Plant Doctor Archive

Ideal soil mix

Question WE have a property in Westport that we previously rented out. The soil has been much improved by previous tenants who I can no longer locate. It appears that the soil is a mix of horse manure/grass clippings and sawdust. Can you please let me know if this would be correct and at what ratios? Would I need to add anything to the mix prior to adding to garden, such as lime, etc?

Answer I ASKED Ingrid Ennis, our resident soil expert for her advice. Ingrid suggests:

I would recommend a soil test first to figure out nutrient status and pH of the soil. Then a decision can be made about whether lime is needed or further nutrients. The best thing to do is to get a soil test done by the local horticultural or agricultural supplies merchant, rather than use garden centre kits. Normally an organic mix such as the one described will be slightly acidic.

If the soil is within the optimal pH range for your plants then you are unlikely to need lime. Most plants grow well in a pH range of 6–7. However, it may pay to check what your plants require.

If I was going to add sawdust, grass clippings and horse manure to a soil I would do it in the following ratio:

Horse manure 60%
Sawdust 20%
Grass clippings 20%

or 3:1:1 in the order listed above and well mixed.

Then I would leave it to settle for at least a month before I planted into it, with a thin (0.5 cm) layer of grass clippings on top. This helps to protect the organic matter in the horse manure from break-down by UV rays.