Earthworm Castings — The Ideal Proportion in Soil for Young Garden Plants

In this project, you will evaluate the capacity of the soil to support plant growth—also called soil productivity—of soil samples composed of different mixtures of potting soil and vermicompost. You should plan to have at least three pots per plant variety for each mixture of soil and castings. It is possible to limit the study to one particular plant type, but two or three types might give more convincing results. As an example, for two plant types (3 pots × 2 types = 6 pots) and three different soil mixtures (6 pots × 3 soil mixtures), you will need 18 pots. The size of your pots will depend on how long you want to run your test.

1. Prepare the pots with mixtures of earthworm castings and potting soil. You need at least three pots per plant variety for each mixture of soil and castings.
   1. Select the mixtures you will test. Some possible mixtures of earthworm castings are 0%, 20%, 40%, 60%, 80% and 100%. We recommend 0%, 40% and 80%.
   2. Create your mixtures. As an example, to create 100 cups of a mixture of 40% castings, add 40 cups of earthworm castings to 60 cups of potting soil. Mix well.
   3. Fill and label your pots.

Figure 2. Fill identical pots with the prepared soil mixtures. Add water-resistant labels.

2. Select plant varieties to be used for the experiment. (Some options: Tagetes, Lactuca sativa, and Viola tricolor.) Buy three healthy looking young plants for each soil composition you will test.
3. Plant one plant per pot.
4. Place the pots in locations where they will get equal amount of light, ambient temperature and make sure you provide them with equal amounts of water.
5. Start a log in your lab notebook, writing down the start of the test and taking regular notes (such as twice a week) on the plants' growth and health. Look for ways to gather quantitative data, like the number of buds, the height of the plant, etcetera. Following resource can help you:Measure plant growth.
6. At the end of the experiment, photograph each of the plants. You can use these photographs to decorate your Display Board.
7. Present your quantitative data in tables and graphs. These will help you detect trends.
   1. Below is an example table listing the number of flowers counted over the total testing period for one particular plant type. Note that you should also average your three test samples (your three pots with identical soil composition).
      
      

      Number of flowers produced over the total test period for Plant A
      Soil Mixture	0 % vermicompost	40 % vermicompost	80 % vermicompost
      Pot 1
      Pot 2
      Pot 3
      Average

      Table 1. Example of a table gathering quantitative data.
      
      
   2. The data in Table 1 can easily be represented with a bar graph, showing the soil composition on the horizontal (x-axis) and the average number of flowers produced on the vertical (y-axis).
   3. For help with data analysis and setting up tables, see Data Analysis & Graphs.
8. Looking at your results, what do you conclude? Did vermicompost mixed in with potting soil help plants grow? For a guide on how to summarize your results and write conclusions based on your data, see Conclusions.