# Why Do Plants Wilt?

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### Problem:

Can a bit of shade help stop your outdoor plants from wilting?

### Materials:

• Umbrella
• 2 planter boxes
• Soil
• Sprayer
• 6 lettuce plants
• Thermometer
• Moisture meter
• Notebook and pencil

### Procedure

1. Is it hot outside? That’s perfect! Grab your water bottle and head off to find the warmest place outside your house.
2. How can you find a warm place? Walk around until you see some plants that look wilted, with droopy leaves. You can also use your thermometer. Hold it by the top so it doesn’t read your body temperature. Stand in each spot for a few minutes and see if the temperature on the thermometer changes.
3. Get two small planter boxes and six lettuce plants. Lettuce wilts in the hot sun, so it’s a good plant for a heat experiment. Add soil to your planter boxes, and spray the soil with water.
4. Now plant your lettuce plants. Put three in each container. Put both containers in the hot sun.
5. In this experiment, you’re going to give one batch of lettuce shade. The other will be in the hot sun. Create a hypothesis: your best guess about what is going to happen. Will the lettuce wilt? Will the lettuce in the shade wilt less than the lettuce in the hot sun? How about the temperature? Will it be different in each planter box?
6. Now, place the thermometer on top of the soil in each planter box. The temperature should be the same.
7. Add an umbrella to the side of one of the planter boxes. Make sure that the umbrella’s shade covers the lettuce plants in that box but doesn’t go as far as the other.
8. After one hour, take the temperature on top of the soil of the two planter boxes again. Make a note of it in your notebook. Is it different? The same?
9. Next, water the lettuce in each planter box. Wait for several hours. Now, use the moisture meter to see how wet the soil is in each planter. Write the readings down in your notebook.
10. Take a look at the lettuce plants in each planter. Do they look wilted? Do they look different or the same?

### Results:

It may be a little cooler under the umbrella, but this depends on the air temperature and local winds. The plants will likely look less wilted. The soil underneath the umbrella will be moister than the soil with no umbrella.

### Why?

Have you ever stood in a parking lot on a warm day and then moved underneath the shade of a nearby tree? It sure is cooler under there, isn’t it?

Temperature readings depend on many things. They depend on how warm the air is in general, and they depend on how the air is moving. For example, an ocean breeze can cool you down. These readings also depend on the heat that’s stored in the ground. In a parking lot, the blacktop stores a lot of heat and radiates it out again, making it feel like you’re standing in an oven. Forest and garden soils don’t tend to do this as much, especially if they don’t have a lot of plants and leaves to cover the soil.

Depending on the movement of the air, the heat in the air, and the heat stored in the ground, you may or may not find that adding shade to your plants changes the temperature of the soil in the planter boxes.

Plants may wilt because the soil is dry and the plants don’t have enough to drink. If you add shade, this means that the sun no longer beats down directly on the soil, helping the soil stay damp. Less water evaporates from the soil, and the plants don’t wilt as much. Even if the air temperature is about the same, adding shade can still keep your plants happy, because the plants stay moist for a longer time.