Here in the UK at the moment the beautiful Autumnal weather has created a splash of colour across the trees. This inspired me to have a go at a rainbow leaf walk. I wanted to see if I could find a leaf to represent each colour of the rainbow and to find out a bit more about why leaves change colour. Here’s how I got on…
Go on a leaf rainbow walk
Finding a range of different coloured leaves turned out to be a doddle. A mere 10 minutes in to my walk, I’d already built up quite a collection of different colours. If you’re going to have a go at this with children, first set some ground rules:
- Only collect leaves that have fallen on the ground (remember, a tree is a living thing)
- Check carefully before you pick leaves up incase there is rubbish nearby etc.
- If there are any bugs or insects on your leaves, carefully brush them on to the ground nearby.
- Keep your hands away from your mouth and wash them carefully afterwards.
Then have fun collecting. Here’s my rainbow of leafy colours!
If you want to add a further challenge to this activity, why not have a go at making sure that each leaf is a different size or shape? You could also use an app such as ‘Leafsnap‘ to identify which tree the leaf has come from.
Naturally you should have no trouble finding leaves of all shades of green. Reds, oranges and yellows also proved relatively easy to find, along with browns and even purples and blacks. However, I struggled with blue.
This got me thinking.
Why are leaves different colours?
This comes down to an important pigment called chlorophyll. To put it simply, chlorophyll is the substance that allows plants to absorb energy from the sun and turn it into food. This process is called photosynthesis. Every leaf has chlorophyll in it. You may have noticed that not all leaves are green. These leaves still contain chlorophyll but they also contain other pigments too that no longer make the leaf look green.
As leaves prepare to fall in the Autumn, a layer of cells forms across the bottom of the leaf. This slowly restricts the movement of food across the leaf. In some trees it also also produces a pigment called anthocyanin. This is what gives leaves their red colouring. The more sunlight and dry weather, the brighter the red will be!
The less sunlight the leaves get, the yellower they turn (we also see the same happen to grass if it is covered over). Inside the leaves is a pigment called carotene. You may have guessed from the name that we also see this pigment in carrots! Is the leaves stop photosynthesising, the yellow carotene remains, turning the leaf a yellowy colour.
The lack of sunlight and food eventually causes the leaves to turn brown. These leaves litter the ground under the tree and eventually decay, acting as a natural fertiliser for the ground.
And as for blue? There’s no true blue pigment in plants so it’s rare to see a blue colour in their leaves.
If you have a go at this activity, do share your leaf rainbows with me using the twitter handle @howtostem.
For more, quick, easy-to-resource STEM activities, check out my book 15-Minute STEM.