Facts and figures on soil bacteria

Question ...

I am setting questions for a gardening quiz for my village gardening club. I would like to use the question "to the nearest million, how many bacteria are in a teaspoonful of healthy soil?" Do you have the answer? The only answer I have been able to find is "that there are more bacteria than people living in the world" - not precise enough I'm afraid.

Answer ...

One gram of soil (about 1/5 tea-spoon) can contain over 100 million bacteria, 1 million actinomycetes and 100,000 fungi. The weight of these organisms would only account for 0.05 percent of the weight of the soil. The size of a single bacteria is approximately 1 micron or 1 millionth of a metre - 100,000 bacteria placed end to end would measure 1 cm.

Garden Organic members can see our expert factsheets for further advice on organic gardening. Access to factsheets requires a members' password.