Before packing your lilac blossoms into a quart sized glass jar, make sure they are free of bugs and that there are no green stems attached. Add the blueberries or blackberries to the jar, as well. This will give your syrup a nice lavender color.
Place the sugar and water in a saucepan and bring to a boil over medium/high heat, whisking together to dissolve the sugar into the water. Let boil for 2 minutes, then remove from heat.
Pour the hot syrup carefully into the jar of lilacs until the syrup reaches the top of the jar.
Cover the jar with a cloth and let sit on the counter for 4-5 hours, or even overnight for the strongest flavor.
When you have finished steeping the syrup in the blossoms, strain the syrup through a fine mesh sieve, pressing on the blossoms to extract all of the syrup. Stir the lemon juice into the syrup. Place syrup in an airtight container and store in the fridge.
Will keep for several months.
Recipe by The Kitchen McCabe at https://www.thekitchenmccabe.com/2017/05/25/lilac-syrup/