Practically anything that is able to rot and absorb moisture can be used to make compost for science projects. For example, you can use newspaper, magazines and egg boxes. However, while these materials can make good compost for some plants, the compost lacks nutrients, whereas compost made from rotting vegetation or similar is high in nutrients. It depends on the plants requirements as to which are better. Some plants won’t grow in nutrient compost. You can test the effects by putting one plant into rich compost made from rotting vegetation and the other into torn-up paper and cardboard that has been allowed to soak for a few days. Measure the development of each plant over a couple of weeks. You may be surprised to find the plant in the paper and cardboard compost has grown better. If it does, it’s because it likes to grow in compost that contains few nutrients.
Use two same size plastic containers and make a few small holes in the bottom of them for this second science project. Fill one container 1/3 full and the other 2/3 full using the same type of soil. Chop up a few banana skins into fairly small pieces and mix the skins into the soil that it’s a 1/3 full and then put in more soil, so both container are 2/3 full. Label the containers and leave them for two weeks. Put two plants the same size and type into the containers. Make daily notes for a couple of weeks about the development of each plant. One will grow larger and quicker than the other, depending on the nutrient requirements of the plants.
Some gardeners advocate the use of used tea leaves as compost. Undertake this science project to test if it has any effect on the plant in the compost-free container from the previous project. Remove some of the soil and put a few handfuls of used damp tea leaves into the container. Mix the leaves with the remaining soil and add a little more soil on top. Water the plant well. Record what happens on a daily basis for a couple of weeks. See if the plant develops differently. Record if growth speed up, slows down or stays the same. Compare the plant that has banana compost against the plant that has tea leaf compost.
Different types of compost have different levels of water retention. This affects a plants growth; some plants like well-drained compost, while others like to have continually moist or even wet conditions. Use two different types of compost: one that has high water retention and one that doesn’t retain much moisture. Typically, peat-based compost retains water, while a compost that contains manure drains better. Put two plants that are the same into two containers, one that has moisture-retention compost and one that doesn’t. Water both plants equally and record what happens to the plants. You will see that one plant will grow better than the other, depending on the plant's requirement for water.