20 minutes to set up, then a week of waiting. This project is best in spring or summer.

• an old cereal box
• a pair of scissors
• a few pebbles or skewers

1 Ask the children to draw the first letter of their name on the plain side of a cereal box.

2 Get them to cut it out in bubble writing so it's nice and fat.

3 Ask them to put it in on the grass in their garden. They should try to find a patch of grass which is in the sun most of the day.

4 They need to hold it down with pebbles or by pushing some skewers through it, then leave it for a week. When they remove the cardboard, they should find that the grass has gone yellow in the shape of their letter.

5 The children could try it again with some shapes, such as a crescent moon or a triangle.

• This activity will turn the lawn yellow where the cardboard is placed, but it won't be a permanent change. As soon as the light gets back on the grass, it'll begin to go green again.
• The green colouring in plant leaves is called chlorophyll. It traps the sun's energy - to produce food which makes the plant grow. Plants need light to be able to make chlorophyll. When there's no light, the plant stops producing this green pigment and their leaves go yellow. As soon as the plant is in the light again, it's stimulated to make chlorophyll, turning the leaves green and putting its food-making processes back into production.