Project: grow lettuce in a jar

Students will

• Explain how a Kratky jar gives roots both water and air without a pump.
• Put the steps for building a lettuce jar in order.
• Describe what to expect as the water level drops over the weeks.

New words

Kratky

A way to grow where you fill a tub once. As the water drops, the top roots get air.

air gap

The space of air between the bottom of the pot and the top of the water.

Talk about it

Why might a system with no moving parts be a good one to build first?

Check questions and answers

1. This jar has no pump. Where do the top roots get air?

   • In the air gap above the water (answer) Right. As the water drops, the gap gives the roots air.
   • From bubbles in the water Not quite. There is no pump, so there are no bubbles.
   • Through the glass Not quite. Air can't pass through glass. Look above the water.

2. After two weeks, the water is lower. What do you do?

   • Leave it. The gap is part of the plan. (answer) Right. The roots grow down to follow the water.
   • Fill the jar back to the top Not quite. That would drown the roots that breathe air.
   • Pour it out and start over Not quite. Nothing is wrong. The plant is drinking.

3. Why do you wrap the jar in dark paper?

   • To keep light out of the water (answer) Right. Light lets green slime grow in the water.
   • To keep the plant warm Not quite. The wrap is about light, not heat.
   • So the jar looks nice Not quite. It does a real job. Think about light.

4. Who mixes the plant food into the water?

   • An adult (answer) Right. Plant food is strong stuff. An adult measures and mixes it.
   • You, and you taste it to check Not quite. Never taste plant food. It is not for eating.
   • Nobody. Plain water works fine. Not quite. Plain water has no food. The lettuce would go hungry.

Teacher note

The printable project sheet is at /project/lettuce-in-a-jar/sheet/. Its amounts and timings follow University of Hawaii and University of Florida extension guides to non-circulating lettuce growing.