Experiments with Compost
For many years gardeners and farmers alike have added worm castings to the soil to increase the health of their flowers and crops. Although this does not add a significant amount of nutrients into the soil, it does in fact enhance the microbial activity of the soil. With this in mind, the increase in microbial activity allows for a greater amount of beneficial microbes that aid in plant growth.
To understanding the effects of worm castings on plant growth and development, Lisa Wickland of Bellingham, Washington conducted experimental trials on various flowers and vegetables. The first of many experiments involved growing marigolds in 0 to 50% worm castings. Those grown in 20% worm castings had the greatest germination rate as well as increased growth compared to all other treatments. The picture below depicts the marigolds before their true leaves appeared. It seems that past 20% worm castings, the soil will reach a saturation point where as it no longer increases plant growth and can potentially damage the plant. This is especially noticeably during seed germination. Therefore, caution should be used when planting with worm castings.
Additional experiments were conducted by varying the amount of worm castings added to 5' square bins planted with carrots.
Within these bins, the carrots were grown in a consistent mixture of soil and organic fertilizers such as bone meal, blood meal, kelp and green sand. One of the bins served as the control, with 0% worm castings added as well as two additional bins with 10 and 20% worm castings. The carrots were kept well watered and monitored for germination, growth and development. As you can see below, the carrots grown in 20% worm castings had considerably greater growth rate than those grown without worm castings. The germination rate was also greater with the carrots grown in 10 and 20 % worm castings than those lacking the worm castings.
Although the reasons for such a notable difference in plants grown with worm castings is still unclear, with current research new information is becoming available every day.
More sites about compost use: Disease Suppressive Potting Mixes, & Compost use.