I am yet to find a child who doesn't love a sensory bottle. A great way to reuse old plastic bottles, these ones by Chalk Academy are marvellous – they double up as rain sticks. Easy to make, but do make sure you get that lid on securely!
There are a million uses for toilet roll tubes. Two of my favourites include seed starter pots and bird feeders (cover them with peanut butter and bird seed). Have a look at Honey & Lime for full instructions.
Do let us know what you're up to for Earth Day, and please tell us about any brilliant crafts you've spotted.