Potting Mix Problems 

This is a transcript of a recent email conversation (19th November 2006) with Elaine Ingham (president, Soil Foodweb Institute) regarding why potting soil becomes poorly drained and why synthetic fertilisers seem to work better.

Stephen: Can you offer me some suggestions on how to keep my potting soil from being turned into compost by microorganisms? It seems after a few months the potting soil begins to drain poorly and the plants get water-logged.

Also, most of my plants in containers don't seem to grow as fast with organic fertilisers as with synthetic types. Any suggestion on how to make the organic fertilisers work better, without breaking down my potting soil. Thanks.

Elaine: What you are really telling me here is that you are water-logging the potting mix and it is becoming anaerobic.

Aerobic decomposition will result in improvement in air passageways, hallways, and pore structure in the soil. This structure is built by good, aerobic organisms.

But, if the plant pots are allowed to get water-logged, if the potting mix is compacted, then the beneficial organisms will be lost, and the plant diseases will be able to gain an upper hand.

Organic fertilisers don't work well without the proper set of organisms in the potting mix.

To maintain the right set of aerobic organisms, you may have to initially inoculate the potting mix with the right set of organisms, and make sure you don't over-water.

If you have any soil microbe questions either contact me , or email This e-mail address is being protected from spambots. You need JavaScript enabled to view it