A self-watering grow box has a water store called a reservoir and a way for water to reach the growing mix. In our small model a cotton wick connects the water to moist potting mix. Water moves along the wick by capillary action. The name does not mean ‘never check it’. Plants, water levels and the container still need attention. Our model uses potting mix, so do not call it hydroponics just because it has a water reservoir.

Use two clean, stable containers that an adult has approved: an outer water container and an inner planting pot that fits securely above it. The adult makes any holes and threads a clean cotton wick through the inner pot. One end reaches the water and the other lies in moist potting mix. The upper container must sit securely, not balance on a narrow edge. Use a suitable seedling and keep the assembly where it cannot tip.

The adult chooses a design with appropriate drainage or overflow and a covered reservoir. Do not leave open standing water for mosquitoes. Never reuse a container that held chemicals, and do not handle sharp cut plastic. A simple purchased self-watering pot is an equally good demonstration. Before planting, test whether the wick becomes damp and whether the mix stays moist rather than soaked. A working model should solve a watering problem safely.

Put the seedling at a suitable depth, press the mix gently and give the initial watering advised by the adult. Keep it in suitable light for that plant. Check the reservoir and the mix regularly. If the wick loses contact with the water, it cannot do its job. If the mix is waterlogged, tell the adult; roots need air as well as water. Do not add more water just because the word ‘watering’ is in the name.

A self-watering box may reduce the frequency of watering, but it does not feed, inspect or protect the plant automatically. An adult manages fertiliser and pest problems. Wash hands after working with potting mix or plants. Do not taste leaves unless an adult has identified an edible plant and prepared it safely. You can do the whole lesson by planning a box and observing a teacher’s demonstration.

Give the plant a name or number and record the planting date. Measure from the same starting point at the soil surface to the same kind of endpoint each time. Record centimetres, date, leaf number and an observation such as ‘one new leaf’. A drawing can show a change that a height measurement misses. Do not stretch, pull or dig up the plant to obtain a measurement.

Suppose Monday’s height is 6 cm and Friday’s is 8 cm. The increase is 2 cm. This is an observation about this plant over that interval, not a promise that every plant grows 2 cm each week. If you compare two plants, keep their kind, light and measuring routine as similar as possible. Record a zero change honestly. Careful records help you ask better questions rather than inventing a successful result.