Prepare the flower heads by removing as much stalk as you can. Place them into a bucket of cold water and swish them gently about to remove any bugs and dirt. Place on a dry tea towel while you prepare the cordial.
Wash and thinly slice the lemons and oranges (if you have no oranges you could use simply lemons).
Place the sugar and water into the large pot. Bring to the boil (or until all the sugar has dissolved).
Place the flower heads into the syrup and bring back to the boil. Once it begins to boil - take off the heat.
Add the lemons, oranges and citric acid, stir and cover with a clean tea towel.
Leave the cordial to steep for 24 hours before straining. Place a muslin cloth over a sieve. Strain the cordial through the cloth into a large bowl or measuring jug). Do not squeeze the muslin cloth contents. Allow it to drip.
Pour into the sterilised bottles.