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Posted on Feb 11, 2015 in Soil management | 0 comments

Soil pH

Soil pH

Soil pH refers to how acidic or alkaline it is. 7 is neutral. Anything below 7 is acidic, anything above 7 is alkaline.

Soil pH & nutrient availability

Soil pH affects the availability of nutrients to plants growing there. Plants have varying nutrient requirements so therefore they have varying preferences for soil pH. Most vegetables do best with a soil pH of between 6 & 7.

ph & nutrient availability

Plant pH preferences

Asparagus6.0-8.0Onions6.0-7.0Blueberry, high bush4.5-5.5Chives6.0-7.0
Beans6.0-7.5Parsnip5.5-7.5Cane Berries e.g. Raspberry,
Blackberry, Youngberry
Beetroot6.0-7.5Peas6.0-7.5Cherry, sweet6.5-8.0Fennel5.0-6.0
Broccoli6.0-7.0Potatoes4.8-6.5Citrus trees6.0-7.0Garlic5.5-7.5
Brussel sprouts6.0-7.5Pumpkin/Squash6.0-7.0Grapes5.5-7.0Ginger6.0-8.0
Cabbage6.0-7.5Radishes6.0-7.0Grumichama (Tropical cherry)5.5-6.0Mint7.0-8.0
Cucumbers5.5-7.0Sweet Potatoes/ Kumera5.2-6.0Watermelon5.5-6.5Rosemary5.0-6.0
Eggplant5.5-6.5Tomatoes5.5-7.5  Sage5.5-6.5
Kale6.0-7.5Turnip5.7-7.0  Spearmint5.5-7.5
Leek6.0-8.0    Thyme5.5-7.0

Source: The Gardeners Network

To increase pH

To raise soil pH (make it more alkaline), use agricultural lime (calcium carbonate). The amount needed will vary depending on soil type and its current pH. It may take a few months to take effect. Follow instructions on the packaging.

Use of Dolomite is only a good idea if your soil is deficient in magnesium.
Note: Many of the acidic soils in SE QLD are already high in magnesium. Adding more is a waste of money and can cause the ratio of calcium to magnesium to be out of balance.

To lower pH

To lower soil pH (make it more acidic), elemental sulphur / agricultural sulphur is most often used. It can take months or even years for elemental sulphur to work and even then it may still creep up due to the pH of water and compost used in the garden. Additions of naturally acidic materials such as peat most, pine needles and aged sawdust can also help. 2 tbsp vinegar diluted in 4 litres of water can be used as a temporary solution. This can be used whilst waiting for other solutions to work.

To make an acidic soil mix suitable for blueberries, mix equal amounts of peat moss and an acidic potting mix e.g. rose mix.

Results for my beds

Vegetable bedsDatePH and Comments
Bed 1 – BlueberryFeb 20155
Bed 2Feb 20156 – light application of lime added
Bed 3Feb 20156 – light application of lime added
Bed 4Feb 20156 – light application of lime added
Bed 5Feb 20156 – light application of lime added
Bed 6Feb 20156 – light application of lime added


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