Science Experiment: Which Types of Soils Cause Sunflowers to Grow Larger?

Sandy Soil

• A sandy soil type is any soil that has over 70 percent sand. Sand is a texture size classification of the mineral ingredients in soil between 2mm (0.079 inches) and 0.05mm (0.002 inches). Mix seven parts sand with three parts of potting soil and plant sunflower seeds in it. Keep all nutrient, water and light conditions equal with the other soil types you are comparing.

Organic Matter Soil

• Organic matter type soils are rich in nitrogen, phosphorous and potassium which help sunflowers grow larger. Use pure potting soil mixed with compost and manure to make a very nutrient-rich type of soil such as would be found in a well-tended garden.

Loam

• A loam type soil is one with equal parts of sand, silt and clay. Loam soils typically have a good soil structure. Good soil structure is a measure of how well the soil particles stick together to form small aggregates that are good for plants to grow in. For example, sandy soils have poor soil structure because there are very few aggregates. Because of the good soil structure of a loam soil, a plant will have a firm foundation to grow its roots and good access to water. However, a loam soil is classified based on its texture not its nutrient level. That is, you can have a loam soil with good soil structure that is not very fertile. To make a loam soil, combine equal parts of sand, silt and clay together and mix thoroughly. The soil under your grass may also be a loam, and you could collect some of it to plant sunflowers in.

Results

• Sandy type soils are typically harder for sunflowers to grow in. They may have a well-developed root system, but because of the course texture of the soil and low organic matter, water and nutrients quickly leave the soil. Thus, sunflowers grown in sandy soils will be small. Sunflowers grown in soils with rich organic matter should thrive because of the abundance of essential plant nutrients as well as the increased water-holding capacity. This soil should have the largest sunflowers growing in it and demonstrate the size a sunflower can get to in ideal conditions. Make sure the manure or compost that you add to this soil is well broken down, otherwise it might actually take nitrogen from the soil rather than adding it. The loam soil type should have medium-sized sunflowers in it, as compared to the other two soil types.