2026–27 · Backup lesson · Spring 2027
Compare Drainage Before Choosing Potting Material
Adult extension of: Which Soil Holds Water?
Unscheduled alternative · available resource
Run equal-water drainage tests on two planting materials and measure the water collected after a fixed wait. Use the limited comparison to discuss which material might suit a plant’s moisture needs and what further checks are required.
Curriculum skill focus: Absorption, drainage, comparison, measurement, sensory discrimination
01 · Learning
Objectives
- Control sample volume, container, and water input in a comparison.
- Measure drainage at the same elapsed time.
- Explain why retaining the most water is not always best for a plant.
02 · Preparation
Materials
Two contrasting clean planting materials such as coarse sand and potting mix; matching perforated cups and catch cups; identical mesh liners; measuring jug; scoop; timer; labels; tray; optional scale; plant-care guidance.
03 · Practice
Adult project
- 1
Select a planting job and read the plant’s moisture needs. Compare the two materials visually or with a tool, predict which will drain more water, and choose a pouring, timing, measuring, or observation role.
- 2
Prepare matching cups with identical drainage holes and liners. Add equal volumes with similar packing, document whether samples began dry or damp, and label them; starting moisture can change the result.
- 3
Place cups above separate catch containers and slowly add the same measured water volume to each at a similar rate. Start the timer and prevent spilled or overflowed water from being counted as drainage.
- 4
At a fixed interval, measure collected water in each catch cup. Record the amount and any pooling on the surface, then continue waiting if drainage is still active and a later comparison is useful.
- 5
Compare collected amounts. Describe less drainage as less water recovered during this test, not automatically an exact measure of long-term water storage; discuss initial moisture, evaporation, and retained water in the apparatus.
- 6
Use the results and plant-care guidance to propose a material or blend for the selected job. Label the comparison, dispose of wet mix appropriately, and plan a real-container moisture check before making a larger planting decision.
Evidence & interpretation
What the investigation shows
Water movement depends on pore sizes, structure, compaction, organic matter, and initial moisture. Potting mix is not identical to field soil, and a brief drainage trial does not fully measure plant-available water or root health.
Practical connection
Why this work matters
Container choices balance water availability, drainage, and root aeration rather than simply maximizing water retention.
Participation by choice
Individual access options
- Use prefilled cups and direct equal pours while a partner manages the wet materials.
- Read large measurement marks, compare catch levels side by side, or receive spoken volume readings.
- Choose sealed sample viewing and photo records if soil texture is unwelcome; stop or take a dry-task role without pressure.
Review & transfer
Reflect on the work
- What did you keep the same to make the comparison useful?
- Why might the material that held more water be unsuitable for some plants?