Lab / experiment Grade 5 Engineering & Design

Fenmere Orchard Mulch Depth: A Grade 5 Water-Saving Fair Test

Teams weigh three soil cups over two days to find whether thin or thick mulch holds water better, then recommend a ring depth for a fictional orchard.

Grade: Grade 5
Subject: Engineering & Design
Material: Lab / experiment
Time: 2 sessions, ~80 min total
Prep: Moderate prep
Materials: 3 identical clear plastic cups or small foil pans, per team, Potting soil, enough to fill each cup about two-thirds full, Shredded bark, wood chips, or torn paper strips for mulch, Digital kitchen scale reading to 0.1 gram, Measuring cup or graduated cylinder, Ruler, Marker and masking tape, Tray to hold the three cups together

Standards

3-5-ETS1-3 NGSS

Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.

How this material aligns: The three cups differ only in mulch depth while soil, water, and location are held steady, and question 5 has students name those controls, which is this standard's fair test.

All materials for 3-5-ETS1-3 →

3-5-ETS1-2 NGSS

Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.

How this material aligns: Question 6 makes teams weigh thin rings on many trees against thick rings on fewer trees under one mulch supply, comparing two solutions against a stated limit.

All materials for 3-5-ETS1-2 →

5.NBT.B.7 Common Core Math

Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.

How this material aligns: Questions 2 and 3 require subtracting recorded masses written to tenths of a gram and then comparing those differences, which is the decimal subtraction this standard names.

All materials for 5.NBT.B.7 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-23.

Objectives

Students will hold soil, water, and location steady while changing only mulch depth.
Students will subtract recorded masses to find how much water each cup lost.
Students will recommend a mulch depth for an orchard working under a limited mulch supply.

Vocabulary

Evaporation: Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.

Also: mulch, mass, controlled variable, orchard

Teacher overview

The investigation question is whether covering soil with mulch keeps water in it, and if so, whether a thicker layer keeps more. The fictional Fenmere Orchard has young apple trees and a watering bill it wants to lower, so it has asked for a recommendation on how deep to build the mulch ring around each trunk. Teams set up three cups of the same soil with the same water, cover them with nothing, a thin layer, and a thick layer, and weigh them twice across two days. Mass lost is water lost, because nothing else leaves a cup sitting on a tray.

The misconception worth naming first is what the scale is actually measuring. Students who see a cup get lighter often say the soil dried out or the water sank in, as though the water moved somewhere inside the cup. Water leaving the cup by soaking downward is not possible here, since the cups have no holes, so the only route out is evaporation from the surface. Making that argument out loud, before the first weighing, is what turns the mass reading into evidence. A second point: teams frequently want to water all three cups again on day two because one looks dry. Doing so ends the test. The whole comparison depends on each cup receiving water exactly once, at the start.

This lab runs across two sessions: about 40 minutes to set up and take the first masses, then about 40 minutes two days later to take the second masses and complete the analysis.

Fenmere Orchard Mulch Depth: A Grade 5 Water-Saving Fair Test — Grade 5 Engineering & Design

Name: ____________________________ Date: ______________

Procedure

Safety. Do not taste soil, mulch, or water at any point in this lab. Wash hands with soap after handling soil. Wipe spills on the floor right away so no one slips. Keep the scale away from the edge of the table, and have an adult move it.

Step 1. Label three cups with tape: Bare, Thin, and Thick. Write your team name on each one.

Step 2. Fill all three cups about two-thirds full with the same potting soil. Level the surface with a finger. Use the same soil from the same bag for all three.

Step 3. Place all three cups on one tray. Set the tray where it will not be moved for two days, away from a sunny window and away from a heat vent, so all three cups share the same conditions.

Step 4. Measure 50 milliliters of water. Pour it slowly and evenly over the soil in the Bare cup. Repeat with exactly 50 milliliters into each of the other two cups. Every cup gets the same water, poured the same way.

Step 5. Leave the Bare cup uncovered. Spread mulch over the Thin cup until the layer is about 1 centimeter deep, checking with a ruler. Spread mulch over the Thick cup until the layer is about 3 centimeters deep.

Step 6. Weigh each cup on the scale, one at a time, right after the mulch goes on. Record each mass in grams to one decimal place in the Day 0 column. Weigh the cup with its mulch on, since the mulch stays with the cup for the whole test.

Step 7. Do not water, move, or stir any cup for the next two days. Write the day and time of your Day 0 weighing on the tray so the second weighing happens as close to two full days later as you can manage.

