Canberra Organic Growers Society

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2 Comments on “Soil Problems”

1. Annabel Douglas-Hill Says:
   23 March, 2010 at 10:18 am

   I wouldn’t think it would be a continuing problem. Get a pH test done first to see what the pH is – you can get the gear at any gardening shop. I grow beautiful healthy trees and vegetables on limestone soil where the soil has a pH of 8-9 and where the limestone forms a hard rocky base underneath the topsoil. (I have figs/ almonds/ spinach/natives). Look up in Wikipedia. Builders lime or slaked lime is simply calcium hydroxide and is used on acidic soils to make them more alkaline (what has happened to yours, but in excess). In contrast Limestone is calcium carbonate…. the carbon is the missing ingredient in builders lime /slaked lime. Where the plants are dying the alkalinity must be so high as to be burning their roots. You can rake the builder’s lime into the soil, put aside the bigger pieces of lime, that may have hardened into lumps, make a well around trees and shrubs and put in compost, organic matter, charcoal, (all Carbon forms), anything that will create an acidic environment where bacteria can work on the soil. Superphosphate is also good to acidify soil, and while it is a chemical fertilizer, the sulphur in the super-phosphate reacts with water to form a natural acid that will neutralise the alkalinity. Keep the soil moist so the soil bacteria remain active. You can also sprinkle Iron Sulphate around trees to make it more acidic for them. There are plenty of bulk bags of acidic medium at the shops, Bunnings can advise. And many plants tolerate high pH but over time the pH will reduce down to 7 with natural organic acids and be less troublesome. My father who was a chemist and was against chemical fertilizers only because they leached out quickly and killed the soil bacteria, but a similar thing, but the opposite, has happened with the builders lime. With compost and organic matter thrown in- and some earthworms added at a later date – the soil should revert to good health. Good luck for your garden.

   Annabel Hill

   [Editor's Note: Neither superphosphate nor iron sulphate are allowed means of decreasing pH under the Australian Standard (AS 6000) for Organic and Biodynamic Produce. However, elemental sulphur is permitted]

2. Jess Drake Says:
   23 March, 2010 at 10:54 am

   Yes – it could be the lime in that area causing problems. If the soil is very alkaline from lime, then it is likely.

   I would either dig it all out (to be safe) or neutralize using something acid. Try fresh green waste, fresh manure, fresh veggie scraps. You don’t want to use composted stuff, as it won’t be acidic enough.

   It is likely that you won’t be able to grow plants there for 6months – 1 year depending on rainfall.

   John Field (a COGS member and soil scientist) is a good bet if you see him around.

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