Measure the elder flower cordial into one liter (quart) measuring jug.
Muddle 2 of the mint leaves and 1 of the strawberries, along with the rose geranium leaves and rose petals if using, into the cordial in the bottom of the jug, using a spoon to bruise them to release their flavours. You can leave it for up to two hours at this stage to infuse, or proceed after 5-10 minutes with a milder taste.
Prepare your decorations: break apart the elderflower into very small heads or individual flowers; have ready two rose-geranium flowers or a couple of small rose petals; carefully take the stem end off the back of the borage flowers.
Just before serving, add the cold soda water to the jug with the cordial and herbals, and strain the mix into a second pouring jug. Add the ice and the cold rose lemonade, and stir well for about one minute until icy cold.
Either add all the fruit, mint and blossom decorations to the serving jug itself, to pour into glasses randomly with the drink; or reserve some for individual glasses if you prefer, which makes a personal (and neater) touch.
Garnish with one strawberry and one mint leaf, and add a borage flower, a rose geranium flower and a little sprinkling of the elder flowers.