You will need:

4 x pieces of balsa wood approximately 25cm in length and 10cm in width

A hot glue gun

A glass jar (that is narrower than 10cm and no taller than 20cm)

What to do: 

Heat your glue gun and squeeze some glue on the edges of one of your balsa pieces (lengthways)

Press two of the other balsa pieces onto the glue (lengthways)

Squeeze some more glue onto the edges of the final piece of balsa wood and push it into place to form a box

Fill the jar with water and place into the box (the box does not have a bottom)

Pop your flowers in and – voila!