Plant a Tree
Trees are massively important, not just for wildlife but they play an important role in preventing flash floods too and the good news is, even a small garden can have a tree!
Trees are of extreme value, not only to wildlife but to us, humans too: they provide us with oxygen, shelter (ever sought refuge under a large tree during a summer downpour?), they also give us building materials and sometimes fuel to heat our homes. But not only that, trees also stabilise the soil so that less nutrients are washed out and furthermore, they alleviate flash floods as the roots absorb the rain before it can wash down the streets (and into houses).
Here is the best thing: we can all plant a tree no matter the size of your garden!
You could even have a small tree in a pot on a balcony. This is just a guidance for what trees you can plant; a quick internet search will give you other options too. Or ask your local, independent garden centre as they can sometimes order particular trees in and also do bare rooted trees, which are much cheaper.
Trees for balconies
Apple 'Greenfinch Columnar'
Apple 'Discovery'
Italian Cypress
Snowy mespilus
Trees for Small Gardens
Hawthorn
Sloe
Crab Apple
Dwarf Cherry
Plus all the above
Trees for Medium Gardens
Elder tree (think elderberry wine!)
Rowan
Goat willow
Small leaved lime
Plus all the above
Trees for Large Gardens
Oak
Beech
Bird Cherry
Walnut
Hazels and cobnuts
All fruit trees
Plus all of the above
How to plant a tree
This website from the RHS has very good instructions on how to plant a tree, step-by-step and including pictures