The Bottle Garden Plan

Every class at Hana’s school in Osaka, Japan, looked after a small vegetable garden. Hana’s class grew tomatoes, cucumbers and sweet potatoes. But there was a problem: the summer holidays were coming, and for two weeks nobody would be at school to water the plants.

“The tomatoes will dry up,” said Hana’s friend Kenji gloomily. “All our work will be wasted.”

Their teacher, Ms Mori, smiled. “Then let’s think like engineers. What do plants need, and how can we give it to them while we are away?”

The class had lots of ideas. Someone suggested asking the school caretaker, but he was going on holiday too. Someone else suggested a giant umbrella to keep the sun off, but plants need sunlight to grow.

Hana thought about the empty plastic bottles in the recycling bin. “What if each plant had its own water bottle?” she said. “If we make a tiny hole in the lid and push the bottle upside down into the soil, the water will drip out very slowly.”

Kenji’s face brightened. “But if the hole is too big, the water will all run out in one day. We need to test it!”

For the next week, the class experimented. They made holes with a thick nail, a thin nail and a pin. They timed how long each bottle took to empty. The pin hole was too slow, and the thick nail hole was far too fast. The thin nail hole was just right: a big bottle lasted about four days.

“So each plant needs two bottles to last a week,” said Kenji, doing the maths. The families agreed to take turns visiting once a week to refill them.

When school started again, the tomatoes were red and ripe, and the cucumbers were longer than Kenji’s hand. Ms Mori pinned a sign on the garden gate: “Designed by the Class 4 Engineers”.