be less available.
To complicate matters – some plants prefer a different pH to others. For example while potatoes do well with a pH of 6.5, Rhododendrons prefer a pH of around 5.
| Very Acid | Moderately Acid | Slightly Acid | Very Alkaline |
| pH 5.0 to 5.8 | pH 5.5 to 6.8 | pH 6.0 to 6.8 | pH 7.0 to 8.0 |
| Blueberry
Celeriac Crabapple Eggplant Endive Potato Raspberry Rhubarb Shallot Sorrel Sweet potato Watermelon |
Bean
Brussel’s sprouts Carrot Corn Garlic Parsley Pea Pepper Pumpkin Radish Squash Sunflower Tomato Turnip |
Asparagus
Beet Bok choy Broccoli Gooseberry Grape Kale Kohlrabi Lettuce Mustard Okra Onion Pansy Peach Pear Spinach Silverbeet |
Cabbage
Cauliflower Celery Chinese cabbage Cucumber Olive Pomegranate Thyme
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Why does pH Vary?
Many things can change the pH of a soil, including temperature, rainfall and the type of vegetation previously grown can all effect the soil pH
How to correct the pH in your soil
Applying additives to your soil such as compost, mulch, lime or gypsum will adjust your pH. Organic matter (such as compost) will neutralise the soil, whereas chemical fertilisers tend to make the soil more acidic.
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To raise pH if soil is acidic add: Lime Wood ash (calcium carbonate, potassium, phosphorus, trace elements) |
TO lower pH if soil is alkaline add: Pine needles Leaves Sulphur Sawdust Peatmoss |
