Does colored mulch affect the growth rate of a plant?

Purpose: To determine if different colored plastic (or mulch) on the soil surface affects the temperature of soil.

Materials: Digital thermometer; potting soil; 8 pots; colored mulch in black, white, and red; window sill with full sun; tape. For the colored mulch, you can use different paint colors to paint black plastic, or you might use different colored plastic bags or mulch from the store.

Procedure: Fill pots with equal amounts of soil. Place 2 uncovered pots on the window sill where there is full sun. Cover 2 pots with black plastic, 2 pots with white plastic, and 2 pots with red plastic. Make sure the plastic covers the top of the pot, and tape it to the pot. Place these pots on the window sill. In 24 hours, record your first temperature measurements. You can do this by sticking the temperature probe in the drainage hole of the pot. For 10 days, record the temperatures for each pot in the morning and afternoon. Note the differences in temperature among the colors, and record observations.

Think About This:

1. Which pot had the highest soil temperature?

2. What color kept the soil the coolest?

3. Why do you think that some mulch colors make the soil hotter or cooler?

Return to: Ways to boss around a plant – experiments for middle schoolers


USDA-ARS. Does Colored Mulch Affect Soil Temperature? June 2009l