The small white flowers are specifically modelled on the flowers of the Hawthorn tree or May Bush that are in bloom in the UK around Beltane. If you decide to make coloured flowers, try to pick ones that directly relate to Beltane.

Some tips about making this as a headdress

Do use a mercerised cotton as opposed to a wool yarn as it will give the right stiffness needed to make leaves stand up.
Don’t worry if your yarn is a slightly different weight, but just make sure your hook size is about a size smaller than normally used for the yarn,
If making it as a circlet, you may want to use wire to give a framework to it. Or make it open and give it ties.
You don’t have to make the whole headdress, you can just make samples of leaves and flowers and clip them in your hair.
If you would like the stitch structure of the leaves, i.e. in Standard Crochet Stitch diagrams, I have one available or you can go to the Anticraft site to download one.
Or download from here

Still got floppy leaves? You can use a hair product (eco friendly please) that stiffens hair on this. Or dip into some Eco Friendly glue and leave to dry.