Earthworms are known to be key components of healthy garden soils. They not only aerate the soil with their tunneling, but their droppings or 'castings' are known to be a good plant food, as well. Now researchers at Mississippi State University are looking at the benefits of using earthworm castings in potting soil to enhance container plant growth.
In the study, marigolds were grown in pots containing different potting mixtures: 7 parts peat:1 part perlite; 4 parts bark:1 part sand; and in straight earthworm castings. Researchers also added castings at 1:1, 2:1, and 3:1 ratios into the other mixes. They recorded the growth and flowering of the marigolds weekly.
The marigolds grown in the earthworm casting mix had greater stem diameter, better flowering, and better root growth than those grown in the other mixes. Similar results were found in pots with castings added to the other mixes: the higher the proportion of earthworm castings, the better the plant growth.
For more information on this research, go to: American Society for Horticultural Science.