Step 8. Two days later, weigh each cup again in the same order, on the same scale. Record each mass to one decimal place in the Day 2 column.

Step 9. Subtract to find the mass lost by each cup, and fill in the last column. Then answer the analysis questions.

Step 10. When the lab is over, empty the soil into a planter or the trash, not into a sink, and wipe the tray and the scale.

Data & Analysis

Record every mass in grams to one decimal place. Mass lost is the Day 0 mass minus the Day 2 mass.

Cup	Mulch depth	Day 0 mass (g)	Day 2 mass (g)	Mass lost (g)
Bare	none
Thin	about 1 cm
Thick	about 3 cm

Which cup lost the most mass over the two days? Give the cup's name and its mass lost from your own table.
Find the mass lost by each of the three cups by subtracting. Which cup lost the least?
How much more mass did the Bare cup lose than the Thick cup? Show your subtraction.
Fenmere Orchard's rule is that a mulch ring must lose less water than bare ground. Which of your two mulch depths met that rule?
Name the one thing your team changed on purpose across the three cups. Then name two things your team kept the same.
Fenmere Orchard has 400 young trees. Its mulch pile is enough for either 150 thick rings or 450 thin rings this spring. Using your data, recommend one of those two plans and give a reason.
Name one thing about a real orchard that this cup test does not copy. Describe one change you would make to the test to fix it.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: Results vary by team; the Bare cup is the usual answer.
Accept any cup named as long as it carries the largest mass lost in that team's own table. If a mulched cup lost the most, ask the team whether that cup was placed near a vent or a window.
Answer: Results vary by team; the Thick cup usually loses the least.
Accept three subtractions that match the recorded masses, each labeled in grams, with the smallest difference named. Check that students subtracted Day 2 from Day 0 and not the reverse.
Answer: Results vary by team.
Accept any difference that equals the Bare cup's mass lost minus the Thick cup's mass lost, shown as a subtraction and labeled in grams. Many classes see a difference of a few grams over two days, which is small but consistent across teams.
Answer: Results vary by team; both depths usually meet the rule.
Accept any answer in which the depths named lost less mass than the Bare cup in that team's table, and accept a finding that only one depth met the rule when the data says so.
Answer: The one change was the mulch depth.
Accept any two controls the team actually held steady, such as the same soil, the same 50 milliliters of water, the same cup size, the same tray, or the same weighing times. Do not accept "the mulch" as a control, since mulch depth is the thing being tested.
Answer: Accept either plan when the team gives a reason drawn from its own data.
The 450 thin rings plan is the stronger answer in most classes, because the thin cup usually saves nearly as much water as the thick cup while covering all 400 trees instead of only 150. Accept the 150 thick rings plan if that team's data shows a large gap between thin and thick.
Answer: Answers vary; accept any honest limit of the model paired with a matching fix.
Common limits students name are that real soil drains downward while a sealed cup cannot, that real trees pull water up through their roots, that real weather brings rain, wind, and sun, and that a real mulch ring is far wider than a cup. Reasonable fixes include poking drain holes, planting a seedling in each cup, running the test outdoors, or extending the test past two days.

Differentiation

Support

Set up these teams' cups in advance, with the soil already leveled and the tape labels written, so their first task is pouring the measured water. Give them a recording sheet with the subtraction already framed as Day 0 minus Day 2 and a place-value chart for the decimal work. Reading the scale aloud to a partner who writes it down keeps the recording accurate.

Extension

Ask these teams to add a fourth cup with a mulch depth of their own choosing and to predict, before weighing, where it will land between the thin and thick results. They should also graph all four mass-lost values as a bar graph and describe whether adding more mulch keeps paying off at the same rate, which is a question a real orchard has to answer before buying another truckload.

ELL supports

Pre-teach "mulch," "mass," "evaporation," and "bare" using the actual materials and a drawing of water leaving a soil surface as arrows. Label each cup with both a word and a picture. Provide this frame for questions 4 and 6: "The ___ cup lost ___ grams, so I recommend ___ ." Allow students to record data as numbers only and to answer question 7 with a labeled sketch.

Extensions

Students can repeat the comparison outdoors in a garden bed or a large planter, where rain and sun are part of the test, and see whether the indoor result holds. A grower, a garden center employee, or a groundskeeper visiting the class can describe how deep they build mulch rings and why they keep mulch pulled back from the trunk, which is a design detail this cup test cannot show.