Science Experiment: What Makes Drought-Tolerant Plants Work?

This science project is great for all ages.

Some Plants are "Thirsty," and Others are not

A few centuries ago, people could not go to the nursery to buy whatever plants they wanted. They could not turn on the hose or sprinkler system to water their plants. Grasses were wild, growing in clumps and helping to hold sandy soil in place to prevent erosion. The notion of a lawn simply did not exist.

The plants that grew in northeast Florida were “native” plants, meaning that they had grown here for years. They grew naturally, without cultivation or extra care. Native Americans knew how to live in concert with these plants, and they fed and nourished themselves with them.

By the sixteenth century, Florida’s new European settlers started to introduce plants from other parts of the world. If those plants could not adapt to Florida’s climate, they died.

By the eighteenth century, Florida’s residents had started cultivating plants that could only thrive if they were watered.

Today, you find the most common of these plants on lawns. Lush grass lawns are beautiful to look at, but they are not natural. Without extra watering, most of them would die.

Many other common household plants and shrubs would die too if not for ample watering by a doting caretaker. In fact, if you ask any gardener, you will quickly discover that some plants require large amounts of water to thrive, and others require very little.

Plants that thrive in the Florida climate without additional water or cultivation are called either native plants or Florida-friendly plants. They are extremely important to the future of our region: they will extend our supply of fresh water because outdoor water use – irrigation – is the largest single use of water in northeast Florida.

The Basic Science: What makes a plant drought tolerant?

Plants adapt to dry conditions in many different ways. In this science project, you will study qualities and characteristics of drought-tolerant plants to help you understand how they work and to identify which plants are drought tolerant and which are not.

Some plants, for example, flower in winter or spring, and then go dormant during the long, hot summer months. For example, think of the beautiful spring bulbs, like tulips, daffodils, and irises. They grow, flower, and die before the dry season ever arrives.

Some plants have deep roots that can find and capture water, even in small quantities. They tend to do better in hot climates than plants with shallow root structures.

Some plants have leaf, stem and root structures that promote “evapotranspiration,” which is the movement of water through a plant. Water enters a plant through its roots, then moves through the stalk, stems, or trunk, and eventually evaporates into the atmosphere through the leaves and flowers. One of the primary goals of drought-tolerant landscaping is to use plants with low rates of evapotranspiration.

Project

Part 1: Comparing rates of evapotranspiration

Materials:

• Vases or jars of similar size and with similar openings
• A variety of flowering plants, greenery, and shrubs

Procedure:

1. Fill each jar with identical amounts of measured water.

2. Leave one jar empty. It will be your experimental control.

3. For the other jars, you will want to use a wide variety of flora, but be sure to put only one type of plant or flower into each jar.

• Put cuttings or bouquets into each jar. Note the name of the plant on the jar or on an index card beneath the jar.
• Use as large a variety of different types of plants as you can find. You will want plants with:
• Woody stalks and soft, watery stalks
• Thin stalks and thick stalks
• Small-petals on the flowers and large, showy petals on the flowers
• Smooth leaves, shiny leaves and waxy leaves

4. Put all of your “vases” in windows that get similar amounts of sun.

5. Observe the rate of evapotranspiration from each vase. When a plant needs more water, re-fill the jar, keeping careful measurements of the amount of water you add.

6. Continue this experiment for as long as you can.

7. Describe and plot the rate of evapotranspiration for the various plants you tested.

Part 2: Examining characteristics of high-water-consuming and low-water-consuming plants

In the first part of this project, you measured rates of evapotranspiration, or water consumption. In the second part, you will examine and identify common characteristics of high-water-consuming and low-water-consuming plants.

1. Begin the process by creating a chart that contains as much of the following information as you can gather:

• name of the plant
• amount of water use (very high, high, medium, low, very low)
• descriptions of
  • the leaf
  • the flower
  • the stem
  • the roots
  • the stomata

NOTE: The stoma of a leaf is the visible veiny structure that allows water vapor and other gases to pass through the leaf. Here is a handy way to observe the stoma and prepare to draw it. (The plural of “stoma,” by the way, is “stomata.”)

a. Paint the back of various leaves with clear fingernail polish, and allow it to dry.

b. Apply a piece of scotch tape to the back of the leaf over the clear fingernail polish.

c. Pull off the tape. The fingernail polish will stick to it, leaving a permanent impression of the stoma on the tape. You can now observe it clearly with a hand lens or mount it, color it, and draw it.

2. Identify common characteristics of high- and low-water-consuming plants.

3. Go to a nursery or speak with a landscaper about your findings.

4. Gather a sampling of plants that you have not previously tested. Determine their water consumption by comparing their qualities to the qualities you observed in the plants you measured. Check with a nursery to see if your observations and conclusions are correct.

5. Present your classification system to your classmates along with a sampling of various plants (that they will not have identified). Have them classify the plants by following your information.

Extenders

1. Compile a list of tips for managing water use on a garden. Your tips may include some of
these:

• Keep the size of the garden small.
• Use mulch and compost to help hold moisture.
• Control weed so the plants do not have to compete for the water.
• Grow drought-tolerant plants.

2. Visit a botanical garden and learn about “Xeriscape” – low water-consuming – gardening techniques.

3. Create a poster or advertising jingle that conveys the importance of saving water outdoors.

4. Plan a Xeriscape garden for your home.

5. Share your work with your school’s facilities staff and see if some of your school’s outdoor area can be landscaped in low-water-consuming and drought tolerant plants.

6. Research plants that are native to your community. Interview people to find out if those plants require much or little maintenance. Do they require a green thumb, or are they easy to grow?

7. Research the uses of water in northeast Florida: How much goes to residential landscaping? Agriculture? Indoor water uses?

8. Develop a water conservation strategy for the landscaping of your home, your school, or your community.